803 research outputs found
Effective action of a five-dimensional domain wall
We calculate the four-dimensional low-energy effective action for the
perturbations of a two-scalar domain wall model in five dimensions. Comparison
of the effective action to the Nambu-Goto action reveals the presence of an
additional coupling between the light scalar field and the massless translation
mode (branon excitation), which can be written in terms of the curvature scalar
of the induced metric. We comment on the impact of this interaction to branon
physics.Comment: 24 page
Compact extra-dimensions as solution to the strong CP problem
We show that the strong CP problem can, in principle, be solved dynamically
by adding extra-dimensions with compact topology. To this aim we consider a toy
model for QCD, which contains a vacuum angle and a strong CP like problem. We
further consider a higher dimensional theory, which has a trivial vacuum
structure and which reproduces the perturbative properties of the toy model in
the low-energy limit. In the weak coupling regime, where our computations are
valid, we show that the vacuum structure of the low-energy action is still
trivial and the strong CP problem is solved. No axion-like particle occur in
this setup and therefore it is not ruled out by astrophysical bounds.Comment: Discussion adde
One-loop fermionic corrections to the instanton transition in two dimensional chiral Higgs model
The one-loop fermionic contribution to the probability of an instanton
transition with fermion number violation is calculated in the chiral Abelian
Higgs model in 1+1 dimensions, where the fermions have a Yukawa coupling to the
scalar field. The dependence of the determinant on fermionic, scalar and vector
mass is determined. We show in detail how to renormalize the fermionic
determinant in partial wave analysis, which is convenient for computations.Comment: 36 pages, 5 figure
Towards flavour diffusion coefficient and electrical conductivity without ultraviolet contamination
By subtracting from a recent lattice measurement of the thermal
vector-current correlator the known 5-loop vacuum contribution, we demonstrate
that the remainder is small and shows no visible short-distance divergence. It
can therefore in principle be subjected to model-independent analytic
continuation. Testing a particular implementation, we obtain estimates for the
flavour-diffusion coefficient (2 pi T D \gsim 0.8) and electrical conductivity
which are significantly smaller than previous results. Although systematic
errors remain beyond control at present, some aspects of our approach could be
of a wider applicability.Comment: 7 pages. v2: clarifications added, published versio
Hemodialysis for cefepime intoxication: A case report
Introduction: We report a case of cefepime intoxication with acute
severe neurologic symptoms, which was treated by temporary hemodialysis.
Patients (or Materials) and Methods: Cefepime 2 g BID for endovascular
prosthesis infection was prescribed to a frail, chronically ill
88-year-old woman with a serum creatinine of 199 ÎŒmol/L and an
estimated creatinine clearance of 13 mL/min (Cockroft formula). Two
days later, she was transferred to a neurocritical care unit because
of acute aphasia, myoclonic jerks, and delirium with a Glasgow
coma scale score of 12/15. The following day, in the absence of
other causes, cefepime intoxication was hypothesized, and cefepime
was withdrawn after a total of 7 doses = 14 g. Over the next 24
hours, two 3-hour hemodialysis (HD) sessions were performed under
cefepime concentration monitoring.
Results: Cefepime plasma levels were measured by liquid chromatography/
mass spectrometry. There is no validated reference range,
but a study (Chapuis T et al, Critical Care, 2010) found a 50% risk
of neurotoxicity with residual levels > 15 mg/L. In our patient, levels
were 83.3 mg/L 10 hours after last dose, 24.1 mg/L immediately after
the first HD session, 13.4 mg/L immediately before the second HD
session, and 2.5 mg/L immediately after the second HD session. The
patient made a full clinical recovery over the next 48 hours. The 70%
to 80% fall in plasmatic levels observed during each HD session is
in accordance with literature data (Schmaldienst S et al, Eur J Clin
Pharmacol, 2000, and Manyor LM et al, Pharmacotherapy, 2008).
According to kinetic simulation, cefepime dropped at a concentration
< 15 mg/L 15 hours earlier with HD than it would have without.
Conclusion: Neuropsychiatric adverse effects of beta-lactam antibiotics
can be easily overlooked by clinicians. One should be especially
cautious with their use in very old and frail patients in whom plasma
creatinine poorly estimates renal function and cognitive impairment
is highly prevalent. Temporary hemodialysis effectively clears
cefepime, but its role in hastening clinical recovery may be limited
Colour-electric spectral function at next-to-leading order
The spectral function related to the correlator of two colour-electric fields
along a Polyakov loop determines the momentum diffusion coefficient of a heavy
quark near rest with respect to a heat bath. We compute this spectral function
at next-to-leading order, O(alpha_s^2), in the weak-coupling expansion. The
high-frequency part of our result (omega >> T), which is shown to be
temperature-independent, is accurately determined thanks to asymptotic freedom;
the low-frequency part of our result (omega << T), in which Hard Thermal Loop
resummation is needed in order to cure infrared divergences, agrees with a
previously determined expression. Our result may help to calibrate the overall
normalization of a lattice-extracted spectral function in a perturbative
frequency domain T << omega << 1/a, paving the way for a non-perturbative
estimate of the momentum diffusion coefficient at omega -> 0. We also evaluate
the colour-electric Euclidean correlator, which could be directly compared with
lattice simulations. As an aside we determine the Euclidean correlator in the
lattice strong-coupling expansion, showing that through a limiting procedure it
can in principle be defined also in the confined phase of pure Yang-Mills
theory, even if a practical measurement could be very noisy there.Comment: 38 page
Ultraviolet asymptotics of scalar and pseudoscalar correlators in hot Yang-Mills theory
Inspired by recent lattice measurements, we determine the short-distance (a
> omega >> pi T) asymptotics
of scalar (trace anomaly) and pseudoscalar (topological charge density)
correlators at 2-loop order in hot Yang-Mills theory. The results are expressed
in the form of an Operator Product Expansion. We confirm and refine the
determination of a number of Wilson coefficients; however some discrepancies
with recent literature are detected as well, and employing the correct values
might help, on the qualitative level, to understand some of the features
observed in the lattice measurements. On the other hand, the Wilson
coefficients show slow convergence and it appears uncertain whether this
approach can lead to quantitative comparisons with lattice data. Nevertheless,
as we outline, our general results might serve as theoretical starting points
for a number of perhaps phenomenologically more successful lines of
investigation.Comment: 27 pages. v2: minor improvements, published versio
Intermediate distance correlators in hot Yang-Mills theory
Lattice measurements of spatial correlation functions of the operators FF and
FF-dual in thermal SU(3) gauge theory have revealed a clear difference between
the two channels at "intermediate" distances, x ~ 1/(pi T). This is at odds
with the AdS/CFT limit which predicts the results to coincide. On the other
hand, an OPE analysis at short distances (x << 1/(pi T)) as well as effective
theory methods at long distances (x >> 1/(pi T)) suggest differences. Here we
study the situation at intermediate distances by determining the time-averaged
spatial correlators through a 2-loop computation. We do find unequal results,
however the numerical disparity is small. Apart from theoretical issues, a
future comparison of our results with time-averaged lattice measurements might
also be of phenomenological interest in that understanding the convergence of
the weak-coupling series at intermediate distances may bear on studies of the
thermal broadening of heavy quarkonium resonances.Comment: 31 page
Heavy quark medium polarization at next-to-leading order
We compute the imaginary part of the heavy quark contribution to the photon
polarization tensor, i.e. the quarkonium spectral function in the vector
channel, at next-to-leading order in thermal QCD. Matching our result, which is
valid sufficiently far away from the two-quark threshold, with a previously
determined resummed expression, which is valid close to the threshold, we
obtain a phenomenological estimate for the spectral function valid for all
non-zero energies. In particular, the new expression allows to fix the overall
normalization of the previous resummed one. Our result may be helpful for
lattice reconstructions of the spectral function (near the continuum limit),
which necessitate its high energy behaviour as input, and can in principle also
be compared with the dilepton production rate measured in heavy ion collision
experiments. In an appendix analogous results are given for the scalar channel.Comment: 43 pages. v2: a figure and other clarifications added, published
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