Revisiting ultrahigh-energy constraints on decaying super-heavy dark matter

TL;DR

This paper updates constraints on decaying super-heavy dark matter using the latest ultrahigh-energy cosmic-ray and gamma-ray data, providing more stringent limits on dark matter lifetime across a wide mass range.

Contribution

It presents the first combined analysis of UHECR spectrum, composition, and gamma-ray limits to improve constraints on super-heavy dark matter decay.

Findings

Constraints on dark matter lifetime are improved up to 10^12 GeV.

Gamma-ray limits are about ten times more restrictive than cosmic-ray limits.

Dark matter lifetime bounds are doubled for masses above 10^12 GeV.

Abstract

We revisit constraints on decaying very heavy dark matter (VHDM) using the latest ultrahigh-energy cosmic-ray (UHECR; $E\gtrsim 10^{18}$ eV) data and ultrahigh-energy (UHE) $\gamma$-ray flux upper limits, measured by the Pierre Auger Observatory. We present updated limits on the VHDM lifetime ($\tau_\chi$) for masses up to $\sim10^{15}$~GeV, considering decay into quarks, leptons, and massive bosons. In particular, we consider not only the UHECR spectrum but their composition data that favors heavier nuclei. Such a combined analysis improves the limits at $\lesssim 10^{12}$ GeV because VHDM decay does not produce UHECR nuclei. We also show that the constraints from the UHE $\gamma$-ray upper limits are $\sim10$ more stringent than that obtained from cosmic rays, for all of the Standard Model final states we consider. The latter improves our limits to VHDM lifetime by a factor of two for dark matter mass $\gtrsim10^{12}$ GeV.