Cosmological implications of photon-flux upper limits at ultra-high energies in scenarios of Planckian-interacting massive particles for dark matter

TL;DR

This paper uses Pierre Auger Observatory data to set upper limits on ultra-high-energy photon fluxes from decaying super-heavy dark matter particles, constraining their decay couplings and masses, and exploring implications for dark matter models and early universe physics.

Contribution

It provides the first upper bounds on photon fluxes from super-heavy dark matter decay at energies above 10^8 GeV, translating these into constraints on decay couplings and particle masses, including instanton effects.

Findings

Upper limits on secondary photon fluxes above 10^8 GeV.

Constraints on dark matter particle decay couplings, $oxed{ ext{α}_X extless 0.09}$.

Exclusion of masses $M_X extgreater 3 imes 10^{13}$ GeV for $ ext{α}_X=0.09$.

Abstract

Using the data of the Pierre Auger Observatory, we report on a search for signatures that would be suggestive of super-heavy particles decaying in the Galactic halo. From the lack of signal, we present upper limits for different energy thresholds above ${\gtrsim}10^8$\,GeV on the secondary by-product fluxes expected from the decay of the particles. Assuming that the energy density of these super-heavy particles matches that of dark matter observed today, we translate the upper bounds on the particle fluxes into tight constraints on the couplings governing the decay process as a function of the particle mass. Instantons, which are non-perturbative solutions to Yang-Mills equations, can give rise to decay channels otherwise forbidden and transform stable particles into meta-stable ones. Assuming such instanton-induced decay processes, we derive a bound on the reduced coupling constant of gauge interactions in the dark sector: $\alpha_X \lesssim 0.09$, for $10^{9} \lesssim M_X/\text{GeV} < 10^{19}$. Conversely, we obtain that, for instance, a reduced coupling constant $\alpha_X = 0.09$ excludes masses $M_X \gtrsim 3\times 10^{13}~$GeV. In the context of dark matter production from gravitational interactions alone during the reheating epoch, we derive constraints on the parameter space that involves, in addition to $M_X$ and $\alpha_X$, the Hubble rate at the end of inflation, the reheating efficiency, and the non-minimal coupling of the Higgs with curvature.