Constraints on the duality relation from ACT cluster data

TL;DR

This study tests the cosmic distance-duality relation using galaxy cluster and supernova data, finding results consistent with standard physics but hinting at possible photon number variations.

Contribution

It combines ACT galaxy cluster measurements with supernova data to constrain deviations from the distance-duality relation, exploring potential new physics.

Findings

Results are consistent with the standard relation $\,eta=1$.

Data slightly favor negative $\,eta$, suggesting possible photon number increase.

No definitive deviation from standard physics detected.

Abstract

The cosmic distance-duality relation (CDDR), $d_L(z) (1 + z)^{2}/d_{A}(z) = \eta$, where $\eta = 1$ and $d_L(z)$ and $d_A(z)$ are, respectively, the luminosity and the angular diameter distances, holds as long as the number of photons is conserved and gravity is described by a metric theory. Testing such hypotheses is, therefore, an important task for both cosmology and fundamental physics. In this paper we use 91 measurements of the gas mass fraction of galaxy clusters recently reported by the Atacama Cosmology Telescope (ACT) survey along with type Ia supernovae observations of the Union2.1 compilation to probe a possible deviation from the value $\eta = 1$. Although in agreement with the standard hyphothesis, we find that this combination of data tends to favor negative values of $\eta$ which might be associated with some physical processes increasing the number of photons and modifying the above relation to $d_L < (1+z)^2d_A$.