Higgs Inflation: Particle Factory

We study cosmological gravitational particle production (CGPP) in Higgs inflation, wherein the inflaton is a scalar field with quartic self-coupling $\lambda$ and a nonminimal coupling to gravity $\xi$, and which may, but need not be, the Higgs boson of the Standard Model (SM). We find an explosive particle production peaked on a characteristic comoving wavenumber $k\sim {\xi }^{2\mathrm{/}3}aH$ with a peak occupation number that scales with $\xi$. This new peak in production can easily dominate over the conventional (minimally coupled inflation) CGPP even for modest values of $\xi$. The results apply for a wide range of $\xi$, e.g., as low as $\xi =10$, which can be realized for the Standard Model Higgs given suitable RG flow of the quartic coupling. We discuss implications for late time relics such as dark matter.