22 research outputs found
Gravitational waves from deflagration bubbles in first-order phase transitions
The walls of bubbles in a first-order phase transition can propagate either
as detonations, with a velocity larger than the speed of sound, or
deflagrations, which are subsonic. We calculate the gravitational radiation
that is produced by turbulence during a phase transition which develops via
deflagration bubbles. We take into account the fact that a deflagration wall is
preceded by a shock front which distributes the latent heat throughout space
and influences other bubbles. We show that turbulence can induce peak values of
as high as . We discuss the possibility of
detecting at LISA gravitational waves produced in the electroweak phase
transition with wall velocities , which favor electroweak
baryogenesis.Comment: 13 pages, 1 figure; calculations of section IV repeated using recent
results for the GW spectrum from turbulence, comments added in all sections,
references added, conclusions unchange
Development of the electroweak phase transition and baryogenesis
We investigate the evolution of the electroweak phase transition, using a
one-Higgs effective potential that can be regarded as an approximation for the
Minimal Supersymmetric Standard Model. The phase transition occurs in a small
interval around a temperature T_t below the critical one. We calculate this
temperature as a function of the parameters of the potential and of a damping
coefficient related to the viscosity of the plasma. The parameters that are
relevant for baryogenesis, such as the velocity and thickness of the walls of
bubbles and the value of the Higgs field inside them, change significantly in
the range of temperatures where the first-order phase transition can occur.
However, we find that in the likely interval for T_t there is no significant
variation of these parameters. Furthermore, the temperature T_t is in general
not far below the temperature at which bubbles begin to nucleate.Comment: 26 pages, 7 figures; typos corrected, reference adde
Supercooling and phase coexistence in cosmological phase transitions
Cosmological phase transitions are predicted by Particle Physics models, and
have a variety of important cosmological consequences, which depend strongly on
the dynamics of the transition. In this work we investigate in detail the
general features of the development of a first-order phase transition. We find
thermodynamical constraints on some quantities that determine the dynamics,
namely, the latent heat, the radiation energy density and the false-vacuum
energy density. Using a simple model with a Higgs field, we study numerically
the amount and duration of supercooling and the subsequent reheating and phase
coexistence. We analyze the dependence of the dynamics on the different
parameters of the model, namely, the energy scale, the number of degrees of
freedom and the couplings of the scalar field with bosons and fermions. We also
inspect the implications for the cosmological outcomes of the phase transition.Comment: 25 pages, 10 figures. References added and minor corrections. Version
to appear in Phys. Rev.
Analytic approach to the motion of cosmological phase transition fronts
We consider the motion of planar phase-transition fronts in first-order phase
transitions of the Universe. We find the steady state wall velocity as a
function of a friction coefficient and thermodynamical parameters, taking into
account the different hydrodynamic modes of propagation. We obtain analytical
approximations for the velocity by using the thin wall approximation and the
bag equation of state. We compare our results to those of numerical
calculations and discuss the range of validity of the approximations. We
analyze the structure of the stationary solutions. Multiple solutions may exist
for a given set of parameters, even after discarding non-physical ones. We
discuss which of these will be realized in the phase transition as the
stationary wall velocity. Finally, we discuss on the saturation of the friction
at ultra-relativistic velocities and the existence of runaway solutions.Comment: 25 pages, 9 figures. The title has changed. A discussion on the
saturation of the friction and the possibility of runaway walls has been
adde
Effect of reheating on electroweak baryogenesis
The latent heat released during the expansion of bubbles in the electroweak
phase transition reheats the plasma and causes the bubble growth to slow down.
This decrease of the bubble wall velocity affects the result of electroweak
baryogenesis. Since the efficiency of baryogenesis peaks for a wall velocity
, the resulting baryon asymmetry can either be enhanced or
suppressed, depending on the initial value of the wall velocity. We calculate
the evolution of the phase transition taking into account the release of latent
heat. We find that, although in the SM the baryon production is enhanced by
this effect, in the MSSM it causes a suppression to the final baryon asymmetry.Comment: 4 pages, 3 figures. References added. Revised version to be published
in Phys.Rev.
Stability of Modified Electroweak Strings
We discuss the stability of an electroweak string with axions in its core,
which give to the configuration a quasi-topological property, and compare it
with other modifications using instantons in the thin wall approximation.Comment: Minor changes and inclusion of one figure. To be published on Z. f.
Physik C. 11 pages, 1 postcript figur
Detonations and deflagrations in cosmological phase transitions
We study the steady state motion of bubble walls in cosmological phase
transitions. Taking into account the boundary and continuity conditions for the
fluid variables, we calculate numerically the wall velocity as a function of
the nucleation temperature, the latent heat, and a friction parameter. We
determine regions in the space of these parameters in which detonations and/or
deflagrations are allowed. In order to apply the results to a physical case, we
calculate these quantities in a specific model, which consists of an extension
of the Standard Model with singlet scalar fields. We also obtain analytic
approximations for the wall velocity, both in the case of deflagrations and of
detonations.Comment: 31 pages, 14 figures. v2: several clarifications added, a change of
notation. v3: reference added. Version to appear in Nucl. Phys.
First-order cosmological phase transitions in the radiation dominated era
We consider first-order phase transitions of the Universe in the
radiation-dominated era. We argue that in general the velocity of interfaces is
non-relativistic due to the interaction with the plasma and the release of
latent heat. We study the general evolution of such slow phase transitions,
which comprise essentially a short reheating stage and a longer phase
equilibrium stage. We perform a completely analytical description of both
stages. Some rough approximations are needed for the first stage, due to the
non-trivial relations between the quantities that determine the variation of
temperature with time. The second stage, instead, is considerably simplified by
the fact that it develops at a constant temperature, close to the critical one.
Indeed, in this case the equations can be solved exactly, including
back-reaction on the expansion of the Universe. This treatment also applies to
phase transitions mediated by impurities. We also investigate the relations
between the different parameters that govern the characteristics of the phase
transition and its cosmological consequences, and discuss the dependence of
these parameters with the particle content of the theory.Comment: 38 pages, 3 figures; v2: Minor changes, references added; v3: several
typos correcte