2,721 research outputs found
Robustness of Sound Speed and Jet Quenching for Gauge/Gravity Models of Hot QCD
We probe the effectiveness and robustness of a simple gauge/gravity dual
model of the QCD fireball that breaks conformal symmetry by constructing a
family of similar geometries that solve the scalar/gravity equations of motion.
This family has two parameters, one of which is associated to the temperature.
We calculate two quantities, the speed of sound and the jet-quenching
parameter. We find the speed of sound to be universal and robust over all the
geometries when appropriate units are used, while the jet-quenching parameter
varies significantly away from the conformal limit. We note that the overall
structure of the jet-quenching depends strongly on whether the running scalar
is the dilaton or not. We also discuss the variation of the scalar potential
over our family of solutions, and truncate our results to where the associated
error is small.Comment: 21 pages, 9 figures, LaTeX. v2:references added, minor correction to
speed of sound; conclusions unchange
Stability of strings binding heavy-quark mesons
We investigate the stability against small deformations of strings dangling
into AdS_5-Schwarzschild from a moving heavy quark-anti-quark pair. We
speculate that emission of massive string states may be an important part of
the evolution of certain unstable configurations.Comment: 14 pages, 4 figure
Kinetics of Ordering in Fluctuation-Driven First-Order Transitions: Simulations and Dynamical Renormalization
Many systems where interactions compete with each other or with constraints
are well described by a model first introduced by Brazovskii. Such systems
include block copolymers, alloys with modulated phases, Rayleigh-Benard Cells
and type-I superconductors. The hallmark of this model is that the fluctuation
spectrum is isotropic and has a minimum at a nonzero wave vector represented by
the surface of a d-dimensional hyper-sphere. It was shown by Brazovskii that
the fluctuations change the free energy structure from a to a
form with the disordered state metastable for all quench depths.
The transition from the disordered to the periodic, lamellar structure changes
from second order to first order and suggests that the dynamics is governed by
nucleation. Using numerical simulations we have confirmed that the equilibrium
free energy function is indeed of a form. A study of the dynamics,
however, shows that, following a deep quench, the dynamics is described by
unstable growth rather than nucleation. A dynamical calculation, based on a
generalization of the Brazovskii calculations shows that the disordered state
can remain unstable for a long time following the quench.Comment: 18 pages, 15 figures submitted to PR
Solving Solar Neutrino Puzzle via LMA MSW Conversion
We analyze the existing solar neutrino experiment data and show the allowed
regions. The result from SNO's salt phase itself restricts quite a lot the
allowed region's area. Reactor neutrinos play an important role in determining
oscillation parameters. KamLAND gives decisive conclusion on the solution to
the solar neutrino puzzle, in particular, the spectral distortion in the 766.3
Ty KamLAND data gives another new improvement in the constraint of solar
MSW-LMA solutions. We confirm that at 99.73% C.L. the high-LMA solution is
excluded.Comment: 6 eps figure
Screening length and the direction of plasma winds
We study the screening length of a heavy quark-antiquark pair in strongly
coupled gauge theory plasmas flowing at velocity v following a proposal by Liu,
Rajagopal, and Wiedemann. We analyze the screening length as the direction of
the plasma winds vary. To leading order in v, this angle-dependence can be
studied analytically for many theories by extending our previous formalism. We
show that the screening length is locally a minimum (maximum) when the pair is
perpendicular (parallel) to the plasma winds, which has been observed for the
N=4 plasma. Also, we compare AdS/CFT results with weak coupling ones, and we
discuss the subleading dependence on v for the Dp-brane.Comment: 20 pages, 4 figures, JHEP3; v2: discussion added and modifie
Response Functions in Phase Ordering Kinetics
We discuss the behavior of response functions in phase ordering kinetics
within the perturbation theory approach developed earlier. At zeroth order the
results agree with previous gaussian theory calculations. At second order the
nonequilibrium exponents \lambda and \lambda_{R} are changed but remain equal.Comment: 29 page
Supersymmetry for Fermion Masses
It is proposed that supersymmetry (SUSY) maybe used to understand fermion
mass hierarchies. A family symmetry Z_{3L} is introduced, which is the cyclic
symmetry among the three generation SU(2) doublets. SUSY breaks at a high
energy scale ~ 10^{11} GeV. The electroweak energy scale ~ 100 GeV is
unnaturally small. No additional global symmetry, like the R-parity, is
imposed. The Yukawa couplings and R-parity violating couplings all take their
natural values which are about (10^0-10^{-2}). Under the family symmetry, only
the third generation charged fermions get their masses. This family symmetry is
broken in the soft SUSY breaking terms which result in a hierarchical pattern
of the fermion masses. It turns out that for the charged leptons, the tau mass
is from the Higgs vacuum expectation value (VEV) and the sneutrino VEVs, the
muon mass is due to the sneutrino VEVs, and the electron gains its mass due to
both Z_{3L} and SUSY breaking. The large neutrino mixing are produced with
neutralinos playing the partial role of right-handed neutrinos. |V_{e3}| which
is for nu_e-nu_{tau} mixing is expected to be about 0.1. For the quarks, the
third generation masses are from the Higgs VEVs, the second generation masses
are from quantum corrections, and the down quark mass due to the sneutrino
VEVs. It explains m_c/m_s, m_s/m_e, m_d > m_u and so on. Other aspects of the
model are discussed.Comment: 25 pages, 3 figures, revtex4; neutrino oscillation and many
discussions added, smallness of the electron mass due to supersymmetry
pointed out; v3: numerical errors correcte
CD40 signal rewires fatty acid and glutamine metabolism for stimulating macrophage anti-tumorigenic functions.
Exposure of lipopolysaccharide triggers macrophage pro-inflammatory polarization accompanied by metabolic reprogramming, characterized by elevated aerobic glycolysis and a broken tricarboxylic acid cycle. However, in contrast to lipopolysaccharide, CD40 signal is able to drive pro-inflammatory and anti-tumorigenic polarization by some yet undefined metabolic programming. Here we show that CD40 activation triggers fatty acid oxidation (FAO) and glutamine metabolism to promote ATP citrate lyase-dependent epigenetic reprogramming of pro-inflammatory genes and anti-tumorigenic phenotypes in macrophages. Mechanistically, glutamine usage reinforces FAO-induced pro-inflammatory and anti-tumorigenic activation by fine-tuning the NAD <sup>+</sup> /NADH ratio via glutamine-to-lactate conversion. Genetic ablation of important metabolic enzymes involved in CD40-mediated metabolic reprogramming abolishes agonistic anti-CD40-induced antitumor responses and reeducation of tumor-associated macrophages. Together these data show that metabolic reprogramming, which includes FAO and glutamine metabolism, controls the activation of pro-inflammatory and anti-tumorigenic polarization, and highlight a therapeutic potential of metabolic preconditioning of tumor-associated macrophages before agonistic anti-CD40 treatments
Determination of superconducting anisotropy from magnetization data on random powders as applied to LuNiBC, YNiBC and MgB
The recently discovered intermetallic superconductor MgB2 appears to have a
highly anisotopic upper critical field with Hc2(max)/Hc2(min} = \gamma > 5. In
order to determine the temperature dependence of both Hc2(max) and Hc2(min) we
propose a method of extracting the superconducting anisotropy from the
magnetization M(H,T) of randomly oriented powder samples. The method is based
on two features in dM/dT the onset of diamagnetism at Tc(max), that is commonly
associated with Hc2, and a kink in dM/dT at a lower temperature Tc(min).
Results for LuNi2B2C and YNi2B2C powders are in agreement with anisotropic Hc2
obtained from magneto-transport measurements on single crystals. Using this
method on four different types of MgB2 powder samples we are able to determine
Hc2(max)(T) and Hc2(min)(T) with \gamma \approx 6
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