Constraints on superheavy dark matter decaying into $h\nu$, $Z\nu$ and $W\ell$ -- Benchmark example within an extended seesaw framework

TL;DR

This paper derives new, more stringent constraints on the lifetime of superheavy dark matter particles decaying into specific channels, using synchrotron radiation observations, within an extended seesaw particle physics framework.

Contribution

It introduces a novel method to constrain superheavy dark matter decay by analyzing synchrotron radiation, extending previous gamma-ray and neutrino flux bounds, within an extended seesaw model.

Findings

Stronger bounds on dark matter lifetime for masses above 10^{13} GeV.

Upper limits on the mass-mixing parameter δM based on decay channels.

Implications for inflationary cosmology models.

Abstract

Dark matter particles could be superheavy (mass $M_X\gtrsim10^9~$GeV) provided that their lifetime $\tau_X$ is extremely long, i.e. greater than $\simeq 10^{22}~$yr. Such stringent constraints on $\tau_X$ are generally obtained by limiting the prompt emission of ultrahigh energy ($\gtrsim10^9~$GeV) gamma rays and neutrinos from the decay processes to below the corresponding flux upper bounds. In this paper, we show that even more severe bounds can be obtained for $M_X\gtrsim10^{13}~$GeV from the synchrotron radiation of electron decay byproducts in the Galaxy. We illustrate the power of these constraints using generic Higgs-induced $h\nu$ and gauge-induced $Z\nu/W\ell$ decay channels, motivated by particle-physics setups invoking right-handed neutrinos. As a concrete benchmark, we consider a superheavy dark-matter candidate within an extended type-I seesaw framework and show that the lower bounds on lifetime can be translated into upper bounds on a mass-mixing parameter $\delta M$, which must satisfy approximately $\delta M\lesssim 2\times 10^{-17}/[M_X/(10^9~\mathrm{GeV})]^{0.5}$~GeV for $M_X\gtrsim 10^9$~GeV. Some implications in the context of inflationary cosmologies are discussed.