41 research outputs found
Finite Temperature Wave-Function Renormalization, A Comparative Analysis
We compare two competing theories regarding finite temperature wave-function
corrections for the process and for and
related processes of interest for primordial nucleosynthesis. Although the two
methods are distinct (as shown in ) they yield the same finite
temperature correction for all and processes. Both methods
yield an increase in the He/H ratio of .01% due to finite temperature
renormalization rather than a decrease of .16% as previously predicted.Comment: 12 pages, 3 figures. LaTe
Towards the Theory of Cosmological Phase Transitions
We discuss recent progress (and controversies) in the theory of finite
temperature phase transitions. This includes the structure of the effective
potential at a finite temperature, the infrared problem in quantum statistics
of gauge fields, the theory of formation of critical and subcritical bubbles
and the theory of bubble wall propagation.Comment: 50 p
Plasma wave instabilities induced by neutrinos
Quantum field theory is applied to study the interaction of an electron
plasma with an intense neutrino flux. A connection is established between the
field theory results and classical kinetic theory. The dispersion relation and
damping rate of the plasma longitudinal waves are derived in the presence of
neutrinos. It is shown that Supernova neutrinos are never collimated enough to
cause non-linear effects associated with a neutrino resonance. They only induce
neutrino Landau damping, linearly proportional to the neutrino flux and
.Comment: 18 pages, 3 figures, title and references correcte
On the thermal sunset diagram for scalar field theories
We study the so-called `` sunset diagram'', which is one of two-loop
self-energy diagrams, for scalar field theories at finite temperature.
For this purpose, we first find the complete expression of the bubble
diagram, the one-loop subdiagram of the sunset diagram, for arbitrary momentum.
We calculate the temperature independent part and dependent part of the
sunset diagram separately. For the former, we obtain the discontinuous part
first and the finite continuous part next using a twice-subtracted dispersion
relation. For the latter, we express it as a one-dimensional integral in terms
of the bubble diagram.
We also study the structure of the discontinuous part of the sunset diagram.
Physical processes, which are responsible for it, are identified. Processes due
to the scattering with particles in the heat bath exist only at finite
temperature and generate discontinuity for arbitrary momentum, which is a
remarkable feature of the two-loop diagrams at finite temperature.
As an application of our result, we study the effect of the diagram on the
spectral function of the sigma meson at finite temperature in the linear sigma
model, which was obtained at one-loop order previously. At high temperature
where the decay is forbidden, sigma acquires a finite width
of the order of while within the one-loop calculation its width
vanishes. At low temperature, the spectrum does not deviate much from that at
one-loop order. Possible consequences with including other two-loop diagrams
are discussed.Comment: 30 page
One-Loop Renormalization of a Self-Interacting Scalar Field in Nonsimply Connected Spacetimes
Using the effective potential, we study the one-loop renormalization of a
massive self-interacting scalar field at finite temperature in flat manifolds
with one or more compactified spatial dimensions. We prove that, owing to the
compactification and finite temperature, the renormalized physical parameters
of the theory (mass and coupling constant) acquire thermal and topological
contributions. In the case of one compactified spatial dimension at finite
temperature, we find that the corrections to the mass are positive, but those
to the coupling constant are negative. We discuss the possibility of
triviality, i.e. that the renormalized coupling constant goes to zero at some
temperature or at some radius of the compactified spatial dimension.Comment: 16 pages, plain LATE
Multiple emergences of genetically diverse amphibian-infecting chytrids include a globalized hypervirulent recombinant lineage
Batrachochytriumdendrobatidis (Bd) is a globally ubiquitous fungal infection that has emerged to become a primary driver of amphibian biodiversity loss. Despite widespread effort to understand the emergence of this panzootic, the origins of the infection, its patterns of global spread, and principle mode of evolution remain largely unknown. Using comparative population genomics, we discovered three deeply diverged lineages of Bd associated with amphibians. Two of these lineages were found in multiple continents and are associated with known introductions by the amphibian trade.We found that isolates belonging to one clade, the global panzootic lineage (BdGPL) have emerged across at least five continents during the 20th century and are associated with the onset of epizootics in North America, Central America, the Caribbean, Australia, and Europe. The two newly identified divergent lineages, Cape lineage (BdCAPE) and Swiss lineage (BdCH), were found to differ in morphological traits when compared against one another and BdGPL, and we show that BdGPL is hypervirulent. BdGPL uniquely bears the hallmarks of genomic recombination, manifested as extensive intergenomic phylogenetic conflict and patchily distributed heterozygosity. Wepostulate that contact between previously genetically isolated allopatric populations of Bd may have allowed recombination to occur, resulting in the generation, spread, and invasion of the hypervirulent BdGPL leading to contemporary disease-driven losses in amphibian biodiversity.Peer Reviewe
Transport Coefficients and Analytic Continuation in Dual 1+1 Dimensional Models at Finite Temperature
The conductivity of a finite temperature 1+1 dimensional fermion gas
described by the massive Thirring model is shown to be related to the retarded
propagator of the dual boson sine-Gordon model. Duality provides a natural
resummation which resolves infra-red problems, and the boson propagator can be
related to the fermion gas at non-zero temperature and chemical potential or
density. In addition, at high temperatures, we can apply a dimensional
reduction technique to find resummed closed expressions for the boson
self-energy and relate them to the fermion conductivity. Particular attention
is paid to the discussion of analytic continuation. The resummation implicit in
duality provides a powerful alternative to the standard diagrammatic evaluation
of transport coefficients at finite temperature.Comment: 41 pages, 6 figure
Wave Function Renormalization at Finite Temperature
We present a derivation of the medium dependent wave function renormalization
for a spinor field in presence of a thermal bath. We show that, as already
pointed out in literature, projector operators are not multiplicatively
renormalized and the effect involves a non trivial spinor dependence, which
disappears in the zero temperature covariant limit. The results, which differ
from what already found in literature, are then applied to the decay of a
massive scalar boson into two fermions and to the --decay and crossed
related processes relevant for primordial nucleosynthesis.Comment: 11 pages, RevTe
Whole-genome sequencing reveals host factors underlying critical COVID-19
Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease
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Insulator Tests in A High Performance, Square-Bore Railgun
The Center for Electromechanics at The University of Texas at Austin (CEM-UT) has developed a 1 m long, 1.27 cm square-bore railgun for testing different rail, insulator, and projectile materials. This railgun incorporates a unique frame assembly which allows the gun to be assembled and then pressed into the containment vessel with little pressure. After it is pressed together, an external clamp is assembled around it in order to provide the necessary preload to activate the bore seals. The unique feature of the gun assembly allows stock geometry, 2.54 cm x 0.635 cm (1 in. x % in.) cross section, insulating materials to be installed and tested with minimal down time between shots. To date the 1-m long, 1.27 cm square-bore railgun has been used to test the following insulator materials: float glass, polycarbonate, 40% glass filled polycarbonate, G-7 laminate, and quartz glass. The best results have been obtained with quartz glass and glass-filled polycarbonate. Copper and molybdenum flame-sprayed copper have been tried as rail materials with the latter showing greatest success. Currently molybdenum flame sprayed copper rails and glass filled polycarbonate insulators have been repetitively fired at 350 kA levels while maintaining a rail-to-rail resistance of greater than a megohm. During the experiments performed at CEM-UT, much effort was invested in producing a consistent, high-quality bore finish. The indication is that candidate materials to be tested cannot be accurately evaluated if the bore finish is not accurate and smooth.Center for Electromechanic