We study the prediction of the Effective Field Theory of Large Scale Structures (EFTofLSS) for the matter power spectrum at different redshifts. In previous work, we found that the two-loop prediction can match the nonlinear power spectrum measured from $N$-body simulations at redshift zero at percent level up to $k\sim 0.6\,h\, {\rm Mpc}^{-1}$ after fixing a single free parameter, the so-called "speed of sound". We determine the time evolution of this parameter by matching the EFTofLSS prediction to simulation output at different redshifts, and find that it is well-described by a fitting function that only includes one additional parameter. After the two free parameters are fixed, the prediction agrees to percent level with nonlinear data up to $k\sim 1.2\,h\, {\rm Mpc}^{-1}$ at $z=1$ and $k\sim 2.3\,h\, {\rm Mpc}^{-1}$ at $z=3$, a major improvement with respect to other perturbative techniques. We also develop an accurate way to estimate where the EFTofLSS predictions at different loop orders should fail, based on the sizes of the next-order terms that are neglected, and find agreement with the actual comparisons to data. Finally, we use our matter power spectrum results to perform analytical calculations of lensing potential power spectra corresponding to both CMB and galaxy lensing. This opens the door to future direct applications of the EFTofLSS to observations of gravitational clustering on cosmic scales.
We present results of weak lensing cluster counts obtained from 11 sq.deg SuprimeCam data. Although the area is much smaller than previous work dealing with weak lensing peak statistics, the number density of galaxies usable for weak lensing analysis is about twice as large as those. The higher galaxy number density reduces the noise in the weak lensing mass maps, and thus increases the signal-to-noise ratio of peaks of the lensing signal due to massive clusters. This enables us to construct a weak lensing selected cluster sample by adopting a high threshold S/N, such that the contamination rate due to false signals is small. We find 6 peaks with S/N>5. For all the peaks, previously identified clusters of galaxies are matched within a separation of 1 arcmin, demonstrating good correspondence between the peaks and clusters of galaxies. We evaluate the statistical error using mock weak lensing data, and find Npeak=6+/-3.1 in an effective area of 9.0 sq.deg. We compare the measured weak lensing cluster counts with the theoretical model prediction based on halo models and place the constraint on Omega_m-sigma_8 plane which is found to be consistent with currently standard LCDM models. It is demonstrated that the weak lensing cluster counts can place a unique constraint on sigma_8-c_0 plane, where c_0 is the normalization of the dark matter halo mass-concentration relationship. Finally we discuss prospects for ongoing/future wide field optical galaxy surveys.
Reliable halo mass estimation for a given galaxy system plays an important role both in cosmology and galaxy formation studies. Here we set out to find the way that can improve the halo mass estimation for those galaxy systems with limited brightest member galaxies been observed. Using four mock galaxy samples constructed from semi-analytical formation models, the subhalo abundance matching method and the conditional luminosity functions, respectively, we find that the luminosity gap between the brightest and the subsequent brightest member galaxies in a halo (group) can be used to significantly reduce the scatter in the halo mass estimation based on the luminosity of the brightest galaxy alone. Tests show that these corrections can significantly reduce the scatter in the halo mass estimations by $\sim 50\%$ to $\sim 70\%$ in massive halos depending on which member galaxies are considered. Comparing to the traditional ranking method, we find that this method works better for groups with less than five members, or in observations with very bright magnitude cut.
Spherical collapse of the Bose-Einstein Condensate (BEC) dark matter model is studied. The evolution of perturbed quantities like the density of the collapsed region and its expansion rate are calculated for two scenarios. Firstly, we consider the case of a sharp phase transition (which happens when the critical temperature is reached) from the normal dark matter state to the condensate one. In the second case studied we consider a smooth first order phase transition where there is a continuous conversion of "normal" dark matter to the BEC phase. We calculate in detail the perturbative quantities at nonlinear level presenting numerical results for the physics of the collapse for a wide range of the model's space parameter. The model is properly compared to the standard dark matter scenario.
We apply the modified kinetic theory to study generation of magnetic field due to anomaly in a primordial plasma of the standard model particles at temperature $T>80$~TeV. It is known that a chiral imbalance in such plasma can lead to instabilities responsible for the origin of the magnetic fields. We have shown that inclusion of the Berry curvature term in the kinetic equation along with the collision term in the relaxation approximation can lead to the chiral vorticity effect. This effect was not considered in the earlier literature based on the heuristic application of the kinetic theory. But in the collisionless regime there may not be any vorticity generation. We also argued that the chiral imbalance in the collisionless regime remains subdominant for the primordial plasma compared to the case where the collisions are important.
In this paper we present the first results from implementing two scalar-tensor modified gravity theories, the symmetron and the Hu-Sawicki $f(R)$-gravity model, into a hydrodynamic N-body code with dark matter particles and a baryonic ideal gas. The study is a continuation of previous work where the symmetron and $f(R)$ have been successfully implemented in the RAMSES code, but for dark matter only. By running simulations, we show that the deviation from $\Lambda$CDM in these models for the gas density profiles are significantly lower than the dark matter equivalents. When it comes to the matter power-spectrum we find that hydrodynamic simulations agree very well with dark matter only simulations as long as we consider scales larger than $k\sim 0.5$ h/Mpc. In general the effects of modified gravity on the baryonic gas is found to not always mirror the effects it has on the dark matter. The largest signature is found when considering temperature profiles. We find that the gas temperatures in the modified gravity model studied here show deviations, when compared to $\Lambda$CDM, that can be a factor of a few larger than the deviations found in density profiles and power spectra.
If dark matter is embedded in a non-trivial dark sector, it may annihilate and decay to lighter dark-sector states which subsequently decay to the Standard Model. Such scenarios - with annihilation followed by cascading dark-sector decays - can explain the apparent excess GeV gamma-rays identified in the central Milky Way, while evading bounds from dark matter direct detection experiments. Each 'step' in the cascade will modify the observable signatures of dark matter annihilation and decay, shifting the resulting photons and other final state particles to lower energies and broadening their spectra. We explore, in a model-independent way, the effect of multi-step dark-sector cascades on the preferred regions of parameter space to explain the GeV excess. We find that the broadening effects of multi-step cascades can admit final states dominated by particles that would usually produce too sharply peaked photon spectra; in general, if the cascades are hierarchical (each particle decays to substantially lighter particles), the preferred mass range for the dark matter is in all cases 20-150 GeV. Decay chains that have nearly-degenerate steps, where the products are close to half the mass of the progenitor, can admit much higher DM masses. We map out the region of mass/cross-section parameter space where cascades (degenerate, hierarchical or a combination) can fit the signal, for a range of final states. In the current work, we study multi-step cascades in the context of explaining the GeV excess, but many aspects of our results are general and can be extended to other applications.
Hidden sector scenarios in which dark matter (DM) interacts with the Standard Model matter fields through the exchange of massive Z' bosons are well motivated by certain string theory constructions. In this work, we thoroughly study the phenomenological aspects of such scenarios and find that they present a clear and testable consequence for direct DM searches. We show that such string motivated St\"uckelberg portals naturally lead to isospin violating interactions of DM particles with nuclei. We find that the relations between the DM coupling to neutrons and protons for both, spin-independent (fn/fp) and spin-dependent (an/ap) interactions, are very flexible depending on the charges of the quarks under the extra U(1) gauge groups. We show that within this construction these ratios are generically different from plus and minus 1 (i.e. different couplings to protons and neutrons) leading to a potentially measurable distinction from other popular portals. Finally, we incorporate bounds from searches for dijet and dilepton resonances at the LHC as well as LUX bounds on the elastic scattering of DM off nucleons to determine the experimentally allowed values of fn/fp and an/ap.
Gas outflows are believed to play a pivotal role in shaping galaxies, as they regulate both star formation and black hole growth. Despite their ubiquitous presence, the origin and the acceleration mechanism of such powerful and extended winds is not yet understood. Direct observations of the cold gas component in objects with detected outflows at other wavelengths are needed to assess the impact of the outflow on the host galaxy interstellar medium (ISM). We observed with the Plateau de Bure Interferometer an obscured quasar at z~1.5, XID2028, for which the presence of an ionised outflow has been unambiguously signalled by NIR spectroscopy. The detection of CO(3-2) emission in this source allows us to infer the molecular gas content and compare it to the ISM mass derived from the dust emission. We then analyze the results in the context of recent insights on scaling relations, which describe the gas content of the overall population of star-forming galaxies at a similar redshifts. The Star formation efficiency (~100) and gas mass (M_gas=2.1-9.5x10^{10} M_sun) inferred from the CO(3-2) line depend on the underlying assumptions on the excitation of the transition and the CO-to-H2 conversion factor. However, the combination of this information and the ISM mass estimated from the dust mass suggests that the ISM/gas content of XID2028 is significantly lower than expected for its observed M$_\star$, sSFR and redshift, based on the most up-to-date calibrations (with gas fraction <20% and depletion time scale <340 Myr). Overall, the constraints we obtain from the far infrared and millimeter data suggest that we are observing QSO feedback able to remove the gas from the host
High-precision astrometry throughout the Local Group is a unique capability of the Hubble Space Telescope (HST), with potential for transformative science, including constraining the nature of dark matter, probing the epoch of reionization, and understanding key physics of galaxy evolution. While Gaia will provide unparalleled astrometric precision for bright stars in the inner halo of the Milky Way, HST is the only current mission capable of measuring accurate proper motions for systems at greater distances (> 80 kpc), which represents the vast majority of galaxies in the Local Group. The next generation of proper-motion measurements will require long time baselines, spanning many years to decades and possibly multiple telescopes, combining HST with the James Webb Space Telescope (JWST) or the Wide-Field Infrared Survey Telescope (WFIRST). However, the current HST allocation process is not conducive to such multi-cycle/multi-mission science, which will bear fruit primarily over many years. We propose an HST astrometry initiative to enable long-time-baseline, multi-mission science, which we suggest could be used to provide comprehensive kinematic measurements of all dwarf galaxies and high surface-density stellar streams in the Local Group with HST's Advanced Camera for Surveys (ACS) or Wide Field Camera 3 (WFC3). Such an initiative not only would produce forefront scientific results within the next 5 years of HST's life, but also would serve as a critical anchor point for future missions to obtain unprecedented astrometric accuracy, ensuring that HST leaves a unique and lasting legacy for decades to come.
The first N-body simulation of interacting galaxies, even producing spiral arms, was performed by Erik Holmberg in Lund (1941), not with a numerical computer, but by his arrangement of movable light-bulbs and photocells to measure the luminosity at each bulb and thereby estimate the gravitational force. A decade later, and with the arrival of the first programable computers, computations of galactic dynamics were performed, which were later transferred into a N-body simulation movie. I present here the background details for this work with a description of the important elements to note in the movie which may be retrieved at this http URL .
The so-called black hole shadow is a dark region which is expected to appear in a fine image of optical observation of black holes. It is essentially an absorption cross section of black hole, and the boundary of shadow is determined by unstable circular orbits of photons (UCOP). If there exists a compact object possessing UCOP but no black hole horizon, it can provide us the same shadow image with black holes, and a detection of shadow image cannot be a direct evidence of black hole existence. However, we show that a static spherical polytropic ball of perfect fluid cannot possess UCOP, if the sound speed at centre is subluminal. This implies that, if the polytrope is a good model of stellar matter in compact objects, a detection of shadow image is regarded as a good evidence of black hole existence. As a by-product, we have found an upper bound of mass-to-radius radio of polytropic ball, $M/R < 0.281$.
We construct an extension of standard flat FLRW cosmology with matter, possessing local D = 1, N = 1 proper-time supersymmetry. The fundamental equation for the resulting mini-superspace models of quantum universes is a Dirac-like analogue of the Friedmann and Wheeler-DeWitt equations. We provide solutions of this equation for specific matter configurations based on the supersymmetric O(3) and O(2, 1) sigma-models. It turns out that in the compact model the volume rate of growth of the universe is quantized and non-vanishing due to the zero-point energy of the scalar fields. In the non-compact model the spectrum of the growth rates is continuous but subject to an uncertainty relation involving the scale and the growth factor.
We analyze the time evolution of the luminosity of a cluster of Population III protostars formed in the early universe. We argue from the Jeans criterion that primordial gas can collapse to form a cluster of first stars that evolve relatively independently of one another (i.e., with negligible gravitational interaction). We model the collapse of individual protostellar clumps using 2+1D nonaxisymmetric numerical hydrodynamics simulations. Each collapse produces a protostar surrounded by a massive disk (i.e., $M_{\rm disk} / M_{*} \gtrsim 0.1$), whose evolution we follow for a further 30--40 kyr. Gravitational instabilities result in the fragmentation and the formation of gravitationally bound clumps within the disk. The accretion of these fragments by the host protostar produces accretion and luminosity bursts on the order of $10^6\,\LSun$. Within the cluster, we show that a simultaneity of such events across several protostellar cluster members can elevate the cluster luminosity to 5--10${\times}$ greater than expected, and that the cluster spends $\sim15\%$ of it's star-forming history at these levels. This enhanced luminosity effect is particularly enabled in clusters of modest size with $\simeq$ 10--20 members. In one such instance, we identify a confluence of burst events that raise the luminosity to nearly $1000{\times}$ greater than the cluster mean luminosity, resulting in $L > 10^8\,\LSun$. This phenomenon arises solely through the gravitational-instability--driven episodic fragmentation and accretion that characterizes this early stage of protostellar evolution.
In scalar-tensor theories, presence of matter in the vicinity of black holes can lead to the so called "spontaneous scalarisation" instability that can trigger the development of scalar hair. In the Brans-Dicke type theories, this effect can be understood as a result of tachyonic effective mass of the scalar field, induced by the purely conformal coupling to matter. Here this instability, in matter configurations around both Schwarzschild and rotating black holes, is explored in more general scalar-tensor theories featuring non-conformal, i.e. "disformal", couplings to matter. It is found that on one hand the disformal coupling can add to scalarisation b making the configuration more unstable. On the other hand, especially large enough disformal part of the coupling tends quite generically to stabilise the system.
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We present the spectroscopic redshift catalog from a wide-field survey of the fields of 28 galaxy-mass strong gravitational lenses. We discuss the acquisition and reduction of the survey data, collected over 40 nights of 6.5m MMT and Magellan time, employing four different multi-object spectrographs. We determine that no biases are introduced by combining datasets obtained with different instrument/spectrograph combinations. Special care is taken to determine redshift uncertainties using repeat observations. The redshift catalog consists of 9768 new and unique galaxy redshifts. 82.4% of the catalog redshifts are between z=0.1 and z=0.7, and the catalog median redshift is z=0.36. The data from this survey will be used to study the lens environments and line-of-sight structures to gain a better understanding of the effects of large scale structure on lens statistics and lens-derived parameters.
We investigate the luminosity and redshift dependence of the quasar continuum by means of composite spectrum using a large non-BAL radio-quiet quasar sample drawn from the Sloan Digital Sky Survey. Quasar continuum slopes in the UV-Opt band are measured at two different wavelength ranges, i.e., $\alpha_{\nu12}$ ($1000\sim 2000 \rm\AA$) and $\alpha_{\nu24}$ ($2000 \sim 4000 \rm\AA$) derived from power law fitting. Generally, the UV spectra slope becomes harder (higher $\alpha_{\nu}$) towards higher bolometric luminosity. On the other hand, when quasars are further grouped into luminosity bins, we find both $\alpha_{\nu12}$ and $\alpha_{\nu24}$ show significant anti-correlation with redshift (i.e., quasar continuum becomes redder towards higher redshift). We suggest that the cosmic dust extinction is very likely the cause of this observed $\alpha_\nu-z$ relation. We build a simple cosmic dust extinction model to quantify the observed reddening tendency and find an effective dust density $n\sigma_v \sim 10^{-5}h~\rm Mpc^{-1}$ at $z<1.5$. The other possibilities that could produce such a reddening effect have also been discussed.
We present a measurement of the $B$-mode polarization power spectrum (the $BB$ spectrum) from 100 $\mathrm{deg}^2$ of sky observed with SPTpol, a polarization-sensitive receiver currently installed on the South Pole Telescope. The observations used in this work were taken during 2012 and early 2013 and include data in spectral bands centered at 95 and 150 GHz. We report the $BB$ spectrum in five bins in multipole space, spanning the range $300 \le \ell \le 2300$, and for three spectral combinations: 95 GHz $\times$ 95 GHz, 95 GHz $\times$ 150 GHz, and 150 GHz $\times$ 150 GHz. We subtract small ($< 0.5 \sigma$ in units of statistical uncertainty) biases from these spectra and account for the uncertainty in those biases. The resulting power spectra are inconsistent with zero power but consistent with predictions for the $BB$ spectrum arising from the gravitational lensing of $E$-mode polarization. If we assume no other source of $BB$ power besides lensed $B$ modes, we determine a preference for lensed $B$ modes of $4.9 \sigma$. After marginalizing over tensor power and foregrounds, namely polarized emission from galactic dust and extragalactic sources, this significance is $4.3 \sigma$. Fitting for a single parameter, $A_\mathrm{lens}$, that multiplies the predicted lensed $B$-mode spectrum, and marginalizing over tensor power and foregrounds, we find $A_\mathrm{lens} = 1.08 \pm 0.26$, indicating that our measured spectra are consistent with the signal expected from gravitational lensing. The data presented here provide the best measurement to date of the $B$-mode power spectrum on these angular scales.
Recent discoveries of super-massive black holes at high redshifts indicate a possible tension with the standard Lambda CDM paradigm of early universe cosmology which has difficulties in explaining the origin of the required nonlinear compact seeds which trigger the formation of these super-massive black holes. Here we show that cosmic string loops which result from a scaling solution of strings formed during a phase transition in the very early universe lead to an additional source of compact seeds. The number density of string-induced seeds dominates at high redshifts and can help trigger the formation of the observed super-massive black holes.
We present a python package "ScalPy" for studying the late time scalar field cosmology for a wide variety of scalar field models, namely the quintessence, tachyon and Galileon model. The package solves the autonomous system of equations for power law and exponential potential. But it can be easily generalized to add more complicated potential. For completeness, we also include the standard parameterization for dark energy models, e.g. the $\Lambda$CDM, $w$CDM, $w_{0}w_{a}$CDM as well as the GCG parameterization. The package also solves the linear growth equation for matter perturbations on sub-horizon scales. All the important observables related to background universe as well as to the perturbed universe, e.g. luminosity distance ($D_{L}(z)$), angular diameter distance ($D_{A}(z)$), normalized Hubble parameter ($h(z)$), lookback time ($t_{L}$), equation of state for the dark energy ($w(z)$), growth rate ($f=\frac{d \ln\delta}{d \ln a}$), linear matter power spectra ($P(k)$), and its normalization $\sigma_{8}$ can be obtained from this package. The code is further integrated with the publicly available MCMC hammer "emcee" to constrain the different models using the presently available observational data.
The intra-cluster medium contains cosmic rays and magnetic fields that are manifested through the large scale synchrotron sources, termed as radio halos, relics and mini-halos. The Extended Giant Metrewave Radio Telescope (GMRT) Radio Halo Survey (EGRHS) is an extension of the GMRT Radio Halo Survey (GRHS) designed to search for radio halos using GMRT 610/235 MHz observations. The GRHS+EGRHS consists of 64 clusters in the redshift range 0.2 -- 0.4 that have an X-ray luminosity larger than 5x10^44 erg/s in the 0.1 -- 2.4 keV band and with declinations > -31 deg in the REFLEX and eBCS X-ray cluster catalogues. In this second paper in the series, GMRT 610/235 MHz data on the last batch of 11 galaxy clusters and the statistical analysis of the full sample are presented. A new mini-halo in RXJ2129.6+0005 and candidate diffuse sources in Z5247, A2552 and Z1953 are discovered. A unique feature of this survey are the upper limits on the detections of 1 Mpc sized radio halos; 4 new are presented here making a total of 31 in the survey. Of the sample, 58 clusters that have adequately sensitive radio information were used to obtain the most accurate occurrence fractions so far. The occurrence of radio halos in our X-ray selected sample is ~22%, that of mini-halos is 13% and that of relics is ~5%. The radio power - X-ray luminosity diagrams for the radio halos and mini-halos with the detections and upper limits are presented. The morphological estimators namely, centroid shift (w), concentration parameter (c) and power ratios (P_3/P_0) derived from the Chandra X-ray images are used as proxies for the dynamical states of the GRHS+EGRHS clusters. The clusters with radio halos and mini-halos occupy distinct quadrants in the c-w, c-P_3/P_0 and w - P_3/P_0 planes, corresponding to the more and less morphological disturbance, respectively. The non-detections span both the quadrants.
Observations indicate that most universal matter are invisible and gravitational constant $G(t)$ maybe depends on the time. The theory of variation of $G$ (VG) is explored in this paper, with naturally resulting to the invisible components in universe. We utilize the observational data: lookback time data, model-independent gamma ray bursts data, growth function of matter linear perturbations, type Ia supernovae data with systematic errors, cosmic microwave background, and baryon acoustic oscillation data from the radial scale measurement and the peak-positions measurement, to restrict the unified model (UM) of dark components in VG theory. Using the best-fit values of parameters with the covariance matrix, constraints on the variation of $G$ are $(\frac{G}{G_{0}})_{z=3.5}\simeq 1.0003^{+0.0014}_{-0.0016}$ and $(\frac{\dot{G}}{G})_{today}\simeq 0.7977^{+2.3566}_{-2.3566}\times 10^{-13} yr^{-1}$ in a flat geometry, the small uncertainties around constants. Limit on equation of state of dark matter is $w_{0dm}=0.0151^{+0.0171}_{-0.0171}$ with assuming $w_{0de}=-1$ in the UM model, and dark energy is $w_{0de}=-0.9986^{+0.0011}_{-0.0011}$ with assuming $w_{0dm}=0$ at prior. Restriction on UM parameters are $B_{s}=0.7662^{+0.0127+0.0248}_{-0.0125-0.0269}$ and $\alpha=0.0204^{+0.0201+0.0425}_{-0.0217-0.0398}$ with $1\sigma$ and $2\sigma$ confidence level. For the non-flat case, at $1\sigma$ confidence level the $\Lambda$CDM ($\Omega_{k}=0$, $\beta=0$ and $\alpha=0$) is not included in VG-UM model, and larger errors are given: $\Omega_{k}=-0.0311^{+0.0259+0.0517}_{-0.0248-0.0501}$, $(\frac{G}{G_{0}})_{z=3.5}\simeq 0.9917^{+0.0104}_{-0.0131}$ and $(\frac{\dot{G}}{G})_{today}\simeq 19.3678^{+21.8262}_{-21.8262}\times 10^{-13}yr^{-1}$.
The theory of bigravity offers one of the simplest possibilities to describe a massive graviton while having self-accelerating cosmological solutions without a cosmological constant. However, it has been shown recently that bigravity is affected by early-time fast growing modes on the tensor sector. Here we argue that we can only trust the linear analysis up to when perturbations are in the linear regime and use a cut-off to stop the growing of the metric perturbations. This analysis, although more consistent, still leads to growing tensor modes that are unacceptably large for the theory to be compatible with measurements of the cosmic microwave background (CMB), both in temperature and polarization spectra. In order to suppress the growing modes and make the model compatible with CMB spectra, we find it necessary to either fine-tune the initial conditions, modify the theory or set the cut-off for the tensor perturbations of the second metric much lower than unity. Initial conditions such that the growing mode is sufficiently suppresed can be achieved in scenarios in which inflation ends at the GeV scale.
Measuring radio source counts is critical for characterizing new extragalactic populations, brings a wealth of science within reach and will inform forecasts for SKA and its pathfinders. Yet there is currently great debate (and few measurements) about the behaviour of the 1.4-GHz counts in the microJy regime. One way to push the counts to these levels is via 'stacking', the covariance of a map with a catalogue at higher resolution and (often) a different wavelength. For the first time, we cast stacking in a fully bayesian framework, applying it to (i) the SKADS simulation and (ii) VLA data stacked at the positions of sources from the VIDEO survey. In the former case, the algorithm recovers the counts correctly when applied to the catalogue, but is biased high when confusion comes into play. This needs to be accounted for in the analysis of data from any relatively-low-resolution SKA pathfinders. For the latter case, the observed radio source counts remain flat below the 5-sigma level of 85 microJy as far as 40 microJy, then fall off earlier than the flux hinted at by the SKADS simulations and a recent P(D) analysis (which is the only other measurement from the literature at these flux-density levels, itself extrapolated in frequency). Division into galaxy type via spectral-energy distribution reveals that normal spiral galaxies dominate the counts at these fluxes.
Creation of Cold Dark Matter (CCDM), in the context of Einstein Field Equations, leads to a negative creation pressure, which can be used to explain the accelerated expansion of the Universe. Recently, it has been shown that the dynamics of expansion of such models can not be distinguished from the concordance $\Lambda$CDM model, even at higher orders in the evolution of density perturbations, leading at the so called "dark degeneracy". However, depending on the form of the CDM creation rate, the inclusion of spatial curvature leads to a different behavior of CCDM when compared to $\Lambda$CDM, even at background level. With a simple form for the creation rate, namely, $\Gamma\propto\frac{1}{H}$, we show that this model can be distinguished from $\Lambda$CDM, provided the Universe has some amount of spatial curvature. Observationally, however, the current limits on spatial flatness from CMB indicate that neither of the models are significantly favored against the other by current data, at least in the background level.
Hierarchical structure formation implies that the number of subhalos within a dark matter halo depends not only on halo mass, but also on the formation history of the halo. This dependence on the formation history, which is highly correlated with halo concentration, can account for the super-Poissonian scatter in subhalo occupation at a fixed halo mass that has been previously measured in simulations. Here we propose a model to predict the subhalo abundance function for individual host halos, that incorporates both halo mass and concentration. We combine results of cosmological simulations with a new suite of zoom-in simulations of Milky Way-mass halos to calibrate our model. We show the model can successfully reproduce the mean and the scatter of subhalo occupation in these simulations. The implications of this correlation between subhalo abundance and halo concentration are further investigated. We also discuss cases in which inferences about halo properties can be affected if this correlation between subhalo abundance and halo concentration is ignored; in these cases our model would give a more accurate inference. We propose that with future deep surveys, satellite occupation in the low-mass regime can be used to verify the existence of halo assembly bias.
Heat input roughly balances radiative cooling in the gaseous cores of galaxy clusters even when the central cooling time is short, implying that cooling triggers a feedback loop that maintains thermal balance. Furthermore, cores with short cooling times tend to have multiphase structure, suggesting that the intracluster medium (ICM) becomes locally thermally unstable for cooling times < 1 Gyr. In this work, we use 2D and 3D hydrodynamic simulations to study the onset of condensation in idealized galaxy-cluster cores. In particular, we look at how the condensation process depends on the ratio of cooling time to freefall time and on the geometry of the gravitational potential. We conclude that the ICM can always evolve to a state in which condensation occurs if given enough time, but that an initial timescale ratio tcool /tff < 10 is needed for thermal instability to grow quickly enough to affect realistic cluster cores within a timescale that is relevant for cosmological structure formation. We find that instability leads to convection and that perturbations continue to grow while the gas convects. Condensation occurs when the timescale ratio in the low-entropy tail of the perturbation distribution drops below tcool /tff < 3, even if the volume-averaged timescale ratio is substantially greater. In our simulations, the geometry of the gravitational potential does not have a strong effect on thermal stability. Finally, we find that if condensation is powering feedback, a conversion efficiency of around 10^-3 for converting the condensed mass into thermal energy is sufficient to maintain thermal balance in the ICM.
The process of gravitational collapse excites the fields propagating in the background geometry and gives rise to thermal radiation. We demonstrate by explicit calculations that the density matrix corresponding to such radiation actually describes a pure state. While Hawking's leading order density matrix contains only the diagonal terms, we calculate the off-diagonal correlation terms. These correlations start very small, but then grow in time. The cumulative effect is that the correlations become comparable to the leading order terms and significantly modify the density matrix. While the trace of the Hawking's density matrix squared goes from unity to zero during the evolution, the trace of the total density matrix squared remains unity at all times and all frequencies. This implies that the process of radiation from a collapsing object is unitary.
Cluster mergers may play a fundamental role in the formation and evolution of cluster galaxies. Stroe et al. (2014) revealed unexpected over-densities of candidate H$\alpha$ emitters near the ~1 Mpc-wide shock fronts of the massive (~2x10$^{15}$M$_{\odot}$) "Sausage" merging cluster, CIZA J2242.8+5301. We used Keck/DEIMOS and WHT/AF2 to confirm 83 H$\alpha$ emitters in and around the merging cluster. We find that cluster star-forming galaxies in the hottest X-ray gas and/or in the cluster sub-cores (away from the shock fronts) show high [SII]6716/[SII]6761 and high [SII]6716/H$\alpha$, implying very low electron densities (<30x lower than all other star-forming galaxies outside the cluster) and significant contribution from supernovae, respectively. All cluster star-forming galaxies near the cluster centre show evidence of significant outflows (blueshifted Na D~200-300km/s), likely driven by supernovae. Strong outflows are also found for the cluster H$\alpha$ AGN. H$\alpha$ star-forming galaxies in the merging cluster follow the z~0 mass-metallicity relation, showing systematically higher metallicity (~0.15-0.2 dex) than H$\alpha$ emitters outside the cluster (projected R>2.5 Mpc). This suggests that the shock front may have triggered remaining metal-rich gas which galaxies were able to retain into forming stars. Our observations show that the merger of impressively massive (~10$^{15}$M$_\odot$) clusters can provide the conditions for significant star-formation and AGN activity, but, as we witness strong feedback by star-forming galaxies and AGN (and given how massive the merging cluster is), such sources will likely quench in a few 100 Myrs.
We have used the publicly released Dark Energy Survey data to hunt for new satellites of the Milky Way in the Southern hemisphere. Our search yielded a large number of promising candidates. In this paper, we announce the discovery of 9 new unambiguous ultra-faint objects, whose authenticity can be established with the DES data alone. Based on the morphological properties, three of the new satellites are dwarf galaxies, one of which is located at the very outskirts of the Milky Way, at a distance of 380 kpc. The remaining 6 objects have sizes and luminosities comparable to the Segue 1 satellite and can not be classified straightforwardly without follow-up spectroscopic observations. The satellites we have discovered cluster around the LMC and the SMC. We show that such spatial distribution is unlikely under the assumption of isotropy, and, therefore, conclude that at least some of the new satellites must have been associated with the Magellanic Clouds in the past.
We present an X-ray and multiwavelength study of 33 weak emission-line quasars (WLQs) and 18 quasars that are analogs of the extreme WLQ, PHL 1811, at z ~ 0.5-2.9. New Chandra 1.5-9.5 ks exploratory observations were obtained for 32 objects while the others have archival X-ray observations. Significant fractions of these luminous type 1 quasars are distinctly X-ray weak compared to typical quasars, including 16 (48%) of the WLQs and 17 (94%) of the PHL 1811 analogs with average X-ray weakness factors of 17 and 39, respectively. We measure a relatively hard ($\Gamma=1.16_{-0.32}^{+0.37}$) effective power-law photon index for a stack of the X-ray weak subsample, suggesting X-ray absorption, and spectral analysis of one PHL 1811 analog, J1521+5202, also indicates significant intrinsic X-ray absorption. We compare composite SDSS spectra for the X-ray weak and X-ray normal populations and find several optical-UV tracers of X-ray weakness; e.g., Fe II rest-frame equivalent width and relative color. We describe how orientation effects under our previously proposed "shielding-gas" scenario can likely unify the X-ray weak and X-ray normal populations. We suggest that the shielding gas may naturally be understood as a geometrically thick inner accretion disk that shields the broad line region from the ionizing continuum. If WLQs and PHL 1811 analogs have very high Eddington ratios, the inner disk could be significantly puffed up (e.g., a slim disk). Shielding of the broad emission-line region by a geometrically thick disk may have a significant role in setting the broad distributions of C IV rest-frame equivalent width and blueshift for quasars more generally.
We present near-infrared (NIR) time-series spectroscopy, as well as complementary ultraviolet (UV), optical, and NIR data, of the Type Ia supernova (SN Ia) iPTF13ebh, which was discovered within two days from the estimated time of explosion. The first NIR spectrum was taken merely 2.3 days after explosion and may be the earliest NIR spectrum yet obtained of a SN Ia. The most striking features in the spectrum are several NIR C I lines, and the C I {\lambda}1.0693 {\mu}m line is the strongest ever observed in a SN Ia. Interestingly, no strong optical C II counterparts were found, even though the optical spectroscopic time series began early and is densely-cadenced. Except at the very early epochs, within a few days from the time of explosion, we show that the strong NIR C I compared to the weaker optical C II appears to be general in SNe Ia. iPTF13ebh is a fast decliner with {\Delta}m15(B) = 1.79 $\pm$ 0.01, and its absolute magnitude obeys the linear part of the width-luminosity relation. It is therefore categorized as a "transitional" event, on the fast-declining end of normal SNe Ia as opposed to subluminous/91bg-like objects. iPTF13ebh shows NIR spectroscopic properties that are distinct from both the normal and subluminous/91bg-like classes, bridging the observed characteristics of the two classes. These NIR observations suggest composition and density of the inner core similar to that of 91bg-like events, and a deep reaching carbon burning layer not observed in slower declining SNe Ia. There is also a substantial difference between the explosion times inferred from the early-time light curve and the velocity evolution of the Si II {\lambda}0.6355 {\mu}m line, implying a long dark phase of ~ 4 days.
We present a search for gamma-ray emission from the direction of the newly discovered dwarf galaxy Reticulum 2. Using Fermi-LAT data, we detect a signal that exceeds expected backgrounds between ~2-10 GeV and is consistent with annihilation of dark matter for particle masses less than a few x 10^2 GeV. Modeling the background as a Poisson process based on Fermi-LAT diffuse models, and taking into account trials factors, we detect emission with p-value less than 9.8 x 10^-5 (>3.7 sigma). An alternative, model-independent treatment of background reduces the significance, raising the p-value to 9.7 x 10^-3 (2.3 sigma). Even in this case, however, Reticulum 2 has the most significant gamma-ray signal of any known dwarf galaxy. If Reticulum 2 has a dark matter halo that is similar to those inferred for other nearby dwarfs, the signal is consistent with the s-wave relic abundance cross section for annihilation.
The relativistic generalization of the Newtonian Lagrangian perturbation theory is investigated. In previous works, the first-order trace solutions that are generated by the spatially projected gravitoelectric part of the Weyl tensor were given together with extensions and applications for accessing the nonperturbative regime. We here furnish construction rules to obtain from Newtonian solutions the gravitoelectric class of relativistic solutions, for which we give the complete perturbation and solution schemes at any order of the perturbations. By construction, these schemes generalize the complete hierarchy of solutions of the Newtonian Lagrangian perturbation theory.
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We study the properties of gas in and around 10^12 solar mass halos at z=2 using a suite of high-resolution cosmological hydrodynamic 'zoom' simulations. We quantify the thermal and dynamical structure of these gaseous reservoirs in terms of their mean radial distributions and angular variability along different sightlines. With each halo simulated at three levels of increasing resolution, the highest reaching a baryon mass resolution of ~10,000 solar masses, we study the interaction of filamentary inflow and the quasi-static hot halo atmosphere. We highlight the discrepancy between the spatial resolution available in the halo gas as opposed to within the galaxy itself, and find that stream morphologies become increasingly complex at higher resolution, with large coherent flows revealing density and temperature structure at progressively smaller scales. Moreover, multiple gas components co-exist at the same radius within the halo, making radially averaged analyses misleading. This is particularly true where the hot, quasi-static, high entropy halo atmosphere interacts with cold, rapidly inflowing, low entropy accretion. We investigate the process of gas virialization and identify different regimes for the heating of gas as it accretes from the intergalactic medium. Haloes at this mass have a well-defined virial shock, associated with a sharp jump in temperature and entropy at ~1.25 r_vir. The presence, radius, and radial width of this boundary feature, however, vary not only from halo to halo, but also as a function of angular direction, covering roughly ~85% of the 4pi sphere. Our findings are relevant for the proper interpretation of observations pertaining to the circumgalactic medium, including evidence for large amounts of cold gas surrounding massive haloes at intermediate redshifts.
We describe a NOVel form of Adaptive softening (NovA) for collisionless $N$-body simulations, implemented in the Ramses adaptive mesh refinement code. We introduce a refinement criterion that the particle distribution within each cell be sufficiently isotropic, as measured by its moment of inertia tensor. In this way, collapse is only refined if it occurs along all three axes, ensuring that the softening $\epsilon$ is always of order twice the largest inter-particle spacing in a cell. This more conservative force softening criterion is designed to minimise spurious two-body effects, while maintaining high force resolution in collapsed regions of the flow. We test NovA using an antisymmetric perturbed plane wave collapse (`Valinia' test) before applying it to warm dark matter (WDM) simulations. For the Valinia test, we show that -- unlike the standard $N$-body method -- NovA produces no numerical fragmentation while still being able to correctly capture fine caustics and shells around the collapsing regions. For the WDM simulations, we find that NovA converges significantly more rapidly than standard $N$-body, producing little or no spurious halos on small scales. We show, however, that determining whether or not halos exist below the free streaming mass $M_{\rm fs}$ is complicated by the fact that our halo finder (AHF) likely incorrectly labels some caustics and criss-crossing filaments as halos, while one or two particularly massive filaments appear to fragment in any version of NovA where refinement is allowed. Such massive filaments may be physically unstable to collapse, as is the case for infinite, static, self-gravitating cylinders. We will use NovA in forthcoming papers to study the issue of halo formation below $M_{\rm fs}$; filament stability; and to obtain new constraints on the temperature of dark matter.
A sample of 46 nearby clusters observed with Chandra is analyzed to produce radial density, temperature, entropy and metallicity profiles, as well as other morphological measurements. The entropy profiles are computed to larger radial extents than in previous Chandra cluster sample analyses. We find that the iron mass fraction measured in the inner 0.15 R500 shows a larger dispersion across the sample of low-mass clusters, than it does for the sample of high-mass clusters. We interpret this finding as the result of the mixing of more haloes in large clusters than in small clusters, which leads to an averaging of the metal content in the large clusters, and thus less dispersion of metallicity for high-mass clusters. This interpretation lends support to the idea that the low-entropy, metal-rich gas of merging haloes reaches clusters' centers, which explains observations of Core-Collapse Supernova products metallicity peaks, and which is seen in hydrodynamical simulations. The gas in these merging haloes would have to reach the centers of clusters without mixing in the outer regions, in order to support our interpretation. On the other hand, metallicity dispersion does not change with mass in the outer regions of clusters, suggesting that most of the outer metals come from a source with a more uniform metallicity level, such as during pre-enrichment. We also measure a correlation between the metal content in low-mass clusters and the degree to which their Intra-Cluster Medium (ICM) is morphologically disturbed, as measured by centroid shift. This suggests an alternative interpretation of the large width of the metallicity distribution in low-mass clusters, whereby a metallicity boost in the center of low-mass clusters is induced as a transitional state, during mergers.
The current cosmological paradigm sees the formation and evolution of the
cosmic large-scale structure as governed by the gravitational attraction of the
Dark Matter (DM) and the repulsion of the Dark Energy (DE).
We characterize the relative importance of uniform and constant dark energy,
as given by the Lambda term in the standard LCDM cosmology, in galaxy systems
of different scales, from groups to superclusters.
An instructive "Lambda significance graph" is introduced where the matter-DE
density ratio <rho_M>/rho_Lambda for different galaxy systems is plotted
against the radius R. This presents gravitation and DE dominated regions and
shows directly the zero velocity radius, the zero-gravity radius, and the
Einstein-Straus radius for any fixed value of mass.
Example galaxy groups and clusters from the local universe illustrate the use
of the Lambda significance graph. These are generally located deep in the
gravity-dominated region <rho_M}>/rho_Lambda > 2, being virialized. Extended
clusters and main bodies of superclusters can reach down near the border line
between gravity-dominated and DE dominated regions <rho_M>/rho_Lambda = 2. The
scale--mass relation from the standard 2-point correlation function intersects
this balance line near the correlation lenght.
The log <rho_M>/rho_Lambda vs. log R diagram is a useful and versatile way to
characterize the dynamical state of systems of galaxies within the Lambda
dominated expanding universe.
In 1914, Eddington derived a formula for the difference between the mean
absolute magnitudes of stars "in space" or gathered "from the sky". Malmquist
(1920) derived a general relation for this difference in Euclidean space. Here
we study this statistical bias in cosmology, clarifying and expanding previous
work.
We derived the Malmquist relation within a general cosmological framework,
including Friedmann's model, analogously to the way Malmquist showed in 1936
that his formula is also valid in the presence of extinction in Euclidean
space. We also discuss some conceptual aspects that explain the wide scope of
the bias relation.
The Malmquist formula for the intrinsic difference <M>_m - M_0 = - sigma_M^2
dlna(m)/dm is also valid for observations made in an expanding Friedmann
universe. This is holds true for bolometric and finite-band magnitudes when
a(m) refers to the distribution of observed (uncorrected for K-effect or
z-dependent extinction) apparent magnitudes.
We perform a detailed 2-dimensional weak gravitational lensing analysis of the nearby (z = 0.058) galaxy cluster Abell 3128 using deep ugrz imaging from the Dark Energy Camera (DECam). We have designed a pipeline to remove instrumental artifacts from DECam images and stack multiple dithered observations without inducing a spurious ellipticity signal. We develop a new technique to characterize the spatial variation of the PSF which enables us to circularize the field to better than 0.5% and thereby extract the intrinsic galaxy ellipticities. By fitting photometric redshifts to sources in the observation, we are able to select a sample of background galaxies for weak lensing analysis free from low-redshift contaminants. Photometric redshifts are also used to select a high-redshift galaxy subsample with which we successfully isolate the signal from an interloping z = 0.44 cluster. We estimate the total mass of Abell 3128 by fitting the tangential ellipticity of background galaxies with the weak lensing shear profile of an NFW halo, and also perform NFW fits to substructures detected in the 2-D mass maps of the cluster. This study yields one of the highest resolution mass maps of a low-z cluster to date, and is the first step in a larger effort to characterize the redshift evolution of mass substructures in clusters.
A new analytical model for constraining the extent of gravitationally bound structure in the Universe is presented. This model is based on a simple modification of the spherical collapse model (SCM), and its performance in predicting the limits of bound structure in N-body simulations is compared to that of two previous models with the aid of new software named COLDGaS-- compute unified device architecture (CUDA) object location determination in GADGET2 snapshots -- which was developed by the author. All of these models can be distilled down to a single unique parameter {\xi}, here named the critical parameter, which was found to have values of 3 and 1.18 from the previous studies, and a value of 1.89 from the modified SCM. While still on the conservative side, this new model tends to better identify what structure is gravitationally bound in simulations. All three analytical models are applied to the Corona Borealis supercluster, with the modified SCM and {\xi} = 1.18 model making predictions that are in agreement with recent work showing that A2056, A2061, A2065, A2067, and A2089 comprise a gravitationally bound supercluster. As an additional test, the modified SCM is used to estimate the mass within the turn around radius of the Virgo cluster, providing results in good agreement with studies relating the virial mass of clusters to the total mass within turn around.
We point out that kinetic and St\"uckelberg mixings that are generically present in the low energy effective action of axions can significantly widen the window of axion decay constants. We show that an effective super-Planckian decay constant can be obtained even when the axion kinetic matrix has only sub-Planckian entries. Our minimal model involves only two axions, a St\"uckelberg U(1) and a modest rank instanton generating non-Abelian group. Below the mass of the St\"uckelberg U(1), there is only a single axion with a non-perturbatively generated potential. In contrast to previous approaches, the enhancement of the axion decay constant is not tied to the number of degrees of freedom introduced. We also discuss how kinetic mixings can lower the decay constant to the desired axion dark matter window. String theory embeddings of this scenario and their phenomenological features are briefly discussed.
In this paper we investigate the decoupling limit of a particular class of multi-gravity theories, i.e. of theories of interacting spin-2 fields. We explicitly compute the interactions of helicity-0 modes in this limit, showing that they take on the form of multi-Galileons and dual forms. In the process we extend the recently discovered Galileon dualities, deriving a set of new multi-Galileon dualities. These are also intrinsically connected to healthy, but higher-derivative, multi-scalar field theories akin to `beyond Horndeski' models.
We extract constraints on the transition redshift $z_{tr}$, determining the onset of cosmic acceleration, predicted by an effective cosmographic construction, in the framework of $f(T)$ gravity. In particular, employing cosmography we obtain bounds on the viable $f(T)$ forms and their derivatives. Since this procedure is model independent, as long as the scalar curvature is fixed, we are able to determine intervals for $z_{tr}$. In this way we guarantee that the Solar-System constraints are preserved and moreover we extract bounds on the transition time and the free parameters of the scenario. We find that the transition redshifts predicted by $f(T)$ cosmology, although compatible with the standard $\Lambda$CDM predictions, are slightly smaller. Finally, in order to obtain observational constraints on $f(T)$ cosmology, we perform a Monte Carlo fitting using supernova data, involving the most recent union 2.1 data set.
We study the general multi-axion systems, focusing on the possibility of large field inflation driven by axions. We find that through axion mixing from a non-diagonal metric on the moduli space and/or from St\"uckelberg coupling to a U(1) gauge field, an effectively super-Planckian decay constant can be generated without the need of "alignment" in the axion decay constants. We also investigate the consistency conditions related to the gauge symmetries in the multi-axion systems, such as vanishing gauge anomalies and the potential presence of generalized Chern-Simons terms. Our scenario applies generally to field theory models whose axion periodicities are intrinsically sub-Planckian, but it is most naturally realized in string theory. The types of axion mixings invoked in our scenario appear quite commonly in D-brane models, and we present its implementation in type II superstring theory. Explicit stringy models exhibiting all the characteristics of our ideas are constructed within the frameworks of Type IIA intersecting D6-brane models on T6/OR and Type IIB intersecting D7-brane models on Swiss-Cheese Calabi-Yau orientifolds.
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Ten years of operations of the Swift satellite have allow us to collect a small sample of long Gamma-Ray Bursts (GRBs) at redshift larger than six. I will review here the present status of this research field and discuss the possible use of GRBs as a fundamental new tool to explore the early Universe, complementary to quasar and galaxy surveys.
A galaxy group catalog is built from the sample of the 2MASS Redshift Survey almost complete to Ks=11.75 over 91% of the sky. Constraints in the construction of the groups were provided by scaling relations determined by close examination of well defined groups with masses between 10^11 and 10^15 Msun. Group masses inferred from Ks luminosities are statistically in agreement with masses calculated from application of the virial theorem. While groups have been identified over the full redshift range of the sample, the properties of the nearest and farthest groups are uncertain and subsequent analysis has only considered groups with velocities between 3,000 and 10,000 km/s. The 24,044 galaxies in this range are identified with 13,607 entities, 3,461 of them with two or more members. A group mass function is constructed. The Sheth-Tormen formalism provides a good fit to the shape of the mass function for group masses above 6/h x 10^12 Msun but the count normalization is poor. Summing all the mass associated with the galaxy groups between 3,000 and 10,000 km/s gives a density of collapsed matter as a fraction of the critical density of Omega_collapsed = 0.16.
Previous analysis of the fossil-group/cluster RXJ1159+5531 with X-ray observations from a central Chandra pointing and an offset-North Suzaku pointing indicate a radial intracluster medium (ICM) entropy profile at the virial radius ($R_{\rm vir}$) consistent with predictions from gravity-only cosmological simulations, in contrast to other cool-core clusters. To examine the generality of these results, we present three new Suzaku observations that, in conjunction with the North pointing, provide complete azimuthal coverage out to $R_{\rm vir}$. With two new Chandra ACIS-I observations overlapping the North Suzaku pointing, we have resolved $\gtrsim$50\% of the cosmic X-ray background there. We present radial profiles of the ICM density, temperature, entropy, and pressure obtained for each of the four directions. We measure only modest azimuthal scatter in the ICM properties at $R_{\rm 200}$ between the Suzaku pointings: 7.6\% in temperature and 8.6\% in density, while the systematic errors can be significant. The temperature scatter, in particular, is lower than that studied at $R_{\rm 200}$ for a small number of other clusters observed with Suzaku. These azimuthal measurements verify that RXJ1159+5531 is a regular, highly relaxed system. The well-behaved entropy profiles we have measured for RXJ1159+5531 disfavor the weakening of the accretion shock as an explanation of the entropy flattening found in other cool-core clusters but is consistent with other explanations such as gas clumping, electron-ion non-equilibrium, non-thermal pressure support, and cosmic ray acceleration. Finally, we mention that the large-scale galaxy density distribution of RXJ1159+5531 seems to have little impact on its gas properties near $R_{\rm vir}$.
With the temperature power spectrum of the cosmic microwave background (CMB) at least four orders of magnitude larger than the B-mode polarisation power spectrum, any instrumental imperfections that couple temperature to polarisation must be carefully controlled and/or removed. Here we present two new map-making algorithms that can create polarisation maps that are clean of temperature-to-polarisation leakage systematics due to differential gain and pointing between a detector pair. Where a half wave plate is used, we show that the spin-2 systematic due to differential ellipticity can also by removed using our algorithms. The algorithms require no prior knowledge of the imperfections or temperature sky to remove the temperature leakage. Instead, they calculate the systematic and polarisation maps in one step directly from the time ordered data (TOD). The first algorithm is designed to work with scan strategies that have a good range of crossing angles for each map pixel and the second for scan strategies that have a limited range of crossing angles. The first algorithm can also be used to identify if systematic errors that have a particular spin are present in a TOD. We demonstrate the use of both algorithms and the ability to identify systematics with simulations of TOD with realistic scan strategies and instrumental noise.
There is a deep connection between cosmology -- the science of the infinitely large --and particle physics -- the science of the infinitely small. This connection is particularly manifest in neutron particle physics. Basic properties of the neutron -- its Electric Dipole Moment and its lifetime -- are intertwined with baryogenesis and nucleosynthesis in the early Universe. I will cover this topic in the first part, that will also serve as an introduction (or rather a quick recap) of neutron physics and Big Bang cosmology. Then, the rest of the manuscript will be devoted to a new idea: using neutrons to probe models of Dark Energy. In the second part, I will present the chameleon theory: a light scalar field accounting for the late accelerated expansion of the Universe, which interacts with matter in such a way that it does not mediate a fifth force between macroscopic bodies. However, neutrons can alleviate the chameleon mechanism and reveal the presence of the scalar field with properly designed experiments. In the third part, I will describe a recent experiment performed with a neutron interferometer at the Institut Laue Langevin that sets already interesting constraints on the chameleon theory. Last, the chameleon field can be probed by measuring the quantum states of neutrons bouncing over a mirror. In the fourth part I will present the status and prospects of the GRANIT experiment at the ILL.
We examine the consequences of the effective field theory (EFT) of dark matter-nucleon scattering for current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. We demonstrate that spectral differences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. We also discuss the implications of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.
The standard Bayesian model formalism comparison cannot be applied to most cosmological models as they lack well-motivated parameter priors. However, if the data-set being used is separable then it is possible to use some of the data to obtain the necessary parameter distributions, the rest of the data being retained for model comparison. While such methods are not fully prescriptive, they provide a route to applying Bayesian model comparison in cosmological situations where it could not otherwise be used.
Natural (axionic) inflation provides a well-motivated and predictive scheme for the description of the early universe. It leads to sizeable primordial tensor modes and thus a high mass scale of the inflationary potential. Naively this seems to be at odds with low (TeV) scale supersymmetry, especially when embedded in superstring theory. We show that low scale supersymmetry is compatible with natural (high scale) inflation. The mechanism requires the presence of two axions that are provided through the moduli of string theory.
We study the inverse seesaw mechanism for neutrino masses and phenomenological consequences in the context of conformal electro-weak symmetry breaking. The main difference to the usual case is that all explicit fermion mass terms including Majorana masses for neutrinos are forbidden. All fermion mass terms arise therefore from vacuum expectation values of suitable scalars times some Yukawa couplings. This leads to interesting consequences for model building, neutrino mass phenomenology and the Dark Matter abundance. In the context of the inverse seesaw we find a favoured scenario with heavy pseudo-Dirac sterile neutrinos at the TeV scale, which in the conformal framework conspire with the electro-weak scale to generate keV scale warm Dark Matter. The mass scale relations provide naturally the correct relic abundance due to a freeze-in mechanism. We demonstrate also how conformal symmetry decouples the right-handed neutrino mass scale and effective lepton number violation. We find that lepton flavour violating processes can be well within the reach of modern experiments. Furthermore, interesting decay signatures are expected at the LHC.
We report the discovery of rapid variations of a high-velocity CIV broad absorption line trough in the quasar SDSS J141007.74+541203.3. This object was intensively observed in 2014 as a part of the Sloan Digital Sky Survey Reverberation Mapping Project, during which 32 epochs of spectroscopy were obtained with the Baryon Oscillation Spectroscopic Survey spectrograph. We observe significant (>4sigma) variability in the equivalent width of the broad (~4000 km/s wide) CIV trough on rest-frame timescales as short as 1.20 days (~29 hours), the shortest broad absorption line variability timescale yet reported. The equivalent width varied by ~10% on these short timescales, and by about a factor of two over the duration of the campaign. We evaluate several potential causes of the variability, concluding that the most likely cause is a rapid response to changes in the incident ionizing continuum. If the outflow is at a radius where the recombination rate is higher than the ionization rate, the timescale of variability places a lower limit on the density of the absorbing gas of n_e > 3.9 x 10^5 cm^-3. The broad absorption line variability characteristics of this quasar are consistent with those observed in previous studies of quasars, indicating that such short-term variability may in fact be common and thus can be used to learn about outflow characteristics and contributions to quasar/host-galaxy feedback scenarios.
The problem of families, "Why are there three families of fermions?", is a long awaited question to be answered within a reasonable framework. We propose anti-SU(N) groups for the unification of families in grand unification (GUT) groups, where the separation of color and weak gauge groups in the GUT is achieved by antisymmetric tensor Brout-Englert-Higgs boson instead of an adjoint representation. Theories of anti-SU(N)'s are proposed for the unification of families. The Z{12-I) orbifold compactification, where the missing partner mechanism is realized.
H-poor super-luminous supernovae (SLSNe) are a rare and poorly understood class of explosion. We assemble the largest sample (24) of such objects to date, with griz light curves and optical spectra. We parameterize the light curve through rise and decline timescales, finding that these are highly correlated. Magnetar-powered models reproduce the correlation, with the diversity in rise and decline driven by the diffusion timescale. Circumstellar interaction models can exhibit a similar rise-decline relation, but for only a narrow density range, which may be problematic for these models. We see a similar correlation in normal SNe Ibc (powered by 56Ni), though SLSNe rise and decline more slowly, and their peak luminosity requires an additional energy source. We find that SLSN light curves are approximately 3.5 mag brighter and 3 times broader than SNe Ibc, but that the intrinsic shapes are similar. Some SLSNe (2007bi-like) have very broad light curves, possibly indicating two progenitor channels, but statistical tests do not distinguish separate populations in our sample. The spectral evolution is also presented. Velocities measured from the Fe II 5169 line are similar for SLSNe and SNe Ic, suggesting that the difference in diffusion time is dominated by the ejected mass. If the opacities in SLSNe are similar to other SNe Ibc, then the average ejected mass in SLSNe is higher by more than a factor of two. Assuming kappa = 0.1 cm2/g, we estimate a mean (median) SLSN ejecta mass of ~10 Msun (6 Msun), with a range of ~3-30 Msun, though doubling the opacity would bring the mass estimates in line with other SNe Ibc. The velocities of many SLSNe are constant, indicating a dense shell of ejecta. We conclude that the most probable mechanism for generating SLSNe is the explosion of a star similar to, but more massive than, a typical SN Ic progenitor, powered by an engine such as a magnetar.
We present a survey of star clusters in the halo of IC 10, a starburst galaxy in the Local Group based on Subaru R band images and NOAO Local Group Survey UBVRI images. We find five new star clusters. All these star clusters are located far from the center of IC 10, while previously known star clusters are mostly in the main body. Interestingly the distribution of these star clusters shows an asymmetrical structure elongated along the east and south-west direction. We derive UBVRI photometry of 66 star clusters including these new star clusters as well as previously known star clusters. Ages of the star clusters are estimated from the comparison of their UBVRI spectral energy distribution with the simple stellar population models. We find that the star clusters in the halo are all older than 1 Gyr, while those in the main body have various ages from very young (several Myr) to old (>1 Gyr). The young clusters (<10 Myr) are mostly located in the H{\alpha} emission regions and are concentrated on a small region at 2' in the south-east direction from the galaxy center, while the old clusters are distributed in a wider area than the disk. Intermediate-age clusters (~100 Myr) are found in two groups. One is close to the location of the young clusters and the other is at ~4' from the location of the young clusters. The latter may be related with past merger or tidal interaction.
We analyze the direct detection signals of a toy model consisting of a Dirac dark matter particle which couples to one Standard Model fermion via a scalar mediator. For all scenarios, the dark matter particle scatters off nucleons via one loop-induced electromagnetic and electroweak moments, as well as via the one-loop exchange of a Higgs boson. Besides, and depending on the details of the model, the scattering can also be mediated at tree level via the exchange of the scalar mediator or at one loop via gluon-gluon interactions. We show that, for thermally produced dark matter particles, the current limits from the LUX experiment on these scenarios are remarkably strong, even for dark matter coupling only to leptons. We also discuss future prospects for XENON1T and DARWIN and we argue that multi-ton xenon detectors will be able to probe practically the whole parameter space of the model consistent with thermal production and perturbativity. We also discuss briefly the implications of our results for the dark matter interpretation of the Galactic GeV excess.
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Recent observations of the cosmic microwave background (CMB) anisotropies and the distribution of galaxies, galaxy clusters, and the Lyman Alpha forest have constrained the shape of the power spectrum of matter fluctuations on large scales k < few h/Mpc. We explore a new technique to constrain the matter power spectrum on smaller scales, assuming the dark matter is a Weakly Interacting Massive Particle (WIMP) that annihilates at early epochs. Energy released by dark matter annihilation can modify the spectrum of CMB temperature fluctuations and thus CMB experiments such as Planck have been able to constrain the quantity f <sigma v> /m < 1/88 picobarn c / GeV, where f is the fraction of energy absorbed by gas, <sigma v> is the annihilation rate assumed constant, and m is the particle mass. We assume the standard scale-invariant primordial matter power spectrum of P_prim(k) ~ k^{n_s} at large scales k < k_p, while we adopt the modified power law of P_prim(k) ~ k_p^{n_s} (k/k_p)^{m_s} at small scales. We then aim at deriving constraints on m_s. For m_s > n_s, the excess small-scale power results in a much larger number of nonlinear small mass halos, particularly at high redshifts. Dark matter annihilation in these halos releases sufficient energy to partially ionize the gas, and consequently modify the spectrum of CMB fluctuations. We show that the recent Planck data can already be used to constrain the power spectrum on small scales. For a simple model with an NFW profile with halo concentration parameter c_200 = 5 and f <sigma v> / m = 1/100 picobarn c / GeV, we can limit the mass variance sigma_{max} < 100 at the 95% confidence level, corresponding to a power law index m_s < 1.43 (1.63) for k_p = 100 (1000) h/Mpc. Our results are also relevant to theories that feature a running spectral index.
We test the hypothesis that the polarization vectors of flat-spectrum radio sources (FSRS) in the JVAS/CLASS 8.4-GHz surveys are randomly oriented on the sky. The sample with robust polarization measurements is made of $4155$ objects and redshift information is known for $1531$ of them. We performed two statistical analyses: one in two dimensions and the other in three dimensions when distance is available. We find significant large-scale alignments of polarization vectors for samples containing only quasars (QSO) among the varieties of FSRS's. While these correlations prove difficult to explain either by a physical effect or by biases in the dataset, the fact that the QSO's which have significantly aligned polarization vectors are found in regions of the sky where optical polarization alignments were previously found is striking.
We show that in a certain, angle-averaged squeezed limit, the $N$-point function of matter is related to the response of the matter power spectrum to a long-wavelength density perturbation, $P^{-1}d^nP(k|\delta_L)/d\delta_L^n|_{\delta_L=0}$, with $n=N-2$. By performing N-body simulations with a homogeneous overdensity superimposed on a flat Friedmann-Robertson-Lema\^itre-Walker (FRLW) universe using the \emph{separate universe} approach, we obtain measurements of the nonlinear matter power spectrum response up to $n=3$, which is equivalent to measuring the fully nonlinear matter $3-$ to $5-$point function in this squeezed limit. The sub-percent to few percent accuracy of those measurements is unprecedented. We then test the hypothesis that nonlinear $N$-point functions at a given time are a function of the linear power spectrum at that time, which is predicted by standard perturbation theory (SPT) and its variants that are based on the ideal pressureless fluid equations. Specifically, we compare the responses computed from the separate universe simulations and simulations with a rescaled initial (linear) power spectrum amplitude. We find discrepancies of 10\% at $k\simeq 0.2 - 0.5 \,h\,{\rm Mpc}^{-1}$ for $5-$ to $3-$point functions at $z=0$. The discrepancy occurs at higher wavenumbers at $z=2$. Thus, SPT and its variants, carried out to arbitrarily high order, are guaranteed to fail to describe matter $N$-point functions ($N>2$) around that scale.
The Swift AGN and Cluster Survey (SACS) uses 125 deg^2 of Swift XRT serendipitous fields with variable depths surrounding gamma-ray bursts to provide a medium depth (4e-15 erg/s/cm^2) and area survey filling the gap between deep, narrow Chandra/XMM-Newton surveys and wide, shallow ROSAT surveys. Here we present a catalog of 22,563 point sources and 442 extended sources and examine the number counts of the AGN and galaxy cluster populations. SACS provides excellent constraints on the AGN number counts at the bright end with negligible uncertainties due to cosmic variance, and these constraints are consistent with previous measurements. We use Wise mid-infrared (MIR) colors to classify the sources. For AGN we can roughly separate the point sources into MIR-red and MIR-blue AGN, finding roughly equal numbers of each type in the soft X-ray band (0.5-2 keV), but fewer MIR-blue sources in the hard X-ray band (2-8 keV). The cluster number counts, with 5% uncertainties from cosmic variance, are also consistent with previous surveys but span a much larger continuous flux range. Deep optical or IR follow-up observations of this cluster sample will significantly increase the number of higher redshift (z > 0.5) X-ray-selected clusters.
Artificial fragmentation of the matter density field causes the formation of spurious groups of particles in N-body simulations of non-standard Dark Matter (DM) models which are characterized by a small scale cut-off in the linear matter power spectrum. These spurious halos alter the prediction of the mass function in a range of masses where differences among DM models are most relevant to observational tests. Using a suite of high resolution simulations we show that the contamination of artificial groups of particles significantly affect the statistics of halo spin, shape and virial state parameters. We find that spurious halos have systematically larger spin values, are highly elliptical or prolate and significantly deviate from virial equilibrium. These characteristics allow us to detect the presence of spurious halos even in non-standard DM models for which the low-mass end of the mass function remains well behaved. We show that selecting halos near the virial equilibrium provides a simple and effective method to remove the bulk of spurious halos from numerical halo catalogs and consistently recover the halo mass function at low masses.
The time evolution of the equation of state $w$ for quintessence models with a scalar field as dark energy is studied up to the third derivative ($d^3w/da^3$) with respect to scale factor $a$, in order to predict the future observations and specify the scalar potential parameters with the observables. The third derivative of $w$ for general potential $V$ was derived and applied to several types of potential. They are the inverse power-law ($V=M^{4+\alpha}/Q^{\alpha}$), exponential ($V=M^4\exp{(\beta M/Q)}$), mixed ( $V=M^{4+\gamma}\exp{(\beta M/Q)}/Q^{\gamma}$), cosine ($V=M^4(\cos (Q/f)+1)$) and the Gaussian types ($V=M^4\exp(-Q^2/\sigma^2)$), which are prototypical potentials for the freezing and thawing models. If the parameter number for a potential form is $ n$, it is necessary to find at least for $n+2$ independent observations to identify the potential form and the evolution of scalar field ($Q$ and $ \dot{Q} $). Such observations would be the values of $ \Omega_Q, w, dw/da. \cdots $, and $ dw^n/da^n$. From these specific potentials, we could predict the $ n+1 $ and higher derivative of $w$ ; $ dw^{n+1}/da^{n+1}, \cdots$. Since four of the above mentioned potentials have two parameters, it is necessary to calculate the third derivative of $w$ for them to estimate the predict values. If they are tested observationally, it will be understood whether the dark energy could be described by the scalar field with this potential. At least it will satisfy the necessary conditions.
We give new constraints on small-scale non-Gaussianity of primordial curvature perturbations by the use of anisotropies in acoustic reheating. Mixing of local thermal or local kinetic equilibrium systems with different temperatures yields a locally averaged temperature rise, which is proportional to the square of temperature perturbations damping in the photon diffusion scale. Such secondary temperature perturbations are indistinguishable from the standard temperature perturbations linearly coming from primordial curvature perturbations and hence should be subdominant compared to the standard ones. We show that small-scale higher order correlation functions (connected non-Gaussian and disconnected Gaussian parts) of primordial curvature perturbations can be probed by investigating auto power spectrum of the generated secondary perturbations and the cross power spectrum with the standard perturbations. This is simply because these power spectra come from higher order correlation functions of primordial curvature perturbations with non-linear parameters such as $f_{\rm NL}$ and $\tau_{\rm NL}$ since secondary temperature perturbations are second order effects. Thus, the observational results $l(l+1)C^{TT}_l\simeq 6\times 10^{-10}$ at large scales give a robust and universal upper bound on small-scale non-Gaussianities of primordial curvature perturbations.
Theoretical and observational cosmology have enjoyed a number of significant successes over the last two decades. Cosmic microwave background measurements from the Wilkinson Microwave Anisotropy Probe and Planck, together with large-scale structure and supernova (SN) searches, have put very tight constraints on cosmological parameters. Type Ia supernovae (SNIa) played a central role in the discovery of the accelerated expansion of the Universe, recognised by the Nobel Prize in Physics in 2011. The last decade has seen an enormous increase in the amount of high quality SN observations, with SN catalogues now containing hundreds of objects. This number is expected to increase to thousands in the next few years, as data from next-generation missions, such as the Dark Energy Survey and Large Synoptic Survey Telescope become available. In order to exploit the vast amount of forthcoming high quality data, it is extremely important to develop robust and efficient statistical analysis methods to answer cosmological questions, most notably determining the nature of dark energy. To address these problems my work is based on nested-sampling approaches to parameter estimation and model selection and neural networks for machine-learning. Using advanced Bayesian techniques, I constrain the properties of dark-matter haloes along the SN lines-of-sight via their weak gravitational lensing effects, develop methods for classifying SNe photometrically from their lightcurves, and present results on more general issues associated with constraining cosmological parameters and testing the consistency of different SN compilations.
In the framework of the MSSM, we examine several simplified models where only a few superpartners are light. This allows us to study WIMP-nucleus scattering in terms of a handful of MSSM parameters and thereby scrutinize their impact on dark matter direct-detection experiments. Focusing on spin-independent WIMP-nucleon scattering, we derive simplified, analytic expressions for the Wilson coefficients associated with Higgs and squark exchange. We utilize these results to study the complementarity of constraints due to direct-detection, flavor, and collider experiments. We also identify parameter configurations that produce (almost) vanishing cross sections. In the proximity of these so-called blind spots, the amount of isospin violation is found to be much larger than typically expected in the MSSM. This feature is a generic property of parameter regions where cross sections are suppressed, and highlights the importance of a careful analysis of the nucleon couplings and the associated hadronic uncertainties. This becomes especially relevant once the increased sensitivity of future direct-detection experiments corners the MSSM into these regions of parameter space.
We calculate finite-temperature corrections to the decay rate of a generic neutral (pseudo)scalar particle that decays into (pseudo)scalars or fermion-antifermion pairs. The ratio of the finite-temperature decay rate to the zero-temperature decay rate is presented. Thermal effects are largest in the limit where the decaying particle is nonrelativistic but with a mass well below the background temperature, but significant effects are possible even when we relax the former assumption. We discuss cosmological scenarios under which these conditions can be achieved.
A family of spherical halo models with flat circular velocity curves is presented. This includes models in which the rotation curve has a finite central value but declines outwards (like the Jaffe model). It includes models in which the rotation curve is rising in the inner parts, but flattens asymptotically (like the Binney model). The family encompasses models with both finite and singular (cuspy) density profiles. The self-consistent distribution function depending on binding energy $E$ and angular momentum $L$ is derived and the kinematical properties of the models discussed. These really describe the properties of the total matter (both luminous and dark). For comparison with observations, it is better to consider tracer populations of stars. These can be used to represent elliptical galaxies or the spheroidal components of spiral galaxies. Accordingly, we study the properties of tracers with power-law or Einasto profiles moving in the doubloon potential. Under the assumption of spherical alignment, we provide a simple way to solve the Jeans equations for the velocity dispersions. This choice of alignment is supported by observations on the stellar halo of the Milky Way. Power-law tracers have prolate spheroidal velocity ellipsoids everywhere. However, this is not the case for Einasto tracers, for which the velocity ellipsoids change from prolate to oblate spheroidal near the pole. Asymptotic forms of the velocity distributions close to the escape speed are also derived, with an eye to application to the high velocity stars in the Milky Way. Power-law tracers have power-law or Maxwellian velocity distributions tails, whereas Einasto tracers have super-exponential cut-offs.
In this work, we present a study of a purely kinetic k-essence model, characterized basically by a parameter $\alpha$ in presence of a bulk dissipative term, whose relationship between viscous pressure $\Pi$ and energy density $\rho$ of the background follows a polytropic type law $\Pi \propto \rho^{\lambda+1/2}$, where $\lambda$, in principle, is a parameter without restrictions. Analytical solutions for the energy density of the k-essence field are found in two specific cases: $\lambda=1/2$ and $\lambda=(1-\alpha)/2\alpha$, and then we show that these solutions posses the same functional form than the non-viscous counterpart. Finally, both approach are contrasted with observational data from type Ia supernova, and the most recent Hubble parameter measurements, and therefore, the best values for the parameters of the theory are founds.
We compute the cosmological power spectrum in a non-commutative space-time using a canonical approach. The power spectrum is computed at leading order in the non-commutative parameter \theta^{\mu\nu} and in the spatial separation (x'-x)^{i}. We obtain an anisotropic dipolar imaginary primordial power spectrum of the form which was recently anticipated in the literature on the basis of the observed dipole modulation in CMBR data.
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