Cosmology has made enormous progress through studies of the cosmic microwave background, however the subtle signals being now sought such as B-mode polarisation due to primordial gravitational waves are increasingly hard to disentangle from residual Galactic foregrounds in the derived CMB maps. We revisit our finding that on large angular scales there are traces of the nearby old supernova remnant Loop I in the WMAP 9-year map of the CMB and confirm this with the new SMICA map from the Planck satellite.
In this paper we present a large database of weak lensing light cones constructed using different snapshots from the Big MultiDark simulation (BigMDPL). The ray-tracing through different multiple planes has been performed with the GLAMER code accounting both for single source redshifts and for sources distributed along the cosmic time. This first paper presents weak lensing forecasts and results according to the geometry of the VIPERS-W1 and VIPERS-W4 field of view. Additional fields will be available on our database and new ones can be run upon request. Our database also contains some tools for lensing analysis. In this paper we present results for convergence power spectra, one point and high order weak lensing statistics useful for forecasts and for cosmological studies. Covariance matrices have also been computed for the different realisations of the W1 and W4 fields. In addition we compute also galaxy-shear and projected density contrasts for different halo masses at two lens redshifts according to the CFHTLS source redshift distribution both using stacking and cross-correlation techniques, finding very good agreement.
We study the possibility that particle production during inflation can source the required power spectrum for dark matter (DM) primordial black holes (PBH) formation. We consider the scalar and the gauge quanta production in inflation models, where in the latter case, we focus in two sectors: inflaton coupled i) directly and ii) gravitationally to a $U(1)$ gauge field. We do not assume any specific potential for the inflaton field. Hence, in the gauge production case, in a model independent way we show that the non-production of DM PBHs puts stronger upper bound on the particle production parameter. Our analysis show that this bound is more stringent than the bounds from the bispectrum and the tensor-to-scalar ratio derived by gauge production in these models. In the scenario where the inflaton field coupled to a scalar field, we put an upper bound on the amplitude of the generated scalar power spectrum by non-production of PBHs. As a by-product we also show that the required scalar power spectrum for PBHs formation is lower when the density perturbations are non-Gaussian in comparison to the Gaussian density perturbations.
We present an application of Large Deviation Theory to the problem of structure growth on large-scale structure cosmology. Starting from gaussian distributed overdensities on concentric spherical shells, we show that a Large Deviation Principle holds for the densities on the corresponding shells after gravitational evolution if no shell-crossing happens. As consequences of the Large Deviation Principle we obtain the cumulant generating function for the non-linear densities, and present formulae to compute the cumulant generating function for general window functions.
In this article, we describe a new estimate of the Cosmic Microwave Background (CMB) intensity map reconstructed by a joint analysis of the full Planck 2015 data (PR2) and WMAP nine-years. It provides more than a mere update of the CMB map introduced in (Bobin et al. 2014b) since it benefits from an improvement of the component separation method L-GMCA (Local-Generalized Morphological Component Analysis) that allows the efficient separation of correlated components (Bobin et al. 2015). Based on the most recent CMB data, we further confirm previous results (Bobin et al. 2014b) showing that the proposed CMB map estimate exhibits appealing characteristics for astrophysical and cosmological applications: i) it is a full sky map that did not require any inpainting or interpolation post-processing, ii) foreground contamination is showed to be very low even on the galactic center, iii) it does not exhibit any detectable trace of thermal SZ contamination. We show that its power spectrum is in good agreement with the Planck PR2 official theoretical best-fit power spectrum. Finally, following the principle of reproducible research, we provide the codes to reproduce the L-GMCA, which makes it the only reproducible CMB map.
The supernova Hubble diagram residual contains valuable information on both the present matter power spectrum and its growth history. In this paper we show that this information can be retrieved with precision by combining both peculiar velocity and weak-lensing analysis on the data. To wit, peculiar velocity induces correlations on the nearby supernovae while lensing induces a non-Gaussian dispersion in faraway objects. We show that both effects have almost orthogonal degeneracies and discuss how they can be extracted simultaneously from the data. We analyze the JLA supernova catalog in a 14-dimensional parameter space, assuming a flexible growth-rate index gamma. We arrive at the following marginalized constraints: sigma8 = $1.16^{+0.23}_{-0.47}$ and gamma = $0.80^{+0.29}_{-0.34}$. We note that these constraints complement well the ones obtained from other data sets. Assuming instead GR as the correct gravitation theory (and thus gamma = 0.55), the constraints in sigma8 tighten further: sigma8 = $0.89^{+0.18}_{-0.21}$.
In dynamical system describing evolution of universe with the flat Friedmann-Robertson-Walker symmetry filled with barotropic dust matter and non-minimally coupled scalar field with a constant potential function an invariant manifold of the de Sitter state is used to obtain exact solutions of the reduced dynamics. Using observational data coming from distant supernovae type Ia, the Hubble function $H(z)$ measurements and information coming from the Alcock-Paczy$\'n$ski test we find cosmological constraints on the non-minimal coupling constant $\xi$ between the scalar curvature and the scalar field. For all investigated models we can exclude negative values of this parameter at the $68\%$ confidence level. We obtain coherence with values needed for conformal coupling of the scalar field in higher dimensional theories of gravity.
We present generic bounds on magnetic fields produced from cosmic inflation. By investigating field bounds on the vector potential, we constrain both the quantum mechanical production of magnetic fields and their classical growth in a model independent way. For classical growth, we show that only if the reheating temperature is as low as T_{reh} <~ 10^2 MeV can magnetic fields of 10^{-15} G be produced on Mpc scales in the present universe. For purely quantum mechanical scenarios, even stronger constraints are derived. Our bounds on classical and quantum mechanical scenarios apply to generic theories of inflationary magnetogenesis with a two-derivative time kinetic term for the vector potential. In both cases, the magnetic field strength is limited by the gravitational back-reaction of the electric fields that are produced simultaneously. As an example of quantum mechanical scenarios, we construct vector field theories whose time diffeomorphisms are spontaneously broken, and explore magnetic field generation in theories with a variable speed of light. Transitions of quantum vector field fluctuations into classical fluctuations are also analyzed in the examples.
The triggering mechanisms for Active Galactic Nuclei (AGN) are still debated. Some of the most popular ones include galaxy interactions (IT) and disk instabilities (DI). Using an advanced semi analytic model (SAM) of galaxy formation, coupled to accurate halo occupation distribution modeling, we investigate the imprint left by each separate triggering process on the clustering strength of AGN at small and large scales. Our main results are as follows: i) DIs, irrespective of their exact implementation in the SAM, tend to fall short in triggering AGN activity in galaxies at the center of halos with $M_h>10^{13.5} h^{-1}M_{\odot}$. On the contrary, the IT scenario predicts abundance of active, central galaxies that generally agrees well with observations at every halo mass. ii) The relative number of satellite AGN in DIs at intermediate-to-low luminosities is always significantly higher than in IT models, especially in groups and clusters. The low AGN satellite fraction predicted for the IT scenario might suggest that different feeding modes could simultaneously contribute to the triggering of satellite AGN. iii) Both scenarios are quite degenerate in matching large-scale clustering measurements, suggesting that the sole average bias might not be an effective observational constraint. iv) Our analysis suggests the presence of both a mild luminosity and a more consistent redshift dependence in the AGN clustering, with AGN inhabiting progressively less massive dark matter halos as the redshift increases. We also discuss the impact of different observational selection cuts in measuring AGN clustering, including possible discrepancies between optical and X-ray surveys.
As part of the Megamaser Cosmology Project (MCP), here we present a new
geometric distance measurement to the megamaser galaxy NGC 5765b. Through a
series of VLBI observations, we have confirmed the water masers trace a thin,
sub-parsec Keplerian disk around the nucleus, implying an enclosed mass of 4.55
$\pm$ 0.40 $\times~10^{7}M_\odot$. Meanwhile, from single dish monitoring of
the maser spectra over two years, we measured the secular drifts of maser
features near the systemic velocity of the galaxy with rates between 0.5 and
1.2 km s$^{-1}$ yr$^{-1}$. Fitting a warped, thin disk model to these
measurements, we determine a Hubble Constant $H_{0}$ of 66.0 $\pm$ 6.0 km
s$^{-1}$ Mpc$^{-1}$ with the angular-diameter distance to NGC 5765b of 126.3
$\pm$ 11.6 Mpc.
Apart from the distance measurement, we also investigate some physical
properties related to the maser disk in NGC 5765b. The high-velocity features
are spatially distributed into several clumps, which may indicate the existence
of a spiral density wave associated with the accretion disk. For the
red-shifted features, the envelope defined by the peak maser intensities
increases with radius. The profile of the systemic masers in NGC 5765b is
smooth and shows almost no structural changes over the two years of monitoring
time, which differs from the more variable case of NGC 4258.
We detect a new suspected giant radio galaxy (GRG) discovered by KAT-7. The GRG core is identified with the WISE source J013313.50-130330.5, an extragalactic source based on its infrared colors and consistent with a misaligned AGN-type spectrum at $z\approx 0.3$. The multi-$\nu$ spectral energy distribution (SED) of the object associated to the GRG core shows a synchrotron peak at $\nu \approx 10^{14}$ Hz consistent with the SED of a radio galaxy blazar-like core. The angular size of the lobes are $\sim 4 ^{\prime}$ for the NW lobe and $\sim 1.2 ^{\prime}$ for the SE lobe, corresponding to projected linear distances of $\sim 1078$ kpc and $\sim 324$ kpc, respectively. The best-fit parameters for the SED of the GRG core and the value of jet boosting parameter $\delta =2$, indicate that the GRG jet has maximum inclination $\theta \approx 30$ deg with respect to the line of sight, a value obtained for $\delta=\Gamma$, while the minimum value of $\theta$ is not constrained due to the degeneracy existing with the value of Lorentz factor $\Gamma$. Given the photometric redshift $z \approx 0.3$, this GRG shows a core luminosity of $P_{1.4 GHz} \approx 5.52 \times 10^{24}$ W Hz$^{-1}$, and a luminosity $P_{1.4 GHz} \approx 1.29 \times 10^{25}$ W Hz$^{-1}$ for the NW lobe and $P_{1.4 GHz} \approx 0.46 \times 10^{25}$ W Hz$^{-1}$ for the SE lobe, consistent with the typical GRG luminosities. The radio lobes show a fractional linear polarization $\approx 9 \%$ consistent with typical values found in other GRG lobes.
Theories of gravity with a preferred foliation usually display arbitrarily fast signal propagation, changing the black hole definition. A new inescapable barrier, the universal horizon, has been defined and many static and spherically symmetric examples have been studied in the literature. Here, we translate the usual definition of universal horizon in terms of an optical scalar built with the preferred flow defined by the preferred spacetime foliation. The new expression have the advantage of being of quasi-local nature and not depend on specific spacetime symmetries to be well defined. Therefore, we propose it as a definition for general quasi-local universal horizons. We also to give a general (peeling) surface gravity definition for general spacetimes. Using the new formalism we show that there are no universal analog of cosmological horizons for FLRW models, for any scale factor function and we also state that quasi-local universal horizons are restricted to trapped regions of the spacetime. We analyze the evolution of the universal horizon area under simplifying assumptions and we conclude with our view on the next steps for the understanding of black holes in non relativistic gravity theories.
All quintessence potentials that are either monotonic or have a minimum at negative values of the potential, generically predict a future collapse of the scale factor to a "doomsday" singularity. We show that this doomsday is generically avoided in models with a proper non-minimal coupling of the quintessence scalar field to the curvature scalar $R$. For simplicity we consider linear quintessence potential $V=-s\phi$ and linear non-minimal coupling $F=1-\lambda \phi$. However our result is generic and is due to the fact that the non-minimal coupling modifies the effective potential that determines the dynamics of the scalar field. Thus for each positive value of the parameter $s$ we find a critical value $\lambda_{crit}(s)$ such that for $\lambda>\lambda_{crit}(s)$ the negative potential energy does not dominate the universe and the cosmic doomsday Big Crunch singularity is avoided because the scalar field eventually rolls up its potential. We find that $\lambda_{crit}(s)$ increases approximately linearly with $s$. For $\lambda>\lambda_{crit}(s)$ the potential energy of the scalar field becomes positive and eventually dominates and the dark energy equation of state parameter tends to $w=-1$ leading to a deSitter Universe.
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The alignment of the CMB Cold Spot and the Eridanus Supervoid suggests a physical connection between these two relatively rare objects. We use galaxy catalogues with photometric (2MPZ) and spectroscopic (6dF) redshift measurements, supplemented by low-redshift compilations of cosmic voids, in order to improve the 3D mapping of the matter density in the Eridanus constellation. We find evidence for a supervoid with an important elongation in the line-of-sight, effectively spanning the total redshift range $z<0.3$. Our tomographic imaging reveals significant substructure in the Eridanus Supervoid, with a potential interpretation of a long, fully connected system of voids. We improve the analysis by extending the line-of-sight measurements into the antipodal direction, that interestingly crosses the Northern Local Supervoid at the lowest redshifts, and intersects very rich superclusters like Hercules and Corona Borealis, in the region of the Coma and Sloan Great Walls, as a possible compensation for the large-scale matter deficit of Eridanus. We model the matter density profiles with ellipsoidal supervoids, and find that large-scale structure measurements are consistent with a central matter underdensity $\delta_0 \approx -0.25$, with transverse radius $r_{0}^{\perp}\approx55$ Mpc/h and line-of-sight radius $r_{0}^{\parallel}\approx440$ Mpc/h. Based on these findings, we propose a potential explanation for the Cold Spot in the CMB, and for the hot ring feature around it, as a combination of a positive primordial fluctuation and an extremely cold Integrated Sachs-Wolfe imprint.
Models of cosmic inflation suggest that our universe underwent an early phase of accelerated expansion, driven by the dynamics of one or more scalar fields. Inflationary models make specific, quantitative predictions for several observable quantities, including particular patterns of temperature anistropies in the cosmic microwave background radiation. Realistic models of high-energy physics include many scalar fields at high energies. Moreover, we may expect these fields to have nonminimal couplings to the spacetime curvature. Such couplings are quite generic, arising as renormalization counterterms when quantizing scalar fields in curved spacetime. In this chapter I review recent research on a general class of multifield inflationary models with nonminimal couplings. Models in this class exhibit a strong attractor behavior: across a wide range of couplings and initial conditions, the fields evolve along a single-field trajectory for most of inflation. Across large regions of phase space and parameter space, therefore, models in this general class yield robust predictions for observable quantities that fall squarely within the "sweet spot" of recent observations.
Interdependence of luminosity distance and angular diameter distance, shown by the distance duality relation (DDR) is very significant in observational Cosmology. Any deviation from this relation highlights the emergence of new physics. Our aim in this work is to check the consistency of this relation using a very efficient non-parametric method, LOESS with SIMEX. This technique avoids dependency on the cosmological model and works with a minimal set of assumptions. We use the Union 2.1 SNe Ia data for luminosity distance while the angular diameter distances are obtained from X-ray surface brightness and Sunyaev-Zeldovich (S-Z) effect measurement of galaxy clusters by assuming elliptical and spherical profiles. We find no evidence of deviation from {\eta} = 1 and both geometries of galaxy clusters are fairly compatible within 1{\sigma}.
We discuss mixed inflaton and spectator field models where both the fields are responsible for the observed density fluctuations. We use the current CMB data to constrain both the general mixed model as well as some specific representative scenarios, and collate the results with the model predictions for the CMB spectral $\mu$ distortion. We find the posterior distribution of $\mu$ using MCMC chains and demonstrate that the standard single-field inflaton model typically predicts $\mu \sim 10^{-8}$ with a relatively narrow distribution, whereas for the mixed models, the distribution turns out to be much broader, and $\mu$ could be larger by almost an order of magnitude. Hence future experiments of $\mu$ distortion could provide a tool for the critical testing of the mixed source models of the primordial perturbation.
We explore the scalar field quintessence freezing model of dark energy with the inverse Ratra-Peebles potential. We study the cosmic expansion and the large scale structure growth rate. We use recent measurements of the growth rate and the baryon acoustic oscillation peak positions to constrain the matter density $\Omega_\mathrm{m}$ parameter and the model parameter $\alpha$ that describes the steepness of the scalar field potential. We solve jointly the equations for the background expansion and for the growth rate of matter perturbations. The obtained theoretical results are compared with the observational data. We perform the Baysian data analysis to derive constraints on the model parameters.
We probe the hypothesis of cosmological isotropy using the Planck Sunyaev-Zeldovich (PSZ) galaxy clusters data set. Our analyses consist on a hemispherical comparison of the clusters angular distribution, searching for a preferred direction in the large-scale structure of the Universe. We obtain a maximal dipolar signal at the direction $(l,b) = (53.44^{\circ},41.81^{\circ})$ whose antipode points toward $(l,b) = (233.44^{\circ},-41.81^{\circ})$. Interestingly, this antipode is marginally consistent with the anomalous Cold Spot found in the Cosmic Microwave Background, located at $(l,b) \simeq (209^ {\circ},-57^ {\circ})$, which might be possibly aligned with a supervoid at $z \sim 0.2$ with $\sim 200 \; \mathrm{Mpc/h}$ of radius. The statistical significance of this result is assessed with ensembles of Monte Carlo realisations, finding that only a small number of runs are able to reproduce a close direction to this one, hence rejecting the null hypothesis of such direction being a random fluctuation of the data. Moreover, the PSZ catalogue presents a mild discrepancy with the isotropic realisations unless we correct some effects, such as the non-uniform exposure function of Planck's observational strategy, on the simulated data sets. We also perform a similar analysis to a smaller, albeit optimised sub-sample of PSZ sources, finding a better concordance with isotropic realisations, yet no correlation with the supervoid is obtained this time. Thus, we conclude that the dipole anisotropy found on galaxy clusters angular distribution can be partially attributed to an anomalous feature in the large-scale structure, though the significance of this result is sufficiently reduced when corrections to systematic effects are taken into account.
We propose an alternative classical theory of gravity which assumes that background geometry of the Universe is fixed four dimensional Euclidean space and gravity is a vector field $A_{k}$ in this space which breaks the Euclidean symmetry. Direction of $A_{k}$ gives the time coordinate, while perpendicular directions are spatial coordinates. Vector gravitational field is coupled to matter universally and minimally through the equivalent metric $f_{ik}$ which is a functional of $A_{k}$. We show that such assumptions yield a unique theory of gravity, it is free of black holes and to the best of our knowledge it passes all available tests. For cosmology our theory predicts the same evolution of the Universe as general relativity with cosmological constant and zero spatial curvature. However, the present theory provides explanation of the dark energy as energy of gravitational field induced by the Universe expansion and yields, with no free parameters, the value of $\Omega _{\Lambda }=2/3\approx 0.67$ which agrees with the recent Planck result $\Omega _{\Lambda }=0.686\pm 0.02$. Such striking agreement with cosmological data indicates that gravity has a vector, rather than tensor, origin. Vector gravity can be tested by making more accurate measurement of the time delay of radar signal traveling near the Sun, by improving accuracy of the light deflection experiments or measuring polarization of gravitational waves which differs from those in general relativity. Resolving the supermassive object at the center of our Galaxy with VLBA could provide another possible test of gravity and also shed light on the nature of dark matter as we argued in JCAP ${\bf 10}$, 018 (2007).
Light fields get large scale fluctuations during inflation. If some of them are electrically charged, then large scale fluctuations of the electric charge will be generated. As a consequence, any finite portion of the Universe, including our observable one, will carry a net electric charge. This fact does not require any form of breaking of the gauge symmetry at any time. We discuss under which conditions such a charge is maintained until the end of inflation, and we estimate its expected magnitude both in the case of charged fermions and of charged scalars. While one charged fermion species yields a charge density that is several orders of magnitude below the observational constraints, charged scalars can easily exceed those constraints.
We use the Illustris simulation to study the relative contributions of in situ star formation and stellar accretion to the build-up of galaxies over an unprecedentedly wide range of masses ($M_{\ast} = 10^9-10^{12} \, {\rm M_{\odot}}$), galaxy types, environments, and assembly histories. We find that the `two-phase' picture of galaxy formation predicted by some models is a good approximation only for the most massive galaxies in our simulation -- namely, the stellar mass growth of galaxies below a few times $10^{11} \, {\rm M_{\odot}}$ is dominated by in situ star formation at all redshifts, while galaxies above this mass at $z \lesssim 1$ grow primarily by accretion of stars via mergers. The fraction of the total stellar mass of galaxies at $z=0$ contributed by accreted stars shows a strong dependence on galaxy stellar mass, ranging from about 10% for Milky Way-sized galaxies to over 80% for $M_{\ast} \approx 10^{12} \, {\rm M_{\odot}}$ objects, yet with a large galaxy-to-galaxy variation. At a fixed stellar mass, elliptical galaxies and those formed at the centres of younger haloes exhibit larger fractions of ex situ stars than disc-like galaxies and those formed in older haloes. On average, $\sim$50% of the ex situ stellar mass comes from major mergers (stellar mass ratio $\mu > 1/4$), $\sim$20% from minor mergers ($1/10 < \mu < 1/4$), $\sim$20% from very minor mergers ($\mu < 1/10$), and $\sim$10% from stars that were stripped from surviving galaxies (e.g. flybys or ongoing mergers). These components are spatially segregated, with in situ stars dominating the innermost regions of galaxies, and ex situ stars being deposited at larger galactocentric distances in order of decreasing merger mass ratio. The `transition' radius where ex situ stars begin to dominate over the in situ class decreases for more massive galaxies and correlates strongly with the total ex situ fraction.
We derive H{\alpha} fluxes for a large spectroscopic and photometric-redshift-selected sample of sources over GOODS-North and South in the redshift range z = 3.8-5.0 with deep HST, Spitzer/IRAC, and ground-based observations. The H{\alpha} flux is inferred based on the offset between the IRAC 3.6 {\mu}m flux and that predicted from the best-fit SED. We demonstrate that the H{\alpha} flux correlates well with dust- corrected UV star-formation rate (SFR) and therefore can serve as an independent SFR indicator. However, we also find a systematic offset in the SFR_H{\alpha}/SFR_UV ratios for z ~ 4-5 galaxies relative to local relations (assuming the same dust corrections for nebular regions and stellar light). We show that we can resolve the modest tension in the inferred SFRs by assuming bluer intrinsic UV slopes (increasing the dust correction), a rising star-formation history or assuming a low metallicity stellar population with a hard ionizing spectrum (increasing the L_H{\alpha}/SFR ratio). Using H{\alpha} as a SFR indicator, we find a higher normalization of the star formation main sequence compared to recent SED-based determinations and also derive the SFR functions at z ~ 4-8. In addition, we assess for the first time the burstiness of star formation in z ~ 4 galaxies on <100 Myr time scales by comparing UV and H{\alpha}-based sSFRs; their one-to-one relationship argues against significantly bursty star-formation histories. Further progress will be made on these results, by incorporating new results from ALMA to constrain the dust-obscured star formation in high-redshift UV-selected samples.
We have studied a sample of 89 very isolated elliptical galaxies at z < 0.08 and compared their properties with elliptical galaxies located in a high-density environment such as the Coma supercluster. Our aim is to probe the role of environment on the morphological transformation and quenching of elliptical galaxies as a function of mass. In addition, we elucidate about the nature of a particular set of blue and star-forming isolated ellipticals identified here. We study physical properties of ellipticals such as color, specific star formation rate, galaxy size and stellar age as a function of stellar mass and environment based on SDSS data. We analyze in more detail the blue star-forming isolated ellipticals through photometric characterization using GALFIT and infer their star formation history using STARLIGHT. Among the isolated ellipticals ~ 20% are blue, 8% are star-forming and ~ 10% are recently quenched, while among the Coma ellipticals ~ 8% are blue and just <= 1% are star-forming or recently quenched. There are four isolated galaxies (~ 4.5%) that are blue and star-forming at the same time. These galaxies, with masses between 7 x 10^9 and 2 x 10^10 h-2 M_sun, are also the youngest galaxies with light-weighted stellar ages <= 1 Gyr and exhibit bluer colors toward the galaxy center. Around 30-60% of their present-day luminosity, but only < 5% of their present-day mass, is due to star formation in the last 1 Gyr. The processes of morphological transformation and quenching seem to be in general independent of environment since most of elliptical galaxies are "red and dead", although the transition to the red sequence should be faster for isolated ellipticals. In some cases, the isolated environment seems to propitiate the rejuvenation of ellipticals by recent (< 1 Gyr) cold gas accretion.
We develop new scenarios of large field inflation in type IIA string compactifications in which the key ingredient is a D6-brane that creates a potential for a B-field axion. The potential has the multi-branched structure typical of F-term axion monodromy models and, near its supersymmetric minima, it is described by a 4d supergravity model of chaotic inflation with a stabiliser field. The same statement applies to the D6-brane Wilson line, which can also be considered as an inflaton candidate. We analyse both cases in the context of type IIA moduli stabilisation, finding an effective potential for the inflaton system and a simple mechanism to lower the inflaton mass with respect to closed string moduli stabilised by fluxes. Finally, we compute the B-field potential for trans-Planckian field values by means of the DBI action. The effect of Planck suppressed corrections is a flattened potential which, in terms of the compactification parameters, interpolates between linear and quadratic inflation. This renders the cosmological parameters of these models compatible with current experimental bounds, with the tensor-to-scalar ratio ranging as 0.08 < r < 0.12
The duration distribution of 947 GRBs observed by $Swift$/BAT, as well as its subsample of 347 events with measured redshift, allowing to examine the durations in both the observer and rest frames, are examined. Using a maximum log-likelihood method, mixtures of two and three standard Gaussians are fitted to each sample, and the adequate model is chosen based on the value of the difference in the log-likelihoods, Akaike information criterion and Bayesian information criterion. It is found that a two-Gaussian is a better description than a three-Gaussian, and that the presumed intermediate-duration class is unlikely to be present in the $Swift$ duration data.
Is Cosmic Censorship special to General Relativity, or can it survive a violation of equivalence principle? Recent studies have shown that singularities in Lorentz violating Einstein-Aether (or Horava-Lifhsitz) theories can lie behind a universal horizon in simple black hole spacetimes. Even infinitely fast signals cannot escape these universal horizons. We extend this result, for an incompressible aether, to 3+1d dynamical or spinning spacetimes which possess inner killing horizons, and show that a universal horizon always forms in between the outer and (would-be) inner horizons. This finding suggests a notion of Cosmic Censorship, given that geometry in these theories never evolves beyond the universal horizon (avoiding potentially singular inner killing horizons). A surprising result is that there are 3 distinct possible stationary universal horizons for a spinning black hole, only one of which matches the dynamical spherical solution. This motivates dynamical studies of collapse in Einstein-Aether theories beyond spherical symmetry, which may reveal instabilities around the spherical solution.
Assuming the existence of a cosmological constant depending on time, we study the evolution of this field in a local region of spacetime. Solving the standard equations of Einstein Relativity in the weak field approximation we find two asymptotes in the behavior of the cosmological constant. Their meaning is the existence of an inflationary era both in the far past and in the future. A trace of the initial acceleration of the Universe can be found also in the local behavior of cosmological constant.
In this paper we apply the tools of the dynamical systems theory in order to uncover the whole asymptotic structure of the vacuum interactions of a galileon model with a cubic derivative interaction term. It is shown that, contrary to what occurs in the presence of background matter, the galileon interactions of vacuum appreciably modify the late-time cosmic dynamics. In particular, a local late-time attractor representing phantom behavior arises which is inevitably associated with a big rip singularity. It seems that the gravitational interactions of the background matter with the galileon screen the effects of the gravitational self-interactions of the galileon, thus erasing any potential modification of the late-time dynamics by the galileon vacuum processes. Unlike other galileon models inspired in the DGP scenario, self-accelerating solutions do not arise in this model.
Very recently the Dark Energy Survey (DES) Collaboration has released their second group of Dwarf spheroidal (dSph) galaxy candidates. With the publicly-available Pass 8 data of Fermi-LAT we search for $\gamma-$ray emissions from the directions of these eight newly discovered dSph galaxy candidates. No statistically significant $\gamma-$ray signal has been found in the combined analysis of these sources. With the empirically estimated J-factors of these sources, the constraint on the annihilation channel of $\chi\chi \rightarrow \tau^{+}\tau^{-}$ is comparable to the bound set by the joint analysis of fifteen previously known dSphs with kinematically constrained J-factors for the dark matter mass $m_\chi>250$ GeV. In the direction of Tuc III, one of the nearest dSph galaxy candidates that is $\sim 25$ kpc away, there is a weak $\gamma-$ray signal and its peak test statistic (TS) value for the dark matter annihilation channel $\chi\chi\rightarrow \tau^{+}\tau^{-1}$ is $\approx 6.7$. The significance of the possible signal likely increases with time. The combined analysis of $\gamma-$rays in the directions of Reticulum 2, the other "nearby" source reported in early 2015 by DES collaboration, and Tuc III yields more significant though still weak signal and in the case of $\chi\chi\rightarrow \tau^{+}\tau^{-1}$ we have the highest ${\rm TS}\approx 14$ for $m_\chi \approx 16$ GeV. More data is highly needed to pin down the physical origin.
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We show that a significant correlation (up to 5sigma) emerges between the
bulge index, defined to be larger for larger bulge/disk ratio, in spiral
galaxies with similar luminosities in the Galaxy Zoo 2 of SDSS and the number
of tidal-dwarf galaxies in the catalogue by Kaviraj et al. (2012).
In the standard cold or warm dark-matter cosmological models the number of
satellite galaxies correlates with the circular velocity of the dark matter
host halo. In generalized-gravity models without cold or warm dark matter such
a correlation does not exist, because host galaxies cannot capture in-falling
dwarf galaxies due to the absence of dark-matter-induced dynamical friction.
However, in such models a correlation is expected to exist between the bulge
mass and the number of satellite galaxies, because bulges and tidal-dwarf
satellite galaxies form in encounters between host galaxies. This is not
predicted by dark matter models in which bulge mass and the number of
satellites are a priori uncorrelated because higher bulge/disk ratios do not
imply higher dark/luminous ratios. Hence, our correlation reproduces the
prediction of scenarios without dark matter, whereas an explanation is not
found readily from the a priori predictions of the standard scenario with dark
matter. Further research is needed to explore whether some application of the
standard theory may explain this correlation.
We apply the Karhunen-Lo\'eve (KL) methods to cosmic microwave background (CMB) datasets, and show that we can recover the input cosmology and obtain the marginalized likelihoods in $\Lambda$CDM cosmologies in under a minute, much faster than Markov Chain Monte Carlo (MCMC) methods. This is achieved by forming a linear combination of the power spectra at each multipole $l$, and solving a system of simultaneous equations such that the Fisher matrix is locally unchanged. Instead of carrying out a full likelihood evaluation over the whole parameter space, we need evaluate the likelihood only for the parameter of interest, with the data compression effectively marginalizing over all other parameters. The weighting vectors contain insight about the physical effects of the parameters on the cosmic microwave background (CMB) anisotropy power spectrum $C_l$. The shape and amplitude of these vectors give an intuitive feel for the physics of the CMB, the sensitivity of the observed spectrum to cosmological parameters, and the relative sensitivity of different experiments to cosmological parameters. We test this method on exact theory $C_l$ as well as on a WMAP-like (Wilkinson Microwave Anisotropy Probe) CMB dataset generated from a random realization of a fiducial cosmology, comparing the compression results to those from a full likelihood analysis using CosmoMC. After showing that the method works, we apply it to the temperature power spectrum from the WMAP 7-year data release, and discuss the successes and limitations of our method as applied to a real dataset.
The bulk of cosmic matter resides in a dilute reservoir that fills the space between galaxies, the intergalactic medium (IGM). The history of this reservoir is intimately tied to the cosmic histories of structure formation, star formation, and supermassive black hole accretion. Our models for the IGM at intermediate redshifts (2<z<5) are a tremendous success, quantitatively explaining the statistics of Lyman-alpha absorption of intergalactic hydrogen. However, at both lower and higher redshifts (and around galaxies) much is still unknown about the IGM. We review the theoretical models and measurements that form the basis for the modern understanding of the IGM, and we discuss unsolved puzzles (ranging from the largely unconstrained process of reionization at high-z to the missing baryon problem at low-z), highlighting the efforts that have the potential to solve them.
Analysis of the correlation between the angular positions of distant radio galaxies on the spherical sky and the orientations of their polarization vectors with respect to their major axes indicates a dipolar anisotropy in the large scale. We have considered FRW metric with a single mode of large-scale scalar perturbation which includes both anisotropy and inhomogeneity. Using Newman-Penrose formalism, we have determined the effect of the perturbation on the change of the angle between the galaxy major axis and its polarization vector as the radiation propagates. We argue that this perturbation can lead to the observed dipole anisotropy in the distribution of radio polarization.
We want to characterize the dynamical state of galaxy clusters detected with the Sunyaev-Zeldovich (SZ) effect by Planck and compare them with the dynamical state of clusters selected in X-rays survey. We analyzed a representative subsample of the Planck SZ catalogue, containing the 132 clusters with the highest signal to noise ratio and characterize their dynamical state using as indicator the projected offset between the peak of the X-ray emission and the position of the Brightest cluster galaxy. We study the distribution of our indicator in our sample and compare it to its distribution in X-ray selected samples (HIFLUGCS, MACS and REXCESS). The distributions are significantly different and the fraction of relaxed objects is smaller in the Planck sample ($52 \pm 4 \%$) than in X-ray samples ($\simeq 74\%$) We interpret this result as an indication of different selection effects affecting X-rays (e.g. "cool core bias") and SZ surveys of galaxy clusters.
Motivated by recent claims of a compelling ~3.5 keV emission line from nearby galaxies and galaxy clusters, we investigate a novel plasma model incorporating a charge exchange component obtained from theoretical scattering calculations. Fitting this kind of component with a standard thermal model yields positive residuals around 3.5 keV, produced mostly by S XVI transitions from principal quantum numbers n > 8 to the ground. Such high-n states can only be populated by the charge exchange process. In this scenario, the observed 3.5 keV line flux in clusters can be naturally explained by an interaction in an effective volume of ~1 kpc^3 between a ~3 keV temperature plasma and cold dense clouds moving at a few hundred km/s. The S XVI lines at ~3.5 keV also provide a unique diagnostic of the charge exchange phenomenon in hot cosmic plasmas.
We introduce methods which allow observed galaxy clustering to be used together with observed luminosity or stellar mass functions to constrain the physics of galaxy formation. We show how the projected two-point correlation function of galaxies in a large semi-analytic simulation can be estimated to better than ~10% using only a very small subsample of the subhalo merger trees. This allows measured correlations to be used as constraints in a Monte Carlo Markov Chain exploration of the astrophysical and cosmological parameter space. An important part of our scheme is an analytic profile which captures the simulated satellite distribution extremely well out to several halo virial radii. This is essential to reproduce the correlation properties of the full simulation at intermediate separations. As a first application, we use low-redshift clustering and abundance measurements to constrain a recent version of the Munich semi-analytic model. The preferred values of most parameters are consistent with those found previously, with significantly improved constraints and somewhat shifted "best" values for parameters that primarily affect spatial distributions. Our methods allow multi-epoch data on galaxy clustering and abundance to be used as joint constraints on galaxy formation. This may lead to significant constraints on cosmological parameters even after marginalising over galaxy formation physics.
We demonstrate how the image analysis technique of wavelet decomposition can be applied to the gamma-ray sky to separate emission on different angular scales. New structures on scales that differ from the scales of the conventional astrophysical foreground and background uncertainties can be robustly extracted, allowing a model-independent characterization with no presumption of exact signal morphology. As a test case, we generate mock gamma-ray data to demonstrate our ability to extract extended signals without assuming a fixed spatial template. For some point source luminosity functions, our technique also allows us to differentiate a diffuse signal in gamma-rays from dark matter annihilation and extended gamma-ray point source populations in a data-driven way.
We compare global predictions from the EAGLE hydrodynamical simulation, and two semi-analytic (SA) models of galaxy formation, L-GALAXIES and GALFORM. All three models include the key physical processes considered to be essential for the formation and evolution of galaxies and their parameters are calibrated against a small number of observables at $z\approx 0$. The two SA models have been applied to merger trees constructed from the EAGLE dark matter only simulation. GALFORM has been run with two prescriptions for the ram pressure stripping of hot gas from satellites: instantaneous or gradual stripping. We find that at $z\leq 2$, both the galaxy stellar mass functions for stellar masses $M_{*} < 10^{10.5} {\rm M}_{\odot}$ and the median specific star formation rates (sSFRs) in the three models agree to better than 0.4 dex. The evolution of the sSFR predicted by the three models closely follows the mass assembly history of dark matter haloes. Where we do find interesting differences we vary model parameters or select subsets of galaxies to determine the main cause of the difference. In both EAGLE and L-GALAXIES there are more central passive galaxies with $M_{*} < 10^{9.5} {\rm M}_{\odot}$ than in GALFORM. This difference is related to galaxies that have entered and then left a larger halo and which are treated as satellites in GALFORM. In the range 0<z<1, the slope of the evolution of the star formation rate density in EAGLE is a factor of $\approx 1.5$ steeper than for the two SA models. The median sizes for galaxies with $M_{*} > 10^{9.5} {\rm M}_{\odot}$ differ in some instances by an order of magnitude, while the stellar mass-size relation in EAGLE is a factor of $\approx 2$ tighter than for the two SA models. Our results suggest the need for a revision of the galactic wind treatment in SA models and of the effect that the baryonic self-gravity has on the underlying dark matter.
Visibility scintillation resulting from wave propagation through the turbulent ionosphere can be an important sources of noise at low radio frequencies ($\nu\lesssim 200$ MHz). Many low frequency experiments are underway to detect the power spectrum of brightness temperature fluctuations of the neutral-hydrogen $21$-cm signal from the Epoch of Reionization (EOR: $12\gtrsim z\gtrsim 7$, $100\lesssim \nu \lesssim 175$ MHz). In this paper, we derive scintillation noise power-spectra in such experiments while taking into account the effects of typical data processing operations such as self-calibration and Fourier synthesis. We find that for minimally redundant arrays such as LOFAR and MWA, scintillation noise is of the same order of magnitude as thermal noise, has a spectral coherence dictated by stretching of the snapshot $uv$-coverage with frequency, and thus is confined to the well known wedge-like structure in the cylindrical ($2$-dimensional) power spectrum space. Compact, fully redundant ($d_{\rm core}\lesssim r_{\rm F} \approx 300$ m at $150$ MHz) arrays such as HERA and SKA-LOW (core) will be scintillation noise dominated at all baselines, but the spatial and frequency coherence of this noise will allow it to be removed along with spectrally smooth foregrounds.
Though simple inflationary models describe the CMB well, their corrections are often plagued by infrared effects that obstruct a reliable calculation of late-time behaviour. We adapt to cosmology tools designed to address similar issues in other physical systems with the goal of making reliable late-time inflationary predictions. The main such tool is Open EFTs which reduce in the inflationary case to Stochastic Inflation plus calculable corrections. We apply this to a simple inflationary model that is complicated enough to have dangerous IR behaviour yet simple enough to allow the inference of late-time behaviour. We find corrections to standard Stochastic Inflationary predictions for the noise and drift, and we find these corrections ensure the IR finiteness of both these quantities. The late-time probability distribution, ${\cal P}(\phi)$, for super-Hubble field fluctuations are obtained as functions of the noise and drift and so these too are IR finite. We compare our results to other methods (such as large-$N$ models) and find they agree when these models are reliable. In all cases we can explore in detail we find IR secular effects describe the slow accumulation of small perturbations to give a big effect: a significant distortion of the late-time probability distribution for the field. But the energy density associated with this is only of order $H^4$ at late times and so does {\em not} generate a dramatic gravitational back-reaction.
Recently, an interesting inflationary scenario, named Gauss-Bonnet inflation, is proposed by Kanti et al.~\cite{Kanti:2015pda,Kanti:2015dra}. In the model, there is no inflaton potential but the inflaton couples to the Guass-Bonnet term. In the case of quadratic coupling, they find inflation occurs with graceful exit. The scenario is attractive because of the natural set-up. However, we show there exists the gradient instability in the tensor perturbations in this inflationary model. We further prove the no-go theorem for the Gauss-Bonnet inflation without an inflaton potential.
We present a model for the seeding and evolution of magnetic fields in galaxies by supernovae (SN). SN explosions during galaxy assembly provide seed fields, which are subsequently amplified by compression, shear flows and random motions. Our model explains the origin of microG magnetic fields within galactic structures. We implement our model in the MHD version of the cosmological simulation code Gadget-3 and couple it with a multi-phase description of the interstellar medium. We perform simulations of Milky Way-like galactic halo formation and analyze the distribution and strength of the magnetic field. We investigate the intrinsic rotation measure (RM) evolution and find RM values exceeding 1000 rad/m*m at high redshifts and RM values around 10 rad/m*m at present-day. We compare our simulations to a limited set of observational data points and find encouraging similarities. In our model, galactic magnetic fields are a natural consequence of the very basic processes of star formation and galaxy assembly.
Using the cosmological hydrodynamics simulation Horizon-AGN, we investigate the spatial distribution of satellite galaxies relative to their central counterpart in the redshift range between 0.3 and 0.8. We find that, on average, these satellites tend to be located on the galactic plane of the central object. This effect is detected for central galaxies with a stellar mass larger than 10^10 solar masses and found to be strongest for red passive galaxies, while blue galaxies exhibit a weaker trend. For galaxies with a minor axis parallel to the direction of the nearest filament, we find that the coplanarity is stronger in the vicinity of the central galaxy, and decreases when moving towards the outskirts of the host halo. By contrast, the spatial distribution of satellite galaxies relative to their closest filament follows the opposite trend: their tendency to align with them dominates at large distances from the central galaxy, and fades away in its vicinity. Relying on mock catalogs of galaxies in that redshift range, we show that massive red centrals with a spin perpendicular to their filament also have corotating satellites well aligned with both the galactic plane and the filament. On the other hand, lower-mass blue centrals with a spin parallel to their filament have satellites flowing straight along this filament, and hence orthogonally to their galactic plane. The orbit of these satellites is then progressively bent towards a better alignment with the galactic plane as they penetrate the central region of their host halo. The kinematics previously described are consistent with satellite infall and spin build-up via quasi-polar flows, followed by a re-orientation of the spin of massive red galaxies through mergers.
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Observations of the cosmic microwave background indicate that baryons account for 5% of the Universe's total energy content. In the local Universe, the census of all observed baryons falls short of this estimate by a factor of two. Cosmological simulations indicate that the missing baryons might not have condensed into virialized haloes, but reside throughout the filaments of the cosmic web (where matter density is larger than average) as a low-density plasma at temperatures of $10^5-10^7$ kelvin, known as the warm-hot intergalactic medium. There have been previous claims of the detection of warm baryons along the line of sight to distant blazars and of hot gas between interacting clusters. These observations were, however, unable to trace the large-scale filamentary structure, or to estimate the total amount of warm baryons in a representative volume of the Universe. Here we report X-ray observations of filamentary structures of gas at $10^7$ kelvin associated with the galaxy cluster Abell 2744. Previous observations of this cluster were unable to resolve and remove coincidental X-ray point sources. After subtracting these, we reveal hot gas structures that are coherent over scales of 8 mergaparsecs. The filaments coincide with over-densities of galaxies and dark matter, with 5-10% of their mass in baryonic gas. This gas has been heated up by the cluster's gravitational pull and is now feeding its core. Our findings strengthen evidence for a picture of the Universe in which a large fraction of the missing baryons reside in the filaments of the cosmic web.
White dwarfs (WDs) are the most promising captors of dark matter (DM) particles in the crests that are expected to build up in the cores of dense stellar clusters. The DM particles could reach sufficient densities in WD cores to liberate energy through self-annihilation. The extinction associated with our Galactic Centre, the most promising region where to look for such effects, makes it impossible to detect the potential associated luminosity of the DM-burning WDs. However, in smaller stellar systems which are close enough to us and not heavily extincted, such as $\omega-$Cen, we may be able to detect DM-burning WDs. We investigate the prospects of detection of DM-burning WDs in a stellar cluster harbouring an IMBH, which leads to higher densities of DM at the centre as compared with clusters without one. We calculate the capture rate of WIMPs by a WD around an IMBH and estimate the luminosity that a WD would emit depending on its distance to the center of the cluster. Direct-summation $N-$body simulations of $\omega-$Cen yield a non-negligible number of WDs in the range of radii of interest. We apply our assumption to published HST/ACS observations of stars in the center of $\omega-$Cen to search for DM burning WDs and, although we are not able to identify any evident candidate because of crowding and incompleteness, we proof that their bunching up at high luminosities would be unique. We predict that DM burning will lead to a truncation of the cooling sequence at the faint end. The detection of DM burning in future observations of dense stellar clusters, such as globular clusters or ultra-compact dwarf galaxies could allow us to probe different models of DM distributions and characteristics such as the DM particle scattering cross section on nucleons. On the other hand, if DM-burning WDs really exist, their number and properties could give hints to the existence of IMBHs.
Certain inflationary models as well as realisations of phase transitions in the early Universe predict the formation of primordial black holes. For most mass ranges, the fraction of matter in the form of primordial black holes is limited by many different observations on various scales. Primordial black holes are assumed to be formed when overdensities that cross the horizon have Schwarzschild radii larger than the horizon. Traditionally it was therefore assumed that primordial black-hole masses were equal to the horizon mass at their time of formation. However, detailed calculations of their collapse show that primordial black holes formed at each point in time should rather form a spectrum of different masses, obeying critical scaling. Though this has been known for more than fifteen years, the effect of this scaling behaviour is largely ignored when considering predictions for primordial black hole mass spectra. In this paper we consider the critical collapse scaling for a variety of models which produce primordial black holes, and find that it generally leads to a shift, broadening and an overall decrease of the mass contained in primordial black holes. This effect is model and parameter dependent and cannot be contained by a constant rescaling of the spectrum; it can become extremely important and should be taken into account when comparing to observational constraints.
We revisit the possibility of constraining the properties of dark matter (DM) by studying the epoch of cosmic reionization. Previous studies have shown that DM annihilation was unlikely to have provided a large fraction of the photons that ionized the universe, but instead played a subdominant role relative to stars and quasars. The DM, however, begins to efficiently annihilate with the formation of primordial microhalos at $z\sim100-200$, much earlier than the formation of the first stars. Therefore, if DM annihilation ionized the universe at even the percent level over the interval $z \sim 20-100$, it can leave a significant imprint on the global optical depth, $\tau$. Moreover, we show that cosmic microwave background (CMB) polarization data and future 21 cm measurements will enable us to more directly probe the DM contribution to the optical depth. In order to compute the annihilation rate throughout the epoch of reionization, we adopt the latest results from structure formation studies and explore the impact of various free parameters on our results. We show that future measurements could make it possible to place constraints on the dark matter's annihilation cross section that are at a level comparable to those obtained from the observations of dwarf galaxies, cosmic ray measurements, and studies of recombination.
Within the scheme of conformal cyclic cosmology (CCC), information can be transmitted from aeon to aeon. Accordingly, the "Fermi paradox" and the SETI programme - of communication by remote civilizations - may be examined from a novel perspective: such information could, in principle, be encoded in the cosmic microwave background. The current empirical status of CCC is also discussed.
We use the Dark-ages, Reionization And Galaxy-formation Observables from Numerical Simulations (DRAGONS) framework to investigate the effect of galaxy-formation physics on the morphology and statistics of ionized hydrogen (HII) regions during the Epoch of Reioinization (EoR). DRAGONS self-consistently couples a semi-analytic galaxy-formation model with the inhomogeneous ionizing UV background, and can therefore be used to study the dependence of morphology and statistics of reionization on feedback phenomena of the ionizing source galaxy population. Changes in galaxy-formation physics modify the sizes of HII regions and the amplitude and shape of 21-cm power spectra. Of the galaxy physics investigated, we find that supernova feedback plays the most important role in reionization, with HII regions up to $\approx 20$ per cent smaller and a fractional difference in the amplitude of power spectra of up to $\approx 17$ per cent at fixed ionized fraction in the absence of this feedback. We compare our galaxy-formation-based reionization models with past calculations that assume constant stellar-to-halo mass ratios and find that with the correct choice of minimum halo mass, such models can mimic the predicted reionization morphology. Reionization morphology at fixed neutral fraction is therefore not uniquely determined by the details of galaxy formation, but is sensitive to the mass of the haloes hosting the bulk of the ionizing sources. Simple EoR parametrizations are therefore accurate predictors of reionization statistics. However, a complete understanding of reionization using future 21-cm observations will require interpretation with realistic galaxy-formation models, in combination with other observations.
Both WMAP and Planck data show the significant odd-multipole preference in the large scales of cosmic microwave background (CMB) radiation temperature anisotropies, which is a crucial clue for the violation of the cosmological principle, if it originates from the cosmological reasons. By defining various direction dependent statistics in the full-sky Planck 2015 maps, like those in the previous works [P. Naselsky \emph{et al}., Astrophys. J. {\bf 749}, 31 (2012); W. Zhao, Phys. Rev. D {\bf 89}, 023101 (2014)], we found that the CMB parity asymmetry has a preferred direction, which is independent of the choices of the statistics. In particular, this preferred axis is strongly aligned with those in the CMB quadrupole and octopole, as well as that in CMB kinematic dipole, which hints their non-cosmological origin. In the realistic observations, the foreground residuals are inevitable, which should be masked to avoid the possible influence on cosmological results. In this paper, we extend our previous analyses to the masked Planck 2015 data. By defining the similar direction dependent statistic in the masked map, we find the direction preference of the CMB parity asymmetry, and also the preferred axis is coincided with that found in the full-sky analysis. So, our conclusions on the CMB parity violation and its directional properties are stabilized.
We discuss a scenario where the DAMA modulation effect is explained by a Weakly Interacting Massive Particle (WIMP) which upscatters inelastically to a heavier state and predominantly couples to the spin of protons. In this scenario constraints from xenon and germanium targets are evaded dynamically, due to the suppression of the WIMP coupling to neutrons, while those from fluorine targets are evaded kinematically, because the minimal WIMP incoming speed required to trigger upscatters off fluorine exceeds the maximal WIMP velocity in the Galaxy, or is very close to it. In this scenario WIMP scatterings off sodium are usually sensitive to the large-speed tail of the WIMP velocity distribution and modulated fractions of the signal close to unity arise in a natural way. On the other hand, a halo-independent analysis with more conservative assumptions about the WIMP velocity distribution allows to extend the viable parameter space to configurations where large modulated fractions are not strictly necessary. We discuss large modulated fractions in the Maxwellian case showing that they imply a departure from the usual cosine time dependence of the expected signal in DAMA. However we explicitly show that the DAMA data is not sensitive to this distortion, both in time and frequency space, even in the extreme case of a 100 % modulated fraction. Moreover the same scenario provides an explanation of the maximum in the energy spectrum of the modulation amplitude detected by DAMA in terms of WIMPs whose minimal incoming speed matches the kinematic threshold for inelastic upscatters. For the elastic case the detection of such maximum suggests an inversion of the modulation phase below the present DAMA energy threshold, while this is not expected for inelastic scattering. This may allow to discriminate between the two scenarios in a future low-threshold analysis of the DAMA data.
The control of photometric redshift (photo-$z$) errors is a crucial and challenging task for precision weak lensing cosmology. The spacial cross-correlations (equivalently, the angular cross power spectra) of galaxies between tomographic photo-$z$ bins are sensitive to the true redshift distribution $n_i(z)$ of each bin and hence can help calibrate the photo-$z$ error distribution for weak lensing surveys. Using Fisher matrix analysis, we investigate the contributions of various components of the angular power spectra to the constraints of $n_i(z)$ parameters and demonstrate the importance of the cross power spectra therein, especially when catastrophic photo-$z$ errors are present. We further study the feasibility of reconstructing $n_i(z)$ from galaxy angular power spectra using Markov Chain Monte Carlo estimation. Considering an LSST-like survey with $10$ photo-$z$ bins, we find that the underlying redshift distribution can be determined with a fractional precision ($\sigma(\theta)/\theta$ for parameter $\theta$) of roughly $1\%$ and $10\%$ for the mean redshift and width of $n_i(z)$, respectively.
Evidences for late-time acceleration of the Universe are provided by multiple complementary probes, such as observations of distant Type Ia supernovae (SNIa), cosmic microwave background (CMB), baryon acoustic oscillations (BAO), large scale structure (LSS), and the integrated Sachs-Wolfe (ISW) effect. In this work we shall focus on the ISW effect, which consists of small secondary fluctuations in the CMB produced whenever the gravitational potentials evolve due to transitions between dominating fluids, e.g., matter to dark energy dominated phase. Therefore, if we assume a flat universe, as supported by primary CMB data, then a detection of the ISW effect can be correlated to a measurement of dark energy and its properties. In this work, we present a Bayesian estimate of the CMB-LSS cross-correlation signal. As local tracers of the matter distribution at large scales we have used the Two Micron All Sky Survey (2MASS) galaxy catalog and, for the CMB temperature fluctuations, the nine-year data release of the Wilkinson Microwave Anisotropy Probe (WMAP9). The method is based on the estimate of the likelihood for measuring a combined set consisting of a CMB temperature and a galaxy contrast maps, provided we have some information on the statistical properties of the fluctuations affecting these maps. The likelihood is estimated by a sampling algorithm, therefore avoiding the computationally demanding techniques of direct evaluation either in pixel or harmonic space. The results show a dominance of cosmic variance over the weak recovered signal, due mainly to the shallowness of the catalog used, with systematics associated to the sampling algorithm playing a secondary role as sources of uncertainty. When combined with other complementary probes, the method presented in this paper is expected to be a useful tool to late-time acceleration studies in cosmology.
Narrow stellar streams in the Milky Way halo are uniquely sensitive to dark-matter subhalos, but many of these may be tidally disrupted. I calculate the interaction between stellar and dark-matter streams using analytical and N-body calculations, showing that disrupting objects can be detected as low-concentration subhalos. Through this effect, we can constrain the streaminess of the halo as well as the orbit and present position of individual dark-matter streams. This will have profound implications for the formation of halos and for direct and indirect-detection dark-matter searches.
We compare the half-light circular velocities, V_{1/2}, of dwarf galaxies in the Local Group to the predicted circular velocity curves of galaxies in the NIHAO suite of LCDM simulations. We use a subset of 34 simulations in which the central galaxy has a stellar luminosity in the range 0.5 x 10^5 < L_V < 2 x 10^8 L_{sun}. The NIHAO galaxy simulations reproduce the relation between stellar mass and halo mass from abundance matching, as well as the observed half-light size vs luminosity relation. The corresponding dissipationless simulations over-predict the V_{1/2}, recovering the problem known as too big to fail (TBTF). By contrast, the NIHAO simulations have expanded dark matter haloes, and provide an excellent match to the distribution of V_{1/2} for galaxies with L_V > 2 x 10^6 L_{sun}. For lower luminosities our simulations predict very little halo response, and tend to over predict the observed circular velocities. In the context of LCDM, this could signal the increased stochasticity of star formation in haloes below M_{halo} \sim 10^{10} M_{sun}, or the role of environmental effects. Thus, haloes that are "too big to fail", do not fail LCDM, but haloes that are "too small to pass" (the galaxy formation threshold) provide a future test of LCDM.
We investigate clustering properties of quasars using a new version of our semi-analytic model of galaxy and quasar formation with state-of-the-art cosmological N-body simulations. In this study, we assume that a major merger of galaxies triggers cold gas accretion on to a supermassive black hole and quasar activity. Our model can reproduce the downsizing trend of the evolution of quasars. We find that the median mass of quasar host dark matter haloes increases with cosmic time by an order of magnitude from z=4 (a few 1e+11 Msun) to z=1 (a few 1e+12 Msun), and depends only weakly on the quasar luminosity. Deriving the quasar bias through the quasar--galaxy cross-correlation function in the model, we find that the quasar bias does not depend on the quasar luminosity, similar to observed trends. This result reflects the fact that quasars with a fixed luminosity have various Eddington ratios and thus have various host halo masses that primarily determine the quasar bias. We also show that the quasar bias increases with redshift, which is in qualitative agreement with observations. Our bias value is lower than the observed values at high redshifts, implying that we need some mechanisms that make quasars inactive in low-mass haloes and/or that make them more active in high-mass haloes.
Dark matter can scatter and excite a nucleus to a low-lying excitation in a direct detection experiment. This signature is distinct from the canonical elastic scattering signal because the inelastic signal also contains the energy deposited from the subsequent prompt de-excitation of the nucleus. A measurement of the elastic and inelastic signal will allow a single experiment to distinguish between a spin-independent and spin-dependent interaction. For the first time, we characterise the inelastic signal for two-phase xenon detectors in which dark matter inelastically scatters off the Xe-129 or Xe-131 isotope. We do this by implementing a realistic simulation of a typical tonne-scale two-phase xenon detector and by carefully estimating the relevant background signals. With our detector simulation, we explore whether the inelastic signal from the axial-vector interaction is detectable with upcoming tonne-scale detectors. We find that two-phase detectors allow for some discrimination between signal and background so that it is possible to detect dark matter that inelastically scatters off either the Xe-129 or Xe-131 isotope for dark matter particles that are heavier than approximately 100 GeV. If, after two years of data, the XENON1T search for elastic scattering nuclei finds no evidence for dark matter, the possibility of ever detecting an inelastic signal from the axial-vector interaction will be almost entirely excluded.
Improving the capabilities of detecting faint X-ray sources is fundamental to
increase the statistics on faint high-z AGN and star-forming galaxies.We
performed a simultaneous Maximum Likelihood PSF fit in the [0.5-2] keV and
[2-7] keV energy bands of the 4 Ms {\em Chandra} Deep Field South (CDFS) data
at the position of the 34930 CANDELS H-band selected galaxies.
For each detected source we provide X-ray photometry and optical counterpart
validation. We validated this technique by means of a raytracing simulation. We
detected a total of 698 X-ray point-sources with a likelihood
$\mathcal{L}$$>$4.98 (i.e. $>$2.7$\sigma$). We show that the prior knowledge of
a deep sample of Optical-NIR galaxies leads to a significant increase of the
detection of faint (i.e. $\sim$10$^{-17}$ cgs in the [0.5-2] keV band) sources
with respect to "blind" X-ray detections. By including previous catalogs, this
work increases the total number of X-ray sources detected in the 4 Ms CDFS,
CANDELS area to 793, which represents the largest sample of extremely faint
X-ray sources assembled to date.
Our results suggest that a large fraction of the optical counterparts of our
X-ray sources determined by likelihood ratio actually coincides with the priors
used for the source detection. Most of the new detected sources are likely
star-forming galaxies or faint absorbed AGN. We identified a few sources
sources with putative photometric redshift z$>$4. Despite the low number
statistics, this sample significantly increases the number of X--ray selected
candidate high-z AGN.
We study the application of a supersymmetric model with two constrained supermultiplets to inflationary cosmology. The first superfield S is a stabilizer chiral superfield satisfying a nilpotency condition of degree 2, S^2=0. The second superfield Phi is the inflaton chiral superfield, which can be combined into a real superfield B=(Phi-Phi*)/2i. The real superfield B is orthogonal to S, S B=0, and satisfies a nilpotency condition of degree 3, B^3=0. We show that these constraints remove from the spectrum the complex scalar sgoldstino, the real scalar inflaton partner (i.e. the "sinflaton"), and the fermionic inflatino. The corresponding supergravity model with de Sitter vacua describes a graviton, a massive gravitino, and one real scalar inflaton, with both the goldstino and inflatino being absent in unitary gauge. We also discuss relaxed superfield constraints where S^2=0 and S Phi* is chiral, which removes the sgoldstino and inflatino, but leaves the sinflaton in the spectrum. The cosmological model building in both of these inflatino-less models offers some advantages over existing constructions.
We construct inflationary models in the context of supergravity with orthogonal nilpotent superfields [1]. When local supersymmetry is gauge-fixed in the unitary gauge, these models describe theories with only a single real scalar (the inflaton), a graviton and a gravitino. Critically, there is no inflatino, no sgoldstino, and no sinflaton in these models. This dramatically simplifies cosmological models which can simultaneously describe inflation, dark energy and SUSY breaking.
We present the Dark-ages Reionization and Galaxy-formation Observables from Numerical Simulations (DRAGONS) program and Tiamat, the collisionless N-body simulation program upon which DRAGONS is built. The primary trait distinguishing Tiamat from other large simulation programs is its density of outputs at high redshift (100 from z=35 to z=5; roughly one every 10 Myr) enabling the construction of very accurate merger trees at an epoch when galaxy formation is rapid and mergers extremely frequent. We find that the friends-of-friends halo mass function agrees well with the prediction of Watson et al. at high masses, but deviates at low masses, perhaps due to our use of a different halo finder or perhaps indicating a break from "universal" behaviour. We then analyse the dynamical evolution of galaxies during the Epoch of Reionization finding that only a small fraction (~20%) of galactic halos are relaxed. We illustrate this using standard relaxation metrics to establish two dynamical recovery time-scales: i) halos need ~1.5 dynamical times following formation, and ii) ~2 dynamical times following a major (3:1) or minor (10:1) merger to be relaxed. This is remarkably consistent across a wide mass range. Lastly, we use a phase-space halo finder to illustrate that major mergers drive long-lived massive phase-space structures which take many dynamical times to dissipate. This can yield significant differences in the inferred mass build-up of galactic halos and we suggest that care must be taken to ensure a physically meaningful match between the galaxy-formation physics of semi-analytic models and the halo finders supplying their input.
We use high resolution N-Body simulations to study the concentration and spin
parameters of dark matter haloes in the mass range $10^8\, {\rm M}_{\odot}\,
h^{-1} < {\rm M} < 10^{11}\, {\rm
M}_{\odot}\, h^{-1}$ and redshifts $5{<}z{<}10$, corresponding to the haloes
of galaxies thought to be responsible for reionization. We build a sub-sample
of equilibrium haloes and contrast their properties to the full population that
also includes unrelaxed systems. Concentrations are calculated by fitting both
NFW and Einasto profiles to the spherically-averaged density profiles of
individual haloes. After removing haloes that are out-of-equilibrium, we find a
$z{>}5$ concentration$-$mass ($c(M)$) relation that is almost flat and well
described by a simple power-law for both NFW and Einasto fits. The intrinsic
scatter around the mean relation is $\Delta c_{\rm{vir}}{\sim1}$ (or 20 per
cent) at $z=5$. We also find that the analytic model proposed by Ludlow et al.
reproduces the mass and redshift-dependence of halo concentrations. Our
best-fit Einasto shape parameter, $\alpha$, depends on peak height, $\nu$, in a
manner that is accurately described by $\alpha {=}0.0070\nu^2{+}0.1839$. The
distribution of the spin parameter, $\lambda$, has a weak dependence on
equilibrium state; $\lambda$ peaks at roughly ${\sim}0.033$ for our relaxed
sample, and at ${\sim}0.04$ for the full population. The spin--virial mass
relation has a mild negative correlation at high redshift.
We study relativistic stars in the simplest model of the de Rham-Gabadadze-Tolley massive gravity which describes the massive graviton without ghost propagating mode. We consider the hydrostatic equilibrium, and obtain the modified Tolman-Oppenheimer-Volkoff equation and the constraint equation coming from the potential terms in the gravitational action. We give analytical and numerical results for quark and neutron stars and discuss the deviations compared with General Relativity and $F(R)$ gravity. It is shown that theory under investigation leads to small deviation from the General Relativity in terms of density profiles and mass-radius relation. Nevertheless, such deviation may be observable in future astrophysical probes.
We show that the measured much larger yield ratio $^3_{\Lambda}$H/$^3$He ($^3_{\overline{\Lambda}}\overline{\text{H}}$/$^3\overline{\text{He}}$) in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV than that in Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV can be understood within a covariant coalescence model if (anti-)$\Lambda$ particles freeze out earlier than (anti-)nucleons but their relative freezeout time is closer at $\sqrt{s_{NN}}=2.76$ TeV than at $\sqrt{s_{NN}}=200$ GeV. The earlier (anti-)$\Lambda$ freezeout can significantly enhance the yield of (anti)hypernucleus $^4_{\Lambda}$H ($^4_{\overline{\Lambda}}\overline{\text{H}}$), leading to that $^4_{\overline{\Lambda}}\overline{\text{H}}$ has an even larger abundance than $^4\overline{\text{He}}$ and provides an easily measured antimatter heavier than $^4\overline{\text{He}}$. The future measurement on $^4_{\Lambda}$H ($^4_{\overline{\Lambda}}\overline{\text{H}}$) would be very useful to understand the (anti-)$\Lambda$ freezeout dynamics and the production mechanism of (anti)hypernuclei in relativistic heavy-ion collisions.
During the first few days after explosion, Type II supernovae (SNe) are dominated by relatively simple physics. Theoretical predictions regarding early-time SN light curves in the ultraviolet (UV) and optical bands are thus quite robust. We present, for the first time, a sample of $57$ $R$-band Type II SN light curves that are well monitored during their rise, having $>5$ detections during the first 10 days after discovery, and a well-constrained time of explosion to within $1-3$ days. We show that the energy per unit mass ($E/M$) can be deduced to roughly a factor of five by comparing early-time optical data to the model of Rabinak & Waxman (2011), while the progenitor radius cannot be determined based on $R$-band data alone. We find that Type II SN explosion energies span a range of $E/M=(0.2-20)\times 10^{51} \; \rm{erg/(10 M}_\odot$), and have a mean energy per unit mass of $\left\langle E/M \right\rangle = 0.85\times 10^{51} \; \rm{erg/(10 M}_\odot$), corrected for Malmquist bias. Assuming a small spread in progenitor masses, this indicates a large intrinsic diversity in explosion energy. Moreover, $E/M$ is positively correlated with the amount of $^{56}\rm{Ni}$ produced in the explosion, as predicted by some recent models of core-collapse SNe. We further present several empirical correlations. The peak magnitude is correlated with the decline rate ($\Delta m_{15}$), the decline rate is weakly correlated with the rise time, and the rise time is not significantly correlated with the peak magnitude. Faster declining SNe are more luminous and have longer rise times. This limits the possible power sources for such events.
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The Planck catalogue of SZ sources limits itself to a significance threshold of 4.5 to ensure a low contamination rate by false cluster candidates. This means that only the most massive clusters at redshift z>0.5, and in particular z>0.7, are expected to enter into the catalogue, with a large number of systems in that redshift regime being expected around and just below that threshold. In this paper, we follow-up a sample of SZ sources from the Planck SZ catalogues from 2013 and 2015. In the latter maps, we consider detections around and at lower significance than the threshold adopted by the Planck Collaboration. To keep the contamination rate low, our 28 candidates are chosen to have significant WISE detections, in combination with non-detections in SDSS/DSS, which effectively selects galaxy cluster candidates at redshifts $z\gtrsim0.5$. By taking r- and z-band imaging with MegaCam@CFHT, we bridge the 4000A rest-frame break over a significant redshift range, thus allowing accurate redshift estimates of red-sequence cluster galaxies up to z~0.8. After discussing the possibility that an overdensity of galaxies coincides -by chance- with a Planck SZ detection, we confirm that 16 of the candidates have likely optical counterparts to their SZ signals, 13 (6) of which have an estimated redshift z>0.5 (z>0.7). The richnesses of these systems are generally lower than expected given the halo masses estimated from the Planck maps. However, when we follow a simplistic model to correct for Eddington bias in the SZ halo mass proxy, the richnesses are consistent with a reference mass-richness relation established for clusters detected at higher significance. This illustrates the benefit of an optical follow-up, not only to obtain redshift estimates, but also to provide an independent mass proxy that is not based on the same data the clusters are detected with, and thus not subject to Eddington bias.
We present galaxy velocity dispersions and dynamical mass estimates for 44 galaxy clusters selected via the Sunyaev-Zel'dovich (SZ) effect by the Atacama Cosmology Telescope. Dynamical masses for 18 clusters are reported here for the first time. Using N-body simulations, we model the different observing strategies used to measure the velocity dispersions and account for systematic effects resulting from these strategies. We find that the galaxy velocity distributions may be treated as isotropic, and that an aperture correction of up to 7 per cent in the velocity dispersion is required if the spectroscopic galaxy sample is sufficiently concentrated towards the cluster centre. Accounting for the radial profile of the velocity dispersion in simulations enables consistent dynamical mass estimates regardless of the observing strategy. Cluster masses $M_{200}$ are in the range $(1-15)\times10^{14}M_\odot$. Comparing with masses estimated from the SZ distortion assuming a gas pressure profile derived from X-ray observations gives a mean SZ-to-dynamical mass ratio of $1.10\pm0.13$, consistent with previous determinations at these mass scales.
We discuss the possibility to implement a viscous cosmological model, attributing to the dark matter component a behaviour described by bulk viscosity. Since bulk viscosity implies negative pressure, this rises the possibility to unify the dark sector. At the same time, the presence of dissipative effects may alleviate the so called small scale problems in the $\Lambda$CDM model. While the unified viscous description for the dark sector does not lead to consistent results, the non-linear behaviour indeed improves the situation with respect to the standard cosmological model.
We point out that a successful inflationary magnetogenesis could be realised if we break the local U(1) gauge symmetry during inflation. The effective electric charge is fixed as a fundamental constant, which allows us to obtain an almost scale invariant magnetic spectrum avoiding both the strong coupling and back reaction problems. We examine the corrections to the primordial curvature perturbation due to these stochastic electromagnetic fields and find that, at both linear and non-linear orders, the contributions from the electromagnetic field are negligible compared to those created from vacuum fluctuations. Finally, the U(1) gauge symmetry is restored at the end of inflation.
Using a generalization of the Madelung transformation, we derive the hydrodynamic representation of the Klein-Gordon-Einstein equations in the weak field limit. We consider a complex self-interacting scalar field with a $\lambda|\varphi|^4$ potential. We study the evolution of the homogeneous background in the fluid representation and derive the linearized equations describing the evolution of small perturbations in a static and in an expanding universe. We compare the results with simplified models in which the gravitational potential is introduced by hand in the Klein-Gordon equation, and assumed to satisfy a (generalized) Poisson equation. We study the evolution of the perturbations in the matter era using the nonrelativistic limit of our formalism. Perturbations whose wavelength is below the Jeans length oscillate in time while pertubations whose wavelength is above the Jeans length grow linearly with the scale factor as in the cold dark matter model. The growth of perturbations in the scalar field model is substantially faster than in the cold dark matter model. When the wavelength of the pertubations approaches the cosmological horizon (Hubble length), a relativistic treatment is mandatory. In that case, we find that relativistic effects attenuate or even prevent the growth of pertubations. This paper exposes the general formalism and provides illustrations in simple cases. Other applications of our formalism will be considered in companion papers.
We investigate the propagation of scalar waves induced by matter sources in the context of scalar-tensor theories of gravity which include screening mechanisms for the scalar degree of freedom. The usual approach when studying these theories in the non-linear regime of cosmological perturbations is based on the assumption that scalar waves travel at the speed of light. Within General Relativity such approximation is good and leads to no loss of accuracy in the estimation of observables. We find, however, that mass terms and non-linearities in the equations of motion lead to propagation and dispersion velocities significantly different from the speed of light. As the group velocity is the one associated to the propagation of signals, a reduction of its value has direct impact on the behavior and dynamics of nonlinear structures within modified gravity theories with screening. For instance, the internal dynamics of galaxies and satellites submerged in large dark matter halos could be affected by the fact that the group velocity is smaller than the speed of light. It is therefore important, within such framework, to take into account the fact that different part of a galaxy will see changes in the environment at different times. A full non-static analysis may be necessary under those conditions.
Studies discerning whether there is a significant correlation between UHECR arrival directions and optical AGN are hampered by the lack of a uniformly selected and complete all-sky optical AGN catalog. To remedy this, we are preparing such a catalog based on the 2MASS Redshift Survey (2MRS), a spectroscopic sample of $\sim 44,500$ galaxies complete to a K magnitude of 11.75 over 91% of the sky. We have analyzed the available optical spectra of these 2MRS galaxies ($\sim 80$% of the galaxies), in order to identify the AGN amongst them with uniform criteria. We present a first-stage release of the AGN catalog for the southern sky, based on spectra from the 6dF Galaxy survey and CTIO telescope. Providing a comparably uniform and complete catalog for the northern sky is more challenging because the spectra for the northern galaxies were taken with different instruments.
Supernovae (SNe) embedded in dense circumstellar material (CSM) may show prominent emission lines in their early-time spectra ($\leq 10$ days after the explosion), owing to recombination of the CSM ionized by the shock-breakout flash. From such spectra ("flash spectroscopy"), we can measure various physical properties of the CSM, as well as the mass-loss rate of the progenitor during the year prior to its explosion. Searching through the Palomar Transient Factory (PTF and iPTF) SN spectroscopy databases from 2009 through 2014, we found 12 Type II SNe showing flash-ionized (FI) signatures in their first spectra. All are younger than 10 days. These events constitute 14\% of all 84 SNe in our sample having a spectrum within 10 days from explosion, and 18\% of SNe~II observed at ages $<5$ days, thereby setting lower limits on the fraction of FI events. We classified as "blue/featureless" (BF) those events having a first spectrum which is similar to that of a black body, without any emission or absorption signatures. It is possible that some BF events had FI signatures at an earlier phase than observed, or that they lack dense CSM around the progenitor. Within 2 days after explosion, 8 out of 11 SNe in our sample are either BF events or show FI signatures. Interestingly, we found that 19 out of 21 SNe brighter than an absolute magnitude $M_R=-18.2$ belong to the FI or BF groups, and that all FI events peaked above $M_R=-17.6$ mag, significantly brighter than average SNe~II.
The Fermi gamma-ray space telescope has revolutionized our understanding of the cosmic gamma-ray background radiation in the GeV band. However, investigation on the cosmic TeV gamma-ray background radiation still remains sparse. Here, we report the lower bound on the cosmic TeV gamma-ray background spectrum placed by the cumulative flux of individual detected extragalactic TeV sources including blazars, radio galaxies, and starburst galaxies. The current limit on the cosmic TeV gamma-ray background above 0.1 TeV is obtained as $3\times10^{-8} (E/100~{\rm GeV})^{-0.6} \exp(-E/2000~{\rm GeV})~{\rm [GeV/cm^2/s/sr]} < E^2dN/dE < 1\times10^{-7} (E/100~{\rm GeV})^{-0.5}~{\rm [GeV/cm^2/s/sr]}$, where the upper bound is set by requirement that the cascade flux from the cosmic TeV gamma-ray background radiation can not exceed the measured cosmic GeV gamma-ray background spectrum (Inoue & Ioka 2012). Two nearby blazars, Mrk 421 and Mrk 501, explain ~70% of the cumulative flux at 0.8-4 TeV, while extreme blazars start to dominate at higher energies. We also provide the cumulative flux from each population, i.e. blazars, radio galaxies, and starburst galaxies which will be the minimum requirement for their contribution to the cosmic TeV gamma-ray background radiation.
Non-Abelian family symmetries offer a very promising explanation for the flavour structure in the Standard Model and its extensions. We explore the possibility that dark matter consists in fermions that transform under a family symmetry, such that the visible and dark sector are linked by the familons - Standard Model gauge singlet scalars, responsible for spontaneously breaking the family symmetry. We study three representative models with non-Abelian family symmetries that have been shown capable to explain the masses and mixing of the Standard Model fermions. One of our central results is the possibility to have dark matter fermions and at least one familon with masses on and even below the experimentally accessible TeV scale. In particular we discuss the characteristic signatures in collider experiments from light familon Fields with a non-Abelian family symmetry, and we show that run I of the LHC is already testing this class of models.
We present the Voigt profile analysis of 132 intervening CIV+CIII components associated with optically-thin HI absorbers at 2.1 < z < 3.4 in the 19 high-quality UVES/VLT and HIRES/Keck QSO spectra. For log N(CIV) = [11.7, 14.1], N(CIII) is proportional to N(CIV) with an exponent (1.42 +- 0.11) and < N(CIII)/N(CIV) > = 1.0 +- 0.3 with a negligible redshift evolution. For 54 CIV components tied (aligned) with HI at log N(HI) = [12.2, 16.0] and log N(CIV) = [11.8, 13.8], the gas temperature T_b estimated from absorption line widths is well-approximated to a Gaussian peaking at log T_b ~ 4.4 +- 0.3 for log T_b = [3.5, 5.5], with a negligible non-thermal contribution. For 32 of 54 tied HI+CIV pairs, also tied with CIII at log N(CIII) = [11.7, 13.8], we ran both photoionisation equilibrium (PIE) and non-PIE (using a fixed temperature T_b) Cloudy models for the Haardt-Madau QSO+galaxy 2012 UV background. We find evidence of bimodality in observed and derived physical properties. High-metallicity branch absorbers have a carbon abundance [C/H]_temp > -1.0, a line-of-sight length L_temp < 20 kpc, and a total (neutral and ionised) hydrogen volume density log n(H, temp) = [-4.5, -3.3] and and log T_b = [3.9, 4.5]. Low-metallicity branch absorbers have [C/H]_temp < -1.0, L_temp = [20, 480] kpc and log n(H, temp) = [-5.2, -4.3] and log T_b ~ 4.5. High-metallicity branch absorbers seem to be originated from extended disks, inner halos or outflowing gas of intervening galaxies, while low-metallicity absorbers are produced by galactic halos or the surrounding IGM filament.
In 2005 Sheldon Glashow has proposed his sinister model, opening the path to composite-dark-matter scenarios, in which heavy stable electrically charged particles bound in neutral atoms play the role of dark matter candidates. Though the general problem of new stable single charged particles, forming with ordinary electrons anomalous isotopes of hydrogen, turned out to be unresolvable in Glashow's scenario, this scenario stimulated development of composite dark matter models, which can avoid the trouble of anomalous isotope overproduction. In the simplest case composite dark matter may consist of -2 charged particles, bound by ordinary Coulomb interaction with primordial helium in OHe dark matter model. The advantage and open problems of this model are discussed.
We present the catalog of optical and infrared counterparts of the Chandra COSMOS-Legacy Survey, a 4.6 Ms Chandra program on the 2.2 square degrees of the COSMOS field, combination of 56 new overlapping observations obtained in Cycle 14 with the previous C-COSMOS survey. In this Paper we report the i, K, and 3.6 micron identifications of the 2273 X-ray point sources detected in the new Cycle 14 observations. We use the likelihood ratio technique to derive the association of optical/infrared (IR) counterparts for 97% of the X-ray sources. We also update the information for the 1743 sources detected in C-COSMOS, using new K and 3.6 micron information not available when the C-COSMOS analysis was performed. The final catalog contains 4016 X-ray sources, 97% of which have an optical/IR counterpart and a photometric redshift, while 54% of the sources have a spectroscopic redshift. The full catalog, including spectroscopic and photometric redshifts and optical and X-ray properties described here in detail, is available online. We study several X-ray to optical (X/O) properties: with our large statistics we put better constraints on the X/O flux ratio locus, finding a shift towards faint optical magnitudes in both soft and hard X-ray band. We confirm the existence of a correlation between X/O and the the 2-10 keV luminosity for Type 2 sources. We extend to low luminosities the analysis of the correlation between the fraction of obscured AGN and the hard band luminosity, finding a different behavior between the optically and X-ray classified obscured fraction.
CR7 is the brightest Lyman-$\alpha$ emitter observed at $z>6$, which shows very strong Lyman-$\alpha$ and HeII 1640 \AA\ line luminosities, but no metal line emission. Previous studies suggest that CR7 hosts either young primordial stars with a total stellar mass of $\sim 10^7\,\mathrm{M}_\odot$ or a black hole of $\sim 10^6\,\mathrm{M}_\odot$. Here, we explore different formation scenarios for CR7 with a semianalytical model, based on the random sampling of dark matter merger trees. We find that primordial stars cannot account for the observed line luminosities because of their short lifetimes and because of early metal enrichment. Black holes that are the remnants of the first stars are either not massive enough, or reside in metal-polluted haloes, ruling out this possible explanation of CR7. Our models instead suggest that direct collapse black holes, which form in metal-free haloes exposed to large Lyman-Werner fluxes, are more likely the origin of CR7. However, this result is derived under optimistic assumptions and future observations are necessary to further constrain the nature of CR7.
We present a simple generalisation of the $\Lambda$CDM model which on the one hand reaches very good agreement with the present day experimental data and provides an internal inflationary mechanism on the other hand. It is based on Palatini modified gravity with quadratic Starobinsky term and generalized Chaplygin gas as a matter source providing, besides a current accelerated expansion, the epoch of endogenous inflation driven by type III freeze singularity. It follows from our statistical analysis that astronomical data favours negative value of the parameter coupling quadratic term into Einstein-Hilbert Lagrangian and as a consequence the bounce instead of initial Big-Bang singularity is preferred.
The theory of the inflationary multiverse changes the way we think about our place in the world. According to its most popular version, our world may consist of infinitely many exponentially large parts, exhibiting different sets of low-energy laws of physics. Since these parts are extremely large, the interior of each of them behaves as if it were a separate universe, practically unaffected by the rest of the world. This picture, combined with the theory of eternal inflation and anthropic considerations, may help to solve many difficult problems of modern physics, including the cosmological constant problem. In this article I will briefly describe this theory and provide links to the some hard to find papers written during the first few years of the development of the inflationary multiverse scenario.
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