Tensions between cosmic microwave background (CMB) observations and the growth of the large-scale structure (LSS) inferred from late-time probes pose a serious challenge to the concordance $\Lambda$CDM cosmological model. State-of-the-art CMB data from the Planck satellite predicts a higher rate of structure growth than what preferred by low-redshift observables. Such tension has hitherto eluded conclusive explanations in terms of straightforward modifications to $\Lambda$CDM, e.g. the inclusion of massive neutrinos or a dynamical dark energy component. Here, we investigate `quartessence' models, where a single dark component mimics both dark matter and dark energy. We show that such models greatly alleviate the tension between high and low redshift observations, thanks to the non-vanishing sound speed of quartessence that inhibits structure growth at late times on scales smaller than its corresponding Jeans' length. In particular, the $3.4\sigma$ tension between CMB and LSS observables is thoroughly reabsorbed. For this reason, we argue that quartessence deserves further investigation and may lead to a deeper understanding of the physics of the dark Universe.
We introduce a methodology to test models with spatial variations of the fine-structure constant $\alpha$, based on the calculation of the angular power spectrum of these measurements. This methodology enables comparisons of observations and theoretical models through their predictions on the statistics of the $\alpha$ variation. Here we apply it to the case of symmetron models. We find no indications of deviations from the standard behavior, with current data providing an upper limit to the strength of the symmetron coupling to gravity ($\log{\beta^2}<-0.9$) when this is the only free parameter, and not able to constrain the model when also the symmetry breaking scale factor $a_{SSB}$ is free to vary.
As the largest, clearly defined building blocks of our Universe, galaxy clusters are interesting astrophysical laboratories and important probes for cosmology. X-ray surveys for galaxy clusters provide one of the best ways to characterise the population of galaxy clusters. We provide a description of the construction of the NORAS II galaxy cluster survey based on X-ray data from the northern part of the ROSAT All-Sky Survey. NORAS II extends the NORAS survey down to a flux limit of 1.8 x 10^(-12) erg s^-1 cm^-2 (0.1 - 2.4 keV) increasing the sample size by about a factor of two. The NORAS II cluster survey now reaches the same quality and depth of its counterpart, the Southern REFLEX II survey, allowing us to combine the two complementary surveys. The paper provides information on the determination of the cluster X-ray parameters, the identification process of the X-ray sources, the statistics of the survey, and the construction of the survey selection function, which we provide in numerical format. Currently NORAS II contains 860 clusters with a median redshift of z = 0.102. We provide a number of statistical functions including the logN-logS and the X-ray luminosity function and compare these to the results from the complementary REFLEX II survey. Using the NORAS II sample to constrain the cosmological parameters, sigma_8 and Omega_m, yields results perfectly consistent with those of REFLEX II. Overall, the results show that the two hemisphere samples, NORAS II and REFLEX II, can be combined without problems to an all-sky sample, just excluding the Zone-of-Avoidance.
Motivated by recent developments in perturbative calculations of the nonlinear evolution of large-scale structure, we present an iterative algorithm to reconstruct the initial conditions in a given volume starting from the dark matter distribution in real space. In our algorithm, objects are first iteratively moved back along estimated potential gradients until a nearly uniform catalog is obtained. The linear initial density is then estimated as the divergence of the cumulative displacement, with an optional second-order correction. This algorithm should undo non-linear effects up to one-loop order, including the higher-order infrared resummation piece. We test the method using dark matter simulations in real space. At redshift $z=0$, we find that after eight iterations the reconstructed density is more than $95\%$ correlated with the initial density at $k\le 0.35\; h\mathrm{Mpc}^{-1}$. The reconstruction also reduces the power in the difference between reconstructed and initial fields by more than two orders of magnitude at $k\le 0.2\; h\mathrm{Mpc}^{-1}$, and it extends the range of scales where the full broad-band shape of the power spectrum matches linear theory by a factor 2-3. As a specific application, we consider measurements of the Baryonic Acoustic Oscillation (BAO) scale that can be improved by reducing the degradation effects of large-scale flows. We find that the method improves the BAO signal-to-noise by a factor 2.7 at redshift $z=0$ and by a factor 2.5 at $z=0.6$ in our idealistic simulations. This improves standard BAO reconstruction by $70\%$ at $z=0$ and $30\%$ at $z=0.6$, and matches the optimal BAO signal and signal-to-noise of the linear density in the same volume.
The recent detection of two faint and extended star clusters in the central regions of two Local Group dwarf galaxies, Eridanus II and Andromeda XXV, raises the question of whether clusters with such low densities can survive the tidal field of cold dark matter haloes with central density cusps. Using both analytic arguments and a suite of collisionless N-body simulations, I show that these clusters are extremely fragile and quickly disrupted in the presence of central cusps $\rho\sim r^{-\alpha}$ with $\alpha\gtrsim 0.2$. Furthermore, the scenario in which the clusters where originally more massive and sank to the center of the halo requires extreme fine tuning and does not naturally reproduce the observed systems. In turn, these clusters are long lived in cored haloes, whose central regions are safe shelters for $\alpha\lesssim 0.2$. The only viable scenario for hosts that have preserved their primoridal cusp to the present time is that the clusters formed at rest at the bottom of the potential, which is easily tested by measurement of the clusters proper velocity within the host. This offers means to readily probe the central density profile of two dwarf galaxies as faint as $L_V\sim5\times 10^5 L_\odot$ and $L_V\sim6\times10^4 L_\odot$, in which stellar feedback is unlikely to be effective.
The velocity anisotropy parameter, beta, is a measure of the kinematic state of orbits in the stellar halo which holds promise for constraining the merger history of the Milky Way (MW). We determine global trends for beta as a function of radius from three suites of simulations, including accretion only and cosmological hydrodynamic simulations. We find that both types of simulations are consistent and predict strong radial anisotropy (<beta>~0.7) for Galactocentric radii greater than 10 kpc. Previous observations of beta for the MW's stellar halo claim a detection of an isotropic or tangential "dip" at r~20 kpc. Using the N-body+SPH simulations, we investigate the temporal persistence, population origin, and severity of "dips" in beta. We find dips in the in situ stellar halo are long-lived, while dips in the accreted stellar halo are short-lived and tied to the recent accretion of satellite material. We also find that a major merger as early as z~1 can result in a present day low (isotropic to tangential) value of beta over a wide range of radii. While all of these mechanisms are plausible drivers for the beta dip observed in the MW, in the simulations, each mechanism has a unique metallicity signature associated with it, implying that future spectroscopic surveys could distinguish between them. Since an accurate knowledge of beta(r) is required for measuring the mass of the MW halo, we note significant transient dips in beta could cause an overestimate of the halo's mass when using spherical Jeans equation modeling.
Low radio frequency surveys are important for testing unified models of radio-loud quasars and radio galaxies. Intrinsically similar sources that are randomly oriented on the sky will have different projected linear sizes. Measuring the projected linear sizes of these sources provides an indication of their orientation. Steep-spectrum isotropic radio emission allows for orientation-free sample selection at low radio frequencies. We use a new radio survey of the Bo\"otes field at 150 MHz made with the Low Frequency Array (LOFAR) to select a sample of radio sources. We identify 44 radio galaxies and 16 quasars with powers $P>10^{25.5}$ W Hz$^{-1}$ at 150 MHz using cross-matched multi-wavelength information from the AGN and Galaxy Evolution Survey (AGES), which provides spectroscopic redshifts. We find that LOFAR-detected radio sources with steep spectra have projected linear sizes that are on average 4.4$\pm$1.4 larger than those with flat spectra. The projected linear sizes of radio galaxies are on average 3.1$\pm$1.0 larger than those of quasars (2.0$\pm$0.3 after correcting for redshift evolution). Combining these results with three previous surveys, we find that the projected linear sizes of radio galaxies and quasars depend on redshift but not on power. The projected linear size ratio does not correlate with either parameter. The LOFAR data is consistent within the uncertainties with theoretical predictions of the correlation between the quasar fraction and linear size ratio, based on an orientation-based unification scheme.
We study the orientations of satellite galaxies in redMaPPer clusters constructed from the Sloan Digital Sky Survey at $0.1<z<0.35$ to determine whether there is any preferential tendency for satellites to point radially toward cluster centers. We analyze the satellite alignment (SA) signal based on three shape measurement methods (re-Gaussianization, de Vaucouleurs, and isophotal shapes), which trace galaxy light profiles at different radii. While no net SA signal is detected using re-Gaussianization shapes across the entire sample, the observed SA signal reaches a statistically significant level when using a subsample of satellites with higher luminosity. We detect the strongest SA signals using isophotal shapes, followed by de Vaucouleurs shapes, and investigate the impact of noise, systematics, and real physical effects such as isophotal twisting in the comparison between the results based on different shape measurement methods. After studying the correlation of the SA signal with a total of 17 galaxy and cluster properties, we find that the measured SA signal is strongest for satellites with the following characteristics: higher luminosity, smaller distance to the cluster center, rounder in shape, higher bulge fraction in the light profile, distributed preferentially along the major axis directions of their centrals, and residing in clusters with less luminous centrals. Finally, we provide physical explanations for the identified dependences, and discuss the connection to theories of SA.
Determining the velocity distribution of halo stars is essential for estimating the mass of the Milky Way and for inferring its formation history. Since the stellar halo is a dynamically hot system, the velocity distribution of halo stars is well described by the 3-dimensional velocity dispersions $(\sigma_r, \sigma_\theta, \sigma_\phi)$, or by the velocity anisotropy parameter $\beta=1-(\sigma_\theta^2+\sigma_\phi^2)/(2\sigma_r^2)$. Direct measurements of $(\sigma_r, \sigma_\theta, \sigma_\phi)$ consistently suggest $\beta =0.5$-$0.7$ for nearby halo stars. In contrast, the value of $\beta$ at large Galactocentric radius $r$ is still controversial, since reliable proper motion data are available for only a handful of stars. In the last decade, several authors have tried to estimate $\beta$ for distant halo stars by fitting the observed line-of-sight velocities at each radius with simple velocity distribution models (local fitting methods). Some results of local fitting methods imply $\beta<0$ at $r \gtrsim 20 \;\rm{kpc}$, which is inconsistent with recent predictions from cosmological simulations. Here we perform mock-catalogue analyses to show that the estimates of $\beta$ based on local fitting methods are reliable only at $r \leq 15 \;\rm{kpc}$ with the current sample size ($\sim10^3$ stars at a given radius). As $r$ increases, the line-of-sight velocity (corrected for the Solar reflex motion) becomes increasingly closer to the Galactocentric radial velocity, so that it becomes increasingly more difficult to estimate tangential velocity dispersion $(\sigma_\theta, \sigma_\phi)$ from line-of-sight velocity distribution. Our results suggest that the forthcoming Gaia data will be crucial for understanding the velocity distribution of halo stars at $r \geq 20\;\rm{kpc}$.
We present clustering properties from 579,492 Lyman break galaxies (LBGs) at $z\sim4-6$ over the 100 deg$^2$ sky (corresponding to a 1.4 Gpc$^3$ volume) identified in early data of the Hyper Suprime-Cam (HSC) Subaru strategic program survey. We derive angular correlation functions (ACFs) of the HSC LBGs with unprecedentedly high statistical accuracies at $z\sim4-6$, and compare them with the halo occupation distribution (HOD) models. We clearly identify significant ACF excesses in $10"<\theta<90"$, the transition scale between 1- and 2-halo terms, suggestive of the existence of the non-linear halo bias effect. Combining the HOD models and previous clustering measurements of faint LBGs at $z\sim4-7$, we investigate dark-matter halo mass ($M_\mathrm{h}$) of the $z\sim4-7$ LBGs and its correlation with various physical properties including the star-formation rate (SFR), the stellar-to-halo mass ratio (SHMR), and the dark-matter mass accretion rate ($\dot{M}_\mathrm{h}$) over a wide-mass range of $M_\mathrm{h}/M_\odot=4\times10^{10}-4\times10^{12}$. We find that the SHMR increases from $z\sim4$ to $7$ by a factor of $\sim4$ at $M_\mathrm{h}\simeq1\times10^{11}\ M_\odot$, while the SHMR shows no strong evolution in the similar redshift range at $M_\mathrm{h}\simeq1\times10^{12}\ M_\odot$. Interestingly, we identify a tight relation of $SFR/\dot{M}_\mathrm{h}-M_\mathrm{h}$ showing no significant evolution beyond 0.15 dex in this wide-mass range over $z\sim4-7$. This weak evolution suggests that the $SFR/\dot{M}_\mathrm{h}-M_\mathrm{h}$ relation is a fundamental relation in high-redshift galaxy formation whose star-formation activities are regulated by the dark-matter mass assembly.
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We present updated constraints on the free-streaming nature of cosmological neutrinos from cosmic microwave background (CMB) power spectra, baryonic acoustic oscillation data, and local measurements of the Hubble constant. Specifically, we consider a Fermi-like four-fermion interaction between massless neutrinos, characterized by an effective coupling constant $ G_{\rm eff}$, and resulting in a neutrino opacity $\dot{\tau}_\nu\propto G_{\rm eff}^2 T_\nu^5$. Using a conservative prior on the parameter $\log_{10}\left(G_{\rm eff} {\rm MeV}^2\right)$, we find a bimodal posterior distribution. The first of these modes is consistent with the standard $\Lambda$CDM cosmology and corresponds to neutrinos decoupling at redshift $z_{\nu,{\rm dec}} > 1.3\times10^5$. The other mode of the posterior, dubbed the "interacting neutrino mode", corresponds to neutrino decoupling occurring within a narrow redshift window centered around $z_{\nu,{\rm dec}}\sim8300$. This mode is characterized by a high value of the effective neutrino coupling constant, together with a lower value of the scalar spectral index and amplitude of fluctuations, and a higher value of the Hubble parameter. Using both a maximum likelihood analysis and the ratio of the two mode's Bayesian evidence, we find the interacting neutrino mode to be statistically disfavored compared to the standard $\Lambda$CDM cosmology. Interestingly, the addition of CMB polarization and direct Hubble constant measurements significantly raises the statistical significance of this secondary mode, indicating that new physics in the neutrino sector could help explain the difference between local measurements of $H_0$, and those inferred from CMB data. A robust consequence of our results is that neutrinos must be free streaming long before the epoch of matter-radiation equality.
A key goal of the Stage IV dark energy experiments Euclid, LSST and WFIRST is to measure the growth of structure with cosmic time from weak lensing analysis over large regions of the sky. Weak lensing cosmology will be challenging: in addition to highly accurate galaxy shape measurements, statistically robust and accurate photometric redshift (photo-z) estimates for billions of faint galaxies will be needed in order to reconstruct the three-dimensional matter distribution. Here we present an overview of and initial results from the Complete Calibration of the Color-Redshift Relation (C3R2) survey, designed specifically to calibrate the empirical galaxy color-redshift relation to the Euclid depth. These redshifts will also be important for the calibrations of LSST and WFIRST. The C3R2 survey is obtaining multiplexed observations with Keck (DEIMOS, LRIS, and MOSFIRE), the Gran Telescopio Canarias (GTC; OSIRIS), and the Very Large Telescope (VLT; FORS2 and KMOS) of a targeted sample of galaxies most important for the redshift calibration. We focus spectroscopic efforts on under-sampled regions of galaxy color space identified in previous work in order to minimize the number of spectroscopic redshifts needed to map the color-redshift relation to the required accuracy. Here we present the C3R2 survey strategy and initial results, including the 1283 high confidence redshifts obtained in the 2016A semester and released as Data Release 1.
In order to understand the nature of the accelerating expansion of the late-time universe, it is important to experimentally determine whether dark energy is cosmological constant or dynamical in nature. If dark energy already exists prior to inflation, which is a reasonable assumption, then one expects that a dynamical dark energy would leave some footprint in the anisotropy of the late-time accelerated expansion. We invoke the quintessence field, one of the simplest dynamical dark energy models, to investigate the effects of its quantum fluctuations (fully correlated with curvature perturbations) during inflation and estimate the anisotropy of the cosmic expansion so induced. For that we calculate the perturbed luminosity distance and its power spectrum, which is an estimator of anisotropicity of late-time accelerated expansion. We find that the gravitational potential at large scales and late times is less decayed in QCDM compared to that in $ \Lambda $CDM so that the smaller the redshift and multipole, the more deficit of power in QCDM. These features may help to distinguish the cosmological constant from a dynamical dark energy. In this regard, the apparent (but not yet statistically significant) power deficit in CMB low multipoles based on $ \Lambda $CDM may even be a smoking gun for QCDM.
Like Scalar Galileons, Einstein-Hilbert action and the Lovelock extensions contain higher order derivatives in action, however their equations of motion are second order. We are lead to ask: Can there exist a corresponding action for spin-1 or electromagnetic fields? By demanding three conditions - theory be described by vector potential $A^\mu$ and its derivatives, Gauge invariance be satisfied, and equations of motion be linear in second derivatives of vector potential - we construct a higher derivative electromagnetic action which does not have ghosts and preserve gauge invariance. We show that the action breaks conformal invariance explicitly and leads to generation of magnetic field during inflation. One unique feature of our model is that appreciable magnetic fields are generated at small wavelengths while tiny magnetic fields at large wavelengths that are consistent with current observations.
We estimate the spin distribution of primordial black holes based on the recent study of the critical phenomena in the gravitational collapse of a rotating radiation fluid. We find that primordial black holes are mostly slowly rotating.
We report the discovery of a diffuse stellar cloud with an angular extent $\gtrsim30^{\prime\prime}$, which we term "Sumo Puff", in data from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). While we do not have a redshift for this object, it is in close angular proximity to a post-merger galaxy at redshift $z=0.0431$ and is projected within a few virial radii (assuming similar redshifts) of two other ${\sim}L_\star$ galaxies, which we use to bracket a potential redshift range of $0.0055 < z < 0.0431$. The object's light distribution is flat, as characterized by a low Sersic index ($n\sim0.3$). It has a low central $g$-band surface brightness of ${\sim}26.4$ mag arcsec$^{-2}$, large effective radius of ${\sim}13^{\prime\prime}$ (${\sim}11$ kpc at $z=0.0431$ and ${\sim}1.5$ kpc at $z=0.0055$), and an elongated morphology ($b/a\sim0.4$). Its red color ($g-i\sim1$) is consistent with a passively evolving stellar population and similar to the nearby post-merger galaxy, and we may see tidal material connecting Sumo Puff with this galaxy. We offer two possible interpretations for the nature of this object: (1) it is an extreme, galaxy-size tidal feature associated with a recent merger event, or (2) it is a foreground dwarf galaxy with properties consistent with a quenched, disturbed ultra-diffuse galaxy. We present a qualitative comparison with simulations that demonstrates the feasibility of forming a structure similar to this object in a merger event. Follow-up spectroscopy and/or deeper imaging to confirm the presence of the bridge of tidal material will be necessary to reveal the true nature of this object.
Usually when applying the mimetic model to the early universe, higher derivative terms are needed to promote the mimetic field to be dynamical. However such models suffer from the ghost and/or the gradient instabilities and simple extensions cannot cure this pathology. We point out in this paper that it is possible to overcome this difficulty by considering the direct couplings of the higher derivatives of the mimetic field to the curvature of the spacetime.
Multiple cosmological observations indicate that dark matter (DM) constitutes 85% of all matter in the Universe [1]. All the current evidence for DM comes from galactic or larger scale observations through the gravitational pull of DM on ordinary matter [1], leaving the microscopic nature of DM a mystery. Ambitious programs in particle physics have mostly focused on searches for WIMPs (Weakly Interacting Massive Particles) as DM candidates [2]. As WIMPs remain elusive, there is a growing interest in alternatives. Some models [3-7] predict DM in the form of spatially large objects ("clumps") that may cause glitches in atomic clocks [6]. Here we use the network of atomic clocks on board the GPS satellites as a 50,000 km aperture detector to search for DM clumps. As DM clumps sweep through the GPS satellite constellation at galactic velocities ~300 km/s, their predicted signature is a correlated propagation of clock glitches through the constellation over a period of a few minutes [6]. By mining 16 years of archival GPS data, we find no evidence for DM clumps in the form of domain walls. This enables us to improve limits on DM couplings to atomic clocks by several orders of magnitude. Our work demonstrates the use of a global network of precision measurement devices in the search for DM. Several global networks including magnetometers, laboratory atomic clocks, and other precision devices are being developed [5,8,9]. We anticipate that our methods will be valuable for probing new physics in this emerging area.
In this work, we investigate the electroweak vacuum instability in the adiabatic or non-adiabatic cosmological background. In the general cosmological background, the vacuum field fluctuations $\left< { \delta \phi }^{ 2 } \right>$ grow in proportional to the cosmological scale. The large vacuum fluctuations of the Higgs field can destabilize the effective Higgs potential, or generate the catastrophic AdS domains or bubbles. These unwanted phenomena cause the catastrophic collapse of the Universe. By using the adiabatic (WKB) expansion or the adiabatic regularization methods, we obtain the exact renormalized vacuum fluctuations $\left< { \delta \phi }^{ 2 } \right>_{\rm ren}$ of the Higgs field in the adiabatic and the non-adiabatic cosmological background. The non-adiabatic Higgs vacuum fluctuations generally cause the catastrophic phenomena. On the other hand, the adiabatic Higgs vacuum fluctuations have little effect on the Higgs vacuum stability. However, in the slowly-varying background by another scalar field $S$, the adiabatic Higgs vacuum fluctuations can destabilize the effective Higgs potential and provide the upper bound of the mass of the background scalar field $S$ as $m_{S} \lesssim 10^{13}\ {\rm GeV}$ where we assume the instability scale $\Lambda_{I} \approx 10^{11}\ {\rm GeV}$.
The range of currently proposed active galactic nucleus (AGN) far-infrared templates results in uncertainties in retrieving host galaxy information from infrared observations and also undermines constraints on the outer part of the AGN torus. We discuss how to test and reconcile these templates. Physically, the fraction of the intrinsic AGN IR-processed luminosity compared with that from the central engine should be consistent with the dust-covering factor. In addition, besides reproducing the composite spectral energy distributions (SEDs) of quasars, a correct AGN IR template combined with an accurate library of star-forming galaxy templates should be able to reproduce the IR properties of the host galaxies, such as the luminosity-dependent SED shapes and aromatic feature strengths. We develop tests based on these expected behaviors and find that the shape of the AGN intrinsic far-IR emission drops off rapidly starting at $\sim20~\mu$m and can be matched by an Elvis et al. (1994)-like template with minor modification. Despite the variations in the near- to mid-IR bands, AGNs in quasars and Seyfert galaxies have remarkably similar intrinsic far-IR SEDs at $\lambda \sim 20$-$100~\mu$ m, suggesting similar emission character of the outermost region of the circumnuclear torus. The variations of the intrinsic AGN IR SEDs among the type-1 quasar population can be explained by the changing relative strengths of four major dust components with similar characteristic temperatures, and there is evidence for compact AGN-heated dusty structures at sub-kpc scales in the far-IR.
Quasi-Normal Modes (QNM) or ringdown phase of gravitational waves provide critical information about the structure of compact objects like Black Holes. Thus, QNMs can be a tool to test General Relativity (GR) and possible deviations from it. In the case of GR, it is known for a long time that a relation between two types of Black Hole perturbations: scalar (Zerilli) and vector (Regge-Wheeler), leads to an equal share of emitted gravitational energy. With the direct detection of Gravitational waves, it is now natural to ask: whether the same relation (between scalar and vector perturbations) holds for modified gravity theories? If not, whether one can use this as a way to probe deviations from General Relativity. As a first step, we show explicitly that the above relation between Regge-Wheeler and Zerilli breaks down for a general f (R) model, and hence the two perturbations do not share equal amounts of emitted gravitational energy. We discuss the implication of this imbalance on observations and the no-hair conjecture.
We propose a new method of detecting Ellis wormholes by use of the images of wormholes surrounded by optically thin dust. First, we derive steady solutions of dust and more general medium surrounding the wormhole by solving relativistic Euler equations. We find two types of dust solutions: one is a static solution with arbitrary density profile, and the other is a solution of dust which passes into the wormhole and escapes into the other side with constant velocity. Next, solving null geodesic equations and radiation transfer equations, we investigate the images of the wormhole surrounded by dust for the above steady solutions. Because the wormhole spacetime possesses unstable circular orbits of photons, a bright ring appears in the image, just as in Schwarzschild spacetime. This indicates that the appearance of a bright ring solely confirms neither a black hole nor a wormhole. However, we find that the intensity contrast between the inside and the outside of the ring are quite different. Therefore, we could tell the difference between an Ellis wormhole and a black hole with high-resolution very-long-baseline-interferometry observations in the near future.
After the first direct detection of gravitational waves (GW), detection of stochastic background of GWs is an important next step, and the first GW event suggests that it is within the reach of the second-generation ground-based GW detectors. Such a GW signal is typically tiny, and can be detected by cross-correlating the data from two spatially-separated detectors if the detector noise is uncorrelated. It has been advocated, however, that the global magnetic fields in the Earth-ionosphere cavity produce the environmental disturbances at low-frequency bands, known as Schumann resonances, which potentially couple with GW detectors. In this paper, we present a simple analytical model to estimate its impact on the detection of stochastic GWs. The model crucially depends on the geometry of detector pair through the directional coupling, and we investigate the basic properties of the correlated magnetic noise based on the analytic expressions. The model reproduces the major trend of the recently measured global correlation between GW detectors via magnetometer. The estimated values of the impact of correlated noise also match those obtained from the measurement. Finally, we give an implication to the detection of stochastic GWs including upcoming detectors, KAGRA and LIGO India. The model suggests that LIGO Hanford-Virgo and Virgo-KAGRA pairs are possibly less sensitive to the correlated noise, and can achieve a better sensitivity to the stochastic GW signal in the most pessimistic case.
As an extension of our previous work, which investigated the shadows of the Ellis wormhole surrounded by nonrotating dust, in this paper we study wormhole shadows in rotating dust flow. First, we derive steady-state solutions of slowly rotating dust surrounding the wormhole by solving relativistic Euler equations. Solving null geodesic equations and radiation transfer equations, we investigate the images of the wormhole surrounded by dust for the above steady-state solutions. Because the Ellis wormhole spacetime possesses unstable circular orbits of photons, a bright ring appears in the image, just as in Schwarzschild spacetime. The bright ring looks distorted due to rotation. Aside from the bright ring, there appear weakly luminous complex patterns by the emission from the other side of the throat. These structure could be detected by high-resolution very-long-baseline-interferometry observations in the near future.
The Extragalactic Background Light (EBL) captures the total integrated emission from stars and galaxies throughout the cosmic history. The amplitude of the near-infrared EBL from space absolute photometry observations has been controversial and depends strongly on the modeling and subtraction of the Zodiacal light foreground. We report the first measurement of the diffuse background spectrum at 0.8-1.7 um from the CIBER experiment. The observations were obtained with an absolute spectrometer over two flights in multiple sky fields to enable the subtraction of Zodiacal light, stars, terrestrial emission, and diffuse Galactic light. After subtracting foregrounds and accounting for systematic errors, we find the nominal EBL brightness, assuming the Kelsall Zodiacal light model, is 42.7+11.9/-10.6 nW/m2/sr at 1.4 um. We also analyzed the data using the Wright Zodiacal light model, which results in a worse statistical fit to the data and an unphysical EBL, falling below the known background light from galaxies at <1.3 um. Using a model-independent analysis based on the minimum EBL brightness, we find an EBL brightness of 28.7+5.1/-3.3 nW/m2/sr at 1.4 um. While the derived EBL amplitude strongly depends on the Zodiacal light model, we find that we cannot fit the spectral data to Zodiacal light, Galactic emission, and EBL from solely integrated galactic light from galaxy counts. The results require a new diffuse component, such as an additional foreground or an excess EBL with a redder spectrum than that of Zodiacal light.
We embed a flipped ${\rm SU}(5) \times {\rm U}(1)$ GUT model in a no-scale supergravity framework, and discuss its predictions for cosmic microwave background observables, which are similar to those of the Starobinsky model of inflation. Measurements of the tilt in the spectrum of scalar perturbations in the cosmic microwave background, $n_s$, constrain significantly the model parameters. We also discuss the model's predictions for neutrino masses, and pay particular attention to the behaviours of scalar fields during and after inflation, reheating and the GUT phase transition. We argue in favor of strong reheating in order to avoid excessive entropy production which could dilute the generated baryon asymmetry.
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We present the correlation function of the luminosity distances in a flat $\Lambda$CDM universe. Decomposing the luminosity distance fluctuation into the velocity, the gravitational potential, and the lensing contributions, we study their individual contributions to the correlation function. The lensing contribution is important at large redshift ($z\gtrsim 0.5$) but only for small angular separation ($\theta \lesssim 3^\circ$), while the velocity contribution dominates over the other contributions at low redshift or at larger separation. However, the gravitational potential contribution is always subdominant at all scale, if the correct gauge-invariant expression is used. The correlation function of the luminosity distances depends significantly on the matter content, especially for the lensing contribution, thus providing a novel tool of estimating cosmological parameters.
A specific value for the cosmological constant, \Lambda, can account for late-time cosmic acceleration. However, motivated by the so-called cosmological constant problem(s), several alternative mechanisms have been explored. To date, a host of well-studied dynamical dark energy and modified gravity models exists. Going beyond \Lambda CDM often comes with additional degrees of freedom (dofs). For these to pass existing observational tests, an efficient screening mechanism must be in place. The linear and quasi-linear regimes of structure formation are ideal probes of such dofs and can capture the onset of screening. We propose here a semi-phenomenological treatment to account for screening dynamics on LSS observables, with special emphasis on Vainshtein-type screening.
In this paper, we consider the singular isothermal sphere lensing model that have a spherically symmetric power-law mass distribution $\rho_{tot}(r)\sim r^{-\gamma}$. We investigate whether the mass density power-law index $\gamma$ is cosmologically evolutionary by using the strong gravitational lensing (SGL) observation, in combination with other cosmological observations. We also check whether the constraint result of $\gamma$ is affected by the cosmological model, by considering several simple dynamical dark energy models. We find that the constraint on $\gamma$ is mainly decided by the SGL observation and independent of the cosmological model, and we find no evidence for the evolution of $\gamma$ from the SGL observation.
We extend previous studies of big bang nucleosynthesis, with the assumption that ordinary matter and dark matter sectors are entangled through the number of degrees of freedom entering the Friedmann equations. This conjecture allows us to find a relation between the temperatures of the weakly interacting matter and dark-matter sectors. The constraints imposed by observations are studied by comparison with calculations of big bang nucleosynthesis for the abundance of light elements. It is found that these constraints are compatible with cold dark matter and a wide range number of dark sectors.
Dwarf galaxies are known to have remarkably low star formation efficiency due to strong feedback. Adopting the dwarf galaxies of the Milky Way as a laboratory, we explore a flexible semi-analytic galaxy formation model to understand how the feedback processes shape the satellite galaxies of the Milky Way. Using Markov-Chain Monte-Carlo, we exhaustively search a large parameter space of the model and rigorously show that the general wisdom of strong outflows as the primary feedback mechanism cannot simultaneously explain the stellar mass function and the mass--metallicity relation of the Milky Way satellites. An extended model that assumes that a fraction of baryons is prevented from collapsing into low-mass halos in the first place can be accurately constrained to simultaneously reproduce those observations. The inference suggests that two different physical mechanisms are needed to explain the two different data sets. In particular, moderate outflows with weak halo mass dependence are needed to explain the mass--metallicity relation, and prevention of baryons falling into shallow gravitational potentials of low-mass halos (e.g. "pre-heating") is needed to explain the low stellar mass fraction for a given subhalo mass.
We study the dark matter phenomenology of non-minimal composite Higgs models with $SO(7)$ broken to the exceptional group $G_2$. In addition to the Higgs, three pseudo-Nambu-Goldstone bosons arise, one of which is electrically neutral. A parity symmetry is enough to ensure this resonance is stable. In fact, if the breaking of the Goldstone symmetry is driven by the fermion sector, this $\mathbb{Z}_2$ symmetry is automatically unbroken in the electroweak phase. In this case, the relic density, as well as the expected indirect, direct and collider signals are then uniquely determined by the value of the compositeness scale, $f$. Current experimental bounds allow to account for a large fraction of the dark matter of the Universe if the dark matter particle is part of an electroweak triplet. The totality of the relic abundance can be accommodated if instead this particle is a composite singlet. In both cases, the scale $f$ and the dark matter mass are of the order of a few TeV.
Considering gravitational waves propagating on the most general 4+N-dimensional space-time, we investigate the effects due to the N extra dimensions on the four-dimensional waves. All wave equations are derived in general and discussed. On Minkowski4 times an arbitrary Ricci-flat compact manifold, we find: a massless wave with an additional polarization, the breathing mode, and extra waves with high frequencies fixed by Kaluza-Klein masses. We discuss whether these two effects could be observed.
We present the SILVERRUSH program strategy and clustering properties investigated with $2,354$ Ly$\alpha$ emitters at $z=5.7$ and $6.6$ found in the early data of the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey exploiting the carefully designed narrowband filters. We derive angular correlation functions with the unprecedentedly large samples of LAEs at $z=6-7$ over the large total area of $14-21$ deg$^2$ corresponding to $0.3-0.5$ comoving Gpc$^2$. We obtain the average large-scale bias values of $b_{\rm avg}=4.1\pm 0.2$ ($4.5\pm 0.6$) at $z=5.7$ ($z=6.6$) for $\gtrsim L^*$ LAEs, indicating the weak evolution of LAE clustering from $z=5.7$ to $6.6$. We compare the LAE clustering results with two independent theoretical models that suggest an increase of an LAE clustering signal by the patchy ionized bubbles at the epoch of reionization (EoR), and estimate the neutral hydrogen fraction to be $x_{\rm HI}=0.3^{+0.1}_{-0.2}$ at $z=6.6$. Based on the halo occupation distribution models, we find that the $\gtrsim L^*$ LAEs are hosted by the dark-matter halos with the average mass of $\log (\left < M_{\rm h} \right >/M_\odot) =11.1^{+0.2}_{-0.4}$ ($10.8^{+0.3}_{-0.5}$) at $z=5.7$ ($6.6$) with a Ly$\alpha$ duty cycle of 1 % or less, where the results of $z=6.6$ LAEs may be slightly biased, due to the increase of the clustering signal at the EoR. Our clustering analysis reveals the low-mass nature of $\gtrsim L^*$ LAEs at $z=6-7$, and that these LAEs probably evolve into massive super-$L^*$ galaxies in the present-day universe.
We present a new mechanism to produce the dark photon ($\gamma'$) in the early universe with a help of the axion ($a$) using a recently proposed dark axion portal. The dark photon, a light gauge boson in the dark sector, can be a relic dark matter if its lifetime is long enough. The main process we consider is a variant of the Primakoff process $f a \to f \gamma'$ mediated by a photon, which is possible with the axion--photon--dark photon coupling. The axion is thermalized in the early universe because of the strong interaction and it can contribute to the non-thermal dark photon production through the dark axion portal coupling. It provides a two-component dark matter sector, and the relic density deficit issue of the axion dark matter can be addressed by the compensation with the dark photon. The dark photon dark matter can also address the reported 3.5 keV $X$-ray excess via the $\gamma' \to \gamma a$ decay.
We present a new catalog of narrow-line Seyfert 1 (NLSy1) galaxies from the Sloan Digital Sky Survey Data Release 12 (SDSS DR12). This was obtained by a systematic analysis through modeling of the continuum and emission lines of the spectra of all the 68,859 SDSS DR12 objects that are classified as "QSO" by the SDSS spectroscopic pipeline with z < 0.8 and a median signal-to-noise ratio (S/N) > 2 per pixel. This catalog contains a total of 11,101 objects, which is about 5 times larger than the previously known NLSy1 galaxies. Their monochromatic continuum luminosity at 5100 A is found to be strongly correlated with H-beta, H-alpha, and [O III] emission line luminosities. The optical Fe II strength in NLSy1 galaxies is about two times larger than the broad- line Seyfert 1 (BLSy1) galaxies. About 5% of the catalog sources are detected in the FIRST survey. The Eddington ratio (XEdd) of NLSy1 galaxies has an average of log XEdd of -0.34, much higher than -1.03 found for BLSy1 galaxies. Their black hole masses (MBH) have an average of log MBH of 6.9 Msun, which is less than BLSy1 galaxies, which have an average of log MBH of 8.0 Msun. The MBH of NLSy1 galaxies is found to be correlated with their host galaxy velocity dispersion. Our analysis suggests that geometrical effects playing an important role in defining NLSy1 galaxies and their MBH deficit is perhaps due to their lower inclination compared to BLSy1 galaxies.
Hamiltonian systems such as the gravitational N-body problem have time-reversal symmetry. However, all numerical N-body integration schemes, including symplectic ones, respect this property only approximately. In this paper, we present the new N-body integrator JANUS, for which we achieve exact time-reversal symmetry by combining integer and floating point arithmetic. JANUS is explicit, formally symplectic and satisfies Liouville's theorem exactly. Its order is even and can be adjusted between two and ten. We discuss the implementation ofJANUS and present tests of its accuracy and speed by performing and analyzing long-term integrations of the Solar System. We show that JANUS is fast and accurate enough to tackle a broad class of dynamical problems. We also discuss the practical and philosophical implications of running exactly time-reversible simulations.
We reinvestigate a claimed sample of 22 X-ray detected active galactic nuclei (AGN) at redshifts z > 4, which has reignited the debate as to whether young galaxies or AGN reionized the Universe. These sources lie within the GOODS-S/CANDELS field, and we examine both the robustness of the claimed X-ray detections (within the Chandra 4Ms imaging) and perform an independent analysis of the photometric redshifts of the optical/infrared counterparts. We confirm the reality of only 15 of the 22 reported X-ray detections, and moreover find that only 12 of the 22 optical/infrared counterpart galaxies actually lie robustly at z > 4. Combining these results we find convincing evidence for only 7 X-ray AGN at z > 4 in the GOODS-S field, of which only one lies at z > 5. We recalculate the evolving far-UV (1500 Angstrom) luminosity density produced by AGN at high redshift, and find that it declines rapidly from z = 4 to z = 6, in agreement with several other recent studies of the evolving AGN luminosity function. The associated rapid decline in inferred hydrogen-ionizing emissivity contributed by AGN falls an order-of-magnitude short of the level required to maintain hydrogen ionization at z ~ 6. We conclude that all available evidence continues to favour a scenario in which young galaxies reionized the Universe, with AGN making, at most, a very minor contribution to cosmic hydrogen reionization.
We present a statistical study on the [C I]($^{3} \rm P_{1} \rightarrow {\rm ^3 P}_{0}$), [C I] ($^{3} \rm P_{2} \rightarrow {\rm ^3 P}_{1}$) lines (hereafter [C I] (1$-$0) and [C I] (2$-$1), respectively) and the CO (1$-$0) line for a sample of (ultra)luminous infrared galaxies [(U)LIRGs]. We explore the correlations between the luminosities of CO (1$-$0) and [C I] lines, and find that $L'_\mathrm{CO(1-0)}$ correlates almost linearly with both $L'_ \mathrm{[CI](1-0)}$ and $L'_\mathrm{[CI](2-1)}$, suggesting that [C I] lines can trace total molecular gas mass at least for (U)LIRGs. We also investigate the dependence of $L'_\mathrm{[CI](1-0)}$/$L'_\mathrm{CO(1-0)}$, $L'_\mathrm{[CI](2-1)}$/$L'_\mathrm{CO(1-0)}$ and $L'_\mathrm{[CI](2-1)}$/$L'_\mathrm{[CI](1-0)}$ on the far-infrared color of 60-to-100 $\mu$m, and find non-correlation, a weak correlation and a modest correlation, respectively. Under the assumption that these two carbon transitions are optically thin, we further calculate the [C I] line excitation temperatures, atomic carbon masses, and the mean [C I] line flux-to-H$_2$ mass conversion factors for our sample. The resulting $\mathrm{H_2}$ masses using these [C I]-based conversion factors roughly agree with those derived from $L'_\mathrm{CO(1-0)}$ and CO-to-H$_2$ conversion factor.
We analyze three-dimensional hydrodynamical simulations of the interaction of jets and the bubbles they inflate with the intra-cluster medium (ICM), and show that the heating of the ICM by mixing hot bubble gas with the ICM operates over tens of millions of years, and hence can smooth the sporadic activity of the jets. The inflation process of hot bubbles by propagating jets forms many vortices, and these vortices mix the hot bubble gas with the ICM. The mixing, hence the heating of the ICM, starts immediately after the jets are launched, but continues for tens of millions of years. We suggest that the smoothing of the active galactic nucleus (AGN) sporadic activity by the long-lived vortices accounts for the recent finding of a gentle energy coupling between AGN heating and the ICM.
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Supernova cosmology without spectra will be the bread and butter mode for future surveys such as LSST. This lack of supernova spectra results in uncertainty in the redshifts which, if ignored, leads to significantly biased estimates of cosmological parameters. Here we present a hierarchical Bayesian formalism -- zBEAMS -- that fully addresses this problem by marginalising over the unknown or contaminated supernova redshifts to produce unbiased cosmological estimates that are competitive with entirely spectroscopic data. zBEAMS provides a unified treatment of both photometric redshifts and host galaxy misidentification (occurring due to chance galaxy alignments or faint hosts), effectively correcting the inevitable contamination in the Hubble diagram. Like its predecessor BEAMS, our formalism also takes care of non-Ia supernova contamination by marginalising over the unknown supernova type. We demonstrate the effectiveness of this technique with simulations of supernovae with photometric redshifts and host galaxy misidentification. A novel feature of the photometric redshift case is the important role played by the redshift distribution of the supernovae.
The relation between the halo field and the matter fluctuations (halo bias), in the presence of massive neutrinos depends on the total neutrino mass, massive neutrinos introduce an additional scale-dependence of the bias which is usually neglected in cosmological analyses. We investigate the magnitude of the systematic effect on interesting cosmological parameters induced by neglecting this scale dependence, finding that while it is not a problem for current surveys, it is non-negligible for future, denser or deeper ones depending on the neutrino mass, the maximum scale used for the analyses and the details of the nuisance parameters considered. However there is a simple recipe to account for the bulk of the effect as to make it fully negligible, which we illustrate and advocate should be included in analysis of forthcoming large-scale structure surveys.
Structure formation at small cosmological scales provides an important frontier for dark matter (DM) research. Scenarios with small DM particle masses, large momenta or hidden interactions tend to suppress the gravitational clustering at small scales. The details of this suppression depend on the DM particle nature, allowing for a direct link between DM models and astrophysical observations. However, most of the astrophysical constraints obtained so far refer to a very specific shape of the power suppression, corresponding to thermal warm dark matter (WDM), i.e., candidates with a Fermi-Dirac or Bose-Einstein momentum distribution. In this work we introduce a new analytical fitting formula for the power spectrum, which is simple yet flexible enough to reproduce the clustering signal of large classes of non-thermal DM models, which are not at all adequately described by the oversimplified notion of WDM. We show that the formula is able to fully cover the parameter space of sterile neutrinos (whether resonantly produced or from particle decay), mixed cold and warm models, fuzzy dark matter, as well as other models suggested by effective theory of structure formation (ETHOS). Based on this fitting formula, we perform a large suite of N-body simulations and we extract important nonlinear statistics, such as the matter power spectrum and the halo mass function. Finally, we present the first preliminary astrophysical constraints from both the number of Milky Way satellites and the Lyman-{\alpha} forest. This paper is a first step towards a general and comprehensive modeling of small-scale departures from the standard cold DM model.
We measure the Planck cluster mass bias using dynamical mass measurements based on velocity dispersions of a subsample of 17 Planck-detected clusters. The velocity dispersions were calculated using redshifts determined from spectra obtained at Gemini observatory with the GMOS multi-object spectrograph. We correct our estimates for effects due to finite aperture, Eddington bias and correlated scatter between velocity dispersion and the Planck mass proxy. The result for the mass bias parameter, $(1-b)$, depends on the value of the galaxy velocity bias $b_v$ adopted from simulations: $(1-b)=(0.51\pm0.09) b_v^3$. Using a velocity bias of $b_v=1.08$ from Munari et al., we obtain $(1-b)=0.64\pm 0.11$, i.e, an error of 17% on the mass bias measurement with 17 clusters. This mass bias value is consistent with most previous weak lensing determinations. It lies within $1\sigma$ of the value needed to reconcile the Planck cluster counts with the Planck primary CMB constraints. We emphasize that uncertainty in the velocity bias severely hampers precision measurements of the mass bias using velocity dispersions. On the other hand, when we fix the Planck mass bias using the constraints from Penna-Lima et al., based on weak lensing measurements, we obtain a positive velocity bias $b_v \gtrsim 0.9$ at $3\sigma$.
Dark Matter (DM) remains a vital, but elusive, component in our current understanding of the universe. Accordingly, many experimental searches are devoted to uncovering its nature. However, both the existing direct detection methods, and the prominent $\gamma$-ray search with the Fermi Large Area Telescope (Fermi-LAT), are most sensitive to DM particles with masses below 1 TeV, and are significantly less sensitive to the hard spectra produced in annihilation via heavy leptons. The High Energy Stereoscopic System (HESS) has had some success in improving on the Fermi-LAT search for higher mass DM particles, particularly annihilating via heavy lepton states. However, the recent discovery of high J-factor dwarf spheroidal galaxies by the Dark Energy Survey (DES) opens up the possibility of investing more HESS observation time in the search for DM $\gamma$-ray signatures in dwarf galaxies. This work explores the potential of HESS to extend its current limits using these new targets, as well as the future constraints derivable with the up-coming Cherenkov Telescope Array (CTA). These limits are further compared with those we derived at low radio frequencies for the Square Kilometre Array (SKA). Finally, we explore the impact of HESS, CTA, and Fermi-LAT on the phenomenology of the "Madala" boson hypothesized based on anomalies in the data from the Large Hadron Collider (LHC) run 1. The power of these limits from differing frequency bands is suggestive of a highly effective multi-frequency DM hunt strategy making use of both existing and up-coming Southern African telescopes.
The recent Madala hypothesis, a conjecture that seeks to explain anomalies within Large Hadron Collider (LHC) data (particularly in the transverse momentum of the Higgs boson), is interesting for more than just a statistical hint at unknown and unpredicted physics. This is because the model itself contains additional new particles that may serve as Dark Matter (DM) candidates. These particles interact with the Standard Model via a scalar mediator boson $S$. More interesting still, the conjectured mass range for the DM candidate ($65$ - $100$ GeV) lies within the region of models viable to try explain the recent Galactic Centre (GC) gamma-ray excess seen by Fermi Large Area Telescope (Fermi-LAT) and the High Energy Stereoscopic System (HESS). Therefore, assuming $S$ decays promptly, it should be possible to check what constraints are imposed upon the effective DM annihilation cross-section in the Madala scenario by hunting signatures of $S$ decay that follows DM annihilation within dense astrophysical structures. In order to make use of existing data, we use the Reticulum II dwarf galaxy and the galactic centre gamma-ray excess data sets from Fermi-LAT, and compare these to the consequences of various decay paths for $S$ in the aforementioned environments. We find that, based on this existing data, we can limit $\tau$ lepton, quark, direct gamma-ray, and weak boson channels to levels below the canonical relic cross-section. This allows us to set new limits on the branching ratios of $S$ decay, which can rule out a Higgs-like decay branching for $S$, in the case where the Madala DM candidate is assumed to comprise all DM.
The standard cosmographic approach consists in performing a series expansion of a cosmological observable around $z=0$ and then using the data to constrain the cosmographic (or kinematic) parameters at present time. Such a procedure works well if applied to redshift ranges inside the $z$-series convergence radius ($z<1$), but can be problematic if we want to cover redshift intervals that fall outside the $z-$series convergence radius. This problem can be circumvented if we work with the $y-$redshift, $y=z/(1+z)$, or the scale factor, $a=1/(1+z)=1-y$, for example. In this paper, we use the scale factor $a$ as the variable of expansion. We expand the luminosity distance and the Hubble parameter around an arbitrary $\tilde{a}$ and use the Supernovae Ia (SNe Ia) and the Hubble parameter data to estimate $H$, $q$, $j$ and $s$ at $z\ne0$ ($\tilde{a}\neq1$). The results obtained from SNe Ia data are compatible with the $\Lambda$CDM model at $2\sigma$ confidence level. On the other hand, at $2\sigma$ confidence level, the results obtained from $H(z)$ data are incompatible with the $\Lambda$CDM model. These conflicting results may indicate a tension between the current SNe Ia and $H(z)$ data sets.
The previously introduced class of two-parametric phenomenological inflationary models in General Relativity in which the slow-roll assumption is replaced by the more general, constant-roll condition is generalized to the case of $f(R)$ gravity. The simple constant-roll condition is defined in the original, Jordan frame, and exact expressions for the scalaron potential in the Einstein frame, for the function $f(R)$ (in the parametric form) and for inflationary dynamics are obtained. The region of the model parameters permitted by the latest observational constraints on the scalar spectral index and the tensor-to-scalar ratio of primordial metric perturbations generated during inflation is determined.
Gravitational lensing of the CMB is a valuable cosmological signal that correlates to tracers of large-scale structure and acts as a important source of confusion for primordial $B$-mode polarization. State-of-the-art lensing reconstruction analyses use quadratic estimators, which are easily applicable to data. However, these estimators are known to be suboptimal, in particular for polarization, and large improvements are expected to be possible for high signal-to-noise polarization experiments. We develop a method and numerical code, $\rm{LensIt}$, that is able to find efficiently the most probable lensing map, introducing no significant approximations to the lensed CMB likelihood, and applicable to beamed and masked data with inhomogeneous noise. It works by iteratively reconstructing the primordial unlensed CMB using a deflection estimate and its inverse, and removing residual lensing from these maps with quadratic estimator techniques. Roughly linear computational cost is maintained due to fast convergence of iterative searches, combined with the local nature of lensing. The method achieves the maximal improvement in signal to noise expected from analytical considerations on the unmasked parts of the sky. Delensing with this optimal map leads to forecast tensor-to-scalar ratio parameter errors improved by a factor $\simeq 2 $ compared to the quadratic estimator in a CMB stage IV configuration.
We build a minimal extension of General Relativity in which Newton's gravitational coupling, $G$, the speed of light, $c$, and the cosmological constant, $\Lambda$, are spacetime variables. This is done while satisfying the contracted Bianchi identity as well as the local conservation of energy momentum tensor. A dynamical constraint is derived, which shows that variations of $G$ and $c$ are coupled to the local matter-energy physical content, while variation of $\Lambda$ is coupled to the local geometry. This constraint presents a natural cosmological screening mechanism that brings new perspective concerning the current observations of a cosmological constant, $\Lambda_0$ in cosmological observations. We also explore early universe background cosmology and show that the proposal provides alternatives to obtain an accelerated expansion, similar to those coming from Varying Speed of Light theories.
In this paper, we investigate the first and second order cosmological perturbations in the light mass Galileon (LMG) scenario. LMG action includes cubic Galileon term along with the standard kinetic term and a potential which is added phenomenologically to achieve late time acceleration. The scalar field is nonminimally coupled to matter in the Einstein frame. Integral solutions of growing and decaying modes are obtained. The effect of the conformal coupling constant ($\beta$), at the perturbation level, has been studied. In this regard, we have studied linear power spectrum and bispectrum. Though different values of $\beta$ has different effects on power spectrum on reduced bispectrum the effect is not significant. It has been found that the redshift-space distortions (RSD) data can be very useful to constrain $\beta$. In this study we consider potentials which can lead to tracker behavior of the scalar field.
Graviton fluctuations induce strong non-perturbative infrared renormalization effects for the cosmological constant. In flat space the functional renormalization flow drives a positive cosmological constant to zero. We propose a simple computation of the graviton contribution to the flow of the effective potential for scalar fields. Within variable gravity we find that the potential increases asymptotically at most quadratically with the scalar field. With effective Planck mass proportional to the scalar field, the solutions of the derived cosmological equations lead to an asymptotically vanishing cosmological "constant" in the infinite future, providing for dynamical dark energy in the present cosmological epoch. Beyond a solution of the cosmological constant problem, our simplified computation also entails a sizeable positive graviton-induced anomalous dimension for the quartic Higgs coupling in the ultraviolet regime, as required for the successful prediction of the Higgs boson mass within the asymptotic safety scenario for quantum gravity.
We present an unprecedentedly large catalog consisting of 2,354 >~ L^* Lya emitters (LAEs) at z=5.7 and 6.6 on the 13.8 and 21.2 deg^2 sky, respectively, that are identified by the SILVERRUSH program with the first narrowband imaging data of the Hyper Suprime-Cam (HSC) survey. We confirm that the LAE catalog is reliable on the basis of 97 LAEs whose spectroscopic redshifts are already determined by this program and the previous studies. This catalogue is also available on-line. Based on this catalogue, we derive the rest-frame Lya equivalent-width distributions of LAEs at z=5.7 and 6.6 that are reasonably explained by the exponential profiles with the scale lengths of 72+/-19 and 119+/-4 A, respectively, showing the increase trend towards high-z. We find that ~700 LAEs with a large equivalent width (LEW) of >~ 240 A are candidates of young-metal poor galaxies and AGNs. We also find that the fraction of LEW LAEs to all ones is moderately large, ~30%. Our LAE catalog includes 11 Lya blobs (LABs) that are LAEs with spatially extended Lya emission whose profile is clearly distinguished from those of stellar objects at the >~ 3sigma level. The number density of the LABs at z=6-7 is ~10^{-7}-10^{-6} Mpc-3, being ~10-100 times lower than those claimed for LABs at z~2-3, suggestive of disappearing LABs at z>~6, albeit with the different selection methods and criteria for the low and high-z LABs.
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We introduce a new Bayesian HI spectral line fitting technique capable of obtaining spectroscopic redshifts for millions of galaxies in radio surveys with the Square Kilometere Array (SKA). This technique is especially well-suited to the low signal-to-noise regime that the redshifted 21-cm HI emission line is expected to be observed in, especially with SKA Phase 1, allowing for robust source detection. After selecting a set of continuum objects relevant to large, cosmological-scale surveys with the first phase of the SKA dish array (SKA1-MID), we simulate data corresponding to their HI line emission as observed by the same telescope. We then use the MultiNest nested sampling code to find the best-fitting parametrised line profile, providing us with a full joint posterior probability distribution for the galaxy properties, including redshift. This provides high quality redshifts, with redshift errors $\Delta z / z <10^{-5}$, from radio data alone for some 1.8 million galaxies in a representative 5000 square degree survey with the SKA1-MID instrument with up-to-date sensitivity profiles. Interestingly, we find that the SNR definition commonly used in forecast papers does not correlate well with the actual detectability of an HI line using our method. We further detail how our method could be improved with per-object priors and how it may be also used to give robust constraints on other observables such as the HI mass function. We also make our line fitting code publicly available for application to other data sets.
The answer is Yes! We indeed find that interacting dark energy can alleviate the current tension on the value of the Hubble constant $H_0$ between the Cosmic Microwave Background anisotropies constraints obtained from the Planck satellite and the recent direct measurements reported by Riess et al. 2016. The combination of these two datasets points towards an evidence for a non-zero dark matter-dark energy coupling $\xi$ at more than two standard deviations, with $\xi=-0.26_{-0.12}^{+0.16}$ at $95\%$ CL. However the $H_0$ tension is better solved when the equation of state of the interacting dark energy component is allowed to freely vary, with a phantom-like equation of state $w=-1.184\pm0.064$ (at $68 \%$ CL), ruling out the pure cosmological constant case, $w=-1$, again at more than two standard deviations. When Planck data are combined with external datasets, as BAO, JLA Supernovae Ia luminosity distances, cosmic shear or lensing data, we find good consistency with the cosmological constant scenario and no compelling evidence for a dark matter-dark energy coupling.
The distribution of diffuse gas in the intergalactic medium (IGM) imprints a series of hydrogen absorption lines on the spectra of distant background quasars known as the Lyman-$\alpha$ forest. Cosmological hydrodynamical simulations predict that IGM density fluctuations are suppressed below a characteristic scale where thermal pressure balances gravity. We measured this pressure-smoothing scale by quantifying absorption correlations in a sample of close quasar pairs. We compared our measurements to hydrodynamical simulations, where pressure smoothing is determined by the integrated thermal history of the IGM. Our findings are consistent with standard models for photoionization heating by the ultraviolet radiation backgrounds that reionized the universe.
The early reionization (ERE) is supposed to be a physical process which happens after recombination, but before the instantaneous reionization caused by the first generation of stars. We investigate the effect of the ERE on the temperature and polarization power spectra of cosmic microwave background (CMB), and adopt principal components analysis (PCA) to model-independently reconstruct the ionization history during the ERE. In addition, we also discuss how the ERE affects the cosmological parameter estimates, and find that the ERE does not impose any significant influences on the tensor-to-scalar ratio $r$ and the neutrino mass at the sensitivities of current experiments. The better CMB polarization data can be used to give a tighter constraint on the ERE and might be important for more precisely constraining cosmological parameters in the future.
A superbubble which advances in a symmetric Navarro--Frenk--White density profile or in an auto-gravitating density profile generates a thick shell with a radius that can reach 10 kpc. The application of the symmetric and asymmetric image theory to this thick 3D shell produces a ring in the 2D map of intensity and a characteristic `U' shape in the case of 1D cut of the intensity. A comparison of such a ring originating from a superbubble is made with the Einstein's ring. A Taylor approximation of order 10 for the angular diameter distance is derived in order to deal with high values of the redshift.
By using the relations between the slow-roll parameters and the power spectrum for the single field slow-roll inflation, we derive the scalar spectral tilt $n_s$ and the tensor to scalar ratio $r$ for the constant slow-roll inflation and obtain the constraint on the slow-roll parameter $\eta$ from the Planck 2015 results. The inflationary potential for the constant slow-roll inflation is then reconstructed in the framework of both general relativity and scalar-tensor theory of gravity, and compared with the recently reconstructed E model potential. In the strong coupling limit, we show that the $\eta$ attractor is reached.
Characterizing the diffuse Galactic synchrotron emission at arcminute angular
scales is needed to reliably remove foregrounds in cosmological 21-cm
measurements. The study of this emission is also interesting in its own right.
Here, we quantify the fluctuations of the diffuse Galactic synchrotron emission
using visibility data for two of the fields observed by the TIFR GMRT Sky
Survey (TGSS). We have used the 2D Tapered Gridded Estimator (TGE) to estimate
the angular power spectrum $(C_{\ell})$ from the visibilities. We find that the
sky signal, after subtracting the point sources, is likely dominated by the
diffuse Galactic synchrotron radiation across the angular multipole range $240
\le \ell \lesssim 500$.
We present a power law fit,
$C_{\ell}=A\times\big(\frac{1000}{l}\big)^{\beta}$, to the measured $C_{\ell}$
over this $\ell$ range. We find that $(A,\beta)$ have values $(356\pm109~{\rm
mK^2},2.8\pm0.3)$ and $(54\pm26~{\rm mK^2},2.2\pm0.4)$ in the two fields. For
the second field, however, there is indication of a significant residual point
source contribution, and for this field we interpret the measured $C_{\ell}$ as
an upper limit for the diffuse Galactic synchrotron emission. While in both
fields the slopes are consistent with earlier measurements, the second field
appears to have an amplitude which is considerably smaller compared to similar
measurements in other parts of the sky.
We perform a dynamical system analysis of a cosmological model with linear dependence between the vacuum density and the Hubble parameter, with constant-rate creation of dark matter. We show that the de Sitter spacetime is an asymptotically stable critical point, future limit of any expanding solution. Our analysis also shows that the Minkowski spacetime is an unstable critical point, which inevitably collapses to a singularity. In this way, such a prescription for the vacuum decay not only predicts the correct future de Sitter limit, but also forbids the existence of a stable Minkowski universe.
We quantify the gas-phase abundance of deuterium in cosmological zoom-in simulations from the Feedback In Realistic Environments project. The cosmic deuterium fraction decreases with time, because mass lost from stars is deuterium-free. At low metallicity, our simulations confirm that the deuterium abundance is very close to the primordial value. The deuterium abundance decreases towards higher metallicity, with very small scatter between the deuterium and oxygen abundance. We compare our simulations to existing high-redshift observations in order to determine a primordial deuterium fraction of (2.549 +/- 0.033) x 10^-5 and stress that future observations at higher metallicity can also be used to constrain this value. At fixed metallicity, the deuterium fraction decreases slightly with decreasing redshift, due to the increased importance of mass loss from intermediate-mass stars. We find that the evolution of the average deuterium fraction in a galaxy correlates with its star formation history. Our simulations are consistent with observations of the Milky Way's interstellar medium: the deuterium fraction at the solar circle is 83-92% of the primordial deuterium fraction. We use our simulations to make predictions for future observations. In particular, the deuterium abundance is lower at smaller galactocentric radii and in higher mass galaxies, showing that stellar mass loss is more important for fuelling star formation in these regimes (and can even dominate). Gas accreting onto galaxies has a deuterium fraction above that of the galaxies' interstellar medium, but below the primordial fraction, because it is a mix of gas accreting from the intergalactic medium and gas previously ejected or stripped from galaxies.
We propose a new thermal freeze-out mechanism for ultra-heavy dark matter. Dark matter coannihilates with a lighter unstable species, leading to an annihilation rate that is exponentially enhanced relative to standard WIMPs. This scenario destabilizes any potential dark matter candidate. In order to remain consistent with astrophysical observations, our proposal necessitates very long-lived states, motivating striking phenomenology associated with the late decays of ultra-heavy dark matter, potentially as massive as the scale of grand unified theories, $M_\text{GUT} \sim 10^{16}$ GeV.
We present $Suzaku$ off-center observations of two poor galaxy groups, NGC 3402 and NGC 5129, with temperatures below 1 keV. Through spectral decomposition, we measure their surface brightnesses and temperatures out to 330 and 680 times the critical density of the universe for NGC 3402 and NGC 5129, respectively. These quantities are consistent with extrapolations from existing inner measurements of the two groups. With the refined X-ray luminosities, both groups prefer $L_X-T$ relations without a break in the group regime. Furthermore, we measure the electron number densities and hydrostatic masses at these radii. We find that the electron number density profiles require three $\beta$ model components, with nearly flat slopes in the 3$^{rd}$ $\beta$ component for both groups. However, we find the effective slope in the outskirts to be $\beta_{out}$ = 0.59 and 0.49 for NGC 3402 and NGC 5129, respectively. Adding the gas mass measured from the X-ray data and stellar mass from group galaxy members, we measure baryon fractions of $f_b$ = 0.113 $\pm$ 0.013 and 0.091 $\pm$ 0.006 for NGC 3402 and NGC 5129, respectively. Combining other poor groups with well measured X-ray emission to the outskirts, we find an average baryon fraction of $f_{b,ave}$ = 0.100 $\pm$ 0.004 for X-ray bright groups with temperatures between 0.8$-$1.3 keV, extending existing constraints to lower mass systems.
In the context of f(R)=R + alpha R^2 gravity, we study the existence of neutron and quark stars with no intermediate approximations in the generalised system of Tolman-Oppenheimer-Volkov equations. Analysis shows that for positive alpha's the scalar curvature does not drop to zero at the star surface (as in General Relativity) but exponentially decreases with distance. Also the stellar mass bounded by star surface decreases when the value alpha increases. Nonetheless distant observers would observe a gravitational mass due to appearance of a so-called gravitational sphere around the star. The non-zero curvature contribution to the gravitational mass eventually is shown to compensate the stellar mass decrease for growing alpha's. We perform our analysis for several equations of state including purely hadronic configurations as well as hyperons and quark stars. In all cases, we assess that the relation between the parameter $\alpha$ and the gravitational mass weakly depend upon the chosen equation of state. Another interesting feature is the increase of the star radius in comparison to General Relativity for stars with masses close to maximal, whereas for intermediate masses around 1.4-1.6 solar masses, the radius of star depends upon alpha very weakly. Also the decrease in the mass bounded by star surface may cause the surface redshift to decrease in R^2-gravity when compared to Einsteinian predictions. This effect is shown to hardly depend upon the observed gravitational mass. Finally, for negative values of alpha our analysis shows that outside the star the scalar curvature has damped oscillations but the contribution of the gravitational sphere into the gravitational mass increases indefinitely with radial distance putting into question the very existence of such relativistic stars.
We study the likelihood which relative minima of random polynomial potentials support the slow-roll conditions for inflation. Consistent with renormalizability and boundedness, the coefficients that appear in the potential are chosen to be order one with respect to the energy scale at which inflation transpires. Investigation of the single field case illustrates a window in which the potentials satisfy the slow-roll conditions. When there are two scalar fields, we find that the probability depends on the choice of distribution for the coefficients. A uniform distribution yields a $0.05\%$ probability of finding a suitable minimum in the random potential whereas a maximum entropy distribution yields a $0.1\%$ probability.
We examine the clustering of quasars over a wide luminosity range, by utilizing 901 quasars at $\overline{z}_{\rm phot}\sim3.8$ with $-24.73<M_{\rm 1450}<-22.23$ photometrically selected from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) S16A Wide2 date release and 342 more luminous quasars at $3.4<z_{\rm spec}<4.6$ having $-28.0<M_{\rm 1450}<-23.95$ from the Sloan Digital Sky Survey (SDSS) that fall in the HSC survey fields. We measure the bias factors of two quasar samples by evaluating the cross-correlation functions (CCFs) between the quasar samples and 25790 bright $z\sim4$ Lyman Break Galaxies (LBGs) in $M_{\rm 1450}<-21.25$ photometrically selected from the HSC dataset. Over an angular scale of \timeform{10.0"} to \timeform{1000.0"}, the bias factors are $5.93^{+1.34}_{-1.43}$ and $2.73^{+2.44}_{-2.55}$ for the low and high luminosity quasars, respectively, indicating no luminosity dependence of quasar clustering at $z\sim4$. It is noted that the bias factor of the luminous quasars estimated by the CCF is smaller than that estimated by the auto-correlation function (ACF) over a similar redshift range, especially on scales below \timeform{40.0"}. Moreover, the bias factor of the less-luminous quasars implies the minimal mass of their host dark matter halos (DMHs) is $0.3$-$2\times10^{12}h^{-1}M_{\odot}$, corresponding to a quasar duty cycle of $0.001$-$0.06$.
Relying on multifractal behavior of pulsar timing residuals ({\it PTR}s), we examine the capability of Multifractal Detrended Fluctuation Analysis (MF-DFA) and Multifractal Detrending Moving Average Analysis (MF-DMA) modified by Singular Value Decomposition (SVD) and Adaptive Detrending (AD), to detect footprint of gravitational waves (GWs) superimposed on {\it PTR}s. Mentioned methods enable us to clarify the type of GWs which is related to the value of Hurst exponent. We introduce three strategies based on generalized Hurst exponent and width of singularity spectrum, to determine the dimensionless amplitude of GWs. For a stochastic gravitational wave background with characteristic strain spectrum as $\mathcal{H}_c(f)\sim \mathcal{A}f^{\zeta}$, the dimensionless amplitude greater than $\mathcal{A}\gtrsim 10^{-17}$ can be recognized irrespective to value of $\zeta$. We also utilize MF-DFA and MF-DMA to explore 20 millisecond pulsars observed by Parkes Pulsar Timing Array (PPTA). Our analysis demonstrates that there exists a cross-over in fluctuation function versus time scale for observed timing residuals representing a universal property and equates to $s_{\times}\sim60$ days. To asses multifractal nature of observed timing residuals, we apply AD and SVD algorithms on time series as pre-processes to remove superimposed trends as much as possible. The scaling exponents determined by MF-DFA and MF-DMA confirm that, all data are classified in non-stationary class elucidating second universality feature. The value of corresponding Hurst exponent is in interval $H \in [0.35,0.85]$. The $q$-dependency of generalized Hurst exponent demonstrates observed {\it PTR}s have multifractal behavior and the source of this multifractality is mainly devoted to correlation of data which is another universality of observed data sets.
We present a unified description of the dark matter and the dark energy sectors, in the framework of shift-symmetric generalized Galileon theories. Considering a particular combination of terms in the Horndesdi Lagrangian in which we have not introduced a cosmological constant or a matter sector, we obtain an effective unified cosmic fluid whose equation of state $w_U$ is zero during the whole matter era, namely from redshifts $z\sim3000$ up to $z\sim2-3$. Then at smaller redshifts it starts decreasing, passing the bound $w_U=-1/3$, which marks the onset of acceleration, at around $z\sim0.5$. At present times it acquires the value $w_U=-0.7$. Finally, it tends toward a de-Sitter phase in the far future. This behaviour is in excellent agreement with observations. Additionally, confrontation with Supernovae type Ia data leads to a very efficient fit. Examining the model at the perturbative level, we show that it is free from pathologies such as ghosts and Laplacian instabilities at all times.
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