Leptogenesis via Collisions: Leaking Lepton Number to the Hidden Sector

Abstract

We propose a leptobaryogenesis mechanism in which the non-zero B −L of the Universe is produced in out-of-equilibrium, lepton number and CP violating scattering processes that convert ordinary particles into particles of some hidden sector. In particular, we consider the processes lφ → l ′ φ ′ ,l ′φ′ mediated by the heavy Majorana neutrinos N of the seesaw mechanism, where l and φ are ordinary lepton and Higgs doublets and l ′ , φ ′ their hidden counterparts. Such a leptogenesis mechanism is effective even if the reheat temperature is much smaller than the heavy neutrino masses. In particular, it can be as low as 10 9 GeV. It is well known that a non-zero baryon asymmetry (BA) can be produced in the initially baryon symmetric universe if three conditions are fulfilled: B-violation, CP-violation and departure from thermal equilibrium [1]. These conditions can be satisfied in the decays of heavy particles of grand unified theories. On the other hand, the sphaleron processes, which violate B + L but conserve B − L, are effective at temperatures from about 10 12 GeV down to 100 GeV [2]. Thus, one actually needs to produce a non-zero B − L rather than just B, a fact that disfavors the simplest baryogenesis picture based on grand unification models like SU (5). When sphalerons are in equilibrium, the baryon number and B − L are related as B = a(B − L), where a is a model dependent order one coefficient [3]. Hence, in order to obtain the observed baryon to entropy density ratio B = n B /s = (0.6 − 1) × 10 −10

Light sterile neutrinos

“…However, if the sterile neutrinos are generated by active-sterile oscillations in the early Universe [256][257][258][259][260][261], they are fully thermalized well before CMB decoupling, resulting in ∆N eff 1, which is disfavored by the bound (69) 19 . This problem led several authors to propose new mechanisms that can relieve the tension: a large lepton asymmetry [259,[300][301][302][303][304][305][306][307][308][309][310], new neutrino interactions [311][312][313][314][315][316][317][318][319][320][321], entropy production after neutrino decoupling [322], neutrino decay [323], very low reheating temperature [324,325], time varying dark energy components [298], a larger cosmic expansion rate at the time of sterile neutrino production [326], inflationary freedom [327]. The authors of Refs.…”

Marriage between the baryonic and dark matters

“…Namely, the energy density transferred from ordinary to mirror sector will be crudely ρ ′ ≈ (8k 1 /g * )ρ [16]. Thus, translating this to the BBN limits, this corresponds to a contribution equivalent to an effective number of extra light neutrinos ∆N ν = 6.14x 4 ≈ k/14.…”

“…The leptogenesis scheme [16,6] which we discuss now is based on scattering processes like lφ → l ′ φ ′ mediated by heavy Majorana neutrinos N rather than on their decay N → lφ . A crucial role in our considerations is played by the reheating temperature T R , at which the inflaton decay and entropy production of the Universe is over, and after which the Universe is dominated by a relativistic plasma of ordinary particle species.…”

“…It is important to stress, that CP-asymmmetry emerges in ∆L = 1 processes as well as in ∆L = 2 processes, due to the interference between the tree-level and one-loop diagrams shown in ref. [16]. The direct calculation gives:…”

Energy dependence of direct detection cross section for asymmetric mirror dark matter

“…To understand small neutrino masses in our sector, we invoke the seesaw mechanism and add three right-handed neutrinos. A novel aspect of our model [26] is that instead of adding RH neutrinos separately to two sectors, we add a common set of three RH neutrinos that provides a second link between the two sectors [27]. Finally, we add a kinetic mixing between the U (1) bosons of the two sectors.…”