A test for cosmic distance duality
  Testing the cosmic distance duality relation (CDDR) constitutes an important
task for cosmology and fundamental physics since any violation of it would be a
clear evidence of new physics. In this {\it Letter}, we propose a new test for
the CDDR using only measurements of the gas mass fraction of galaxy clusters
from Sunyaev-Zeldovich ($f_{SZE}$) and X-ray surface brightness ($f_{X-ray}$)
observations. We show that the relation between current $f_{X-ray}$ and
$f_{SZE}$ observations is given by $f_{SZE}=\eta f_{X-ray}$, where $\eta$
quantifies deviations from the CDDR. Since this latter expression is valid for
the same object in a given galaxy cluster sample, the method proposed removes
possible contaminations from different systematics error sources and redshift
differences involved in luminosity and angular diameter distance measurements.
We apply this cosmological model-independent methodology to the most recent
$f_{X-ray}$ and $f_{SZE}$ data and show that no significant violation of the
CDDR is found.
