Speaker
Description
The problem of Baryon Asymmetry of the Universe can be addressed through nonperturbative interactions that violate baryon ($B$) and lepton ($L$) charges. To this end, we consider the Type-I seesaw model extended by the introduction of a new coloured scalar, coupled to right-handed neutrinos and up-type quarks through a $B$-conserving interaction. The scalar is assumed to be chemically decoupled from the SM thermal bath. Accordingly, the decay channel of the RH-neutrinos produces equal and opposite sign $B$-asymmetries in the two final-state particles. The scalar B-asymmetry ($B_{s}$) remains conserved before the electroweak phase transition. On the other hand, the thermal equilibrium between up-type quarks and the electroweak sphalerons transfers this $B$-asymmetry ($B_u$) into lepton asymmetry, resulting in a net non-vanishing B-asymmetry ($B_s+B_u\neq 0$), in addition to the $B$-asymmetry from the Type-I seesaw interactions. To study this model, we describe the evolution of the lepton and baryon flavour charges by taking into account the complete SM flavours and spectator effects in a baryon- and lepton-flavour basis-invariant way. This extends the validity of the model from $T\sim10^{15}$ GeV down to the weak scale. If the scalar mass is of $\mathcal{O}$(TeV), its signatures might be observed by the LHC detectors as a long-lived particle.
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