Superheavy dark matter through Higgs portal operators

TL;DR

This paper explores how superheavy dark matter particles, called WIMPzillas, can be produced via Higgs portal interactions, expanding the viable parameter space beyond gravitational production alone.

Contribution

It introduces the calculation of thermal (freeze-in) production of WIMPzilla dark matter through Higgs interactions, complementing gravitational production mechanisms.

Findings

Thermal production can dominate over gravitational production in certain parameter regions.

Higgs-WIMPzilla interactions, even if Planck-suppressed, can account for observed dark matter abundance.

Parameter space for superheavy dark matter production is significantly expanded.

Abstract

The WIMPzilla hypothesis is that the dark matter is a super-weakly-interacting and super-heavy particle. Conventionally, the WIMPzilla abundance is set by gravitational particle production during or at the end of inflation. In this study we allow the WIMPzilla to interact directly with Standard Model fields through the Higgs portal, and we calculate the thermal production (freeze-in) of WIMPzilla dark matter from the annihilation of Higgs boson pairs in the plasma. The two particle-physics model parameters are the WIMPzilla mass and the Higgs-WIMPzilla coupling. The two cosmological parameters are the reheating temperature and the expansion rate of the universe at the end of inflation. We delineate the regions of parameters space where either gravitational or thermal production is dominant, and within those regions we identify the parameters that predict the observed dark matter relic abundance. Allowing for thermal production opens up the parameter space, even for Planck-suppressed Higgs-WIMPzilla interactions.