3,197 research outputs found
Gamma flashes from relativistic electron-positron plasma droplets
Ultra-intense lasers are expected to produce, in near future, relativistic
electron-positron plasma droplets. Considering the local photon production rate
in complete leading order in quantum electrodynamics (QED), we point out that
these droplets are interesting sources of gamma ray flashesComment: 4 pages, 6 figures; Text has been revised and new refs. are adde
Flat-top oscillons in an expanding universe
Oscillons are extremely long lived, oscillatory, spatially localized field
configurations that arise from generic initial conditions in a large number of
non-linear field theories. With an eye towards their cosmological implications,
we investigate their properties in an expanding universe. We (1) provide an
analytic solution for one dimensional oscillons (for the models under
consideration) and discuss their generalization to 3 dimensions, (2) discuss
their stability against long wavelength perturbations and (3) estimate the
effects of expansion on their shapes and life-times. In particular, we discuss
a new, extended class of oscillons with surprisingly flat tops. We show that
these flat topped oscillons are more robust against collapse instabilities in
(3+1) dimensions than their usual counterparts. Unlike the solutions found in
the small amplitude analysis, the width of these configurations is a
non-monotonic function of their amplitudes.Comment: v2-matches version published in Phys. Rev D. Updated references and
minor modification to section 4.
Position-dependent-mass; Cylindrical coordinates, separability, exact solvability, and PT-symmetry
The kinetic energy operator with position-dependent-mass in cylindrical
coordinates is obtained. The separability of the corresponding Schr\"odinger
equation is discussed within radial cylindrical mass settings. Azimuthal
symmetry is assumed and spectral signatures of various z-dependent interaction
potentials (Hermitian and non-Hermitian PT-symmetric) are reported.Comment: 16 page
Conserved Density Fluctuation and Temporal Correlation Function in HTL Perturbation Theory
Considering recently developed Hard Thermal Loop perturbation theory that
takes into account the effect of the variation of the external field through
the fluctuations of a conserved quantity we calculate the temporal component of
the Euclidian correlation function in the vector channel. The results are found
to be in good agreement with the very recent results obtained within the
quenched approximation of QCD and small values of the quark mass ()
on improved lattices of size at (),
(), and (), where is
the temporal extent of the lattice. This suggests that the results from lattice
QCD and Hard Thermal Loop perturbation theory are in close proximity for a
quantity associated with the conserved density fluctuation.Comment: 16 pages, 4 figures; One para added in introduction, Fig 1 modified;
Accepted in Phys. Rev.
Profinite completion of Grigorchuk's group is not finitely presented
In this paper we prove that the profinite completion of
the Grigorchuk group is not finitely presented as a profinite
group. We obtain this result by showing that H^2(\mathcal{\hat
G},\field{F}_2) is infinite dimensional. Also several results are proven about
the finite quotients including minimal
presentations and Schur Multipliers
Low Mass Dilepton Rate from the Deconfined Phase
We discuss low mass dilepton rates ( GeV) from the deconfined phase of
QCD using both perturbative and non-perturbative models and compare with those
from lattice gauge theory and in-medium hadron gas. Our analysis suggests that
the rate at very low invariant mass ( MeV) using the nonperturbative
gluon condensate in a semiempirical way within the Green function dominates
over the Born-rate and independent of any uncertainty associated with the
choice of the strong coupling in perturbation theory. On the other hand the
rate from interaction in the deconfined phase is important between 200
MeV M\ge 200M\ge 500$ MeV, constraining on the broad resonance structures
in the dilepton rate at large invariant mass. We also discuss the lattice
constraints on the low mass dilepton rate. Furthermore, we discuss a more
realistic way to advocate the quark-hadron duality hypothesis based on the
dilepton rates from QGP and hadron gas than it is done in the literature.Comment: 24 pages, 9 figures; Discussion added, Accepted in Phys. Rev.
d-Dimensional generalization of the point canonical transformation for a quantum particle with position-dependent mass
The d-dimensional generalization of the point canonical transformation for a
quantum particle endowed with a position-dependent mass in Schrodinger equation
is described. Illustrative examples including; the harmonic oscillator,
Coulomb, spiked harmonic, Kratzer, Morse oscillator, Poschl-Teller and Hulthen
potentials are used as reference potentials to obtain exact energy eigenvalues
and eigenfunctions for target potentials at different position-dependent mass
settings.Comment: 14 pages, no figures, to appear in J. Phys. A: Math. Ge
Colour-singlet clustering of partons and recombination model for hadronization of quark-gluon plasma
colour-singlet restriction, along with flavour and spin symmetry,
on thermal partonic ensemble is shown to recombine the partons with internal
colour structure into colour-singlet multi-quark clusters which can be
identified with various hadronic modes at a given temperature. This provides a
possible basis for recombination model for hadronization of quark-gluon plasma.
This also leads to a natural explanation for the ratio of (anti)protons to
pions and the quark number scaling of the elliptic flow coefficient in
relativistic heavy-ion collisions.Comment: 5 pages; version accepted as a Rapid Communication in Phys. Rev.
Radiative and Collisional Jet Energy Loss in the Quark-Gluon Plasma at RHIC
We calculate and compare bremsstrahlung and collisional energy loss of hard
partons traversing a quark-gluon plasma. Our treatment of both processes is
complete at leading order in the coupling and accounts for the probabilistic
nature of the jet energy loss. We find that the nuclear modification factor
for neutral production in heavy ion collisions is sensitive to
the inclusion of collisional and radiative energy loss contributions while the
averaged energy loss only slightly increases if collisional energy loss is
included for parent parton energies . These results are important for
the understanding of jet quenching in Au+Au collisions at at
RHIC. Comparison with data is performed applying the energy loss calculation to
a relativistic ideal (3+1)-dimensional hydrodynamic description of the
thermalized medium formed at RHIC.Comment: 4 pages, 3 figure
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