Asymmetric dark matter and Baryon asymmetry of the Universe

Abstract

One of the most popular beyond Standard Model (SM) scenarios to explain the hierarchy in fermion masses and mixings is through the introduction of scalar flavons and an Abelian UFN horizontal symmetry. The flavon field can coherently oscillate around its zero temperature minimum due to the thermal corrections to its potential or if soft symmetry-breaking terms are introduced. Out-of-equilibrium decays of these scalars into SM particles in the early universe can potentially lead to the baryon asymmetry (BA). Moreover, owing to the asymmetric dark matter paradigm, flavons decaying into dark particles may set the correct dark matter (DM) abundance. We investigate whether the decays of flavons can simultaneously generate the observed baryon and dark matter abundance of the universe. We extend the SM by a scalar flavon and two fermions representing the dark sector. A Z2 symmetry is introduced in addition to the horizontal UFN symmetry. Since the flavon decay produces entropy, the number density of flavon drops with increasing flavon mass (mσ). We exclude the possibility of higher flavon mass for the successful generation of BA. Also, the bounds from flavor changing neutral current (FCNC) processes suggest a typical limit √ mσΛ > few TeV where Λ is the flavon scale. Even if the flavon scale is too large making the collider experiment irrelevant, a very small mσ decreases the flavon decay width (ΓS ∼ mσ 3 ) causing late decays of flavon which can destroy the BBN predictions. Hence mσ ∼ 1 TeV is a favourable choice for this benchmark model. The relatively long-lived flavon dominates the energy density of the universe while decaying into SM and DM particles. The baryon asymmetry is produced via a mechanism similar to the Dirac leptogenesis from an initial flavon asymmetry which is generated from coherent oscillations of the flavon. The small decay width leads to the decoupling of the LR and DM asymmetry yield equations. We will further study the BEs in order to estimate the asymmetries and get bounds on the decay rates and masses of the DM contents.