Baryogenesis and dark matter with vector-like fermions

Abstract

We show that vector-like fermions can act as the dark matter candidate in the universe whilst also playing a crucial role in electroweak baryogenesis through contributing to the barrier in the one-loop thermal scalar potential. In order for the new fermions to give rise to a strong first order phase transition, we show that one requires rather large Yukawa couplings in the new sector, which are strongly constrained by electroweak precision tests and perturbativity. Strong couplings between the dark matter candidate and the Higgs boson intuitively lead to small values of the relic density and problems with dark matter direct detection bounds. Nevertheless, when considering the most general realisation of the model, we find regions in the parameter space that respect all current constraints and may explain both mysteries simultaneously.

Survey of vector-like fermion extensions of the Standard Model and their phenomenological implications

“…Refs. [35,36] considers a vector-like lepton generation (including new SU(2) singlets) and the possibility of the electromagnetic charge neutral vector-like lepton being a dark matter candidate. They analyze precision electroweak bounds, modifications to Higgs observables and vacuum stability bounds for this extension.…”

Theories relating baryon asymmetry and dark matter

“…The same applies for inert higgs extensions of the SM [13] (higher SU(2) representations were considered in [14,15]). However, models with vector-like fermions are able to produce the total DM density and BAU for a wide range of masses [16]. An even more extended higgs sector, say a 2-higgs-doublet model improves further the prospects of this scenario by providing the needed CP phases [17,18].…”

The minimal fermionic model of electroweak baryogenesis

“…With the exception of the fermionic models presented in [9][10][11][12] and models with dynamical Yukawa couplings [13][14][15][16][17], the literature has overwhelmingly concentrated in coupling new scalars to the Higgs in order to induce the strong first order phase transition, mostly because the barrier may be generated with a negative Higgs quartic stabilized by a threshold (H † H) 3 term as in [18], which at tree level may only be generated by integrating out heavy scalars, or because in a large temperature expansion of the Higgs effective potential, scalars contribute to a negative cubic term which induces a barrier, while fermions do not [2]. For a classification of the extensive literature on scalar models see [19].…”

“…Up to one-loop, the effective potential is determined by the tree level potential (2.2), plus a zero-temperature and a finite temperature 1-loop contribution. The zero-temperature one-loop contribution is given by 12) JHEP12 (2017)064 where µ is the renormalization scale, all couplings must be interpreted as effective couplings at that scale, and a is an index that runs over all boson and fermion fields obtaining mass from the Higgs mechanism. ξ = 1 for fermions, ξ = 0 for bosons.…”