One-loop tensor power spectrum from an excited scalar field during inflation by Atsuhisa Ota et al. on Thursday 24 November

We present a consistent one-loop calculation for the inflationary tensor

power spectrum in the presence of an excited spectator scalar field using the

in-in formalism. We find that the super-horizon primordial power spectrum of

the tensor mode can be scale-invariantly enhanced or reduced by the loop

effects of a subhorizon scalar field. Our calculation also includes the

scalar-induced gravitational wave spectrum classically computed in the previous

literature, which is significant only near the scales where the scalar field is

amplified. The super-horizon enhancement is a higher-order effect of the

interaction Hamiltonian, which can be understood as a Bogoliubov transformation

introduced by nonlinear interactions. On the other hand, the scale-invariant

reduction of the tensor power spectrum may occur due to the fourth-order

scalar-scalar-tensor-tensor coupling. This phenomenon can be understood as the

evolution of an anisotropic Bianchi type-I background in the separate universe

approach. Our result suggests that large-scale measurements may indirectly test

the dramatic effects of small-scale cosmological perturbations through loop

corrections. This possibility opens a new ground in probing the small-scale

physics of the primordial Universe through gravitational wave detectors of

cosmological scales.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.12766v1