Cosmic opacity: Cosmological-model-independent tests and their impact on cosmic acceleration

With assumptions that the violation of the distance-duality relation entirely arises from nonconservation of the photon number and that the absorption is frequency independent in the observed frequency range, we perform cosmological-model-independent tests for the cosmic opacity. The observational data include the largest Union2.1 type Ia supernova sample, which is taken for observed D_L, and galaxy cluster samples compiled by De Filippis et al. and Bonamente et al., which are responsible for providing observed D_A. Two parametrizations, τ(z)=2ɛz and τ(z)=(1+z)^2ɛ-1, are adopted for the optical depth associated with the cosmic absorption. We find that an almost transparent universe is favored by the Filippis et al. sample, but it is only marginally accommodated by the Bonomente et al. samples at 95.4% confidence level (C.L.) (even at 99.7% C.L. when the r<100kpc-cut spherical β model is considered). Taking the possible cosmic absorption (in the 68.3% C.L. range) constrained from the model-independent tests into consideration, we correct the distance moduli of SNe Ia and then use them to study their cosmological implications. The constraints on the ΛCDM show that a decelerating expanding universe with Ω_Λ=0 is only allowed at 99.7% C.L. by observations when the Bonamente et al. sample is considered. Therefore, our analysis suggests that an accelerated cosmic expansion is still needed to account for the dimming of SNe, and the standard cosmological scenario remains being supported by current observations.