2,012 research outputs found
Dynamics near the critical point: the hot renormalization group in quantum field theory
The perturbative approach to the description of long wavelength excitations
at high temperature breaks down near the critical point of a second order phase
transition. We study the \emph{dynamics} of these excitations in a relativistic
scalar field theory at and near the critical point via a renormalization group
approach at high temperature and an expansion in
space-time dimensions. The long wavelength physics is determined by a
non-trivial fixed point of the renormalization group. At the critical point we
find that the dispersion relation and width of quasiparticles of momentum
is and respectively, the
group velocity of quasiparticles vanishes in the long
wavelength limit at the critical point. Away from the critical point for
we find and
with
the finite temperature correlation length . The
new \emph{dynamical} exponent results from anisotropic renormalization in
the spatial and time directions. For a theory with O(N) symmetry we find . Critical slowing down,
i.e, a vanishing width in the long-wavelength limit, and the validity of the
quasiparticle picture emerge naturally from this analysis.Comment: Discussion on new dynamical universality class. To appear in Phys.
Rev.
Investigation into O(N) Invariant Scalar Model Using Auxiliary-Mass Method at Finite Temperature
Using auxiliary-mass method, O(N) invariant scalar model is investigated at
finite temperature. This mass and an evolution equation allow us to calculate
an effective potential without an infrared divergence. Second order phase
transition is indicated by the effective potential. The critical exponents are
determined numerically.Comment: LaTex 8 pages with 3 eps figure
Cantor Spectrum for Schr\"odinger Operators with Potentials arising from Generalized Skew-shifts
We consider continuous -cocycles over a strictly ergodic
homeomorphism which fibers over an almost periodic dynamical system
(generalized skew-shifts). We prove that any cocycle which is not uniformly
hyperbolic can be approximated by one which is conjugate to an
-cocycle. Using this, we show that if a cocycle's homotopy
class does not display a certain obstruction to uniform hyperbolicity, then it
can be -perturbed to become uniformly hyperbolic. For cocycles arising
from Schr\"odinger operators, the obstruction vanishes and we conclude that
uniform hyperbolicity is dense, which implies that for a generic continuous
potential, the spectrum of the corresponding Schr\"odinger operator is a Cantor
set.Comment: Final version. To appear in Duke Mathematical Journa
Infrared Behavior of High-Temperature QCD
The damping rate \gamma_t(p) of on-shell transverse gluons with ultrasoft
momentum p is calculated in the context of next-to-leading-order
hard-thermal-loop-summed perturbation of high-temperature QCD. It is obtained
in an expansion to second order in p. The first coefficient is recovered but
that of order p^2 is found divergent in the infrared. Divergences from
light-like momenta do also occur but are circumvented. Our result and method
are critically discussed, particularly regarding a Ward identity obtained in
the literature. When enforcing the equality between \gamma_t(0) and
\gamma_l(0), a rough estimate of the magnetic mass is obtained. Carrying a
similar calculation in the context of scalar quantum electrodynamics shows that
the early ultrasoft-momentum expansion we make has little to do with the
infrared sensitivity of the result.Comment: REVTEX4, 55 page
Shear Viscosity to Entropy Density Ratio of QCD below the Deconfinement Temperature
Using chiral perturbation theory we investigate the QCD shear viscosity to
entropy density ratio below the deconfinement temperature (~170 MeV) with zero
baryon number density. It is found that the viscosity to entropy density ratio
of QCD is monotonically decreasing in temperature (T) and reaches 0.6 with
estimated ~50% uncertainty at T=120 MeV. A naive extrapolation of the leading
order result shows that the ratio reaches the 1/(4 pi) minimum bound proposed
by Kovtun, Son, and Starinets using string theory methods at T~200 MeV. This
suggests a phase transition or cross over might occur at T less than 200 MeV in
order for the bound to remain valid. Also, it is natural for the ratio to stay
close to the minimum bound around the phase transition temperature as was
recently found in heavy ion collisions.Comment: 12 pages and 2 figure
Heparan sulfates and heparan sulfate binding proteins in sepsis
Heparan sulfates (HSs) are the main components in the glycocalyx which covers endothelial cells and modulates vascular homeostasis through interactions with multiple Heparan sulfate binding proteins (HSBPs). During sepsis, heparanase increases and induces HS shedding. The process causes glycocalyx degradation, exacerbating inflammation and coagulation in sepsis. The circulating heparan sulfate fragments may serve as a host defense system by neutralizing dysregulated Heparan sulfate binding proteins or pro-inflammatory molecules in certain circumstances. Understanding heparan sulfates and heparan sulfate binding proteins in health and sepsis is critical to decipher the dysregulated host response in sepsis and advance drug development. In this review, we will overview the current understanding of HS in glycocalyx under septic condition and the dysfunctional heparan sulfate binding proteins as potential drug targets, particularly, high mobility group box 1 (HMGB1) and histones. Moreover, several drug candidates based on heparan sulfates or related to heparan sulfates, such as heparanase inhibitors or heparin-binding protein (HBP), will be discussed regarding their recent advances. By applying chemical or chemoenzymatic approaches, the structure-function relationship between heparan sulfates and heparan sulfate binding proteins is recently revealed with structurally defined heparan sulfates. Such homogenous heparan sulfates may further facilitate the investigation of the role of heparan sulfates in sepsis and the development of carbohydrate-based therapy
Perturbation theory and non-perturbative renormalization flow in scalar field theory at finite temperature
We use the non-perturbative renormalization group to clarify some features of
perturbation theory in thermal field theory. For the specific case of the
scalar field theory with O(N) symmetry, we solve the flow equations within the
local potential approximation. This approximation reproduces the perturbative
results for the screening mass and the pressure up to order g^3, and starts to
differ at order g^4. The method allows a smooth extrapolation to the regime
where the coupling is not small, very similar to that obtained from a simple
self-consistent approximation.Comment: 42 pages, 19 figures; v2: typos corrected and references added,
version accepted for publication in Nucl. Phys.
Bose--Einstein Condensation and Thermalization of the Quark Gluon Plasma
In ultra-relativistic heavy ion collisions, the matter formed shortly after
the collision is a dense, out of equilibrium, system of gluons characterized by
a semi-hard momentum scale . Simple power counting arguments
indicate that this system is over-occupied: the gluon occupation number is
parametrically large when compared to a system in thermal equilibrium with the
same energy density. On short time scales, soft elastic scatterings tend to
drive the system towards the formation of a Bose--Einstein condensate that
contains a large fraction of the gluons while contributing little to the energy
density. The lifetime and existence of this condensate depends on whether
inelastic processes, that occur on the same time scale as the elastic ones,
preferably increase or decrease the number of gluons. During this overpopulated
stage, and all the way to thermalization, the system behaves as a strongly
interacting fluid, even though the elementary coupling constant is small. We
argue that while complete isotropization may never be reached, the system may
yet evolve for a long time with a fixed anisotropy between average longitudinal
and transverse momenta.Comment: 19 pages, 1 figure, v2 is a substantial re-write aimed at clarifying
the presentation. Major arguments essentially unchanged, except in the
discussion of inelastic processe
Sensitivity of Azimuthal Jet Tomography to Early Time Energy-Loss at RHIC and LHC
We compute the jet path-length dependence of energy-loss for higher azimuthal
harmonics of jet-fragments in a generalized model of energy-loss that can
interpolate between pQCD and AdS/CFT limits and compare results with Glauber
and CGC/KLN initial conditions. We find, however, that even the high-pT second
moment is most sensitive to the poorly known early-time evolution during the
first fm/c. Moreover, we demonstrate that quite generally the energy and
density-dependence leads to an overquenching jet fragments relative to the
first LHC -data, once the parameters of the energy-loss model are fixed
from -data at RHIC.Comment: 4 pages, 2 figures, version accepted for publication in J. Phys. G:
Nucl. Part. Phys. as conference proceedings for Quark Matter 2011, May 23 -
May 28, Annecy, Franc
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