95 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
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
Effective potential at finite temperature in a constant hypermagnetic field: Ring diagrams in the Standard Model
We study the symmetry breaking phenomenon in the standard model during the
electroweak phase transition in the presence of a constant hypermagnetic field.
We compute the finite temperature effective potential up to the contribution of
ring diagrams in the weak field, high temperature limit and show that under
these conditions, the phase transition becomes stronger first order.Comment: 15 pages, 8 Postscript figure
Schwarzschild black holes can wear scalar wigs
We study the evolution of a massive scalar field surrounding a Schwarzschild
black hole and find configurations that can survive for arbitrarily long times,
provided the black hole or the scalar field mass is small enough. In
particular, both ultra-light scalar field dark matter around supermassive black
holes and axion-like scalar fields around primordial black holes can survive
for cosmological times. Moreover, these results are quite generic, in the sense
that fairly arbitrary initial data evolves, at late times, as a combination of
those long-lived configurations.Comment: 5 pages, 3 figures. Accepted for publication in Physical Review
Letter
The HARPS search for southern extra-solar planets I. HD330075 b: a new 'hot Jupiter'
We report on the first extra-solar planet discovered with the brand new HARPS
instrument. The planet is a typical 'hot Jupiter' with m2sini = 0.62 MJup and
an orbital period of 3.39 days, but from the photometric follow-up of its
parent star HD330075 we can exclude the presence of a transit. The induced
radial-velocity variations exceed 100 m/s in semi-amplitude and are easily
detected by state-of-the-art spectro-velocimeters. Nevertheless, the faint
magnitude of the parent star (V = 9.36) benefits from the efficient instrument:
With HARPS less than 10 observing nights and 3 hours of total integration time
were needed to discover the planet and characterize its orbit. The orbital
parameters determined from the observations made during the first HARPS run in
July 2003 have been confirmed by 7 additional observations carried out in
February 2004. The bisector analysis and a photometric follow-up give no hint
for activity-induced radial-velocity variations, indicating that the velocity
curve is best explained by the presence of a low-mass companion to the star. In
this paper we present a set of 21 measurements of excellent quality with
weighted rms as low as 2.0 m/s. These measurements lead to a well defined orbit
and consequently to the precise orbital parameters determination of the
extra-solar planet HD330075b.Comment: 5 pages, 2 figures, accepted for publication by Astronomy and
Astrophysics, see also http://obswww.unige.ch/~udry/planet/planet.htm
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.
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.
Fermion scattering off electroweak phase transition kink walls with hypermagnetic fields
We study the scattering of fermions off a finite width kink wall during the
electroweak phase transition in the presence of a background hypermagnetic
field. We derive and solve the Dirac equation for such fermions and compute the
reflection and transmission coefficients for the case when the fermions move
from the symmetric to the broken symmetry phase. We show that the chiral nature
of the fermion coupling with the background field in the symmetric phase
generates an axial asymmetry in the scattering processes. We discuss possible
implications of such axial charge segregation for baryon number generation.Comment: 9 pages, 3 Postscript figures, uses RevTeX4. Expanded discussion,
published versio
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