Phenomenology of electroweak bubbles and gravity waves in the Littlest Higgs Model with T parity (original) (raw)

An efficient approach to electroweak bubble velocities

2013

Extensions of the Standard Model are being considered as viable settings for a first-order electroweak phase transition which satisfy Sakharov's three conditions for the generation of the baryon asymmetry of the Universe. These extensions provide a sufficiently strong phase transition and remove the main obstacles which appear in the context of the Standard Model: A far-too-high lower bound on the Higgs mass, immediate wipeout of the newly-created baryon asymmetry, and insufficient CP violation. We describe the Universe hydrodynamically as a fluid coupled to the Higgs field via a phenomenological friction term, and study the time evolution of bubbles nucleated during the phase transition. We express the friction term in the hydrodynamic equations in terms of the particle content of the model, calibrate the friction on the basis of existing calculations for the Standard Model, and produce predictions for the velocity of the expanding bubble wall in the stationary regime. This way we develop a very efficient approach to compute bubble velocities. As an example, we apply our formalism to the first-order phase transition of a dimension-6 extension of the Standard Model which, within the present bounds on the Higgs mass, can reproduce the observed baryon asymmetry of the Universe. Depending on the strength of the phase transition, the wall velocity varies from about 0.3 to approaching the speed of light. Our method can easily be adapted to compute wall velocities in other interesting extensions of the Standard Model.

Bubble Wall Velocity in a First Order Electroweak Phase Transition

Physical Review Letters, 1995

We calculate the velocity and thickness of a bubble wall at the electroweak phase transition in the Minimal Standard Model. We model the wall with semiclassical equations of motion and show that friction arises from the deviation of massive particle populations from thermal equilibrium. We treat these with Boltzmann equations in a fluid approximation in the background of the wall. Our analysis improves on the previous work by using the two loop effective potential, accounting for particle transport, and determining the wall thickness dynamically. We find that the wall is significantly thicker than at phase equilibrium, and that the velocity is fairly high, v w ≃ 0.7c, and quite weakly dependent on the Higgs mass.

Velocity of electroweak bubble walls

Nuclear Physics B, 2010

We study the velocity of bubble walls in the electroweak phase transition. For several extensions of the Standard Model, we estimate the friction and calculate the wall velocity, taking into account the hydrodynamics. We find that deflagrations are generally more likely than detonations. Nevertheless, for models with extra bosons, which give a strongly first-order phase transition, the deflagration velocity is in general quite high, 0.1 v w 0.6. Therefore, such phase transitions may produce an important signal of gravitational waves. On the other hand, models with extra fermions which are strongly coupled to the Higgs boson may provide a strongly first-order phase transition and small velocities, 10 −2 v w 10 −1 , as required by electroweak baryogenesis.

Gravitational waves from a very strong electroweak phase transition

We investigate the production of a stochastic background of gravitational waves in the electroweak phase transition. We consider extensions of the Standard Model which can give very strongly first-order phase transitions, such that the transition fronts either propagate as detonations or run away. To compute the bubble wall velocity, we estimate the friction with the plasma and take into account the hydro-dynamics. We track the development of the phase transition up to the percolation time, and we calculate the gravitational wave spectrum generated by bubble collisions , magnetohydrodynamic turbulence, and sound waves. For the kinds of models we consider, we find parameter regions for which the gravitational waves are potentially observable at the planned space-based interferometer eLISA. In such cases, the signal from sound waves is generally dominant, while that from bubble collisions is the least significant of them. Since the sound waves and turbulence mechanisms are diminished for runaway walls, the models with the best prospects of detection at eLISA are those which do not have such solutions. In particular, we find that heavy extra bosons provide stronger gravitational wave signals than tree-level terms.

Hydrodynamics of the electroweak phase transition

2013

This work investigates the hydrodynamics of the expansion of the bubbles of the broken symmetry phase during the electroweak phase transition in the early universe, in which SU(2) electroweak symmetry is broken and fundamental particles acquire mass through the Higgs mechanism. The electroweak phase transition has received renewed attention as a viable setting for the production of the matter-antimatter asymmetry of the universe. The relevant mechanisms are strongly dependent on key parameters like the expansion velocity of the walls of bubbles of the new phase. In addition, the key dynamical parameters of the phase transition may generate signatures (like gravitational waves) which may become detectable in the near future. This work builds on existing hydrodynamical studies of the growth of bubbles of the broken symmetry phase and adapts them to novel scenarios, producing predictions of the wall velocity. The early universe at the time of the electroweak phase transition is modelled as a perfect relativistic fluid. A fundamental problem is to account for the interaction between the so-called cosmic 'plasma' and the bubble wall, which may slow down wall propagation and produce a steady state with finite velocity. This 'friction' is accounted for by a separate term in the hydrodynamical equations. This work adapts existing microphysical calculations of the friction to two physical models chosen because of their suitability as regards producing the baryon asymmetry of the universe: 1) An extension of the Standard Model with dimension-6 operators (for which this is the first calculation of the wall velocity ever produced) and 2) The Light Stop Scenario (LSS) of the Minimal Supersymmetric Standard Model (MSSM) (for which this is the first 2-loop calculation). The predicted values of the wall velocity are coherent and consistent with previous studies, confirming, in particular, the prediction of a low wall velocity for the LSS.

Bubble Wall Velocity at the Electroweak Phase Transition

Phys Rev Lett, 1995

We calculate the velocity and thickness of a bubble wall at the electroweak phase transition in the Minimal Standard Model. We model the wall with semiclassical equations of motion and show that friction arises from the deviation of massive particle populations from thermal equilibrium. We treat these with Boltzmann equations in a fluid approximation in the background of the wall. Our analysis improves on the previous work by using the two loop effective potential, accounting for particle transport, and determining the wall thickness dynamically. We find that the wall is significantly thicker than at phase equilibrium, and that the velocity is fairly high, vwsimeq0.7cv_w \simeq 0.7cvwsimeq0.7c, and quite weakly dependent on the Higgs mass.

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

Physical Review D, 1993

Assuming that the electroweak and QCD phase transitions are first order, upon supercooling, bubbles of the new phase appear. These bubbles grow to macroscopic sizes compared to the natural scales associated with the Compton wavelengths of particle excitations. They propagate by burning the old phase into the new phase at the surface of the bubble. We study the hydrodynamic stability of the burning and find that for the velocities of interest for cosmology in the electroweak phase transition, the shape of the bubble wall is stable under hydrodynamic perturbations. Bubbles formed in the cosmological QCD phase transition are found to be a borderline case between stability and instability.

Ultra-relativistic bubbles from the simplest Higgs portal and their cosmological consequences

Journal of High Energy Physics, 2022

We analyze phase transitions in the minimal extension of the SM with a real singlet scalar field. The novelty of our study is that we identify and analyze in detail the region of parameter space where the first order phase transition can occur and in particular when the bubbles with true vacuum can reach relativistic velocities. This region is interesting since it can lead to the new recently discussed baryogenesis and Dark Matter production mechanisms. We fully analyze different models for the production of Dark Matter and baryogenesis as well as the possibilities of discovery at the current and future experiments.

Phase equilibration in bubble collisions

Physical Review D, 1995

In the context of an Abelian gauge symmetry, spontaneously broken at a first-order transition, we discuss the evolution of the phase difference between the Higgs fields in colliding bubbles. We show that the effect of dissipation, represented by a finite plasma conductivity, is to cause the phases to equlibrate on a time-scale, determined by the conductivity, which can be much smaller than the bubble radii at the time of collision. Currents induced during the phase equilibration generate a magnetic flux, which is determined by the initial phase difference. In a three-bubble collision, the fluxes produced by each pair of bubbles combine, and a vortex can be formed. We find that, under most conditions, the probability of trapping magnetic flux to form a vortex is correctly given by the "geodesic rule".