2,858 research outputs found
Anomalous mass dependence of radiative quark energy loss in a finite-size quark-gluon plasma
We demonstrate that for a finite-size quark-gluon plasma the induced gluon
radiation from heavy quarks is stronger than that for light quarks when the
gluon formation length becomes comparable with (or exceeds) the size of the
plasma. The effect is due to oscillations of the light-cone wave function for
the in-medium transition. The dead cone model by Dokshitzer and
Kharzeev neglecting quantum finite-size effects is not valid in this regime.
The finite-size effects also enhance the photon emission from heavy quarks.Comment: 8 pages, 3 figure
Induced photon emission from quark jets in ultrarelativistic heavy-ion collisions
We study the induced photon bremsstrahlung from a fast quark produced in
AA-collisions due to multiple scattering in quark-gluon plasma. For RHIC and
LHC conditions the induced photon spectrum is sharply peaked at photon energy
close to the initial quark energy. In this region the contribution of the
induced radiation to the photon fragmentation function exceeds the ordinary
vacuum radiation. Contrary to previous analyses our results show that at RHIC
and LHC energies the final-state interaction effects in quark-gluon plasma do
not suppress the direct photon production, and even may enhance it at p_{T}
about 5-15 GeV.Comment: 11 pages, 4 figure
Weak Wave Turbulence Scaling Theory for Diffusion and Relative Diffusion in Turbulent Surface Waves
We examine the applicability of the weak wave turbulence theory in explaining
experimental scaling results obtained for the diffusion and relative diffusion
of particles moving on turbulent surface waves. For capillary waves our
theoretical results are shown to be in good agreement with experimental
results, where a distinct crossover in diffusive behavior is observed at the
driving frequency. For gravity waves our results are discussed in the light of
ocean wave studies.Comment: 5 pages; for related work visit http://www.imedea.uib.es/~victo
Weakly nonlinear waves in magnetized plasma with a slightly non-Maxwellian electron distribution. Part 1, Stability of solitary waves
Weakly nonlinear waves in strongly magnetized plasma with slightly non-isothermal electrons are governed by a modified Zakharov–Kuznetsov (ZK) equation, containing both quadratic and half-order nonlinear terms, which we refer to as the Schamel–Korteweg–de Vries–Zakharov–Kuznetsov (SKdVZK) equation. We present a method to obtain an approximation for the growth rate, γ, of sinusoidal perpendicular perturbations of wavenumber, k, to SKdVZK solitary waves over the entire range of instability. Unlike for (modified) ZK equations with one nonlinear term, in this method there is no analytical expression for kc, the cut-off wavenumber (at which the growth rate is zero) or its corresponding eigenfunction. We therefore obtain approximate expressions for these using an expansion parameter, a, related to the ratio of the nonlinear terms. The expressions are then used to find γ for k near kc as a function of a. The approximant derived from combining these analytical results with the ones for small k agrees very well with the values of γ obtained numerically. It is found that both kc and the maximum growth rate decrease as the electron distribution becomes progressively less peaked than the Maxwellian. We also present new algebraic and rarefactive solitary wave solutions to the equation
Critical density of a soliton gas
We quantify the notion of a dense soliton gas by establishing an upper bound
for the integrated density of states of the quantum-mechanical Schr\"odinger
operator associated with the KdV soliton gas dynamics. As a by-product of our
derivation we find the speed of sound in the soliton gas with Gaussian spectral
distribution function.Comment: 7 page
Classical Strongly Coupled QGP: VII. Energy Loss
We use linear response analysis and the fluctuation-dissipation theorem to
derive the energy loss of a heavy quark in the SU(2) classical Coulomb plasma
in terms of the monopole and non-static structure factor. The result is
valid for all Coulomb couplings , the ratio of the mean potential
to kinetic energy. We use the Liouville equation in the collisionless limit to
assess the SU(2) non-static structure factor. We find the energy loss to be
strongly dependent on . In the liquid phase with , the
energy loss is mostly metallic and soundless with neither a Cerenkov nor a Mach
cone. Our analytical results compare favorably with the SU(2) molecular
dynamics simulations at large momentum and for heavy quark masses.Comment: 18 pages, 15 figures. v2: added references, changed title, replaced
figures for Fig. 7, corrected typo
Massive Cosmologies
We explore the cosmological solutions of a recently proposed extension of
General Relativity with a Lorentz-invariant mass term. We show that the same
constraint that removes the Boulware-Deser ghost in this theory also prohibits
the existence of homogeneous and isotropic cosmological solutions.
Nevertheless, within domains of the size of inverse graviton mass we find
approximately homogeneous and isotropic solutions that can well describe the
past and present of the Universe. At energy densities above a certain crossover
value, these solutions approximate the standard FRW evolution with great
accuracy. As the Universe evolves and density drops below the crossover value
the inhomogeneities become more and more pronounced. In the low density regime
each domain of the size of the inverse graviton mass has essentially non-FRW
cosmology. This scenario imposes an upper bound on the graviton mass, which we
roughly estimate to be an order of magnitude below the present-day value of the
Hubble parameter. The bound becomes especially restrictive if one utilizes an
exact self-accelerated solution that this theory offers. Although the above are
robust predictions of massive gravity with an explicit mass term, we point out
that if the mass parameter emerges from some additional scalar field
condensation, the constraint no longer forbids the homogeneous and isotropic
cosmologies. In the latter case, there will exist an extra light scalar field
at cosmological scales, which is screened by the Vainshtein mechanism at
shorter distances.Comment: 21 page
Collapse and stable self-trapping for Bose-Einstein condensates with 1/r^b type attractive interatomic interaction potential
We consider dynamics of Bose-Einstein condensates with long-range attractive
interaction proportional to and arbitrary angular dependence. It is
shown exactly that collapse of Bose-Einstein condensate without contact
interactions is possible only for . Case is critical and requires
number of particles to exceed critical value to allow collapse. Critical
collapse in that case is strong one trapping into collapsing region a finite
number of particles.
Case is supercritical with expected weak collapse which traps rapidly
decreasing number of particles during approach to collapse. For
singularity at is not strong enough to allow collapse but attractive
interaction admits stable self-trapping even in absence of external
trapping potential
N-wave interactions related to simple Lie algebras. Z_2- reductions and soliton solutions
The reductions of the integrable N-wave type equations solvable by the
inverse scattering method with the generalized Zakharov-Shabat systems L and
related to some simple Lie algebra g are analyzed. The Zakharov- Shabat
dressing method is extended to the case when g is an orthogonal algebra.
Several types of one soliton solutions of the corresponding N- wave equations
and their reductions are studied. We show that to each soliton solution one can
relate a (semi-)simple subalgebra of g. We illustrate our results by 4-wave
equations related to so(5) which find applications in Stockes-anti-Stockes wave
generation.Comment: 18 pages, 1 figure, LaTeX 2e, IOP-style; More clear exposition.
Introduction and Section 5 revised. Some typos are correcte
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