Dirac Leptogenesis in Left-Right Symmetric Models

TL;DR

This paper demonstrates how Dirac leptogenesis can be realized within left-right symmetric models that naturally generate light Dirac neutrino masses and solve the strong CP problem, leading to successful baryogenesis.

Contribution

It introduces a novel mechanism for Dirac leptogenesis in left-right symmetric models with scalar doublets and vector-like leptons, linking neutrino mass generation to baryogenesis.

Findings

Successful baryogenesis achievable with $W_R$ mass around $10^{11}$ GeV.

Neutrino masses generated via one-loop diagrams involving new scalars.

Lepton asymmetry converted to baryon asymmetry through sphalerons.

Abstract

Left-right symmetric models which employ a generalized seesaw mechanism to generate quark and charged lepton masses are known to solve the strong CP problem via parity symmetry, without the need for the axion. These models lead to naturally light Dirac neutrinos with their masses arising through radiatve corrections. In this work, we show how baryogenesis via Dirac leptogenesis can be implemented in this framework. A pair of left-right symmetric scalar doublets $\phi_{L,R}$ carrying $(B-L)$ charge of $3$ is introduced for this purpose, which preserves the parity solution to the strong CP problem. Small neutrino masses are generated through one-loop diagrams mediated by these scalars. The decay of vector-like leptons ($E_i$) involved in the seesaw mechanism to generate charged lepton masses, $E_i \rightarrow \overline{\nu}_{jR} \,\phi_R^-$, creates a right-handed neutrino ($\nu_{R}$) asymmetry, while preserving total lepton number. The compensating lepton asymmetry is converted to baryon asymmetry via electroweak sphalerons. We show that for a large range of model parameters successful baryogenesis can be realized, with the $W_R^\pm$ gauge boson mass of order $10^{11}$ GeV.