# A New Littlest Seesaw Model

## TL;DR

This paper introduces a novel Littlest Seesaw model using the tri-direct CP approach, accurately describing lepton flavor mixing and baryon asymmetry with minimal parameters and explicit flavor symmetry construction.

## Contribution

It presents a new Littlest Seesaw model with specific couplings and phase, achieving excellent lepton mixing predictions and baryon asymmetry generation, along with an explicit flavor symmetry realization.

## Key findings

- Accurately describes lepton flavor mixing including second octant atmospheric angle.
- Generates observed baryon asymmetry with specific right-handed neutrino masses.
- Provides explicit flavor symmetry model construction.

## Abstract

We propose and discuss a new Littlest Seesaw model, realised in the tri-direct CP approach, in which the couplings of the two right-handed neutrinos to the lepton doublets are proportional to $(0,-1,1)$ and $(1,5/2,-1/2)$ respectively with the relative phase $\eta=-\pi/2$. This model can give an excellent description of lepton flavour mixing, including an atmospheric neutrino mixing angle in the second octant, in terms of only two input parameters. We show that the observed baryon asymmetry can be generated for the lightest right-handed neutrino mass $M_{1}=1.176\times 10^{11}$ GeV in SM and $M_{1}=3.992\times 10^{10}$ GeV in MSSM with $\tan\beta=5$. We construct an explicit Littlest Seesaw model based on the flavour symmetry $S_4\times Z_4\times Z_9$ in which the desired alignments and the phase $\eta=-\pi/2$ are achieved.