Michael Joyce

Electroweak baryogenesis from a classical force

We describe a new effect that produces baryons at a first order electroweak phase transition. It operates when there is a {ital CP}-violating field present on propagating bubble walls. The novel aspect is that it involves a purely classical force, which alters the motion of particles across the wall and through diffusion creates a chiral asymmetry in front of the wall. We develop a technique for computing the baryon asymmetry using the Boltzmann equation, and a fluid approximation which allows us to model strong scattering effects. The final formula for the baryon asymmetry has a remarkably simple form.

Nonlocal electroweak baryogenesis. II. The classical regime.

We investigate baryogenesis at a first-order electroweak phase transition in the presence of a CP-violating condensate on the bubble walls, in the regime in which the bubble walls are ``thick, in the sense that fermions interact with the plasma many times as the bubble wall passes. Such a condensate is present in multi-Higgs-doublet extensions of the standard model and may be formed via an instability in the minimal standard model. We concentrate on particles with typical thermal energies in the plasma, whose interactions with the wall are accurately described by the WKB approximation, in which a classical chiral force is evident. The deviations from thermal equilibrium produced by the motion of the wall are then treated using a classical Boltzmann equation which we solve in a fluid approximation. From the resulting equations we find two effects important for baryogenesis: (i) a classical chiral force term due to the CP-violating background and (ii) a term arising from hypercharge-violating interactions which are pushed out of equilibrium by the background field. Provided the wall propagates slower than the speed of sound, both terms lead to the diffusion of a chiral asymmetry in front of the wall. This can produce a baryon asymmetry of the observed magnitude for typical wall velocities and thicknesses. textcopyright{} 1996 The American Physical Society.

Nonlocal electroweak baryogenesis. I. Thin wall regime.

We investigate `non-local schemes for baryogenesis at a first order electroweak phase transition, in which the effects of a

Efficient electroweak baryogenesis from lepton transport

CP

Quasistationary states and the range of pair interactions.

violating condensate on the bubble wall propagate into the unbroken phase where the sphaleron rate is unsupressed. Such a condensate exists in multi-Higgs extensions of the standard model, and may exist due to an instability in the minimal standard model. In this paper we first discuss the general problem of determining the

Constraints and transport in electroweak baryogenesis

CP

Family symmetry, fermion mass matrices and cosmic texture

violating perturbations, distinguishing two regimes (quantum and classical). We then give an analytic treatment of quantum mechanical reflection in the thin wall regime, in which interactions with the plasma can be neglected as a particle propagates across the wall. We focus on leptons because of their much weaker coupling to the plasma. We argue that they are likely to be accurately described by this calculation, but quarks are not. The relative magnitude of the baryon asymmetry produced for different fermions depends on their relative Yukawa couplings ({it not} their zero temperature masses), their transport properties and their interactions. We calculate the baryon asymmetry for various parameter ranges and conclude that asymmetries comparable with observations can be generated.

Formation and relaxation of quasistationary states in particle systems with power-law interactions

Abstract One mechanism for generating a baryon asymmetry at the electroweak phase transition involves propagation of particle asymmetries generated by reflection from the bubble walls into the unbroken phase. Hitherto attention has focussed on top quarks because of their large mass and thus effective scattering from bubble walls. In this paper we point out that leptons may be more efficient mediators of this type of electroweak baryogenesis, particularly for thicker bubble walls favored by perturbative calculations. We carry out an analytic calculation of each stage of the mechanism and conclude it produces a baryon asymmetry compatible with observations for a wide range of parameters.

Attractor nonequilibrium stationary states in perturbed long-range interacting systems.

Quasistationary states are approximately time independent out of equilibrium states which have been observed in a variety of systems of particles interacting by long-range interactions. We investigate here the conditions of their occurrence for a generic pair interaction V(r→∞)~1/r(γ) with γ>0, in d>1 dimensions. We generalize analytic calculations known for gravity in d=3 to determine the scaling parametric dependences of their relaxation rates due to two-body collisions, and report extensive numerical simulations testing their validity. Our results lead to the conclusion that, for γ<d-1, the existence of quasistationary states is ensured by the large distance behavior of the interaction alone, while for γ>d-1 it is conditioned on the short distance properties of the interaction, requiring the presence of a sufficiently large soft core in the interaction potential.

Scaling quasistationary states in long-range systems with dissipation.

Abstract In unconstrained thermal equilibrium a local potential for total or fermionic hypercharge does not bias electroweak anomalous processes. We consider two proposed mechanisms for electroweak baryogenesis in this light. In “spontaneous” baryogenesis, which was argued to apply in the “adiabatic” limit of thick, slow walls, a non-zero result was obtained by setting globally conserved charges to be zero locally. We show that this is a poor approximation unless the walls are very thick (L ⪢ 100T−1). For more realistic wall thicknesses the local equilibrium approached as the wall velocity νw → 0 has zero baryon number violation and nonzero global charges on the wall. In the “charge transport” mechanism, argued to apply to the case of thin fast walls, calculations of the magnitude of the asymmetry also involve the same error. In corrected calculations the local values of global charges should be determined dynamically rather than fixed locally to zero.