Sterile neutrinos in $\Lambda_b^0\to (\Lambda_c^+,p^+)\ell^-_1\ell^-_2\ell^+_3\nu$ decays

TL;DR

This paper investigates how heavy sterile neutrinos can cause lepton number violation and CP violation in certain baryon decays, providing potential signals for new physics beyond the Standard Model.

Contribution

It introduces a detailed analysis of baryon decays involving quasi-degenerate sterile neutrinos, highlighting differences in decay rates and CP violation for Majorana versus Dirac neutrinos.

Findings

CP-averaged branching ratio for Majorana neutrinos is nearly 100 times larger than for Dirac neutrinos in certain decays.

CP-violation effects are significant when neutrino mass differences are comparable to decay widths.

Branching ratios for specific decay channels are similar for Majorana and Dirac neutrinos in some cases.

Abstract

We study lepton number violating and lepton number conserving semi-leptonic decays of heavy baryons $\Lambda_b^0$ to three charged leptons and a neutrino. The decays occur through two intermediate quasi-degenerate GeV-scale sterile neutrinos of either Majorana or Dirac type that can be on-shell. Interference between the intermediate heavy neutrinos leads to CP violation in the final states. Effect of neutrino oscillations between the heavy states are also considered in observables of interests, \emph{i.e.,} branching ratio, and the CP-asymmetry. Given the present constraints on the heavy-to-light mixing elements $|V_{eN}|$ and $|V_{\mu N}|$, CP-averaged branching ratio of $\Lambda_b^0\to (\Lambda_c,p)\mu\mu e\nu$ with intermediate Majorana neutrinos is almost two orders of magnitude larger than for the same with Dirac neutrinos, whereas, CP-averaged branching ratio of $\Lambda_b^0\to (\Lambda_c,p)ee\mu\nu$ is of the same order of magnitude for both Majorana and Dirac neutrino induced decays. CP-violation is found to be appreciable when the neutrino mass difference is comparable with the average decay widths.