68 research outputs found
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
Field Theory for a Deuteron Quantum Liquid
Based on general symmetry principles we study an effective Lagrangian for a
neutral system of condensed spin-1 deuteron nuclei and electrons, at
greater-than-atomic but less-than-nuclear densities. We expect such matter to
be present in thin layers within certain low-mass brown dwarfs. It may also be
produced in future shock-wave-compression experiments as an effective fuel for
laser induced nuclear fusion. We find a background solution of the effective
theory describing a net spin zero condensate of deuterons with their spins
aligned and anti-aligned in a certain spontaneously emerged preferred
direction. The spectrum of low energy collective excitations contains two spin
waves with linear dispersions -- like in antiferromagnets -- as well as gapped
longitudinal and transverse modes related to the Meissner effect -- like in
superconductors. We show that counting of the Nambu-Goldstone modes of
spontaneously broken internal and space-time symmetries obeys, in a nontrivial
way, the rules of the Goldstone theorem for Lorentz non-invariant systems. We
discuss thermodynamic properties of the condensate, and its potential
manifestation in the low-mass brown dwarfs.Comment: 19 LaTeX pages; v2: 2 refs added, JHEP versio
Energy input and response from prompt and early optical afterglow emission in gamma-ray bursts
The taxonomy of optical emission detected during the critical first few
minutes after the onset of a gamma-ray burst (GRB) defines two broad classes:
prompt optical emission correlated with prompt gamma-ray emission, and early
optical afterglow emission uncorrelated with the gamma-ray emission. The
standard theoretical interpretation attributes prompt emission to internal
shocks in the ultra-relativistic outflow generated by the internal engine;
early afterglow emission is attributed to shocks generated by interaction with
the surrounding medium. Here we report on observations of a bright GRB that,
for the first time, clearly show the temporal relationship and relative
strength of the two optical components. The observations indicate that early
afterglow emission can be understood as reverberation of the energy input
measured by prompt emission. Measurements of the early afterglow reverberations
therefore probe the structure of the environment around the burst, whereas the
subsequent response to late-time impulsive energy releases reveals how earlier
flaring episodes have altered the jet and environment parameters. Many GRBs are
generated by the death of massive stars that were born and died before the
Universe was ten per cent of its current age, so GRB afterglow reverberations
provide clues about the environments around some of the first stars.Comment: 13 pages, 4 figures, 1 table. Note: This paper has been accepted for
publication in Nature, but is embargoed for discussion in the popular press
until formal publication in Natur
The optical counterpart to gamma-ray burst GRB970228 observed using the Hubble Space Telescope
Although more than 2,000 astronomical gamma-ray bursts (GRBs) have been
detected, and numerous models proposed to explain their occurrence, they have
remained enigmatic owing to the lack of an obvious counterpart at other
wavelengths. The recent ground-based detection of a transient source in the
vicinity of GRB 970228 may therefore have provided a breakthrough. The optical
counterpart appears to be embedded in an extended source which, if a galaxy as
has been suggested, would lend weight to those models that place GRBs at
cosmological distances. Here we report the observations using the Hubble Space
Telescope of the transient counterpart and extended source 26 and 39 days after
the initial gamma-ray outburst. We find that the counterpart has faded since
the initial detection (and continues to fade), but the extended source exhibits
no significant change in brightness between the two dates of observations
reported here. The size and apparent constancy between the two epochs of HST
observations imply that it is extragalactic, but its faintness makes a
definitive statement about its nature difficult. Nevertheless, the decay
profile of the transient source is consistent with a popular impulsive-fireball
model, which assumes a merger between two neutron stars in a distant galaxy.Comment: 11 pages + 2 figures. To appear in Nature (29 May 1997 issue
An apparently normal gamma-ray burst with an unusually low luminosity
Much of progress in gamma-ray bursts has come from the studies of distant
events (redshift z~1). The brightest GRBs are the most collimated events and
seen across the Universe due to their brilliance. It has long been suspected
that nearest (and most common) events have been missed because they are not so
collimated or under-energetic or both. Here we report soft gamma-ray
observations of GRB 031203, the nearest event to date (z=0.106). This event
with a duration of 40 s and peak energy of >190 keV appears to be a typical
long duration GRB. However, the isotropic gamma-ray energy <~10^50 erg, about
three orders of magnitude smaller than the cosmological population. This event
as well as the other nearby but somewhat controversial event GRB 980425 are
clear outliers for the much discussed isotropic-energy peak-energy relation and
luminosity spectral-lag relations. Radio calorimetry shows that both these
events are under-energetic explosions. We conclude that there does indeed exist
a large population of under-energetic events.Comment: 11 pages, 3 figure
Interpretation of Binary Pulsar Observations
The nature, dynamics and evolution of the three known radio pulsar binaries are discussed. The system containing 1913+16 appears to comprise two ~1.4 M⊙ components, and to undergo orbital decay as predicted by general relativity. It is proposed that 1913+16 has a neutron star companion and that 0655+64 and 0820+02 have white dwarf companions which should be observable optically
The Formation and Evolution of the First Massive Black Holes
The first massive astrophysical black holes likely formed at high redshifts
(z>10) at the centers of low mass (~10^6 Msun) dark matter concentrations.
These black holes grow by mergers and gas accretion, evolve into the population
of bright quasars observed at lower redshifts, and eventually leave the
supermassive black hole remnants that are ubiquitous at the centers of galaxies
in the nearby universe. The astrophysical processes responsible for the
formation of the earliest seed black holes are poorly understood. The purpose
of this review is threefold: (1) to describe theoretical expectations for the
formation and growth of the earliest black holes within the general paradigm of
hierarchical cold dark matter cosmologies, (2) to summarize several relevant
recent observations that have implications for the formation of the earliest
black holes, and (3) to look into the future and assess the power of
forthcoming observations to probe the physics of the first active galactic
nuclei.Comment: 39 pages, review for "Supermassive Black Holes in the Distant
Universe", Ed. A. J. Barger, Kluwer Academic Publisher
The Formation of the First Massive Black Holes
Supermassive black holes (SMBHs) are common in local galactic nuclei, and
SMBHs as massive as several billion solar masses already exist at redshift z=6.
These earliest SMBHs may grow by the combination of radiation-pressure-limited
accretion and mergers of stellar-mass seed BHs, left behind by the first
generation of metal-free stars, or may be formed by more rapid direct collapse
of gas in rare special environments where dense gas can accumulate without
first fragmenting into stars. This chapter offers a review of these two
competing scenarios, as well as some more exotic alternative ideas. It also
briefly discusses how the different models may be distinguished in the future
by observations with JWST, (e)LISA and other instruments.Comment: 47 pages with 306 references; this review is a chapter in "The First
Galaxies - Theoretical Predictions and Observational Clues", Springer
Astrophysics and Space Science Library, Eds. T. Wiklind, V. Bromm & B.
Mobasher, in pres
Evolutionary and pulsational properties of white dwarf stars
Abridged. White dwarf stars are the final evolutionary stage of the vast
majority of stars, including our Sun. The study of white dwarfs has potential
applications to different fields of astrophysics. In particular, they can be
used as independent reliable cosmic clocks, and can also provide valuable
information about the fundamental parameters of a wide variety of stellar
populations, like our Galaxy and open and globular clusters. In addition, the
high densities and temperatures characterizing white dwarfs allow to use these
stars as cosmic laboratories for studying physical processes under extreme
conditions that cannot be achieved in terrestrial laboratories. They can be
used to constrain fundamental properties of elementary particles such as axions
and neutrinos, and to study problems related to the variation of fundamental
constants.
In this work, we review the essentials of the physics of white dwarf stars.
Special emphasis is placed on the physical processes that lead to the formation
of white dwarfs as well as on the different energy sources and processes
responsible for chemical abundance changes that occur along their evolution.
Moreover, in the course of their lives, white dwarfs cross different
pulsational instability strips. The existence of these instability strips
provides astronomers with an unique opportunity to peer into their internal
structure that would otherwise remain hidden from observers. We will show that
this allows to measure with unprecedented precision the stellar masses and to
infer their envelope thicknesses, to probe the core chemical stratification,
and to detect rotation rates and magnetic fields. Consequently, in this work,
we also review the pulsational properties of white dwarfs and the most recent
applications of white dwarf asteroseismology.Comment: 85 pages, 28 figures. To be published in The Astronomy and
Astrophysics Revie
Glutathione pathway gene variation and risk of autism spectrum disorders
Despite evidence that autism is highly heritable with estimates of 15 or more genes involved, few studies have directly examined associations of multiple gene interactions. Since inability to effectively combat oxidative stress has been suggested as a mechanism of autism, we examined genetic variation 42 genes (308 single-nucleotide polymorphisms (SNPs)) related to glutathione, the most important antioxidant in the brain, for both marginal association and multi-gene interaction among 318 case–parent trios from The Autism Genetic Resource Exchange. Models of multi-SNP interactions were estimated using the trio Logic Regression method. A three-SNP joint effect was observed for genotype combinations of SNPs in glutaredoxin, glutaredoxin 3 (GLRX3), and cystathione gamma lyase (CTH); OR = 3.78, 95% CI: 2.36, 6.04. Marginal associations were observed for four genes including two involved in the three-way interaction: CTH, alcohol dehydrogenase 5, gamma-glutamylcysteine synthetase, catalytic subunit and GLRX3. These results suggest that variation in genes involved in counterbalancing oxidative stress may contribute to autism, though replication is necessary
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