Migdal effect and photon bremsstrahlung in effective field theories of dark matter direct detection and coherent elastic neutrino-nucleus scattering

Abstract

Dark matter direct detection experiments have limited sensitivity to light dark matter (below a few GeV), due to the challenges of lowering energy thresholds for the detection of nuclear recoil to below O(keV). While impressive progress has been made on this front, light dark matter remains the least constrained region of dark-matter parameter space. It has been shown that both ionization and excitation due to the Migdal effect and coherently-emitted photon bremsstrahlung from the recoiling atom can provide observable channels for light dark matter that would otherwise have been missed owing to the resulting nuclear recoil falling below the detector threshold. In this paper we extend previous work by calculating the Migdal effect and photon bremmstrahlung rates for a general set of interaction types, including those that are momentum-independent or -dependent, spin-independent or -dependent, as well as examining the rates for a variety of target materials, allowing us to place new experimental limits on some of these interaction types. Additionally, we include a calculation of these effects induced by the coherent scattering on nuclei of solar or atmospheric neutrinos. We demonstrate that the Migdal effect dominates over the bremsstrahlung effect for all targets considered for interactions induced by either dark matter or neutrinos. This reduces photon bremsstrahlung to irrelevancy for future direct detection experiments.

Plasmon production from dark matter scattering

“…In the energy loss rates, this corresponds to a possible continuum of electron recoils away from the plasmon and photon poles. This is similar to the Migdal effect in atoms [30,[45][46][47], where electron excitations are created from nuclear recoils; a first approximation for semiconductors was studied in Ref. [48].…”

“…Charge signals for light DM can also be produced through the Migdal effect [30,[46][47][48], wherein a recoiling nucleus can excite or ionize electrons. While the first discussions of the Migdal effect considered isolated atomic systems, Ref.…”

Cosmic ray boosted sub-GeV gravitationally interacting dark matter in direct detection

“…Instead, the searching for DM scattering off electrons may access the lighter DM [15,16]. Besides, other new methods [17][18][19] and new types of detectors [20,21] have been proposed in the past few years.…”

Migdal effect and photon Bremsstrahlung: improving the sensitivity to light dark matter of liquid argon experiments

“…However, the failure of observing incontrovertible evidences of a DM signal may be interpreted JHEP11(2020)034 as in tension with the WIMP paradigm. These results stimulated the effort of examining alternative signals to nuclear recoil, including dark matter scattering on electrons [19][20][21][22][23][24][25][26][27][28][29][30][31][32] or secondary signals [33][34][35][36], and motivated the interest in sub-GeV/c 2 DM [29,[37][38][39][40].…”

“…Therefore, this new process may lead to energetic photons and ionization electrons produced from the primary interaction. The first process is the Bremsstrahlung photon emission from a nucleus [33], the latter is the Migdal effect [34][35][36], and they both have been already exploited by experimental collaborations [39,[47][48][49].…”