4,648 research outputs found
Transition radiation in the quantum regime as a diffractive phenomenon
We demonstrate that the transition photon radiation and pair creation can be
interpreted as a diffractive phenomenon in terms of the light-cone wave
functions in a way similar to the Good-Walker approach [6] to the diffraction
dissociation. Our formulas for spectra agree with those obtained by Baier and
Katkov [5] within the quasiclassical operator method. However, there is some
disagreement with earlier results by Garibyan [4].Comment: 7 pages. The journal version published in Phys. Lett.
Relating the description of gluon production in pA collisions and parton energy loss in AA collisions
We calculate the classical gluon field of a fast projectile passing through a
dense medium. We show that this allows us to calculate both the initial state
gluon production in proton-nucleus collisions and the final state gluon
radiation off a hard parton produced in nucleus-nucleus collisions. This
unified description of these two phenomena makes the relation between the
saturation scale and the transport coefficient more transparent.
Also, we discuss the validity of the eikonal approximation for gluon
propagation inside the nucleus in proton-nucleus collisions at RHIC energy.Comment: 18 pages, 3 figure
Coexistence of Weak and Strong Wave Turbulence in a Swell Propagation
By performing two parallel numerical experiments -- solving the dynamical
Hamiltonian equations and solving the Hasselmann kinetic equation -- we
examined the applicability of the theory of weak turbulence to the description
of the time evolution of an ensemble of free surface waves (a swell) on deep
water. We observed qualitative coincidence of the results.
To achieve quantitative coincidence, we augmented the kinetic equation by an
empirical dissipation term modelling the strongly nonlinear process of
white-capping. Fitting the two experiments, we determined the dissipation
function due to wave breaking and found that it depends very sharply on the
parameter of nonlinearity (the surface steepness). The onset of white-capping
can be compared to a second-order phase transition. This result corroborates
with experimental observations by Banner, Babanin, Young.Comment: 5 pages, 5 figures, Submitted in Phys. Rev. Letter
Weak compressible magnetohydrodynamic turbulence in the solar corona
This Letter presents a calculation of the power spectra of weakly turbulent
Alfven waves and fast magnetosonic waves ("fast waves") in low-beta plasmas. It
is shown that three-wave interactions transfer energy to high-frequency fast
waves and, to a lesser extent, high-frequency Alfven waves. MHD turbulence is
thus a promising mechanism for producing the high-frequency waves needed to
explain the anisotropic heating of minor ions in the solar corona.Comment: 4 pages, 3 figures, accepted, Phys. Rev. Let
Integrable turbulence generated from modulational instability of cnoidal waves
We study numerically the nonlinear stage of modulational instability (MI) of
cnoidal waves, in the framework of the focusing one-dimensional Nonlinear
Schrodinger (NLS) equation. Cnoidal waves are the exact periodic solutions of
the NLS equation and can be represented as a lattice of overlapping solitons.
MI of these lattices lead to development of "integrable turbulence" [Zakharov
V.E., Stud. Appl. Math. 122, 219-234 (2009)]. We study the major
characteristics of the turbulence for dn-branch of cnoidal waves and
demonstrate how these characteristics depend on the degree of "overlapping"
between the solitons within the cnoidal wave.
Integrable turbulence, that develops from MI of dn-branch of cnoidal waves,
asymptotically approaches to it's stationary state in oscillatory way. During
this process kinetic and potential energies oscillate around their asymptotic
values. The amplitudes of these oscillations decay with time as t^{-a},
1<a<1.5, the phases contain nonlinear phase shift decaying as t^{-1/2}, and the
frequency of the oscillations is equal to the double maximal growth rate of the
MI, s=2g_{max}. In the asymptotic stationary state the ratio of potential to
kinetic energy is equal to -2. The asymptotic PDF of wave amplitudes is close
to Rayleigh distribution for cnoidal waves with strong overlapping, and is
significantly non-Rayleigh one for cnoidal waves with weak overlapping of
solitons. In the latter case the dynamics of the system reduces to two-soliton
collisions, which occur with exponentially small rate and provide up to
two-fold increase in amplitude compared with the original cnoidal wave.Comment: 36 pages, 25 figure
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
Transverse Spectra of Radiation Processes in Medium
We develop a formalism for evaluation of the transverse momentum dependence
of cross sections of the radiation processes in medium. The analysis is based
on the light-cone path integral approach to the induced radiation. The results
are applicable in both QED and QCD
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