16 research outputs found
Stability of cosmological detonation fronts
The steady state propagation of a phase transition front is classified,
according to hydrodynamics, as a deflagration or a detonation, depending on its
velocity with respect to the fluid. These propagation modes are further divided
into three types, namely, weak, Jouguet, and strong solutions, according to
their disturbance of the fluid. However, some of these hydrodynamic modes will
not be realized in a phase transition. One particular cause is the presence of
instabilities. In this work we study the linear stability of weak detonations,
which are generally believed to be stable. After discussing in detail the weak
detonation solution, we consider small perturbations of the interface and the
fluid configuration. When the balance between the driving and friction forces
is taken into account, it turns out that there are actually two different kinds
of weak detonations, which behave very differently as functions of the
parameters. We show that the branch of stronger weak detonations are unstable,
except very close to the Jouguet point, where our approach breaks down.Comment: 34 pages, 11 figures. v2: typos corrected and minor change
Stability of cosmological deflagration fronts
In a cosmological first-order phase transition, bubbles of the stable phase
nucleate and expand in the supercooled metastable phase. In many cases, the
growth of bubbles reaches a stationary state, with bubble walls propagating as
detonations or deflagrations. However, these hydrodynamical solutions may be
unstable under corrugation of the interface. Such instability may drastically
alter some of the cosmological consequences of the phase transition. Here, we
study the hydrodynamical stability of deflagration fronts. We improve upon
previous studies by making a more careful and detailed analysis. In particular,
we take into account the fact that the equation of motion for the phase
interface depends separately on the temperature and fluid velocity on each side
of the wall. Fluid variables on each side of the wall are similar for weakly
first-order phase transitions, but differ significantly for stronger phase
transitions. As a consequence, we find that, for large enough supercooling, any
subsonic wall velocity becomes unstable. Moreover, as the velocity approaches
the speed of sound, perturbations become unstable on all wavelengths. For
smaller supercooling and small wall velocities, our results agree with those of
previous works. Essentially, perturbations on large wavelengths are unstable,
unless the wall velocity is higher than a critical value. We also find a
previously unobserved range of marginally unstable wavelengths. We analyze the
dynamical relevance of the instabilities, and we estimate the characteristic
time and length scales associated to their growth. We discuss the implications
for the electroweak phase transition and its cosmological consequences.Comment: 45 pages, 13 figures. v2: Minor corrections, references added. v3:
Typos corrected, minor modifications and references added (version accepted
in PRD
Primordial magnetic fields from a non-singular bouncing cosmology
Although inflation is a natural candidate to generate the lengths of coherence of magnetic fields needed to explain current observations, it needs to break conformal invariance of electromagnetism to obtain significant magnetic amplitudes. Of the simplest realizations are the kinetically-coupled theories f^2(ϕ)FμνFμν (or IFF theories). However, these are known to suffer from electric fields backreaction or the strong coupling problem. In this work we shall confirm that such class of theories are problematic to support magnetogenesis during inflationary cosmology. On the contrary, we show that a bouncing cosmology with a contracting phase dominated by an equation of state with p>−ρ/3 can support magnetogenesis, evading the backreaction/strong-coupling problem. Finally, we study safe magnetogenesis in a particular bouncing model with an ekpyrotic-like contracting phase. In this case we found that f^2(ϕ)F^2-instabilities might arise during the final kinetic-driven expanding phase for steep ekpyrotic potentials.Fil: Membiela, Federico Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata; Argentina. Centro Brasileiro de Pesquisas Fisicas; Brasil. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales; Argentin
Bubble wall correlations in cosmological phase transitions
We study statistical relationships between bubble walls in cosmological first-order phase transitions. We consider the conditional and joint probabilities for different points on the walls to remain uncollided at given times. We use these results to discuss space and time correlations of bubble walls and their relevance for the consequences of the transition. In our statistical treatment, the kinematics of bubble nucleation and growth is characterized by the nucleation rate and the wall velocity as functions of time. We obtain general expressions in terms of these two quantities, and we consider several specific examples and applications.Fil: Megevand, Ariel Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Físicas de Mar del Plata; ArgentinaFil: Membiela, Federico Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Físicas de Mar del Plata; Argentin
Lower bound on the electroweak wall velocity from hydrodynamic instability
The subsonic expansion of bubbles in a strongly first-order electroweak phase transition is a convenient scenario for electroweak baryogenesis. For most extensions of the Standard Model, stationary subsonic solutions (i.e., deflagrations) exist for the propagation of phase transition fronts. However, deflagrations are known to be hydrodynamically unstable for wall velocities below a certain critical value. We calculate this critical velocity for several extensions of the Standard Model and compare with an estimation of the wall velocity. In general, we find a region in parameter space which gives stable deflagrations as well as favorable conditions for electroweak baryogenesis.Fil: Megevand, Ariel Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata; ArgentinaFil: Membiela, Federico Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata; ArgentinaFil: Sanchez, Alejandro Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata; Argentin
Quintessential inflation from a variable cosmological constant in a 5D vacuum
We explore an effective 4D cosmological model for the universe where the
variable cosmological constant governs its evolution and the pressure remains
negative along all the expansion. This model is introduced from a 5D vacuum
state where the (space-like) extra coordinate is considered as noncompact. The
expansion is produced by the inflaton field, which is considered as
nonminimally coupled to gravity. We conclude from experiental data that the
coupling of the inflaton with gravity should be weak, but variable in different
epochs of the evolution of the universe.Comment: final version (figure included
Inflaton and metric fluctuations in the early universe from a 5D vacuum state
In this letter we complete a previously introduced formalism to study the
gauge-invariant metric fluctuations from a noncompact Kaluza-Klein theory of
gravity, to study the evolution of the early universe. The evolution of both,
metric and inflaton field fluctuations are reciprocally related. We obtain that
<\delta\rho/\rho_b\Phi\delta\phi0.9483 < n_1 < 1$.Comment: version accepted in Phys. Lett.