Kavli Affiliate: Misao Sasaki
| First 5 Authors: Shi Pi, Misao Sasaki, Ao Wang, Jianing Wang,
| Summary:
High-frequency primordial gravitational waves (PGWs) with wave numbers larger
than the Hubble parameter at the end of inflation are originated from the
ultraviolet (UV) modes, which are never stretched out of the horizon. Such a UV
tail of the PGW energy spectrum has a spurious logarithmic divergence. We study
the origin of such a divergence, and find that it comes from the instantaneous
inflation-to-post-inflation transition, which can be removed by considering a
finite duration. For the first time, we obtain a semi-analytical expression for
the PGW energy spectrum. We find that the UV tail decays exponentially, while
the decay rate depends solely on the transition rate. When there is a stiff
post-inflationary stage, the enhanced PGW displays a characteristic spectral
shape of power-law increasing and exponential decaying. We propose a fitting
formula which can be used for signal searching.
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