Amplifying muon-to-positron conversion in nuclei with ultralight dark matter

TL;DR

This paper investigates how ultralight scalar dark matter can enhance muon-to-positron conversion in nuclei, leading to potentially observable signals and new constraints on neutrino-dark matter interactions.

Contribution

It demonstrates that ultralight dark matter can significantly amplify lepton-number violating processes, providing novel experimental constraints and insights into neutrino interactions.

Findings

Ultralight dark matter can increase muon-to-positron conversion rates.

Existing experiments set new bounds on neutrino-dark matter couplings.

Future experiments could surpass cosmological bounds in sensitivity.

Abstract

We present an analysis of the lepton-number and lepton-flavour-violating process of muon-to-positron conversion $\mu^- + N \rightarrow e^+ + N'$, in the presence of an ultralight scalar dark matter (ULSDM) field which couples to neutrinos. The ULSDM contributes to the effective off-diagonal Majorana mass $ m_{\mu e}$, therefore amplifying the rate of muon-to-positron conversion to experimentally observable levels. Using existing bounds from SINDRUM II, COMET, and Mu2e experiments, we derive novel constraints on the flavour-off-diagonal couplings of neutrinos to ULSDM. Our work reveals that upcoming experiments can provide stronger sensitivity to these new couplings than bounds arising from cosmological surveys and terrestrial experiments.