Equivalence Principle and the Baryon Acoustic Peak
  We study the dominant effect of a long wavelength density perturbation
$\delta(\lambda_L)$ on short distance physics. In the non-relativistic limit,
the result is a uniform acceleration, fixed by the equivalence principle, and
typically has no effect on statistical averages due to translational
invariance. This same reasoning has been formalized to obtain a "consistency
condition" on the cosmological correlation functions. In the presence of a
feature, such as the acoustic peak at $l_{\rm BAO}$, this naive expectation
breaks down for $\lambda_L<l_{\rm BAO}$. We calculate a universal piece of the
three-point correlation function in this regime. The same effect is shown to
underlie the spread of the acoustic peak, and is calculable to all orders in
the long modes. This can be used to improve the result of perturbative
calculations - a technique known as "infra-red resummation" - and is explicitly
applied to the one-loop calculation of power spectrum. Finally, the success of
BAO reconstruction schemes is argued to be another empirical evidence for the
validity of the results.
