8,156 research outputs found
Covariant Linear Response Theory of Relativistic QED Plasmas
We start from the QED Lagrangian to describe a charged many-particle system
coupled to the radiation field. A covariant density matrix approach to kinetic
theory of QED plasmas, subjected to a strong external electro-magnetic field
has recently been developed [1,2]. We use the hyperplane formalism in order to
perform a manifest covariant quantization and to implement initial correlations
to the solution of the Liouville-von Neumann equation. A perturbative expansion
in orders of the fine structure constant for the correlation functions as well
as the statistical operator is applied. The non-equilibrium state of the system
is given within generalized linear response theory. Expressions for the
susceptibility tensor, describing the plasma response, are calculated within
different approximations, like the RPA approximation or considering collisions
within the Born-approximation. In particular, the process of relativistic
inverse bremsstrahlung in a plasma is discussed.Comment: Latex 39 pages, 4 figure
Superfluidity in a Three-flavor Fermi Gas with SU(3) Symmetry
We investigate the superfluidity and the associated Nambu-Goldstone modes in
a three-flavor atomic Fermi gas with SU(3) global symmetry. The s-wave pairing
occurs in flavor anti-triplet channel due to the Pauli principle, and the
superfluid state contains both gapped and gapless fermionic excitations.
Corresponding to the spontaneous breaking of the SU(3) symmetry to a SU(2)
symmetry with five broken generators, there are only three Nambu-Goldstone
modes, one is with linear dispersion law and two are with quadratic dispersion
law. The other two expected Nambu-Goldstone modes become massive with a mass
gap of the order of the fermion energy gap in a wide coupling range. The
abnormal number of Nambu-Goldstone modes, the quadratic dispersion law and the
mass gap have significant effect on the low temperature thermodynamics of the
matter.Comment: 9 pages, 2 figures, published versio
Selmer Groups over p-adic Lie Extensions I
Let be an elliptic curve defined over a number field . In this paper,
we study the structure of the -Selmer group of over -adic Lie
extensions of which are obtained by adjoining to the
-division points of an abelian variety defined over . The main focus
of the paper is the calculation of the \Gal(F_\infty/F)-Euler characteristic
of the -Selmer group of . The final section illustrates the main
theory with the example of an elliptic curve of conductor 294.Comment: 23 page
Vector meson spectral function and dilepton production rate in a hot and dense medium within an effective QCD approach
The properties of the vector meson current-current correlation function and
its spectral representation are investigated in details with and without
isoscalar-vector interaction within the framework of effective QCD approach,
namely Nambu-Jona-Lasinio (NJL) model and its Polyakov Loop extended version
(PNJL), at finite temperature and finite density. The influence of the
isoscalarvector interaction on the vector meson correlator is obtained using
the ring resummation known as the Random Phase Approximation (RPA). The
spectral as well as the correlation function in PNJL model show that the vector
meson retains its bound property up to a moderate value of temperature above
the phase transition. Using the vector meson spectral function we, for the
first time, obtained the dilepton production rate from a hot and dense medium
within the framework of PNJL model that takes into account the nonperturbative
effect through the Polyakov Loop fields. The dilepton production rate in PNJL
model is enhanced compared to NJL and Born rate in the deconfined phase due to
the suppression of color degrees of freedom at moderate temperature. The
presence of isoscalar-vector interaction further enhances the dileption rate
over the Born rate in the low mass region. Further, we also have computed the
Euclidean correlation function in vector channel and the conserved density
fluctuation associated with temporal correlation function appropriate for a hot
and dense medium. The dilepton rate and the Euclidean correlator are also
compared with available lattice data and those quantities in PNJL model are
found to agree well in certain domain.Comment: 30 pages, 16 figures, typos corrected, references added, to appear in
JHE
Massive vector current correlator in thermal QCD
We present an NLO analysis of the massive vector current correlator at
temperatures above a few hundred MeV. The physics of this correlator originates
from a transport peak, related to heavy quark diffusion, and from the
quark-antiquark threshold, related to quarkonium physics. In the bottom case
both can be studied with separate effective theories, but for charm these may
not be accurate, so a study within the full theory is needed. Working in
imaginary time, the NLO correlator can be computed in unresummed perturbation
theory; comparing with lattice data, we find good agreement. Subsequently we
inspect how non-perturbative modifications of the transport peak would affect
the imaginary-time correlator. The massive NLO quark-number susceptibility is
also contrasted with numerical measurement.Comment: 28 pages. v2: references and clarifications added, published versio
Density and Spin Linear Response of Atomic Fermi Superfluids with Population Imbalance in BCS-BEC Crossover
We present a theoretical study of the density and spin (representing the two
components) linear response of Fermi superfluids with tunable attractive
interactions and population imbalance. In both linear response theories, we
find that the fluctuations of the order parameter must be treated on equal
footing with the gauge transformations associated with the symmetries of the
Hamiltonian so that important constraints including various sum rules can be
satisfied. Both theories can be applied to the whole BCS-Bose-Einstein
condensation crossover. The spin linear responses are qualitatively different
with and without population imbalance because collective-mode effects from the
fluctuations of the order parameter survive in the presence of population
imbalance, even though the associated symmetry is not broken by the order
parameter. Since a polarized superfluid becomes unstable at low temperatures in
the weak and intermediate coupling regimes, we found that the density and spin
susceptibilities diverge as the system approaches the unstable regime, but the
emergence of phase separation preempts the divergence.Comment: 15 pages, 5 figure
Non-singlet QCD analysis of F_2(x,Q^2) up to NNLO
The significance of NNLO (3-loop) QCD contributions to the flavor non-singlet
sector of F_2^ep and F_2^ed has been studied as compared to uncertainties
(different factorization schemes, higher twist and QED contributions) of
standard NLO (and LO) QCD analyses. The latter effects turn out to be
comparable in size to the NNLO contributions. Therefore the minute NNLO effects
are not observable with presently available data on non-singlet structure
functions.Comment: 14 pages, 2 figure
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