MHz to TeV expectations from scotogenic WIMP dark matter

TL;DR

This paper models the multiwavelength emission from a 1 TeV scotogenic WIMP dark matter candidate in dwarf galaxies, highlighting the importance of combined analyses across different wavelengths to detect signals amidst backgrounds.

Contribution

It introduces a comprehensive calculation of prompt and secondary emissions, including a distinctive triple hump structure, for a scotogenic WIMP in dwarf galaxies and the Milky Way.

Findings

Signal-to-background ratios are around 10^{-3} to 10^{-2} in X-ray to gamma-ray bands.

Secondary emission processes produce a characteristic triple hump in the spectrum.

Joint multi-wavelength analysis is necessary to identify dark matter signals.

Abstract

The indirect search for dark matter is typically restricted to individual photon bands and instruments. In the context of multiwavelength observations, finding a weak signal in large fore- and backgrounds at only one wavelength band is hampered by systematic uncertainties dominating the signal strength. Dark matter particle annihilation is producing Standard Model particles of which the prompt photon emission is searched for in many studies. However, also the secondary emission of charged particles from dark matter annihilation in the TeV range results in comparable or even stronger fluxes in the GHz-GeV range. In this study, we calculate the prompt and secondary emission of a scotogenic WIMP with a mass of $1\,\mathrm{TeV}$ in 27 dwarf galaxies of the Milky Way. For the secondary emission, we include Inverse Compton scattering, bremsstrahlung, and synchrotron radiation, which results in a "triple hump" structure characteristic for only dark matter and no other astrophysical source. In order to determine the best candidates for multi-instrument analyses, we estimate the diffuse emission component of the Milky Way itself, including its own dark matter halo from the same scotogenic WIMP model. We find signal-to-background ratios of individual sources on the order of $10^{-3}$-$10^{-2}$ across X- to $\gamma$-rays assuming $J$-factors for the cold dark matter distribution inferred from observations and no additional boosting due to small-scale clumping. We argue that a joint multi-wavelength analysis of all nearby galaxies as well as the extension towards the Cosmic Gamma-ray Background is required to disentangle possible dark matter signals from astrophysical back- and foregrounds.