Numerical Approach to Multi Dimensional Phase Transitions

We present an algorithm to analyze numerically the bounce solution of first-order phase transitions. Our approach is well suited to treat phase transitions with several fields. The algorithm consists of two parts. In the first part the bounce solution without damping is determined, in which case energy is conserved. In the second part the continuation to the physically relevant case with damping is performed. The presented approach is numerically stable and easily implemented.Comment: 18 pages, 8 figures; some comments, a reference and a table adde

Validity of the kink approximation to the tunneling action

Coleman tunneling in a general scalar potential with two non-degenerate minima is known to have an approximation in terms of a piecewise linear triangular-shaped potential with sharp 'kinks' at the place of the local minima. This approximate potential has a regime where the existence of the bounce solution needs the scalar field to 'wait' for some amount of Euclidean time at one of the 'kinks'. We discuss under which conditions a kink approximation of locally smooth 'cap' regions provides a good estimate for the bounce action.Comment: 7 pages, 4 figures, title changed in version 2 to match published versio

Gravitational Backreaction Effects on the Holographic Phase Transition

We study radion stabilization in the compact Randall-Sundrum model by introducing a bulk scalar field, as in the Goldberger and Wise mechanism, but (partially) taking into account the backreactions from the scalar field on the metric. Our generalization reconciles the radion potential found by Goldberger and Wise with the radion mass obtained with the so-called superpotential method where backreaction is fully considered. Moreover we study the holographic phase transition and its gravitational wave signals in this model. The improved control over backreactions opens up a large region in parameter space and leads, compared to former analysis, to weaker constraints on the rank N of the dual gauge theory. We conclude that, in the regime where the 1/N expansion is justified, the gravitational wave signal is detectable by LISA.Comment: 42 pages, 4 figures; v2: minor changes for the publicatio

Some Cosmological Implications of Hidden Sectors

We discuss some cosmological implications of extensions of the Standard Model with hidden sector scalars coupled to the Higgs boson. We put special emphasis on the conformal case, in which the electroweak symmetry is broken radiatively with a Higgs mass above the experimental limit. Our refined analysis of the electroweak phase transition in this kind of models strengthens the prediction of a strongly first-order phase transition as required by electroweak baryogenesis. We further study gravitational wave production and the possibility of low-scale inflation as well as a viable dark matter candidate.Comment: 23 pages, 8 figures; some comments added, published versio

Production of Gravitational Waves in the nMSSM

During a strongly first-order phase transition gravitational waves are produced by bubble collisions and turbulent plasma motion. We analyze the relevant characteristics of the electroweak phase transition in the nMSSM to determine the generated gravitational wave signal. Additionally, we comment on correlations between the production of gravitational waves and baryogenesis. We conclude that the gravitational wave relic density in this model is generically too small to be detected in the near future by the LISA experiment. We also consider the case of a "Standard Model" with dimension-six Higgs potential, which leads to a slightly stronger signal of gravitational waves.Comment: 29 pages, 7 figures; published version, some comments adde

Supersonic Electroweak Baryogenesis: Achieving Baryogenesis for Fast Bubble Walls

Standard electroweak baryogenesis in the context of a first order phase transition is effective in generating the baryon asymmetry of the universe if the broken phase bubbles expand at subsonic speed, so that CP asymmetric currents can diffuse in front of the wall. Here we present a new mechanism for electroweak baryogenesis which operates for supersonic bubble walls. It relies on the formation of small bubbles of the symmetric phase behind the bubble wall, in the broken phase, due to the heating of the plasma as the wall passes by. We apply the mechanism to a model in which the Higgs field is coupled to several singlets, and find that enough baryon asymmetry is generated for reasonable values of the parameter space

Triplet Leptogenesis in Left-Right Symmetric Seesaw Models

We discuss scalar triplet leptogenesis in a specific left-right symmetric seesaw model. We show that the Majorana phases that are present in the model can be effectively used to saturate the existing upper limit on the CP-asymmetry of the triplets. We solve the relevant Boltzmann equations and analyze the viability of triplet leptogenesis. It is known for this kind of scenario that the efficiency of leptogenesis is maximal if there exists a hierarchy between the branching ratios of the triplet decays into leptons and Higgs particles. We show that triplet leptogenesis typically favors branching ratios with not too strong hierarchies, since maximal efficiency can only be obtained at the expense of suppressed CP-asymmetries.Comment: 16 pages, 5 figures, published versio

Electroweak Baryogenesis in Non-minimal Composite Higgs Models

We address electroweak baryogenesis in the context of composite Higgs models, pointing out that modifications to the Higgs and top quark sectors can play an important role in generating the baryon asymmetry. Our main observation is that composite Higgs models that include a light, gauge singlet scalar in the spectrum [as in the model based on the symmetry breaking pattern SO(6)/SO(5)], provide all necessary ingredients for viable baryogenesis. In particular, the singlet leads to a strongly first-order electroweak phase transition and introduces new sources of CP violation in dimension-five operators involving the top quark. We discuss the amount of baryon asymmetry produced and the experimental constraints on the model.Comment: 15 pages, 7 figure

Hydrodynamic obstruction to bubble expansion

We discuss a hydrodynamic obstruction to bubble wall acceleration during a cosmological first-order phase transition. The obstruction results from the heating of the plasma in the compression wave in front of the phase transition boundary. We provide a simple criterion for the occurrence of the obstruction at subsonic bubble wall velocity in terms of the critical temperature, the phase transition temperature, and the latent heat of the model under consideration. The criterion serves as a sufficient condition of subsonic bubble wall velocities as required by electroweak baryogenesis.Comment: 18 pages, 4 figures; comments and reference added, published versio