Lepton Flavor Violation and Cosmological Constraints on R-parity Violation

TL;DR

This paper examines how tiny lepton flavor violations in supersymmetric models can undermine cosmological constraints on R-parity violation, impacting baryon asymmetry preservation and particle decay predictions.

Contribution

It demonstrates that even minimal slepton mixing angles can break B/3-L_i conservation, challenging previous assumptions about circumventing cosmological constraints.

Findings

Tiny slepton mixing angles spoil B/3-L_i conservation.

Lepton flavor violation observations imply R-parity couplings must be suppressed.

Implications for MSSM particle decay at the LHC.

Abstract

In supersymmetric standard models R-parity violating couplings are severely constrained, since otherwise they would erase the existing baryon asymmetry before the electroweak transition. It is often claimed that this cosmological constraint can be circumvented if the baryon number and one of the lepton flavor numbers are sufficiently conserved in these R-parity violating couplings, because B/3-L_i for each lepton flavor is separately conserved by the sphaleron process. We discuss the effect of lepton flavor violation on the B-L conservation, and show that even tiny slepton mixing angles \theta_{12} \gsim {\cal O}(10^{-4}) and \theta_{23}, \theta_{13}\gsim {\cal O}(10^{-5}) will spoil the separate B/3-L_i conservation. In particular, if lepton flavor violations are observed in experiments such as MEG and B-factories, it will imply that all the R-parity violating couplings must be suppressed to avoid the B-L erasure. We also discuss the implication for the decay of the lightest MSSM particle at the LHC.