Protecting the Baryon Asymmetry in Theories with R - parity

We propose a mechanism for hiding the primordial baryon asymmetry from interactions that could wash it out. It requires the introduction of a baryon number carrying singlet which is in equilibrium in the early universe and shares any existing baryon asymmetry. It decouples from the Standard Model particles before all the interactions required to wash out the asymmetry are in equilibrium (T ' 10 TeV), and decays after the elec-troweak phase transition, but before nucleosynthesis. This mechanism can conserve a baryon asymmetry in models (a) with B ? L = 0, such as many SU(5) GUTs, or (b) with B ? L violating interactions in thermal equilibrium, such as SUSY with broken R-parity. As a result, cosmological constraints on R-parity violating operators are relaxed considerably. Making the observed baryon asymmetry of the universe (BAU) 1, 2, 3] in supersymmetric theories 4] with R-parity violation 5, 6] can be a challenging task. The diiculty is that such theories contain B ? L violating interactions which are naturally in thermal equilibrium above the electroweak phase transition, in conjunction with the anomalous 7] B + L violating Standard Model processes. Together, these interactions can wash out any BAU present in the early universe 8, 9]. The Hubble expansion rate at T ' 100 GeV is then so much smaller than particle interaction rates, that it is diicult (but not impossible 10]) to nd enough perturbative out-of-equilibrium dynamics to (re)generate an asymmetry. Since Supersymmetric theories with R-parity violation have recently attracted attention 5, 6], it is of interest to consider how this problem can be avoided. One way around it is to create the asymmetry at 3] or after the electroweak phase transition 3, 10]. In this letter, we follow a second approach, which is to assume the asymmetry is generated earlier, but protected by an approximate symmetry. We hide the primordial BAU in a pair of SU(3)SU(2)U(1) singlets, S and S, with unit baryon number (B = 1) during the critical period (ie. the time when all interactions required to washed out any BAU are in thermal equilibrium). As S and S decay the BAU will be transferred back to the Standard Model quarks.