A search for a cosmologically-relevant boson in muon decay

TL;DR

This paper reviews the potential for detecting a long-lived, massive boson in muon decay, exploring unexplored parameter space near the kinematic limit with implications for cosmology.

Contribution

It proposes a new search strategy for a long-lived boson in muon decay, highlighting unexplored parameter space relevant for cosmological scenarios.

Findings

Unexplored parameter space close to decay kinematic limit identified

Potential for cosmological impact of the boson discussed

Feasibility of detection with germanium detector technology analyzed

Abstract

Experiments looking for a lepton flavor-violating decay $\mu^{+}\!\!\rightarrow \!e^{+} X^{0}$ are reviewed in light of present-day germanium detector technology, with an eye on scenarios where a long-lived, slow-moving massive boson $X^{0}$ might have a cosmological impact. A broad swath of interesting, unexplored parameter space very close to the kinematic limit of the decay is found to be within the reach of a new proposed search. A number of possible roles for $X^{0}$ in past and present epochs can be investigated.