3,933 research outputs found
A new diagrammatic representation for correlation functions in the in-in formalism
In this paper we provide an alternative method to compute correlation
functions in the in-in formalism, with a modified set of Feynman rules to
compute loop corrections. The diagrammatic expansion is based on an iterative
solution of the equation of motion for the quantum operators with only retarded
propagators, which makes each diagram intrinsically local (whereas in the
standard case locality is the result of several cancellations) and endowed with
a straightforward physical interpretation. While the final result is strictly
equivalent, as a bonus the formulation presented here also contains less graphs
than other diagrammatic approaches to in-in correlation functions. Our method
is particularly suitable for applications to cosmology.Comment: 14 pages, matches the published version. includes a modified version
of axodraw.sty that works with the Revtex4 clas
Nonrandomized comparison of local urokinase thrombolysis versus systemic heparin anticoagulation for superior sagittal sinus thrombosis
Background and Purpose
We sought to compare the safety and efficacy of direct urokinase thrombolysis with systemic heparin anticoagulation for superior sagittal sinus thrombosis (SSST). Methods
At University at Buffalo (NY) and University of Texas (Dallas, Houston), we reviewed 40 consecutive patients with SSST, treated with local urokinase (thrombolysis group) or systemic heparin anticoagulation (heparin group). The thrombolysis group (n=20) received local urokinase into the SSS followed by systemic heparin anticoagulation. The heparin group (n=20) received systemic heparin anticoagulation only. Neurological dysfunction was rated as follows: 0, normal; 1, mild (but able to ambulate and communicate); 2, moderate (unable to ambulate, normal mentation); and 3, severe (unable to ambulate, altered mentation). Results
Age (P=0.49), sex (P=0.20), baseline venous infarction (P=0.73), and predisposing illnesses (P=0.52) were similar between the thrombolysis and heparin groups. Pretreatment neurological function was worse in the thrombolysis group (normal, n=5; mild, n=8; moderate, n=4; severe, n=3) than in the heparin group (normal, n=8; mild, n=8; moderate, n=3; severe, n=1) (P=NS). Discharge neurological function was better in the thrombolysis group (normal, n=16; mild, n=3; moderate, n=1; severe, n=0) than in the heparin group (normal, n=9; mild, n=6; moderate, n=5; severe, n=0) (P=0.019, Mann-Whitney U test). Hemorrhagic complications were 10% (n=2) in the thrombolysis group (subdural hematoma, retroperitoneal hemorrhage) and none in the heparin group (P=0.49). Three of the heparin group patients developed complications of the underlying disease (status epilepticus, hydrocephalus, refractory papilledema). No deaths occurred. Length of hospital stay was similar between the groups (P=0.79). Conclusions
Local thrombolysis with urokinase is fairly well tolerated and may be more effective than systemic heparin anticoagulation alone in treating SSST. A randomized, prospective study comparing these 2 treatments for SSST is warranted
Renormalization of initial conditions and the trans-Planckian problem of inflation
Understanding how a field theory propagates the information contained in a
given initial state is essential for quantifying the sensitivity of the cosmic
microwave background to physics above the Hubble scale during inflation. Here
we examine the renormalization of a scalar theory with nontrivial initial
conditions in the simpler setting of flat space. The renormalization of the
bulk theory proceeds exactly as for the standard vacuum state. However, the
short distance features of the initial conditions can introduce new divergences
which are confined to the surface on which the initial conditions are imposed.
We show how the addition of boundary counterterms removes these divergences and
induces a renormalization group flow in the space of initial conditions.Comment: 22 pages, 4 eps figures, uses RevTe
Time evolution of the chiral phase transition during a spherical expansion
We examine the non-equilibrium time evolution of the hadronic plasma produced
in a relativistic heavy ion collision, assuming a spherical expansion into the
vacuum. We study the linear sigma model to leading order in a large-
expansion. Starting at a temperature above the phase transition, the system
expands and cools, finally settling into the broken symmetry vacuum state. We
consider the proper time evolution of the effective pion mass, the order
parameter , and the particle number distribution. We
examine several different initial conditions and look for instabilities
(exponentially growing long wavelength modes) which can lead to the formation
of disoriented chiral condensates (DCCs). We find that instabilities exist for
proper times which are less than 3 fm/c. We also show that an experimental
signature of domain growth is an increase in the low momentum spectrum of
outgoing pions when compared to an expansion in thermal equilibrium. In
comparison to particle production during a longitudinal expansion, we find that
in a spherical expansion the system reaches the ``out'' regime much faster and
more particles get produced. However the size of the unstable region, which is
related to the domain size of DCCs, is not enhanced.Comment: REVTex, 20 pages, 8 postscript figures embedded with eps
The Role of Nonequilibrium Dynamical Screening in Carrier Thermalization
We investigate the role played by nonequilibrium dynamical screening in the
thermalization of carriers in a simplified two-component two-band model of a
semiconductor. The main feature of our approach is the theoretically sound
treatment of collisions. We abandon Fermi's Golden rule in favor of a
nonequilibrium field theoretic formalism as the former is applicable only in
the long-time regime. We also introduce the concept of nonequilibrium dynamical
screening. The dephasing of excitonic quantum beats as a result of
carrier-carrier scattering is brought out. At low densities it is found that
the dephasing times due to carrier-carrier scattering is in picoseconds and not
femtoseconds, in agreement with experiments. The polarization dephasing rates
are computed as a function of the excited carrier density and it is found that
the dephasing rate for carrier-carrier scattering is proportional to the
carrier density at ultralow densities. The scaling relation is sublinear at
higher densities, which enables a comparison with experiment.Comment: Revised version with additional refs. 12 pages, figs. available upon
request; Submitted to Phys. Rev.
Noise Kernel in Stochastic Gravity and Stress Energy Bi-Tensor of Quantum Fields in Curved Spacetimes
The noise kernel is the vacuum expectation value of the (operator-valued)
stress-energy bi-tensor which describes the fluctuations of a quantum field in
curved spacetimes. It plays the role in stochastic semiclassical gravity based
on the Einstein-Langevin equation similar to the expectation value of the
stress-energy tensor in semiclassical gravity based on the semiclassical
Einstein equation. According to the stochastic gravity program, this two point
function (and by extension the higher order correlations in a hierarchy) of the
stress energy tensor possesses precious statistical mechanical information of
quantum fields in curved spacetime and, by the self-consistency required of
Einstein's equation, provides a probe into the coherence properties of the
gravity sector (as measured by the higher order correlation functions of
gravitons) and the quantum nature of spacetime. It reflects the low and medium
energy (referring to Planck energy as high energy) behavior of any viable
theory of quantum gravity, including string theory. It is also useful for
calculating quantum fluctuations of fields in modern theories of structure
formation and for backreaction problems in cosmological and black holes
spacetimes.
We discuss the properties of this bi-tensor with the method of
point-separation, and derive a regularized expression of the noise-kernel for a
scalar field in general curved spacetimes. One collorary of our finding is that
for a massless conformal field the trace of the noise kernel identically
vanishes. We outline how the general framework and results derived here can be
used for the calculation of noise kernels for Robertson-Walker and
Schwarzschild spacetimes.Comment: 22 Pages, RevTeX; version accepted for publication in PR
Electrocardiographic changes associated with hyperkalaemia in domestic cats
Hyperkalaemia is a life-threatening electrolyte imbalance because it affects cardiac conduction and can lead to fatal arrhythmias if left untreated. The present study describes the occurrence of hyperkalaemia in cats and the electrocardiographic changes associated with this electrolyte imbalance. Hyperkalaemia was identified in 83.33 per cent of the study group subjects. Acute kidney injury and obstructive uropathy were the main clinical conditions associated with it. Electrocardiographic findings in hyperkalaemia in different cats under study included peaked T waves in lead II and the precordial lead CV6LL, atrial standstill and sino-ventricular rhythm, normal sinus rhythm, ventricular tachycardia, first-degree atrio-ventricular block, bradycardia, sinus tachycardia, and atrio-ventricular dissociation. Electrocardiography should always be performed in cases suspected of electrolyte imbalances, particularly hyperkalaemia, so as to identify any fatal arrhythmias and initiate treatment at the earliest
Hydrodynamic transport functions from quantum kinetic theory
Starting from the quantum kinetic field theory [E. Calzetta and B. L. Hu,
Phys. Rev. D37, 2878 (1988)] constructed from the closed-time-path (CTP),
two-particle-irreducible (2PI) effective action we show how to compute from
first principles the shear and bulk viscosity functions in the
hydrodynamic-thermodynamic regime. For a real scalar field with self-interaction we need to include 4 loop graphs in the equation of
motion. This work provides a microscopic field-theoretical basis to the
``effective kinetic theory'' proposed by Jeon and Yaffe [S. Jeon and L. G.
Yaffe, Phys. Rev. D53, 5799 (1996)], while our result for the bulk viscosity
reproduces their expression derived from linear response theory and the
imaginary-time formalism of thermal field theory. Though unavoidably involved
in calculations of this sort, we feel that the approach using fundamental
quantum kinetic field theory is conceptually clearer and methodically simpler
than the effective kinetic theory approach, as the success of the latter
requires clever rendition of diagrammatic resummations which is neither
straightforward nor failsafe. Moreover, the method based on the CTP-2PI
effective action illustrated here for a scalar field can be formulated entirely
in terms of functional integral quantization, which makes it an appealing
method for a first-principles calculation of transport functions of a thermal
non-abelian gauge theory, e.g., QCD quark-gluon plasma produced from heavy ion
collisions.Comment: 25 pages revtex, 11 postscript figures. Final version accepted for
publicatio
The Boltzmann equation for colourless plasmons in hot QCD plasma. Semiclassical approximation
Within the framework of the semiclassical approximation, we derive the
Boltzmann equation describing the dynamics of colorless plasmons in a hot QCD
plasma. The probability of the plasmon-plasmon scattering at the leading order
in the coupling constant is obtained. This probability is gauge-independent at
least in the class of the covariant and temporal gauges. It is noted that the
structure of the scattering kernel possesses important qualitative difference
from the corresponding one in the Abelian plasma, in spite of the fact that we
focused our study on the colorless soft excitations. It is shown that
four-plasmon decay is suppressed by the power of relative to the process of
nonlinear scattering of plasmons by thermal particles at the soft momentum
scale. It is stated that the former process becomes important in going to the
ultrasoft region of the momentum scale.Comment: 41, LaTeX, minor changes, identical to published versio
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