84,835 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
Unifying Requirements and Code: an Example
Requirements and code, in conventional software engineering wisdom, belong to
entirely different worlds. Is it possible to unify these two worlds? A unified
framework could help make software easier to change and reuse. To explore the
feasibility of such an approach, the case study reported here takes a classic
example from the requirements engineering literature and describes it using a
programming language framework to express both domain and machine properties.
The paper describes the solution, discusses its benefits and limitations, and
assesses its scalability.Comment: 13 pages; 7 figures; to appear in Ershov Informatics Conference, PSI,
Kazan, Russia (LNCS), 201
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
QCD at non-zero temperature from the lattice
I review the status of lattice QCD calculations at non-zero temperature.
After summarizing what is known about the equilibrium properties of strongly
interacting matter, I discuss in more detail recent results concerning the
quark-mass dependence of the thermal phase transition and the status of
calculations of non-equilibrium properties.Comment: 20 pages, 2 figures, proceedings of the Lattice 2015 conference in
Kobe, Japa
Top Quark Properties
Recent measurements of top-quark properties at the LHC and at the Tevatron
are presented. The results include precision measurements of standard model
parameters, such as the top-quark mass, the measurement of angular
distributions as well as the search for anomalous couplings.Comment: Conference proceedings for Lepton Photon, Ljubljana, 17-22 August
2015, 12 pages, 10 figure
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