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General relativity reproduces main current cosmological observations, assuming the validity of the cosmic distance duality relation (CDDR) at all scales and epochs. However, CDDR is poorly tested in the redshift interval between the farthest observed Type Ia supernovae and that of the cosmic microwave background. We present a new idea of testing the validity of CDDR, through the multiple measurements of high-redshift quasars. Luminosity distances are derived from the relation between the UV and X-ray luminosities of quasars, while angular diameter distances are obtained from the compact structure in radio quasars. This will create a valuable opportunity where two different cosmological distances from the same kind of objects at high redshifts are compared. Our constraints are more stringent than other currently available results based on different observational data and show no evidence for the deviation from CDDR at z ∼ 3. Such an accurate model-independent test of fundamental cosmological principles can become a milestone in precision cosmology. [ABSTRACT FROM AUTHOR]

Astrophysical observations provide a unique opportunity to test possible signatures of Lorentz invariance violation (LIV), due to the high energies and long distances involved. In quantum theory of gravity, one may expect the modification of the dispersion relation between energy and momentum for photons, which can be probed with the time lag (the arrival time delay between light curves in different energy bands) of gamma-ray bursts (GRBs). In this paper, by using the detailed time delay measurements of GRB 160625B at different energy bands, as well as 23 time delay GRBs covering the redshift range of z = 0.168–2.5 (which were measured at different energy channels from the light curves), we propose an improved model-independent method (based on the newly compiled sample of H(z) measurements) to probe the energy-dependent velocity due to the modified dispersion relation for photons. In the framework of a more complex and reasonable theoretical expression to describe the time delays, our results imply that the intrinsic time lags can be better described with more GRB time delay data. More importantly, through direct fitting of the time delay measurements of a sample of GRBs, our limit on the LIV energy scale is comparable to that with unknown constant for the intrinsic time lag, much lower than the Planck energy scale in both linear LIV and quadratic LIV cases. [ABSTRACT FROM AUTHOR]

Cosmological applications of H ii galaxies and giant extragalactic H ii regions (GEHRs) to construct the Hubble diagram at high redshifts require knowledge of the “L–σ” relation of the standard candles used. In this paper, we study the properties of a large sample of 156 sources (25 high-z H ii galaxies, 107 local H ii galaxies, and 24 GEHRs) compiled by Terlevich et al. Using the cosmological distances reconstructed through two new cosmology-independent methods, we investigate the correlation between the Hβ emission-line luminosity L and the ionized gas velocity dispersion σ. The method is based on non-parametric reconstruction using the measurements of Hubble parameters from cosmic clocks, as well as the simulated data of gravitational waves from the third-generation gravitational wave detector (the Einstein Telescope, ET), which can be considered as standard sirens. Assuming the relation between emission-line luminosity and ionized gas velocity dispersion, , we find that the full sample provides a tight constraint on the correlation parameters. However, similar analysis done on three different subsamples seems to support the scheme of treating H ii galaxies and GEHRs with distinct strategies. Using the corrected “L–σ” relation for the H ii observational sample beyond the current reach of Type Ia supernovae, we obtain values of the matter density parameter, Ωm = 0.314 ± 0.054 (calibrated with standard clocks) and Ωm = 0.311 ± 0.049 (calibrated with standard sirens), in the spatially flat ΛCDM cosmology. [ABSTRACT FROM AUTHOR]

In this paper, we present a scheme to investigate the opacity of the universe in a cosmological-model-independent way, with the combination of current and future measurements of an SN Ia sample and galactic-scale strong gravitational lensing systems with SNe Ia acting as background sources. The observational data include the current newly compiled SNe Ia data (Pantheon sample) and a simulated sample of SNe Ia observed by the forthcoming Large Synoptic Survey Telescope (LSST), which are taken for luminosity distances (DL) possibly affected by the cosmic opacity, as well as strongly lensed SNe Ia observed by the LSST, which are responsible for providing the observed time-delay distance unaffected by the cosmic opacity. Focusing on only one specific type of standard cosmological probe, this provides an original method to measure cosmic opacity at high precision. Working on the simulated sample of strongly lensed SNe Ia observed by the LSST in the 10 yr z-band search, our results show that, with the combination of the current newly compiled SNe Ia data (Pantheon sample), there is no significant deviation from the transparency of the universe at the current observational data level. Moreover, strongly lensed SNe Ia in a 10 yr LSST z-band search would produce more robust constraints on the validity of cosmic transparency, with a larger sample of unlensed SNe Ia detected in the future LSST survey. We have also discussed the ways in which our methodology could be improved, with the combination of current and future available data in the gravitational wave and electromagnetic domain. [ABSTRACT FROM AUTHOR]

Strong gravitational lensing systems (SGL) encode cosmology information in source/lens distance ratios as , which can be used to precisely constrain cosmological parameters. In this paper, based on future measurements of 390 strong-lensing systems from the forthcoming Large Synoptic Survey Telescope (LSST) survey, we have successfully reconstructed the distance ratio (with the source redshift zs ∼ 4.0) directly from the data without assuming any parametric form. A recently developed method based on a model-independent reconstruction approach, Gaussian Processes, is used in our study of these strong-lensing systems. Our results show that independent measurement of the matter density parameter (Ωm) can be expected from such strong-lensing statistics. More specifically, one can expect Ωm to be estimated at the precision of ΔΩm ∼ 0.015 in the concordance ΛCDM model, which provides comparable constraints on Ωm with Planck 2015 results. In the framework of modified gravity theory (Dvali–Gabadadze–Porrati), 390 detectable galactic lenses from the future LSST survey can lead to stringent fits of ΔΩm ∼ 0.030. Finally, we have discussed three possible sources of systematic errors (sample incompleteness, the determination of length of lens redshift bin, and the choice of lens redshift shells), and quantified their effects on the final cosmological constraints. Our results strongly indicate that future strong-lensing surveys, with the accumulation of a larger and more accurate sample of detectable galactic lenses, will considerably benefit from the methodology described in this analysis. [ABSTRACT FROM AUTHOR]

Probing the speed of light is an important test of general relativity, but the measurements of c using objects in the distant universe have been almost completely unexplored. In this paper, we propose an idea to use the multiple measurements of galactic-scale strong gravitational lensing systems with Type Ia supernovae acting as background sources to estimate the speed of light. This provides an original method to measure the speed of light using objects located at different redshifts that emitted their light in a distant past. Moreover, we predict that strongly lensed Type Ia supernovae observed by the Large Synoptic Survey Telescope (LSST) would produce robust constraints on Δc/c at the level of 10−3. We also discuss whether future surveys such as LSST may succeed in detecting any hypothetical variation of c predicted by theories in which fundamental constants have a dynamical nature. [ABSTRACT FROM AUTHOR]

In this paper, by analyzing the dynamics of inhomogeneous quintessence dark energy, we find that the gradient energy of dark energy will oscillate and gradually vanish, which indicates the gradient energy of the scalar field present in the early universe does not affect the current dynamics of the universe. Moreover, with the decaying of gradient energy, there exists a possible mutual transformation between kinetic energy and gradient energy. In the framework of interacting dark energy models, we argue that inhomogeneous dark energy may have a significant effect on the evolution of the cosmic background, the investigation of which still requires fully relativistic N-body numerical simulations in the future. [ABSTRACT FROM AUTHOR]

Based on a mass-selected sample of galaxy-scale strong gravitational lenses from the SLACS, BELLS, LSD, and SL2S surveys and using a well-motivated fiducial set of lens-galaxy parameters, we tested the weak-field metric on kiloparsec scales and found a constraint on the post-Newtonian parameter under the assumption of a flat ΛCDM universe with parameters taken from Planck observations. General relativity (GR) predicts exactly γ = 1. Uncertainties concerning the total mass density profile, anisotropy of the velocity dispersion, and the shape of the light profile combine to systematic uncertainties of ∼25%. By applying a cosmological model-independent method to the simulated future LSST data, we found a significant degeneracy between the PPN γ parameter and the spatial curvature of the universe. Setting a prior on the cosmic curvature parameter −0.007 < Ωk < 0.006, we obtained the constraint on the PPN parameter that . We conclude that strong lensing systems with measured stellar velocity dispersions may serve as another important probe to investigate validity of the GR, if the mass-dynamical structure of the lensing galaxies is accurately constrained in future lens surveys. [ABSTRACT FROM AUTHOR]

In this paper, we use a recently compiled data set, which comprises 118 galactic-scale strong gravitational lensing (SGL) systems to constrain the statistical property of the SGL system as well as the curvature of the universe without assuming any fiducial cosmological model. Based on the singular isothermal ellipsoid (SIE) model of the SGL system, we obtain that the constrained curvature parameter is close to zero from the SGL data, which is consistent with the latest result of Planck measurement. More interestingly, we find that the parameter f in the SIE model is strongly correlated with the curvature . Neglecting this correlation in the analysis will significantly overestimate the constraining power of SGL data on the curvature. Furthermore, the obtained constraint on f is different from previous results: (68% confidence level [C.L.]), which means that the standard singular isothermal sphere (SIS) model (f = 1) is disfavored by the current SGL data at more than a C.L. We also divide all of the SGL data into two parts according to the centric stellar velocity dispersion and find that the larger the value of for the subsample, the more favored the standard SIS model is. Finally, we extend the SIE model by assuming the power-law density profiles for the total mass density, , and luminosity density, , and obtain the constraints on the power-law indices: and at a 68% C.L. When assuming the power-law index , this scenario is totally disfavored by the current SGL data, . [ABSTRACT FROM AUTHOR]

The two-point diagnostics Om(zi, zj) and Omh2(zi, zj) have been introduced as an interesting tool for testing the validity of the Λ cold dark matter (ΛCDM) model. Recently, Sahni et al. combined two independent measurements of H(z) from baryon acoustic oscillation (BAO) data with the value of the Hubble constant H0, and used the second of these diagnostics to test the ΛCDM (a constant equation-of-state parameter for dark energy) model. Their result indicated a considerable tension between observations and predictions of the ΛCDM model. Since reliable data concerning the expansion rates of the universe at different redshifts H(z) are crucial for the successful application of this method, we investigate both two-point diagnostics on the most comprehensive set of N = 36 measurements of H(z) from BAOs and the differential ages (DAs) of passively evolving galaxies. We discuss the uncertainties of the two-point diagnostics and find that they are strongly non-Gaussian and follow the patterns deeply rooted in their very construction. Therefore we propose that non-parametric median statistics is the most appropriate way of treating this problem. Our results support the claims that ΛCDM is in tension with H(z) data according to the two-point diagnostics developed by Shafieloo, Sahni, and Starobinsky. However, other alternatives to the ΛCDM model, such as the wCDM or Chevalier–Polarski–Linder models, perform even worse. We also note that there are serious systematic differences between the BAO and DA methods that ought to be better understood before H(z) measurements can compete with other probes methods. [ABSTRACT FROM AUTHOR]

Under very general assumptions of the metric theory of spacetime, photons traveling along null geodesics and photon number conservation, two observable concepts of cosmic distance, i.e., the angular diameter and the luminosity distances are related to each other by the so-called distance duality relation (DDR) . Observational validation of this relation is quite important because any evidence of its violation could be a signal of new physics. In this paper we introduce a new method to test the DDR based on strong gravitational lensing systems and type Ia supernovae (SNe Ia) under a flat universe. The method itself is worth attention because unlike previously proposed techniques, it does not depend on all other prior assumptions concerning the details of cosmological model. We tested it using a new compilation of strong lensing (SL) systems and JLA compilation of SNe Ia and found no evidence of DDR violation. For completeness, we also combined it with previous cluster data and showed its power on constraining the DDR. It could become a promising new probe in the future in light of forthcoming massive SL surveys and because of expected advances in galaxy cluster modeling. [ABSTRACT FROM AUTHOR]

In the quantum theory of gravity, for photons we expect the Lorentz Invariance Violation (LIV) and the modification of the dispersion relation between energy and momentum. The effect of the energy-dependent velocity due to the modified dispersion relation for photons was studied in the standard cosmological context by using a sample of gamma-ray bursts (GRBs). In this paper we mainly discuss the possible LIV effect of using different cosmological models for the accelerating universe. Due to the degeneracies among model parameters, the GRBs’ time delay data are combined with the cosmic microwave background data from the Planck first-year release, the baryon acoustic oscillation data at six different redshifts, and Union2 Type Ia supernovae data to constrain both the model parameters and the LIV effect. We find no evidence of the LIV. [ABSTRACT FROM AUTHOR]

In this paper, we assemble a catalog of 118 strong gravitational lensing systems from the Sloan Lens ACS Survey, BOSS emission-line lens survey, Lens Structure and Dynamics, and Strong Lensing Legacy Survey and use them to constrain the cosmic equation of state. In particular, we consider two cases of dark energy phenomenology: the XCDM model, where dark energy is modeled by a fluid with constant w equation-of-state parameter, and in the Chevalier–Polarski–Linder (CPL) parameterization, where w is allowed to evolve with redshift, . We assume spherically symmetric mass distribution in lensing galaxies, but we relax the rigid assumption of the SIS model in favor of a more general power-law index γ, also allowing it to evolve with redshifts . Our results for the XCDM cosmology show agreement with values (concerning both w and γ parameters) obtained by other authors. We go further and constrain the CPL parameters jointly with . The resulting confidence regions for the parameters are much better than those obtained with a similar method in the past. They are also showing a trend of being complementary to the Type Ia supernova data. Our analysis demonstrates that strong gravitational lensing systems can be used to probe cosmological parameters like the cosmic equation of state for dark energy. Moreover, they have a potential to judge whether the cosmic equation of state evolved with time or not. [ABSTRACT FROM AUTHOR]

Cosmological applications of the “redshift—angular size” test require knowledge of the linear size of the “standard rod” used. In this paper, we study the properties of a large sample of 140 mas compact radio sources with flux densities measured at 6 and 20 cm, compiled by Gurvits et al. Using the best-fitted cosmological parameters given by Planck/WMAP9 observations, we investigate the characteristic length lm, as well as its dependence on the source luminosity L and redshift lm = lLβ (1 + z)n. For the full sample, measurements of the angular size θ provide a tight constraint on the linear size parameters. We find that cosmological evolution of the linear size is small and consistent with previous analysis. However, a substantial evolution of linear sizes with luminosity is still required (β ≃ 0.17). Furthermore, similar analysis done on sub-samples defined by different source optical counterparts and different redshift ranges seems to support the scheme of treating radio galaxies and quasars with distinct strategies. Finally, a cosmological-model-independent method is discussed to probe the properties of the angular size of milliarcsecond radio quasars. Using the corrected redshift—angular size relation for the quasar sample, we obtained a value of the matter density parameter, , in the spatially flat ΛCDM cosmology. [ABSTRACT FROM AUTHOR]