59,982 research outputs found
The transverse structure of the QCD string
The characterization of the transverse structure of the QCD string is
discussed. We formulate a conjecture as to how the stress-energy tensor of the
underlying gauge theory couples to the string degrees of freedom. A consequence
of the conjecture is that the energy density and the longitudinal-stress
operators measure the distribution of the transverse position of the string, to
leading order in the string fluctuations, whereas the transverse-stress
operator does not. We interpret recent numerical measurements of the transverse
size of the confining string and show that the difference of the energy and
longitudinal-stress operators is the appropriate probe to use when comparing
with the next-to-leading order string prediction. Secondly we derive the
constraints imposed by open-closed string duality on the transverse structure
of the string. We show that a total of three independent `gravitational' form
factors characterize the transverse profile of the closed string, and obtain
the interpretation of recent effective string theory calculations: the square
radius of a closed string of length \beta, defined from the slope of its
gravitational form factor, is given by (d-1)/(2\pi\sigma)\log(\beta/(4r_0)) in
d space dimensions. This is to be compared with the well-known result that the
width of the open-string at mid-point grows as (d-1)/(2\pi\sigma) log(r/r_0).
We also obtain predictions for transition form factors among closed-string
states.Comment: 21 pages, 1 figur
Density, short-range order and the quark-gluon plasma
We study the thermal part of the energy density spatial correlator in the
quark-gluon plasma. We describe its qualitative form at high temperatures. We
then calculate it out to distances approx. 1.5/T in SU(3) gauge theory lattice
simulations for the range of temperatures 0.9<= T/T_c<= 2.2. The
vacuum-subtracted correlator exhibits non-monotonic behavior, and is almost
conformal by 2T_c. Its broad maximum at r approx. 0.6/T suggests a dense medium
with only weak short-range order, similar to a non-relativistic fluid near the
liquid-gas phase transition, where eta/s is minimal.Comment: 4 pages, 4 figure
Lattice Gauge Theory Sum Rule for the Shear Channel
An exact expression is derived for the thermal correlator of
shear stress in SU() lattice gauge theory. I remove a logarithmic
divergence by taking a suitable linear combination of the shear correlator and
the correlator of the energy density. The operator product expansion shows that
the same linear combination has a finite limit when . It
follows that the vacuum-subtracted shear spectral function vanishes at large
frequencies at least as fast as and obeys a sum rule. The
trace anomaly makes a potential contribution to the spectral sum rule which
remains to be fully calculated, but which I estimate to be numerically small
for . By contrast with the bulk channel, the shear channel
spectral density is then overall enhanced as compared to the spectral density
in vacuo.Comment: 11 pages, no figure
Cutoff Effects on Energy-Momentum Tensor Correlators in Lattice Gauge Theory
We investigate the discretization errors affecting correlators of the
energy-momentum tensor at finite temperature in SU() gauge
theory with the Wilson action and two different discretizations of
. We do so by using lattice perturbation theory and
non-perturbative Monte-Carlo simulations. These correlators, which are
functions of Euclidean time and spatial momentum , are the
starting point for a lattice study of the transport properties of the gluon
plasma. We find that the correlator of the energy has much
larger discretization errors than the correlator of momentum . Secondly, the shear and diagonal stress correlators ( and
) require \Nt\geq 8 for the point to be in the scaling
region and the cutoff effect to be less than 10%. We then show that their
discretization errors on an anisotropic lattice with \as/\at=2 are comparable
to those on the isotropic lattice with the same temporal lattice spacing.
Finally, we also study finite correlators.Comment: 16 pages, 5 figure
High-Precision Thermodynamics and Hagedorn Density of States
We compute the entropy density of the confined phase of QCD without quarks on
the lattice to very high accuracy. The results are compared to the entropy
density of free glueballs, where we include all the known glueball states below
the two-particle threshold. We find that an excellent, parameter-free
description of the entropy density between 0.7Tc and Tc is obtained by
extending the spectrum with the exponential spectrum of the closed bosonic
string.Comment: 4 pages, 3 figure
Vector screening masses in the quark-gluon plasma and their physical significance
Static and non-static thermal screening states that couple to the conserved
vector current are investigated in the high-temperature phase of QCD. Their
masses and couplings to the current are determined at weak coupling, as well as
using two-flavor lattice QCD simulations. A consistent picture emerges from the
comparison, providing evidence that non-static Matsubara modes can indeed be
treated perturbatively. We elaborate on the physical significance of the
screening masses.Comment: 4 pages, 3 figures. Submitted as a contribution to the proceedings of
the Quark Matter 2014 conference (talk given by H. Meyer
A relation between screening masses and real-time rates
Thermal screening masses related to the conserved vector current are
determined for the case that the current carries a non-zero Matsubara
frequency, both in a weak-coupling approach and through lattice QCD. We point
out that such screening masses are sensitive to the same infrared physics as
light-cone real-time rates. In particular, on the perturbative side, the
inhomogeneous Schrodinger equation determining screening correlators is shown
to have the same general form as the equation implementing LPM resummation for
the soft-dilepton and photon production rates from a hot QCD plasma. The static
potential appearing in the equation is identical to that whose soft part has
been determined up to NLO and on the lattice in the context of jet quenching.
Numerical results based on this potential suggest that screening masses
overshoot the free results (multiples of 2piT) more strongly than at zero
Matsubara frequency. Four-dimensional lattice simulations in two-flavour QCD at
temperatures of 250 and 340 MeV confirm the non-static screening masses at the
10% level. Overall our results lend support to studies of jet quenching based
on the same potential at T > 250 MeV.Comment: 32 pages. v2: clarifications added, typos corrected; published
versio
Integrability of the critical point of the Kagom\'e three-state Potts mode
The vicinity of the critical point of the three-state Potts model on a
Kagom\'e lattice is studied by mean of Random Matrix Theory. Strong evidence
that the critical point is integrable is given.Comment: 1 LaTex file + 3 eps files 7 page
r-Process Nucleosynthesis in Shocked Surface Layers of O-Ne-Mg Cores
We demonstrate that rapid expansion of the shocked surface layers of an
O-Ne-Mg core following its collapse can result in r-process nucleosynthesis. As
the supernova shock accelerates through these layers, it makes them expand so
rapidly that free nucleons remain in disequilibrium with alpha-particles
throughout most of the expansion. This allows heavy r-process isotopes
including the actinides to form in spite of the very low initial neutron excess
of the matter. We estimate that yields of heavy r-process nuclei from this site
may be sufficient to explain the Galactic inventory of these isotopes.Comment: 11 pages, 1 figure, to appear in the Astrophysical Journal Letter
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