Constraints on the duality relation from ACT cluster data
  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
$d_L < (1+z)^2d_A$.
