A Mellin Space Approach to Cosmological Correlators
  We propose a Mellin space approach to the evaluation of late-time
momentum-space correlation functions of quantum fields in
$\left(d+1\right)$-dimensional de Sitter space. The Mellin-Barnes
representation makes manifest the analytic structure of late-time correlators
and, more generally, provides a convenient general $d$ framework for the study
of conformal correlators in momentum space. In this work we focus on tree-level
correlation functions of general scalars as a prototype, including $n$-point
contact diagrams and $4$-point exchanges. For generic scalars, both the contact
and exchange diagrams are given by (generalised) Hypergeometric functions,
which reduce to existing expressions available in the literature for $d=3$ and
external scalars which are either simultaneously conformally coupled or
massless. This approach can also be used for the perturbative bulk evaluation
of momentum-space boundary correlators in $\left(d+1\right)$-dimensional
anti-de Sitter space (Witten diagrams).
