Abstract: We develop a statistical estimator to infer the redshift probability distribution of a photometric sample of galaxies from its angular cross-correlation in redshift bins with an overlapping spectroscopic sample. This estimator is a minimum-variance weighted quadratic function of the data: a quadratic estimator. This extends and modifies the methodology presented by McQuinn & White. The derived source redshift distribution is degenerate with the source galaxy bias, which must be constrained via additional assumptions. We apply this estimator to constrain source galaxy redshift distributions in theKilo-Degree imaging survey through crosscorrelation with the spectroscopic 2-degree Field Lensing Survey, presenting results first as a binned step-wise distribution in the range z < 0.8, and then building a continuous distribution using a Gaussian process model. We demonstrate the robustness of our methodology using mock catalogues constructed from N-body simulations, and comparisons with other techniques for inferring the redshift distribution.

Abstract: The construction of the cosmic distance-duality relation (CDDR) has been widely studied However, its consistency with various new observables remains a topic of interest We present a new way to constrain the CDDR $\eta(z)$ using different dynamic and geometric properties of strong gravitational lenses (SGL) along with SNe Ia observations We use a sample of $102$ SGL with the measurement of corresponding velocity dispersion $\sigma_0$ and Einstein radius $\theta_E$ In addition, we also use a dataset of $12$ two image lensing systems containing the measure of time delay $\Delta t$ between source images Jointly these two datasets give us the angular diameter distance $D_{A_{ol}}$ of the lens Further, for luminosity distance, we use the $740$ observations from JLA compilation of SNe Ia To study the combined behavior of these datasets we use a model independent method, Gaussian Process (GP) We also check the efficiency of GP by applying it on simulated datasets, which are generated in a phenomenological way by using realistic cosmological error bars Finally, we conclude that the combined bounds from the SGL and SNe Ia observation do not favor any deviation of CDDR and are in concordance with the standard value ($\eta=1$) within $2\sigma$ confidence region, which further strengthens the theoretical acceptance of CDDR

Abstract: In this paper, we perform a cosmological model-independent test of the cosmic distance-duality relation (CDDR) in terms of the ratio of angular diameter distance (ADD) $D=D_{\rm A}^{\rm sl}/D_{\rm A}^{\,\rm s}$ from strong gravitational lensing (SGL) and the ratio of luminosity distance (LD) $D^\ast=D_{\rm L}^{\,\rm l}/D_{\rm L}^{\,\rm s}$ obtained from the joint of type Ia supernovae (SNIa) Union2.1 compilation and the latest Gamma-Ray Bursts (GRBs) data, where the superscripts s and l correspond to the redshifts $z_{\,\rm s}$ and $z_{\,\rm l}$ at the source and lens from SGL samples. The purpose of combining GRB data with SNIa compilation is to test CDDR in a wider redshift range. The LD associated with the redshits of the observed ADD, is obtained through two cosmological model-independent methods, namely, method A: binning the SNIa+GRBs data, and method B: reconstructing the function of DL by combining the Crossing Statistic with the smoothing method. We find that CDDR is compatible with the observations at $1\sigma$ confidence level for the power law model which is assumed to describe the mass distribution of lensing systems with method B in a wider redshift range.

Abstract: Recent results have shown that a field non-minimally coupled to the electromagnetic Lagrangian can induce a violation of the Einstein equivalence principle. { This kind of coupling is present in a very wide class of gravitation theories.} In a cosmological context, this would break the validity of the cosmic distance duality relation as well as cause a time variation of the fine structure constant. Here, we improve constraints on this scenario by using four different observables: the luminosity distance of type Ia supernovae, the angular diameter distance of galaxy clusters, the gas mass fraction of galaxy clusters and the temperature of the cosmic microwave background at different redshifts. We consider four standard parametrizations adopted in the literature and show that, due to a high complementarity of the data, the errors are shrunk between 20\% and 40\% depending on the parametrization. We also show that our constraints are weakly affected by the geometry considered to describe the galaxy clusters. In short, no violation of the Einstein equivalence principle is detected up to redshifts $\sim$ 3.

Abstract: To understand the expansion dynamics of the universe from galaxy cluster scales, using the angular diameter distance (ADD) data from two different galaxy cluster surveys, we constrain four cosmological models to explore the underlying value of $H_0$ and employ the model-independent Gaussian Processes to investigate the evolution of the equation of state of dark energy. The ADD data in the X-ray bands consists of two samples covering the redshift ranges [0.023, 0.784] and [0.14, 0.89], respectively. We find that: (i) For these two samples, the obtained values of $H_0$ are more consistent with the recent local observation by Riess et al. than the global measurement by the Plank Collaboration, and the $\Lambda$CDM model is still preferred utilizing the information criterions; (ii) For the first sample, there is no evidence of dynamical dark energy (DDE) at the $2\sigma$ confidence level (CL); (iii) For the second one, the reconstructed equation of state of dark energy exhibits a phantom-crossing behavior in the relatively low redshift range over the $2\sigma$ CL, which gives a hint that the late-time universe may be actually dominated by the DDE from galaxy cluster scales; (iv) By adding a combination of Type Ia Supernovae, cosmic chronometers and Planck-2015 shift parameter and HII galaxy measurements into both ADD samples, the DDE exists evidently over the $2\sigma$ CL.

Abstract: The cosmological constant problem has become one of the most important ones in modern cosmology. In this paper, we try to construct a model that can avoid the cosmological constant problem and have the potential to explain the apparent late-time accelerating expansion of the universe in both luminosity distance and angular diameter distance measurement channels. In our model, the core is to modify the relation between cosmological redshift and scale factor for photons. We point out three ways to test our hypothesis: the supernova time dilation; the gravitational waves and its electromagnetic counterparts emitted by the binary neutron star systems; and the Sandage–Loeb effect. All of this method is feasible now or in the near future.

Abstract: The Baryon Acoustic Oscillations (BAO) imprinted a characteristic correlation length in the large-scale structure of the universe that can be used as a standard ruler for mapping out the cosmic expansion history. Here, we discuss the application of the angular two-point correlation function, \(w(\theta )\), to a sample of luminous red galaxies of the Sloan Digital Sky Survey (SDSS) and derive two new measurements of the BAO angular scale at \(z = 0.235\) and \(z = 0.365\). Since noise and systematics may hinder the identification of the BAO signature in the \(w - \theta \) plane, we also introduce a potential new method to localize the acoustic bump in a model-independent way. We use these new measurements along with previous data to constrain cosmological parameters of dark energy models and to derive a new estimate of the acoustic scale \(r_s\).

Abstract: One of the fundamental results used in observational cosmology is the distance duality relation (DDR), which relates the luminosity distance, ${\mathrm{D}}_{\mathrm{L}}$, with angular diameter distance, ${\mathrm{D}}_{\mathrm{A}}$, at a given redshift $z$. We employ the observed limits of this relation to constrain the coupling of axionlike particles (ALPs) with photons. With our detailed $3D$ ALP-photon mixing simulation in standard $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ universe and latest DDR limits observed in Holanda and Barros [Phys. Rev. D 94, 023524 (2016)]. we limit the coupling constant ${g}_{\ensuremath{\phi}}\ensuremath{\le}6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}(\frac{nG}{⟨B{⟩}_{\mathrm{Mpc}}})$ for ALPs of mass $\ensuremath{\le}{10}^{\ensuremath{-}15}\text{ }\text{ }\mathrm{eV}$. The DDR observations can provide very stringent constraint on ALPs mixing in the future. Also any deviation in DDR can be conventionally explained as photons decaying to axions or vice-versa.

Abstract: In this paper, we perform a cosmological model-independent test of the cosmic distance–duality relation (CDDR) in terms of the ratio of angular diameter distance (ADD) D = DAsl/D As from strong gravitational lensing (SGL) and the ratio of luminosity distance (LD) D∗ = D Ll/D Ls obtained from the joint of type Ia supernovae (SNIa) Union2.1 compilation and the latest Gamma-Ray Bursts (GRBs) data, where the superscripts s and l correspond to the redshifts zs and zl at the source and lens from SGL samples. The purpose of combining GRB data with SNIa compilation is to test CDDR in a wider redshift range. The LD associated with the redshifts of the observed ADD is obtained through two cosmological model-independent methods, namely, method A: binning the SNIa+GRBs data, and method B: reconstructing the function of DL by combining the Crossing Statistic with the smoothing method. We find that CDDR is compatible with the observations at 1σ confidence level for the power law model which is assumed to describe the mass distribution of lensing systems with method B in a wider redshift range.

Abstract: Light propagation in two Swiss-cheese models based on anisotropic Szekeres structures is studied and compared with light propagation in Swiss-cheese models based on the Szekeres models' underlying Lemaitre-Tolman-Bondi models. The study shows that the anisotropy of the Szekeres models has only a small effect on quantities such as redshift-distance relations, projected shear and expansion rate along individual light rays. The average angular diameter distance to the last scattering surface is computed for each model. Contrary to earlier studies, the results obtained here are (mostly) in agreement with perturbative results. In particular, a small negative shift, $\ensuremath{\delta}{D}_{A}\ensuremath{\mathrel{:=}}\frac{{D}_{A}\ensuremath{-}{D}_{A,bg}}{{D}_{A,bg}}$, in the angular diameter distance is obtained upon line-of-sight averaging in three of the four models. The results are, however, not statistically significant. In the fourth model, there is a small positive shift which has an especially small statistical significance. The line-of-sight averaged inverse magnification at $z=1100$ is consistent with 1 to a high level of confidence for all models, indicating that the area of the surface corresponding to $z=1100$ is close to that of the background.

Abstract: Recent results have shown that a field non-minimally coupled to the electromagnetic Lagrangian can induce a violation of the Einstein equivalence principle. { This kind of coupling is present in a very wide class of gravitation theories.} In a cosmological context, this would break the validity of the cosmic distance duality relation as well as cause a time variation of the fine structure constant. Here, we improve constraints on this scenario by using four different observables: the luminosity distance of type Ia supernovae, the angular diameter distance of galaxy clusters, the gas mass fraction of galaxy clusters and the temperature of the cosmic microwave background at different redshifts. We consider four standard parametrizations adopted in the literature and show that, due to a high complementarity of the data, the errors are shrunk between 20\% and 40\% depending on the parametrization. We also show that our constraints are weakly affected by the geometry considered to describe the galaxy clusters. In short, no violation of the Einstein equivalence principle is detected up to redshifts $\sim$ 3.

Abstract: We investigate a new method to recover (if any) a possible varying speed of light (VSL) signal from cosmological data. It comes as an upgrade of [1,2], where it was argued that such signal could be detected at a single redshift location only. Here, we show how it is possible to extract information on a VSL signal on an extended redshift range. We use mock cosmological data from future galaxy surveys (BOSS, DESI, \emph{WFirst-2.4} and SKA): the sound horizon at decoupling imprinted in the clustering of galaxies (BAO) as an angular diameter distance, and the expansion rate derived from those galaxies recognized as cosmic chronometers. We find that, given the forecast sensitivities of such surveys, a $\sim1\%$ VSL signal can be detected at $3\sigma$ confidence level in the redshift interval $z \in [0.,1.55]$. Smaller signals $(\sim0.1\%)$ will be hardly detected (even if some lower possibility for a $1\sigma$ detection is still possible). Finally, we discuss the degeneration between a VSL signal and a non-null spatial curvature; we show that, given present bounds on curvature, any signal, if detected, can be attributed to a VSL signal with a very high confidence. On the other hand, our method turns out to be useful even in the classical scenario of a constant speed of light: in this case, the signal we reconstruct can be totally ascribed to spatial curvature and, thus, we might have a method to detect a $0.01$-order curvature in the same redhift range with a very high confidence.

Abstract: Context. Ultra-compact structure in radio sources (especially in quasars that can be observed up to very high redshifts), with milliarcsecond angular sizes measured by very-long-baseline interferometry (VLBI), is becoming an important astrophysical tool for probing both cosmology and the physical properties of AGN. Aims. We present a newly compiled data set of 120 milliarcsec. compact radio sources representing intermediate-luminosity quasars covering the redshift range 0.46 For a cosmological ruler with intrinsic length l m , the angular size–redshift relation can be written as θ (z) = l m /D A (z , where θ (z ) is the angular size at redshift z , and D A (z ) is the corresponding angular diameter distance. We use a compilation of angular size and redshift data for ultra-compact radio sources from a well-known VLBI survey, and implement a new cosmology-independent technique to calibrate the linear size of this standard ruler, which is also used to test different cosmological models with and without the flat universe assumption. Results. We determine the linear size of this standard ruler as l m = 11.03 ± 0.25 pc, which is the typical radius at which AGN jets become opaque at the observed frequency ν ~ 2 GHz. Our measurement of this linear size is also consistent with the previous and recent radio observations at other different frequencies. In the framework of flat ΛCDM model, we find a high value of the matter density parameter, Ωm = 0.322+0.244 -0.141 , and a low value of the Hubble constant, H 0 = 67.6+7.8 -7.4 km s-1 Mpc-1 , which is in excellent agreement with the cosmic microwave background (CMB) anisotropy measurements by Planck . We obtain Ωm = 0.309+0.215 -0.151 , w = -0.970+0.500 -1.730 at 68.3% CL for the constant w of a dynamical dark-energy model, which demonstrates no significant deviation from the concordance ΛCDM model. Consistent fitting results are also obtained for other cosmological models explaining the cosmic acceleration, like Ricci dark energy (RDE) or the Dvali-Gabadadze-Porrati (DGP) brane-world scenario. While no significant change in w with redshift is detected, there is still considerable room for evolution in w and the transition redshift at which w departing from −1 is located at z ~ 2.0. Our results demonstrate that the method extensively investigated in our work on observational radio quasar data can be used to effectively derive cosmological information. Finally, we find the combination of high-redshift quasars and low-redshift clusters may provide an important source of angular diameter distances, considering the redshift coverage of these two astrophysical probes.

Abstract: We extend a new method to measure possible variation of the speed of light by using Baryon Acoustic Oscillations and the Hubble function onto an inhomogeneous pressure model of the universe. The method relies on the fact that there is a simple relation between the angular diameter distance (DA) maximum and the Hubble function (H) evaluated at the same maximum-condition redshift, which includes the speed of light c. One limit of such a method was the assumption of the vanishing of spatial curvature (though, as it has been shown, a non-zero curvature has negligible effect). In this paper, apart from taking into account an inhomogeneity, we consider non-zero spatial curvature and calculate an exact relation between DA and H. Our main result is the evaluation if current or future missions such as Square Kilometer Array (SKA) can be sensitive enough to detect any spatial variation of c which can in principle be related to the recently observed spatial variation of the fine structure constant (an effect known as α-dipole).