Theoretical Constraints on Neutron--Mirror-Neutron Oscillation

Abstract

Mirror models lead to the possibility that neutron ($n$) can oscillate into its mirror partner ($n'$) inspiring several experimental searches for this phenomenon. The condition for observability of this oscillation is a high degree of degeneracy between the $n$ and $n'$ masses, which can be guaranteed if there is exact parity symmetry taking all particles to their mirror partners. However consistency of these models with big bang nucleosynthesis requires that this parity symmetry be broken in the early universe in a scenario called asymmetric inflation. In this paper we study the consistency of an observable $n-n'$ oscillations signal with asymmetric inflation and derive various theoretical constraints. In particular, we find that the reheat temperature after inflation should lie below 2.5 TeV, and predict a singlet fermion with a mass below 100 GeV. In simple models where the right-handed neutrino is a mediator of baryon number violating interactions we find that the light neutrinos are Dirac fermions with their masses arising radiatively through one-loop diagrams.