We search for a variation of the electromagnetic fine structure constant (α ≡ e2/ℏ c) using a sample of 58 SZ selected clusters in the redshift range (0.2

We carry out a test of the cosmic distance duality relation using a sample of 52 SPT-SZ clusters, along with X-ray measurements from XMM-Newton. To carry out this test, we need an estimate of the luminosity distance (DL) at the redshift of the cluster. For this purpose, we use three independent methods: directly using DL from the closest Type Ia Supernovae from the Union 2.1 sample, non-parametric reconstruction of DL using the same Union 2.1 sample, and finally using H(z) measurements from cosmic chronometers and reconstructing DL using Gaussian Process regression. We use four different functions to characterize the deviations from CDDR. All our results for these (4 × 3) analyses are consistent with CDDR to within 1σ.

In this paper, we implement a new method to test the invariance of the speed of light (c) as a function of redshift, by combining the measurements of galaxy cluster gas mass fraction, H(z) from cosmic chronometers, and Type-Ia supernovae (SNe Ia). In our analyses, we consider both a constant depletion factor (which corresponds to the ratio by which the cluster gas mass fraction is depleted with respect to the universal baryonic mean) and one varying with redshift. We also consider the influence of different H 0 estimates on our results. We look for a variation of c, given by c(z) = c 0(1+c 1 z). We find a degeneracy between our final results on c variation and the assumptions on the gas mass fraction depletion factor. Most of our analyses indicate negligible variation of the speed of light.

We propose a new method to explore a possible departure from the standard time evolution law for the dark matter density. We looked for a violation of this law by using a deformed evolution law, given by $$\rho _c(z) \propto (1+z)^{3+\epsilon }$$ ρ c ( z ) ∝ ( 1 + z ) 3 + ϵ , and then constrain $$\epsilon $$ ϵ . The dataset used for this purpose consists of Strong Gravitational Lensing data obtained from SLOAN Lens ACS, BOSS Emission-line Lens Survey, Strong Legacy Survey SL2S, and SLACS; along with galaxy cluster X-ray gas mass fraction measurements obtained using the Chandra Telescope. Our analyses show that $$\epsilon $$ ϵ is consistent with zero within 1 $$\sigma $$ σ c.l., but the current dataset cannot rule out with high confidence level interacting models of dark matter and dark energy.

The gas mass fraction in galaxy clusters has been widely used to determine cosmological parameters. This method assumes that the ratio of the cluster gas mass fraction to the cosmic baryon fraction ($$\gamma (z)$$ γ ( z ) ) is constant as a function of redshift. In this work, we look for a time evolution of $$\gamma (z)$$ γ ( z ) at $$R_{500}$$ R 500 by using both the SPT-SZ and Planck Early SZ (ESZ) cluster data, in a model-independent fashion without any explicit dependence on the underlying cosmology. For this calculation, we use a non-parametric functional form for the Hubble parameter obtained from Gaussian Process regression using cosmic chronometers. We parameterize $$\gamma (z)$$ γ ( z ) as: $$\gamma (z)= \gamma _0(1+\gamma _1 z)$$ γ ( z ) = γ 0 ( 1 + γ 1 z ) to constrain the redshift evolution. We find contradictory results between both the samples. For SPT-SZ, $$\gamma (z)$$ γ ( z ) decreases as a function of redshift (at more than 5$$\sigma $$ σ ), whereas a positive trend with redshift is found for Planck ESZ data (at more than 4$$\sigma $$ σ ). We however find that the $$\gamma _1$$ γ 1 values for a subset of SPT-SZ and Planck ESZ clusters between the same redshift interval agree to within $$1\sigma $$ 1 σ . When we allow for a dependence on the halo mass in the evolution of the gas depletion factor, the $$4-5\sigma $$ 4 - 5 σ discrepancy reduces to $$2\sigma $$ 2 σ .