Lepton sourced baryon asymmetry in the fourth generation model

TL;DR

This paper shows that the observed baryon asymmetry of the universe can be explained within an extended Standard Model featuring a fourth generation of fermions, using effective operators and CP violation sources from the CKM matrix.

Contribution

It constructs dimension-6 operators induced by fourth generation fermions and evaluates their role in generating the baryon asymmetry, providing a novel mechanism within the SM4 framework.

Findings

Baryon-over-entropy ratio estimated at ~10^{-10}

Effective operators linked to fourth generation fermions induce sufficient CP violation

Framework unambiguously evaluates CPV source strength in SM4

Abstract

We demonstrate that the observed baryon asymmetry in the Universe can be accommodated in the extended Standard Model with sequential fourth generation fermions (SM4). We first construct the dimension-6 effective operators of the type $-i(\Phi^\dagger\Phi)\bar F_L\Phi f_R$ induced by fourth generation quarks, which carry the $CP$ violation (CPV) source from the $4\times 4$ Cabibbo-Kobayashi-Maskawa (CKM) matrix, $\Phi$ ($F_L$, $f_R$) being a Higgs double (left-handed fermion doublet, right-handed fermion singlet). The required inputs of the fourth generation fermion masses were derived in our previous dispersive analyses on heavy quark decays and neutral meson mixing. The similar framework allows the determination of the $4\times 4$ CKM matrix elements $V_{ib'}$, $i=u$, $c$ and $t$, such that the strength of the CPV source can be evaluated unambiguously. The dimension-6 operators associated with fourth generation leptons, as implemented into the formalism for the electroweak baryogenesis in the literature, lead to the baryon-over-entropy ratio $\eta_B\approx 10^{-10}$.