2,367 research outputs found
Quantum Many-Body Dynamics of Dark Solitons in Optical Lattices
We present a fully quantum many-body treatment of dark solitons formed by
ultracold bosonic atoms in one-dimensional optical lattices. Using
time-evolving block decimation to simulate the single-band Bose-Hubbard
Hamiltonian, we consider the quantum dynamics of density and phase engineered
dark solitons as well as the quantum evolution of mean-field dark solitons
injected into the quantum model. The former approach directly models how one
may create quantum entangled dark solitons in experiment. While we have already
presented results regarding the latter approach elsewhere [Phys. Rev. Lett.
{\bf 103}, 140403 (2009)], we expand upon those results in this work. In both
cases, quantum fluctuations cause the dark soliton to fill in and may induce an
inelasticity in soliton-soliton collisions. Comparisons are made to the
Bogoliubov theory which predicts depletion into an anomalous mode that fills in
the soliton. Our many-body treatment allows us to go beyond the Bogoliubov
approximation and calculate explicitly the dynamics of the system's natural
orbitals.Comment: 14 pages, 11 figures -- v3 has only minor changes from v2 -- this is
the print versio
Energy loss in perturbative QCD
We review the properties of energetic parton propagation in hot or cold QCD
matter, as obtained in recent works. Advances in understanding the energy loss
- collisional and radiative - are summarized, with emphasis on the latter: it
features very interesting properties which may help to detect the quark-gluon
plasma produced in heavy ion collisions. We describe two different theoretical
approaches, which lead to the same radiated gluon energy spectrum. The case of
a longitudinally expanding QCD plasma is investigated. The energy lost by a jet
with given opening angle is calculated in view of making predictions for the
suppression (quenching) of hard jet production. Phenomenological implications
for the difference between hot and cold matter are discussed. Numerical
estimates of the loss suggest that it may be significantly enhanced in hot
compared to cold matter.Comment: 49 pages latex file with 11 embedded PS figures. Uses ar.sty
(included), one equation revised. submitted to Annual Review of Nuclear and
Particle Scienc
Regge description of high energy pion pion total cross sections
We have recently presented a Regge description of pion-pion total cross
sections valid above 1.4 GeV, consistent with the few existing experiments,
factorization and crossing symmetry. In this note we show how it also describes
a further large data sample obtained from an analysis of experiments on
and .Comment: 3 pages. To appear in the proceedings of the MESON 2004 workshop,
Krakow, July 2004, to be published in Int. J. Mod. Phys.
Variation of jet quenching from RHIC to LHC and thermal suppression of QCD coupling constant
We perform a joint jet tomographic analysis of the data on the nuclear
modification factor from PHENIX at RHIC and ALICE at LHC. The
computations are performed accounting for radiative and collisional parton
energy loss with running coupling constant. Our results show that the observed
slow variation of from RHIC to LHC indicates that the QCD coupling
constant is suppressed in the quark-gluon plasma produced at LHC.Comment: 9 pages, 2 figure
Hamiltonian formalism and the Garrett-Munk spectrum of internal waves in the ocean
Wave turbulence formalism for long internal waves in a stratified fluid is
developed, based on a natural Hamiltonian description. A kinetic equation
appropriate for the description of spectral energy transfer is derived, and its
self-similar stationary solution corresponding to a direct cascade of energy
toward the short scales is found. This solution is very close to the high
wavenumber limit of the Garrett-Munk spectrum of long internal waves in the
ocean. In fact, a small modification of the Garrett-Munk formalism includes a
spectrum consistent with the one predicted by wave turbulence.Comment: 4 pages latex fil
Instability and Evolution of Nonlinearly Interacting Water Waves
We consider the modulational instability of nonlinearly interacting
two-dimensional waves in deep water, which are described by a pair of
two-dimensional coupled nonlinear Schroedinger equations. We derive a nonlinear
dispersion relation. The latter is numerically analyzed to obtain the regions
and the associated growth rates of the modulational instability. Furthermore,
we follow the long term evolution of the latter by means of computer
simulations of the governing nonlinear equations and demonstrate the formation
of localized coherent wave envelopes. Our results should be useful for
understanding the formation and nonlinear propagation characteristics of large
amplitude freak waves in deep water.Comment: 4 pages, 4 figures, to appear in Physical Review Letter
Condensation of classical nonlinear waves
We study the formation of a large-scale coherent structure (a condensate) in
classical wave equations by considering the defocusing nonlinear Schr\"odinger
equation as a representative model. We formulate a thermodynamic description of
the condensation process by using a wave turbulence theory with ultraviolet
cut-off. In 3 dimensions the equilibrium state undergoes a phase transition for
sufficiently low energy density, while no transition occurs in 2 dimensions, in
analogy with standard Bose-Einstein condensation in quantum systems. Numerical
simulations show that the thermodynamic limit is reached for systems with
computational modes and greater. On the basis of a modified wave
turbulence theory, we show that the nonlinear interaction makes the transition
to condensation subcritical. The theory is in quantitative agreement with the
simulations
Jet quenching with running coupling including radiative and collisional energy losses
We calculate the nuclear modification factor for RHIC and LHC conditions
accounting for the radiative and collisional parton energy loss with the
running coupling constant.We find that the RHIC data can be explained both in
the scenario with the chemically equilibrium quark-gluon plasma and purely
gluonic plasma with slightly different thermal suppression of the coupling
constant. The role of the parton energy gain due to gluon absorption is also
investigated. Our results show that the energy gain gives negligible effect.Comment: 11 pages, 3 figure
Superluminality in DGP
We reconsider the issue of superluminal propagation in the DGP model of
infrared modified gravity. Superluminality was argued to exist in certain
otherwise physical backgrounds by using a particular, physically relevant
scaling limit of the theory. In this paper, we exhibit explicit
five-dimensional solutions of the full theory that are stable against small
fluctuations and that indeed support superluminal excitations. The scaling
limit is neither needed nor invoked in deriving the solutions or in the
analysis of its small fluctuations. To be certain that the superluminality
found here is physical, we analyze the retarded Green's function of the scalar
excitations, finding that it is causal and stable, but has support on a widened
light-cone. We propose to use absence of superluminal propagation as a method
to constrain the parameters of the DGP model. As a first application of the
method, we find that whenever the 4D energy density is a pure cosmological
constant and a hierarchy of scales exists between the 4D and 5D Planck masses,
superluminal propagation unavoidably occurs.Comment: 23 pages. Minor corrections. Version to appear in JHE
Landau Damping and Coherent Structures in Narrow-Banded 1+1 Deep Water Gravity Waves
We study the nonlinear energy transfer around the peak of the spectrum of
surface gravity waves by taking into account nonhomogeneous effects. In the
narrow-banded approximation the kinetic equation resulting from a
nonhomogeneous wave field is a Vlasov-Poisson type equation which includes at
the same time the random version of the Benjamin-Feir instability and the
Landau damping phenomenon. We analytically derive the values of the Phillips'
constant and the enhancement factor for which the
narrow-banded approximation of the JONSWAP spectrum is unstable. By performing
numerical simulations of the nonlinear Schr\"{o}dinger equation we check the
validity of the prediction of the related kinetic equation. We find that the
effect of Landau damping is to suppress the formation of coherent structures.
The problem of predicting freak waves is briefly discussed.Comment: 4 pages, 3 figure
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