19,275 research outputs found
Corrugation of relativistic magnetized shock waves
As a shock front interacts with turbulence, it develops corrugation which
induces outgoing wave modes in the downstream plasma. For a fast shock wave,
the incoming wave modes can either be fast magnetosonic waves originating from
downstream, outrunning the shock, or eigenmodes of the upstream plasma drifting
through the shock. Using linear perturbation theory in relativistic MHD, this
paper provides a general analysis of the corrugation of relativistic magnetized
fast shock waves resulting from their interaction with small amplitude
disturbances. Transfer functions characterizing the linear response for each of
the outgoing modes are calculated as a function of the magnetization of the
upstream medium and as a function of the nature of the incoming wave.
Interestingly, if the latter is an eigenmode of the upstream plasma, we find
that there exists a resonance at which the (linear) response of the shock
becomes large or even diverges. This result may have profound consequences on
the phenomenology of astrophysical relativistic magnetized shock waves.Comment: 14 pages, 9 figures; to appear in Ap
Inverse Symmetry Breaking in Multi-Scalar Field Theories
We review how the phenomena of inverse symmetry breaking (and symmetry
nonrestoration) may arise in the context of relativistic as well as
nonrelativistic multi-scalar field theories. We discuss how the consideration
of thermal effects on the couplings produce different transition patterns for
both theories. For the relativistic case, these effects allow the appearance of
inverse symmetry breaking (and symmetry nonrestoration) at arbitrarily large
temperatures. On the other hand, the same phenomena are suppressed in the
nonrelativistic case, which is relevant for condensed matter physics. In this
case, symmetry nonrestoration does not happen while inverse symmetry is allowed
only to be followed by symmetry restoration characterizing a reentrant phase.
The aim of this paper is to give more insight concerning the, qualitatively
correct, results obtained by using one loop perturbation theory in the
evaluation of thermal masses and couplings.Comment: 7 pages, 3 figures, talk given at the workshop on Quantum Fields
Under the Influence of External Conditions, QFEXT05, Barcelona, sep-200
Symmetry Aspects in Nonrelativistic Multi-Scalar Field Models and Application to a Coupled Two-Species Dilute Bose Gas
We discuss unusual aspects of symmetry that can happen due to entropic
effects in the context of multi-scalar field theories at finite temperature. We
present their consequences, in special, for the case of nonrelativistic models
of hard core spheres. We show that for nonrelativistic models phenomena like
inverse symmetry breaking and symmetry non-restoration cannot take place, but a
reentrant phase at high temperatures is shown to be possible for some region of
parameters. We then develop a model of interest in studies of Bose-Einstein
condensation in dilute atomic gases and discuss about its phase transition
patterns. In this application to a Bose-Einstein condensation model, however,
no reentrant phases are found.Comment: 8 pages, 1 eps figure, IOP style. Based on a talk given by R. O.
Ramos at the QFEXT05 workshop, Barcelona, Spain, September 5-9, 2005. One
reference was update
Nonequilibrium Precursor Model for the Onset of Percolation in a Two-Phase System
Using a Boltzmann equation, we investigate the nonequilibrium dynamics of
nonperturbative fluctuations within the context of Ginzburg-Landau models. As
an illustration, we examine how a two-phase system initially prepared in a
homogeneous, low-temperature phase becomes populated by precursors of the
opposite phase as the temperature is increased. We compute the critical value
of the order parameter for the onset of percolation, which signals the
breakdown of the conventional dilute gas approximation.Comment: 4 pages, 4 eps figures (uses epsf), Revtex. Replaced with version in
press Physical Review
VISIR-VLT high resolution study of the extended emission of four obscured post-AGB candidates
The onset of the asymmetry of planetary nebulae (PNe) is expected to occur
during the late Asymptotic Giant Branch (AGB) and early post-AGB phases of low-
and intermediate-mass stars. Among all post-AGB objects, the most heavily
obscured ones might have escaped the selection criteria of previous studies
detecting extreme axysimmetric structures in young PNe. Since the most heavily
obscured post-AGB sources can be expected to descend from the most massive PN
progenitors, these should exhibit clear asymmetric morphologies. We have
obtained VISIR-VLT mid-IR images of four heavily obscured post-AGB objects
barely resolved in previous Spitzer IRAC observations to analyze their
morphology and physical conditions across the mid-IR. The VISIR-VLT images have
been deconvolved, flux calibrated, and used to construct RGB composite pictures
as well as color and optical depth maps that allow us to study the morphology
and physical properties of the extended emission of these sources. We have
detected extended emission from the four objects in our sample and resolved it
into several structural components that are greatly enhanced in the temperature
and optical depth maps. They reveal the presence of asymmetry in three young
PNe (IRAS 15534-5422, IRAS 17009-4154, and IRAS 18454+0001), where the
asymmetries can be associated with dusty torii and slightly bipolar outflows.
The fourth source (IRAS 18229-1127), a possible post-AGB star, is better
described as a rhomboidal detached shell. The heavily obscured sources in our
sample do not show extreme axisymmetric morphologies. This is at odds with the
expectation of highly asymmetrical morphologies in post-AGB sources descending
from massive PN progenitors. The sources presented in this paper may be
sampling critical early phases in the evolution of massive PN progenitors,
before extreme asymmetries develop.Comment: 9 pages, 4 figure
Local Approximations for Effective Scalar Field Equations of Motion
Fluctuation and dissipation dynamics is examined at all temperature ranges
for the general case of a background time evolving scalar field coupled to
heavy intermediate quantum fields which in turn are coupled to light quantum
fields. The evolution of the background field induces particle production from
the light fields through the action of the intermediate catalyzing heavy
fields. Such field configurations are generically present in most particle
physics models, including Grand Unified and Supersymmetry theories, with
application of this mechanism possible in inflation, heavy ion collision and
phase transition dynamics. The effective evolution equation for the background
field is obtained and a fluctuation-dissipation theorem is derived for this
system. The effective evolution in general is nonlocal in time. Appropriate
conditions are found for when these time nonlocal effects can be approximated
by local terms. Here careful distinction is made between a local expansion and
the special case of a derivative expansion to all orders, which requires
analytic behavior of the evolution equation in Fourier space.Comment: 14 pages, 2 figures. Replaced with published version. Some extra
typos correcte
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