Asymmetric long-lived dark matter and leptogenesis from type-III seesaw framework

TL;DR

This paper presents a model within the type-III seesaw framework that simultaneously explains neutrino masses, asymmetric dark matter, and baryon asymmetry, introducing new particles and mechanisms for early Universe asymmetries and potential collider signatures.

Contribution

It introduces a novel type-III seesaw model with a $Z_2$ symmetry, linking asymmetric dark matter and leptogenesis, and explores collider signatures of scalar triplet components.

Findings

The model successfully generates neutrino masses, baryon asymmetry, and asymmetric dark matter.

It predicts displaced vertex signatures at colliders from scalar triplet decays.

The model provides a pathway for direct detection of dark matter via $ ext{Phi-H}$ mixing.

Abstract

We propose a simple model in the type-III seesaw framework to explain the neutrino mass, asymmetric dark matter (ADM), and baryon asymmetry of the Universe. We extend the standard model with a vector-like singlet lepton ($\chi$) and a hypercharge zero scalar triplet ($\Delta$) in addition to three hypercharge zero triplet fermions($\Sigma_i~,i=1,2,3$). A $Z_2$ symmetry is imposed under which $\chi$ and $\Delta$ are odd, while all other particles are even. As a result, the lightest $Z_2$ odd particle $\chi$ behaves as a candidate of DM. In the early Universe, the $CP$-violating out-of-equilibrium decay of heavy triplet fermions to the Standard Model lepton ($L$) and Higgs ($H$) generate a net lepton asymmetry, while that of triplet fermions to $\chi$ and $\Delta$ generate a net asymmetric DM. The lepton asymmetry is converted to the required baryon asymmetry of the Universe via the electroweak sphalerons, while the asymmetry in $\chi$ remains as a DM relic that we observe today. We introduce a singlet scalar $\Phi$, with mass $M_\phi < M_\chi$, which not only assists to deplete the symmetric component of $\chi$ through the annihilation process: $\bar{\chi} \chi \to \Phi \Phi$ but also paves a path to detect DM $\chi$ at direct search experiments through $\Phi-H$ mixing. The electro-weak symmetry breaking induces a non-zero vacuum expectation value to $\Delta$, which leads to an unstable asymmetric DM ranging from a few MeV to hundreds of GeV. We then explore the displaced vertex signatures of the charged components of the scalar triplet $\Delta$ at colliders.