821 research outputs found
Is Rho-Meson Melting Compatible with Chiral Restoration?
Utilizing in-medium vector spectral functions which describe dilepton data in
ultra-relativistic heavy-ion collisions, we conduct a comprehensive evaluation
of QCD and Weinberg sum rules at finite temperature. The starting point is our
recent study in vacuum, where the sum rules have been quantitatively satisfied
using phenomenological axial-/vector spectral functions which describe hadronic
tau-decay data. In the medium, the temperature dependence of condensates and
chiral order parameters is taken from thermal lattice QCD where available, and
otherwise estimated from a hadron resonance gas. Since little is known about
the in-medium axial-vector spectral function, we model it with a Breit-Wigner
ansatz allowing for smooth temperature variations of its width and mass
parameters. Our study thus amounts to testing the compatibility of the
-broadening found in dilepton experiments with (the approach toward)
chiral restoration, and thereby searching for viable in-medium axial-vector
spectral functions.Comment: 8 pages, 4 figures, updated to be consistent with published versio
Charmonium moving through a strongly coupled QCD plasma: a holographic perspective
We study the properties of charmonium in a strongly coupled QCD-like plasma
at finite momentum. As a basis for this study, a "bottom-up" holographic model
is used which has been previously shown to reproduce charmonium phenomenology
in vacuum and give a reasonable dissociation temperature at zero momentum. The
finite momentum spectral functions are presented and found to be consistent
with recent lattice results. The in-medium dispersion relation and momentum
dependence of decay width of J/Psi have also been studied. We find no signature
of a subluminal limiting velocity from the dispersion relation, while we note
that the dissociation temperature decreases with momentum faster than previous
holographic models. Based upon the dissociation temperature, a maximum momentum
for J/Psi in medium is identified and its phenomenological implications on
J/Psi suppression are discussed.Comment: 23 pages, 8 figures. References added. Published versio
Conservation laws for the classical Toda field theories
We have performed some explicit calculations of the conservation laws for
classical (affine) Toda field theories, and some generalizations of these
models. We show that there is a huge class of generalized models which have an
infinite set of conservation laws, with their integrated charges being in
involution. Amongst these models we find that only the and
() Toda field theories admit such conservation laws for spin-3. We
report on our explicit calculations of spin-4 and spin-5 conservation laws in
the (affine) Toda models. Our perhaps most interesting finding is that there
exist conservation laws in the models ( which have a different
origin than the exponents of the corresponding affine theory or the
energy-momentum tensor of a conformal theory.Comment: 9 pages, Late
Using Conservation Laws to Solve Toda Field Theories
We investigate the question of how the knowledge of sufficiently many local
conservation laws for a model can be utilized to solve the model. We show that
for models where the conservation laws can be written in one-sided forms, like
\barpartial Q_s = 0, the problem can always be reduced to solving a closed
system of ordinary differential equations. We investigate the , , and
Toda field theories in considerable detail from this viewpoint. One of
our findings is that there is in each case a transformation group intrinsic to
the model. This group is built on a specific real form of the Lie algebra used
to label the Toda field theory. It is the group of field transformations which
leaves the conserved densities invariant.Comment: Latex, 24 page
On the form of local conservation laws for some relativistic field theories in 1+1 dimensions
We investigate the possible form of local translation invariant conservation
laws associated with the relativistic field equations
\partial\bar\partial\phi_i=-v_i(\bphi) for a multicomponent field \bphi.
Under the assumptions that (i)~the 's can be expressed as linear
combinations of partial derivatives of a set of
functions w_j(\bphi), (ii)~the space of functions spanned by the 's is
closed under partial derivations, and (iii)~the fields \bphi take values in a
simply connected space, the local conservation laws can either be transformed
to the form (where
and are homogeneous polynomials in the variables
, ,\ldots), or to the parity
transformed version of this expression .Comment: 12 pages, Late
Shear induced normal stress differences in aqueous foams
A finite simple shear deformation of an elastic solid induces unequal normal
stresses. This nonlinear phenomenon, known as the Poynting effect, is governed
by a universal relation between shear strain and first normal stresses
difference, valid for non-dissipative elastic materials. We provide the first
experimental evidence that an analog of the Poynting effect exists in aqueous
foams where besides the elastic stress, there are significant viscous or
plastic stresses. These results are interpreted in the framework of a
constitutive model, derived from a physical description of foam rheology
Quantitative sum rule analysis of low-temperature spectral functions
We analyze QCD and Weinberg-type sum rules in a low-temperature pion gas
using vector and axial-vector spectral functions following from the
model-independent chiral-mixing scheme. Toward this end we employ recently
constructed vacuum spectral functions with ground and first-excited states in
both channels and a universal perturbative continuum; they quantitatively
describe hadronic tau-decay data and satisfy vacuum sum rules. These features
facilitate the implementation of chiral mixing without further assumptions, and
lead to in-medium spectral functions which exhibit a mutual tendency of
compensating resonance and dip structures, suggestive for an approach toward
structureless distributions. In the sum rule analysis, we account for pion mass
corrections, which turn out to be significant. While the Weinberg sum rules
remain satisfied even at high temperatures, the numerical evaluation of the QCD
sum rules for vector and axial-vector channels reveals significant deviations
setting in for temperatures beyond ~140 MeV, suggestive of additional physics
beyond low-energy chiral pion dynamics.Comment: 8 pages, 3 figure
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