42 research outputs found
Enhanced roughness of lipid membranes caused by external electric fields
The behavior of lipid membranes in the presence of an external electric field
is studied and used to examine the influence of such fields on membrane
parameters such as roughness and show that for a micro sized membrane,
roughness grows as the field increases. The dependence of bending rigidity on
the electric field is also studied and an estimation of thickness of the
accumulated charges around lipid membranes in a free-salt solution is
presented.Comment: 9 pages, 6 figures, to appear in Computational Materials Scienc
Phase Transitions of Charged Scalars at Finite Temperature and Chemical Potential
We calculate the grand canonical partition function at the one-loop level for
scalar quantum electrodynamics at finite temperature and chemical potential. A
classical background charge density with a charge opposite that of the scalars
ensures the neutrality of the system. For low density systems we find evidence
of a first order phase transition. We find upper and lower bounds on the
transition temperature below which the charged scalars form a condensate. A
first order phase transition may have consequences for helium-core white dwarf
stars in which it has been argued that such a condensate of charged helium-4
nuclei could exist.Comment: 20 pages, 3 figures. Version accepted for publication in JHE
Thermal Activation Rates in the Chirally Asymmetric Gross-Neveu Model
We address the problem of how to incorporate quantum effects into the
calculation of finite-temperature decay rates for a metastable state of a
quantum field theory. To do this, we consider the Gross-Neveu model with an
explicit chiral symmetry breaking term, which allows for a metastable state.
This theory can be shown to have a "critical bubble" which is a solution to the
*exact* equations of motions (i.e. to all orders in perturbation theory,
including all higher derivative, quantum and thermal corrections). This
configuration mediates the thermal activation of the metastable vacuum to the
true ground state, with a decay rate , where
is the free energy of the critical bubble. We then compare this exact
calculation to various approximations that have been used in previous work. We
find that these approximations all *overestimate* the activation rate.
Furthermore, we study the effect of finite baryon number upon the bubble
profile and the activation barriers. We find that beyond a critical baryon
number the activation barriers disappear altogether.Comment: 20 pages, LaTeX, 9 figures using epsf.tex. Now auto-generates P
Physics of Neutron Star Crusts
The physics of neutron star crusts is vast, involving many different research
fields, from nuclear and condensed matter physics to general relativity. This
review summarizes the progress, which has been achieved over the last few
years, in modeling neutron star crusts, both at the microscopic and macroscopic
levels. The confrontation of these theoretical models with observations is also
briefly discussed.Comment: 182 pages, published version available at
<http://www.livingreviews.org/lrr-2008-10
Pulsating White Dwarf Stars and Precision Asteroseismology
Galactic history is written in the white dwarf stars. Their surface
properties hint at interiors composed of matter under extreme conditions. In
the forty years since their discovery, pulsating white dwarf stars have moved
from side-show curiosities to center stage as important tools for unraveling
the deep mysteries of the Universe. Innovative observational techniques and
theoretical modeling tools have breathed life into precision asteroseismology.
We are just learning to use this powerful tool, confronting theoretical models
with observed frequencies and their time rate-of-change. With this tool, we
calibrate white dwarf cosmochronology; we explore equations of state; we
measure stellar masses, rotation rates, and nuclear reaction rates; we explore
the physics of interior crystallization; we study the structure of the
progenitors of Type Ia supernovae, and we test models of dark matter. The white
dwarf pulsations are at once the heartbeat of galactic history and a window
into unexplored and exotic physics.Comment: 70 pages, 11 figures, to be published in Annual Review of Astronomy
and Astrophysics 200
Cosmic Structure Formation with Topological Defects
Topological defects are ubiquitous in physics. Whenever a symmetry breaking
phase transition occurs, topological defects may form. The best known examples
are vortex lines in type II super conductors or in liquid Helium, and
declination lines in liquid crystals. In an adiabatically expanding universe
which cools down from a very hot initial state, it is quite natural to
postulate that topological defects may have emerged during a phase transition
in the early universe and that they may have played the role of initial
inhomogeneities seeding the formation of cosmic structure. This basic idea goes
back to Kibble (1976). In this report we summarize the progress made in the
investigation of Kibble's idea during the last 25 years. Our understanding of
the formation and evolution of topological defects is reported almost
completely in the beautiful book by Vilenkin & Shellard or the excellent Review
by Hindmarsh & Kibble, and we shall hence be rather short on that topic.
Nevertheless, in order to be self contained, we have included a short chapter
on spontaneous symmetry breaking and defect formation. Our main topic is
however the calculation of structure formation with defects, results which are
not included in the above references.Comment: Review for Physics Reports, 133 pages 29 figures. Updated to match
published version. Better quality and color figures are available at
http://mpej.unige.ch/~durre