Primordial Stochastic Gravitational Wave Background Anisotropies: in-in
  Formalization and Applications
  Primordial non-Gaussianities of the scalar(tensor)-tensor-tensor type
supporting a non-trivial squeezed component are known to induce anisotropies in
the stochastic gravitational wave background. We derive the explicit form of
such anisotropies by making use, for the first time in this context, of the
in-in formalism for cosmological correlation functions. After illustrating the
general method and using it for the minimal single-field slow-roll case, we
apply it to multi-field models, providing both a tree-level and a one-loop
example. First, we make contact with previous results on anisotropies due to
the presence of an extra spin-2 field during inflation. Secondly, we calculate
the 1-loop scalar-tensor-tensor three-point function in the context of
so-called supersolid inflation. The corresponding gravitational wave anisotropy
is induced atop a gravitational signal that may be sufficiently large for
detection.
