Patrick Huet

Large and Small Radius in String Theory

We consider a number of problems associated with the moduli spaces of classical solutions of string theory. In the case of the bosonic and heterotic theories, we show that duality transformations are often gauge transformations. This has implications both for our understanding of these theories and also for physical problems such as domain walls. As a byproduct we show that the four known Type II theories correspond to different ground states of the same theory. We also consider the dependence of the metric of the moduli space of (2,2) theories on the radius of the target manifold. While perturbatively the metric is independent of the radius it is modified by world sheet instantons.

Towards the theory of the electroweak phase transition

We investigate various problems related to the theory of the electroweak phase transition. This includes determination of the nature of the phase transition, discussion of the possible role of the higher-order radiative corrections, and the theory of the formation and evolution of bubbles of the new phase. We show, in particular, that no dangerous linear terms in the scalar field

Electroweak baryogenesis and standard model CP violation

\ensuremath{\varphi}

Creating the baryon asymmetry at the electroweak phase transition

appear in the expression for the effective potential. We have found that, for the Higgs-boson mass smaller than the masses of

Violation of CPT and quantum mechanics in the K0−k0 system

W

Comments on the electroweak phase transition

and

Baryogenesis at the electroweak scale

Z

Hydrodynamic stability analysis of burning bubbles in electroweak theory and in QCD

bosons, the phase transition is of the first order. However, its strength is approximately ⅔ times less than what follows from the one-loop approximation. The phase transition occurs due to production and expansion of critical bubbles. Subcritical bubbles may be important only if the phase transition is very weakly first order. A general analytic expression for the probability of the bubble formation is obtained, which may be used for study of tunneling in a wide class of theories. The bubble-wall velocity depends on many factors, including the ratio of the mean free path of the particles to the thickness of the wall. Thin walls in the electroweak theory have a nonrelativistic velocity, whereas thick walls may be relativistic. A decrease of the cubic term by the factor ⅔ rules out baryogenesis in the minimal version of the electroweak theory. Even though we concentrate in this paper on the phase transition in this theory, most of our results can be applied to more general models as well, where baryogenesis is possible.

Massless fractionally charged states and Gepner compactification

We analyze the mechanism of electroweak baryogenesis proposed by Farrar and Shaposhnikov in which the phase of the CKM mixing matrix is the only source of [ital CP] violation. This mechanism is based on a phase separation of baryons via the scattering of quasiparticles by the wall of an expanding bubble produced at the electroweak phase transition. In agreement with the recent work of Gavela, Hernandez, Orloff, and Pene, we conclude the QCD damping effects reduce the asymmetry produced to a negligible amount. We interpret the damping as quantum decoherence. We compute the asymmetry analytically. Our analysis reflects the observation that only a thin, outer layer of the bubble contributes to the coherent scattering of the quasiparticles. The generality of our arguments rules out any mechanism of electroweak baryogenesis that does not make use of a new source of [ital CP] violation.

Electroweak baryogenesis and the standard model

At temperatures above the weak phase transition, baryon and lepton number are badly violated. We explore the suggestion that the baryon asymmetry might be produced at the transition, if the transitionis first order. We find that the asymmetry is proportional to a CP violating parameter, a large power of the gauge coupling and to factors which depend on the details of the transition. In extensions of the standard model, such as multi-Higgs or supersymmetric models, the result may be consistent with observations.