Probing Sub-GeV Dark Matter via Migdal Effect-Induced Electron Excitations

Felix Kahlhoefer; Liangliang Su

arxiv: 2604.26773 · v1 · submitted 2026-04-29 · ✦ hep-ph

Probing Sub-GeV Dark Matter via Migdal Effect-Induced Electron Excitations

Felix Kahlhoefer , Liangliang Su This is my paper

Pith reviewed 2026-05-07 11:54 UTC · model grok-4.3

classification ✦ hep-ph

keywords darkelectronexcitationsmattermigdaldetectiondirecteffect

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The pith

Migdal-effect electron excitations in superfluid 4He enable direct detection of dark matter down to a few MeV via UV-photon emission.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

Dark matter particles can scatter off atomic nuclei and, through the Migdal effect, also knock electrons into excited states. The paper focuses on the lowest-energy of these excitations, which produce ultraviolet light when the atom relaxes. In superfluid helium this light can be detected. By computing the expected rate of such events for a range of dark-matter masses and interaction strengths, the authors show that the signal remains observable even when the dark-matter particle is only a few MeV in mass—well below the reach of conventional nuclear-recoil searches. The calculation uses standard halo models and the known Migdal formalism but applies them to a new kinematic regime and a new target material.

Core claim

electron excitations induced by the Migdal effect make it possible to probe dark matter-nucleus scattering for dark matter masses as small as a few MeV.

Load-bearing premise

That the Migdal effect remains valid and that UV-photon emission from the lowest excitations can be distinguished from backgrounds at the calculated rates in a realistic superfluid 4He detector.

read the original abstract

The electron ionization predicted by the Migdal effect in dark matter-nucleus scattering enhances experimental sensitivity to sub-GeV dark matter. In this work, we demonstrate that lower-energy electron excitations provide a novel and promising pathway, enabling the detection of even lighter dark matter particles previously considered inaccessible for direct searches. Direct detection experiments employing a superfluid $^4$He target can exploit this channel by observing electronic excitations via UV-photon emission. We calculate the resulting event rates and find that electron excitations induced by the Migdal effect make it possible to probe dark matter-nucleus scattering for dark matter masses as small as a few MeV.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

This calculates Migdal-driven electron excitations in superfluid 4He for UV readout and claims few-MeV DM reach, but the background separation step is the least anchored part of the argument.

read the letter

The main thing to know is that the paper takes the Migdal effect down to the lowest electron excitations in helium and shows how those could produce detectable UV photons, opening a window to DM-nucleus scattering at masses of a few MeV. That is the concrete new claim beyond standard ionization searches. They do a forward rate calculation from ordinary DM scattering inputs and the usual Migdal formalism, without obvious parameter tuning or circular citations. That part is clean and worth having on record for anyone working on light DM direct detection. The helium target plus UV channel is a specific experimental hook that makes the idea testable rather than purely theoretical. The soft spot is exactly where the stress test flags it: the projected sensitivity assumes the UV signal from these excitations can be pulled out above realistic backgrounds in a superfluid 4He setup. The abstract states that rates are computed and that the channel works, but without a shown background spectrum, energy resolution, or rejection efficiency at the relevant UV energies, it is not yet clear whether the few-MeV window actually survives. If backgrounds in that window are comparable to the predicted signal, the reach claim does not follow. This is not a minor detail; it is load-bearing for the headline result. The paper is aimed at the sub-GeV direct detection community, especially groups already thinking about helium targets or Migdal channels. A reader who wants to see how low the threshold could go in principle will get useful rate numbers and a clear experimental mapping. It is coherent on its own terms and shows honest engagement with the literature, so it deserves a serious referee rather than a desk reject. I would send it out, but with the clear expectation that reviewers will press hard on the background model and detector response before the sensitivity numbers can be taken at face value.

Referee Report

1 major / 1 minor

Summary. The paper calculates event rates for lower-energy electron excitations induced by the Migdal effect in dark matter-nucleus scattering. It proposes that these excitations, detected via UV-photon emission in a superfluid ^4He target, enable direct detection of DM-nucleus scattering for masses as low as a few MeV, extending sensitivity below previous thresholds.

Significance. If the UV-photon yields can be reliably distinguished from backgrounds, the result would meaningfully extend the mass reach of direct detection experiments into the few-MeV regime using a well-characterized target material. The forward calculation of rates from standard Migdal formalism and helium response provides a concrete, falsifiable prediction that could guide future detector R&D.

major comments (1)

[Event rate and sensitivity discussion] The central sensitivity claim to few-MeV DM (abstract and concluding section) rests on the assertion that Migdal-induced excitation rates produce observable UV-photon signals above background. However, the manuscript provides no quantitative background spectrum, rejection efficiency, or detector response model for the relevant UV energies in superfluid ^4He, leaving the signal-to-background ratio unanchored.

minor comments (1)

Notation for the excitation energies and photon emission probabilities could be clarified with an explicit table or equation reference to avoid ambiguity when comparing to other Migdal implementations.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claim rests on the validity of the Migdal effect at low momentum transfer, standard galactic halo parameters, and the assumption that UV emission can be observed above background. No new free parameters are introduced in the abstract; the result is a rate calculation using existing formalism.

axioms (2)

domain assumption Migdal effect applies to electron excitations at the lowest energies considered
Invoked to justify the new detection channel
standard math Standard dark-matter halo velocity distribution and local density
Used to compute event rates

pith-pipeline@v0.9.0 · 5395 in / 1266 out tokens · 29406 ms · 2026-05-07T11:54:03.472951+00:00 · methodology

Probing Sub-GeV Dark Matter via Migdal Effect-Induced Electron Excitations

Core claim

Load-bearing premise

discussion (0)