Antonio Riotto

Spontaneous CP violation and baryogenesis in the minimal supersymmetric standard model

We investigate the effects of the spontaneous CP violation at finite temperature in the Minimal Supersymmetric Standard Model on the baryogenesis at the weak scale. After a brief discussion of the case in which the electroweak phase transition is of second order, we study in details the baryogenesis scenario when the transition proceeds via bubble nucleation. We show that the space-time dependent phase for the Higgs vacuum expectation values coming from the spontaneous CP violation can give rise to an efficient generation of baryon number inside the bubble walls if the superpotential parameters and the soft supersymmetry breaking ones are complex. However we find that in order to get the observed value for the baryon asymmetry of the universe the phases of such parameters can be as small as 10−5, giving rise to an electron dipole moment of the neutron well below the current experimental limit. A light Higgs pseudoscalar is needed, and an upper bound on its mass is obtained. Moreover, the condition tan β ⪆ 7 has to be satisfied.

The supersymmetric singlet majoron

Abstract We study the supersymmetrized version of the singlet majoron model and, performing an analysis of the renormalization-group improved potential, we find that a spontaneous breaking of R -parity can be achieved for a wide range of the parameters. Studying the finite-temperature effective potential, we show that the phase transition leading to R -parity breaking can be of the first order and can occur at temperatures below the weak scale, thus avoidimg any constraint coming from the requirement of the preservation of the baryon asymmetry in the early universe.

Towards a nonequilibrium quantum field theory approach to electroweak baryogenesis

We propose a general method to compute {ital CP} violating observables from extensions of the standard model in the context of electroweak baryogenesis. It is an alternative to the one recently developed by Huet and Nelson and relies on a nonequilibrium quantum field theory approach. The method is valid for all shapes and sizes of the bubble wall expanding in the thermal bath during a first-order electroweak phase transition. The quantum physics of {ital CP} violation and its suppression coming from the incoherent nature of thermal processes are also made explicit. {copyright} {ital 1996 The American Physical Society.}

Cosmic ΔB from lepton violating interactions at the electroweak phase transition

Abstract We propose a new mechanism for late cosmological baryon asymmetry in models with first order electroweak phase transition. Lepton asymmetry arises through the decay of particles produced out of equilibrium in bubble collision and is converted into baryon asymmetry by sphalerons. Supersymmetric models with explicitly broken R -parity may provide a suitable framework for the implementation of this mechanism.

Spontaneous breaking of R parity in the minimal supersymmetric standard model revisited

Abstract We reconsider the possibility of spontaneous breaking of R parity in the minimal supersymmetric standard model. By a renormalization group analysis we find the parameter space in which a sneutrino gets a vacuum expectation value, leading to the spontaneous breaking of the lepton number and to the appearance of a phenomenologically unacceptable massless Goldstone boson. We then analyze the effect of operators giving rise to a tiny amount of explicit violation of lepton number, which could emerge as remnants of physics at some superheavy (Planck or GUT) scale in the low energy effective theory. We show that the conspiracy between the spontaneous and the explicit breaking scales can provide a mass to the Goldstone boson larger than the Z 0 boson mass, hence allowing for a non vanishing sneutrino vacuum expectation value without increasing the invisible width of the Z 0 .

Particle currents on a CP violating Higgs background and the spontaneous baryogenesis mechanism

Abstract We compute the particle currents induced on a bubble wall background at finite temperature in a model with CP violation in the Higgs sector. Using a field theory approach we show that fermionic currents arise at one loop, so that a suppression factor O( h t Φ πT ) 2 with respect to previous computations is found. The contributions to the Higgs currents are also derived and their relevancy for the spontaneous baryogenesis mechanism is discussed.

Singlet Majoron model with hidden scale invariance

We investigate an extension of the singlet Majoron model in which the breaking of dilatation symmetry by the mass parameters of the scalar potential is removed by means of a dilation field. Starting from the one-loop renormalization group improved potential, we discuss the ground state of the theory. The flat direction in the classical potential is lifted by quantum corrections and the true vacua are found. Studying the finite temperature potential, we analyze the cosmological consequences of a Jordan-Brans-Dicke dilaton and show that the lepton number is spontaneously broken after the electroweak phase transition, thus avoiding any constraint coming from the requirement of the preservation of the baryon asymmetry in the early Universe. We also find that, contrary to the standard model case, the dilaton and/or neutrino cosmology do not impose any upper bound on the scale of the spontaneous breaking of scale invariance if the

Baryogenesis through collapsing string loops in gauged baryon and lepton models

ensuremath{tau}

Baryogenesis, domain walls and the role of gravity

neutrino is sufficiently heavy.

Oscillons are not present during a first order electroweak phase transition

A scenario for the generation of the baryon asymmetry in the early Universe is proposed in which cosmic string loops, predicted by theories where the baryon and/or lepton numbers are gauged symmetries, collapse during the friction-dominated period of string evolution. This provides a mechanism for the departure from thermal equilibrium necessary to have a nonvanishing baryon asymmetry. Examples of models are given where this idea can be implemented. In particular, the model with the gauge symmetry SU(3)[sub [ital c]][direct product]SU(2)[sub [ital L]][direct product]U(1)[sub [ital Y]][direct product]U(1)[sub [ital B]][direct product]U(1)[sub [ital L]] has the interesting feature where sphaleron processes do not violate the baryon and lepton numbers so that no washout of any initial baryon asymmetry occurs at the electroweak scale.