5,258 research outputs found
Direct solution of the hard pomeron problem for arbitrary conformal weight
A new method is applied to solve the Baxter equation for the one dimensional
system of noncompact spins. Dynamics of such an ensemble is equivalent to that
of a set of reggeized gluons exchanged in the high energy limit of QCD
amplitudes. The technique offers more insight into the old calculation of the
intercept of hard Pomeron, and provides new results in the odderon channel.Comment: Contribution to the ICHEP96 Conference, July 1996, Warsaw, Poland.
LaTeX, 4 pages, 3 epsf figures, includes modified stwol.sty file. Some
references were revise
Hydrodynamic gradient expansion in gauge theory plasmas
We utilize the fluid-gravity duality to investigate the large order behavior
of hydrodynamic gradient expansion of the dynamics of a gauge theory plasma
system. This corresponds to the inclusion of dissipative terms and transport
coefficients of very high order. Using the dual gravity description, we
calculate numerically the form of the stress tensor for a boost-invariant flow
in a hydrodynamic expansion up to terms with 240 derivatives. We observe a
factorial growth of gradient contributions at large orders, which indicates a
zero radius of convergence of the hydrodynamic series. Furthermore, we identify
the leading singularity in the Borel transform of the hydrodynamic energy
density with the lowest nonhydrodynamic excitation corresponding to a
`nonhydrodynamic' quasinormal mode on the gravity side.Comment: v2: 4+2 pages, 2 figures, title changed by journal, supplemental
material incorporated into the preprint, energy density coefficients up to
240th order included in the submission (change in normalization with respect
to v1), matches published versio
Solution of the Odderon Problem
The intercept of the odderon trajectory is derived, by finding the spectrum
of the second integral of motion of the three reggeon system in high energy
QCD. When combined with earlier solution of the appropriate Baxter equation,
this leads to the determination of the low lying states of that system. In
particular, the energy of the lowest state gives the intercept of the odderon
alpha_O(0)=1-0.2472 alpha_s N_c/pi.Comment: 11 pages, 2 Postscript figure
Coupling hydrodynamics to nonequilibrium degrees of freedom in strongly interacting quark-gluon plasma
Relativistic hydrodynamics simulations of quark-gluon plasma play a pivotal
role in our understanding of heavy ion collisions at RHIC and LHC. They are
based on a phenomenological description due to Mueller, Israel, Stewart (MIS)
and others, which incorporates viscous effects and ensures a well-posed initial
value problem. Focusing on the case of conformal plasma we propose a
generalization which includes, in addition, the dynamics of the least damped
far-from-equilibrium degree of freedom found in strongly coupled plasmas
through the AdS/CFT correspondence. We formulate new evolution equations for
general flows and then test them in the case of N=4 super Yang-Mills plasma by
comparing their solutions alongside solutions of MIS theory with numerical
computations of isotropization and boost-invariant flow based on holography. In
these tests the new equations reproduce the results of MIS theory when
initialized close to the hydrodynamic stage of evolution, but give a more
accurate description of the dynamics when initial conditions are set in the
pre-equilibrium regime.Comment: Minor improvements; references adde
On the supergravity description of boost invariant conformal plasma at strong coupling
We study string theory duals of the expanding boost invariant conformal gauge
theory plasmas at strong coupling. The dual supergravity background is
constructed as an asymptotic late-time expansion, corresponding to
equilibration of the gauge theory plasma. The absence of curvature
singularities in the first few orders of the late-time expansion of the dual
gravitational background unambiguously determines the equilibrium equation of
the state, and the shear viscosity of the gauge theory plasma. While the
absence of the leading pole singularities in the gravitational curvature
invariants at the third order in late-time expansion determines the relaxation
time of the plasma, the subleading logarithmic singularity can not be canceled
within a supergravity approximation. Thus, a supergravity approximation to a
dual description of the strongly coupled boost invariant expanding plasma is
inconsistent. Nevertheless we find that the relaxation time determined from
cancellation of pole singularities is quite robust.Comment: 26 pages, no figures; v2: references adde
The characteristics of thermalization of boost-invariant plasma from holography
We report on the approach towards the hydrodynamic regime of boost-invariant
N=4 super Yang-Mills plasma at strong coupling starting from various
far-from-equilibrium states at tau=0. The results are obtained through
numerical solution of Einstein's equations for the dual geometries, as
described in detail in the companion article arXiv:1203.0755. Despite the very
rich far-from-equilibrium evolution, we find surprising regularities in the
form of clear correlations between initial entropy and total produced entropy,
as well as between initial entropy and the temperature at thermalization,
understood as the transition to a hydrodynamic description. For 29 different
initial conditions that we consider, hydrodynamics turns out to be definitely
applicable for proper times larger than 0.7 in units of inverse temperature at
thermalization. We observe a sizable anisotropy in the energy-momentum tensor
at thermalization, which is nevertheless entirely due to hydrodynamic effects.
This suggests that effective thermalization in heavy ion collisions may occur
significantly earlier than true thermalization.Comment: 4 pages, 5 figures; see also the companion article arXiv:1203.0755;
v2: figure corrected (fixes problem with Acrobat); v3: various clarifications
and additional data points added; v4: typo fixed, publishe
Cell Proliferation During Immunological Perturbation in Three Transplanted Tumours
The cell population kinetics of 3 transplantable tumours has been studied under circumstances in which the tumour growth rate was modified by a disturbance of the immunological status of the host. In 2 cases a complete arrest of growth was achieved but in spite of this there was a barely significant change in the median intermitotic time of proliferating cells. The data indicate that growth retardation was associated with a reduction in the proportion of actively proliferating cells and the rate of cell production, with or without an increase in the absolute rate of cell loss
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