Aligning a Majorana fermion's anapole moment with an external current through photon emission mediated by the fermion's generalized polarizabilities

Abstract

The sole static electromagnetic property of a spin-$\frac{1}{2}$ Majorana fermion is its anapole moment. Though they cannot couple to single real photons, these particles can interact with electric currents through virtual photons. If a Majorana fermion is immersed in a background current, there is an energy difference between the spin states of the fermion; the higher energy state has its anapole moment antialigned with the current. In this paper, we address the ability of a system of initially unpolarized Majorana fermions to achieve some degree of polarization relative to a static background current. In considering processes that allow the Majorana fermion's spin to flip to the lower-energy state, we focus upon two irreversible processes: the spontaneous emission of two real photons and the emission of a single real photon emitted in virtual Compton scattering. Both of these processes involve coupling to photons via the fermion's polarizaibilities. We compute the spin-flip transition rates for these processes using a low-energy expansion of the Hamiltonian and construct a toy model to showcase how these rates depend upon the underlying parameters within a model. Applying these ideas to a thermal dark matter (DM) model, we find that when the DM thermally decouples from the Standard Model plasma in the early universe, two-photon emission is negligible but partial polarization for the DM medium can proceed via virtual Compton scattering if sufficient currents exist.

References in corpus (32)

• Package-X 2.0: A Mathematica package for the analytic calculation of one-loop integrals
• Primordial Magnetic Fields from Cosmological First Order Phase Transitions
• Magnetic Fields Produced by Phase Transition Bubbles in the Electroweak Phase Transition
• Anapole Dark Matter
• Virtual Compton Scattering and Generalized Polarizabilities of the Proton
• Low-Energy Compton Scattering of Polarized Photons on Polarized Nucleons
• Compton Scattering and the Spin Structure of the Nucleon at Low Energies
• On the charge radius of the neutrino
• Structure analysis of the virtual Compton scattering amplitude at low energies
• Spin structure of the nucleon at low energies
• Higher Order Polarizabilities of the Proton
• Multi-Component Dark Matter: the vector and fermion case
• Generalized Polarizabilities and the Chiral Structure of the Nucleon
• Generalized Polarizabilities of the Nucleon in Chiral Effective Theories
• Generalized polarizabilities and the spin-averaged amplitude in virtual Compton scattering off the nucleon
• Virtual Compton scattering off the nucleon at low energies
• Generalized dipole polarizabilities and the spatial structure of hadrons
• Anapole Dark Matter at the LHC
• Sum Rules for Magnetic Moments and Polarizabilities in QED and Chiral Effective-Field Theory
• Parity Violation in gamma proton Compton Scattering
• Spin Polarizabilities of the Nucleon from Polarized Low Energy Compton Scattering
• Gamma-ray Signals from Dark Matter Annihilation Via Charged Mediators
• Parity Violation in Polarized-Gamma Proton Compton Scattering
• Anapole dark matter annihilation into photons
• Collider Detection of Dark Matter Electromagnetic Anapole Moments
• The Origin of Primordial Magnetic Fields
• Two-photon interactions with Majorana fermions
• New approach to low energy Virtual Compton Scattering and generalized polarizabilities of the nucleon
• Majorana dark matter through the Higgs portal under the vacuum stability lamppost
• CP-violation in Compton scattering
• Study of Majorana Fermionic Dark Matter
• Virtual Compton scattering off nuclei in the $\Delta$-resonance region