QROCODILE and the Limits of Sub-MeV Dark Matter

Description — 

This paper provides a critical assessment of the 2025 QROCODILE experiment, which employs superconducting nanowire single-photon detectors to probe sub-eV energy deposits from hypothetical sub-MeV dark-matter particles. QROCODILE achieves exceptional technical sensitivity but reports no excess events above background. The analysis presented here places this null result in the wider context of laboratory dark-matter searches and standard cosmology.

Particles in the tens-of-keV mass range cannot seed early structure, satisfy phase-space bounds, or reproduce the observed matter power spectrum; they are therefore cosmologically excluded long before laboratory tests begin. QROCODILE’s constraints reinforce this conclusion and exemplify a broader pattern: experiments continue to advance, but the particulate model does not converge on a viable candidate.

The paper also notes, in passing, that persistent null results motivate consideration of non-particulate frameworks, including geometric approaches. A related example is The Time-Symmetric Parity Constraint Suite (Zenodo, DOI: 10.5281/zenodo.17456148), which interprets cosmological anomalies as consequences of a structural constraint on the spacetime metric rather than unseen matter. No knowledge of such alternatives is required here; the reference is provided for context only.

Revisions and Amendments — 

v.2   This revision clarifies the interpretation of the QROCODILE null result by noting that the published analysis relies on an assumed Galactic-halo model despite detecting no excess events. Minor textual refinements have been made to the abstract and introduction to reflect this and to strengthen the distinction between technical sensitivity and cosmological relevance.

v.3  This update inserts a brief comparison with self-interacting dark matter, referencing Gurian and May’s recent analysis, to situate QROCODILE within the broader landscape of tunable dark-sector models. 

v.5  Identifier added..