Constraints on electromagnetic form factors of sub-GeV dark matter from the Cosmic Microwave Background anisotropy

TL;DR

This paper derives constraints on electromagnetic form factors of sub-GeV dark matter particles using CMB and LSS data, setting upper bounds on their electromagnetic couplings and multipole moments.

Contribution

It provides the first comprehensive bounds on various electromagnetic form factors of sub-GeV dark matter from cosmological observations.

Findings

Upper bound on anapole moment: g_A < 7.163×10^3 GeV^{-2}

Upper bound on electric dipole moment: D < 7.978×10^{-9} e-cm

Upper bound on magnetic dipole moment: μ < 2.959×10^{-7} μ_B

Abstract

We consider dark matter which have non-zero electromagnetic form factors like electric/magnetic dipole moments and anapole moment for fermionic dark matter and Rayleigh form factor for scalar dark matter. We consider dark matter mass $m_\chi > \cal{ O}({\rm MeV})$ and put constraints on their mass and electromagnetic couplings from CMB and LSS observations. Fermionic dark matter with non-zero electromagnetic form factors can annihilate to $e^+ e^-$ and scalar dark matter can annihilate to $2\gamma$ at the time of recombination and distort the CMB. We analyze dark matter with multipole moments with Planck and BAO observations. We find upper bounds on anapole moment $g_{A}<7.163\times 10^{3} \text{GeV}^{-2}$, electric dipole moment ${\cal D}<7.978\times 10^{-9} \text{e-cm}$, magnetic dipole moment ${\mu}<2.959\times 10^{-7} \mu_B$, and the bound on Rayleigh form factor of dark matter is $g_4/\Lambda_4^2<1.085\times 10^{-2}\text{GeV}^{-2}$ with $95\%$C.L.