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| Main Author: | |
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| Format: | Preprint |
| Published: |
2024
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2408.17111 |
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Table of Contents:
- Dark matter particles could be superheavy (mass $M_X\gtrsim10^9~$GeV) provided that their lifetime $τ_X$ is extremely long, i.e. greater than $\simeq 10^{22}~$yr. Such stringent constraints on $τ_X$ 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 $hν$ and gauge-induced $Zν/W\ell$ 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 $δM$, which must satisfy approximately $δM\lesssim 2\times 10^{-17}/[M_X/(10^9~\mathrm{GeV})]^{0.5}$~GeV for $M_X\gtrsim 10^9$~GeV. Some implications in the context of inflationary cosmologies are discussed.