nn̄transitions in nuclei

Abstract

It is shown that there is a double counting in the standard model of nn mixing in the medium, resulting in full cancellation of leading terms. The direct calculation of nn transition followed by annihilation is performed. The lower limit for the free-space nn oscillation time is nn ϳT nn Ͼ10 16 yr, where T nn is the lifetime of neutron bound in a nucleus. This limit exceeds the previous one by 16 orders of magnitude.

Absorption in the final state in reactions and decays in the medium

“…On the one hand, the nn transition probability is very small (see (19)), and on the other hand, the term iImUn plays a crucial role because it enters the leading diagram (see (13)). …”

“…The approach based on the evolution operator is more general than the S-matrix one, since in this case the time-dependence of the process does not need to be W t = 1 − exp(−Γ t t) (see (8)). Also it is infrared-free, which is essential for ab transitions [13].…”

“…However, the phenomenological model describes Wn only. Recall that for the total nn transition probability the phenomenological model gives W t ∼ 1/Γ (see (13)). Since Wn ≪ W t , W a depends inversely on Γ as well:…”

“…1. In particular, all existing calculations of nn transitions in the medium are based on model (5) (see, for example, [13] for future references).…”

Alternative Models of Neutron–antineutron Conversion in Nuclei

“…3 However, in Ref. 4 we abandoned this model for reasons given below. The model based on field-theoretical approach with finite time interval (model 2) has been proposed.…”