Leptogenesis in a Left-Right Symmetric Model with double seesaw

Abstract

We explore the connection between the low-scale CP-violating Dirac phase (δ) and high-scale leptogenesis in a Left-Right Symmetric Model (LRSM) with scalar bidoublet and doublets. The model’s fermion sector includes one sterile neutrino (SL) per generation to enable a double seesaw mechanism in the neutral fermion mass matrix, implemented by performing type-I seesaw twice. The first seesaw generates the Majorana mass term for heavy right-handed (RH) neutrinos (NR), and in the second, the light neutrino mass is linearly dependent on S L mass. We use charge conjugation (C) as the discrete left-right (LR) symmetry, aiding in deriving the Dirac neutrino mass matrix (MD) in terms of light and heavy RH neutrino masses and the light neutrino mixing matrix UPMNS (containing δ). We demonstrate the feasibility of unflavored thermal leptogenesis via RH neutrino decay using the obtained MD and RH neutrino masses as input. A thorough analysis of the Boltzmann equations describing asymmetry evolution is conducted in the unflavored regime, showing that the CP-violating Dirac phase alone can generate the required leptonic asymmetry for given input parameters, with or without Majorana phases. Finally, we discuss constraining our model with current and upcoming oscillation experiments aimed at refining the value of δ.