3,534 research outputs found
The Sphaleron Rate in SU(N) Gauge Theory
The sphaleron rate is defined as the diffusion constant for topological
number NCS = int g^2 F Fdual/32 pi^2. It establishes the rate of equilibration
of axial light quark number in QCD and is of interest both in electroweak
baryogenesis and possibly in heavy ion collisions. We calculate the
weak-coupling behavior of the SU(3) sphaleron rate, as well as making the most
sensible extrapolation towards intermediate coupling which we can. We also
study the behavior of the sphaleron rate at weak coupling at large Nc.Comment: 18 pages with 3 figure
Degrees of Freedom of the Quark Gluon Plasma, tested by Heavy Mesons
Heavy quarks (charm and bottoms) are one of the few probes which are
sensitive to the degrees of freedom of a Quark Gluon Plasma (QGP), which cannot
be revealed by lattice gauge calculations in equilibrium. Due to the rapid
expansion of the QGP energetic heavy quarks do not come to an equilibrium with
the QGP. Their energy loss during the propagation through the QGP medium
depends strongly on the modelling of the interaction of the heavy quarks with
the QGP quarks and gluons, i.e. on the assuption of the degrees of freedom of
the plasma. Here we compare the results of different models, the pQCD based
Monte-Carlo (MC@sHQ), the Dynamical Quasi Particle Model (DQPM) and the
effective mass approach, for the drag force in a thermalized QGP and discuss
the sensitivity of heavy quark energy loss on the properties of the QGP as well
as on non-equilibrium dynamicsComment: proceedings symposion "New Horizons" Makutsi, South Africa, Nov 201
Baryon Washout, Electroweak Phase Transition, and Perturbation Theory
We analyze the conventional perturbative treatment of sphaleron-induced
baryon number washout relevant for electroweak baryogenesis and show that it is
not gauge-independent due to the failure of consistently implementing the
Nielsen identities order-by-order in perturbation theory. We provide a
gauge-independent criterion for baryon number preservation in place of the
conventional (gauge-dependent) criterion needed for successful electroweak
baryogenesis. We also review the arguments leading to the preservation
criterion and analyze several sources of theoretical uncertainties in obtaining
a numerical bound. In various beyond the standard model scenarios, a realistic
perturbative treatment will likely require knowledge of the complete two-loop
finite temperature effective potential and the one-loop sphaleron rate.Comment: 25 pages, 9 figures; v2 minor typos correcte
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
Some Field Theoretic Issues Regarding the Chiral Magnetic Effect
In this paper, we shall address some field theoretic issues regarding the
chiral magnetic effect. The general structure of the magnetic current
consistent with the electromagnetic gauge invariance is obtained and the impact
of the infrared divergence is examined. Some subtleties on the relation between
the chiral magnetic effect and the axial anomaly are clarified through a
careful examination of the infrared limit of the relevant thermal diagrams.Comment: 19 pages, 4 figures in Latex. Typos fixed, version accepted to be
published in JHE
Pointlike probes of superstring-theoretic superfluids
In analogy with an experimental setup used in liquid helium, we use a
pointlike probe to study superfluids which have a gravity dual. In the gravity
description, the probe is represented by a hanging string. We demonstrate that
there is a critical velocity below which the probe particle feels neither drag
nor stochastic forces. Above this critical velocity, there is power-law scaling
for the drag force, and the stochastic forces are characterized by a finite,
velocity-dependent temperature. This temperature participates in two simple and
general relations between the drag force and stochastic forces. The formula we
derive for the critical velocity indicates that the low-energy excitations are
massless, and they demonstrate the power of stringy methods in describing
strongly coupled superfluids.Comment: 17 pages, 2 figures, added a figure, a reference, and moved material
to an appendi
Probes on D3-D7 Quark-Gluon Plasmas
We study the holographic dual model of quenched flavors immersed in a
quark-gluon plasma with massless dynamical quarks in the Veneziano limit. This
is modeled by embedding a probe D7 brane in a background where the backreaction
of massless D7 branes has been taken into account. The background, and hence
the effects, are perturbative in the Veneziano parameter N_f/N_c, therefore
giving small shifts of all magnitudes like the constituent mass, the quark
condensate, and several transport coefficients. We provide qualitative results
for the effect of flavor degrees of freedom on the probes. For example, the
meson melting temperature is enhanced, while the screening length is
diminished. The drag force is also enhanced.Comment: 31 pages, 17 figure
Dose-dependent effects of Allopurinol on human foreskin fibroblast cell and human umbilical vein endothelial cell under hypoxia
Allopurinol, an inhibitor of xanthine oxidase, has been used in clinical trials of patients with cardiovascular and chronic kidney disease. These are two pathologies with extensive links to hypoxia and activation of the transcription factor hypoxia inducible factor (HIF) family. Here we analysed the effects of allopurinol treatment in two different cellular models, and their response to hypoxia. We explored the dose-dependent effect of allopurinol on Human Foreskin Fibroblasts (HFF) and Human Umbilical Vein Endothelial Cells (HUVEC) under hypoxia and normoxia. Under normoxia and hypoxia, high dose allopurinol reduced the accumulation of HIF-1α protein in HFF and HUVEC cells. Allopurinol had only marginal effects on HIF-1α mRNA level in both cellular systems. Interestingly, allopurinol effects over the HIF system were independent of prolyl-hydroxylase activity. Finally, allopurinol treatment reduced angiogenesis traits in HUVEC cells in an in vitro model. Taken together these results indicate that high doses of allopurinol inhibits the HIF system and pro-angiogenic traits in cells
Anomaly/Transport in an Ideal Weyl gas
We study some of the transport processes which are specific to an ideal gas
of relativistic Weyl fermions and relate the corresponding transport
coefficients to various anomaly coefficients of the system. We propose that
these transport processes can be thought of as arising from the continuous
injection of chiral states and their subsequent adiabatic flow driven by
vorticity. This in turn leads to an elegant expression relating the anomaly
induced transport coefficients to the anomaly polynomial of the Ideal Weyl gas.Comment: 35 pages, JHEP forma
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
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