3,416,167 research outputs found
Nature of Decoupling in the Mixed Phase of Extremely Type-II Layered Superconductors
The uniformly frustrated layered XY model is analyzed in its Villain form. A
decouple pancake vortex liquid phase is identified. It is bounded by both
first-order and second-order decoupling lines in the magnetic field versus
temperature plane. These transitions, respectively, can account for the
flux-lattice melting and for the flux-lattice depinning observed in the mixed
phase of clean high-temperature superconductors.Comment: 11 pages of PLAIN TeX, 1 postscript figure, published version, many
change
J/psi production at sqrt(s)=1.96 and 7 TeV: Color-Singlet Model, NNLO* and polarisation
We study J/psi production in pp collisions at sqrt(s)=1.96 and 7 TeV using
the Colour-Singlet Model (CSM), including next-to-leading order (NLO)
corrections and dominant alphaS^5 contributions (NNLO*). We find that the CSM
reproduces the existing data if the upper range of the NNLO* is near the actual
--but presently unknown-- NNLO. The direct yield polarisation for the NLO and
NNLO* is increasingly longitudinal in the helicity frame when P_T gets larger.
Contrary to what is sometimes claimed in the literature, the prompt J/psi yield
polarisation in the CSM is compatible with the experimental data from the CDF
collaboration, when one combines the direct yield with a data-driven range for
the polarisation of J/psi from chi(c).Comment: Contributed to the 22nd International Conference On
Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2011), Annecy,
France, May 23 - 28, 2011. 4 pages, 4 figures, uses iopams.sty, iopart12.clo,
iopart.cls (included
Field-induced magnetic reorientation and effective anisotropy of a ferromagnetic monolayer within spin wave theory
The reorientation of the magnetization of a ferromagnetic monolayer is
calculated with the help of many-body Green's function theory. This allows, in
contrast to other spin wave theories, a satisfactory calculation of magnetic
properties over the entire temperature range of interest since interactions
between spin waves are taken into account. A Heisenberg Hamiltonian plus a
second-order uniaxial single-ion anisotropy and an external magnetic field is
treated by the Tyablikov (Random Phase Approximation: RPA) decoupling of the
exchange interaction term and the Anderson-Callen decoupling of the anisotropy
term. The orientation of the magnetization is determined by the spin components
\la S^\alpha\ra (), which are calculated with the help of the
spectral theorem. The knowledge of the orientation angle allows a
non-perturbative determination of the temperature dependence of the effective
second-order anisotropy coefficient. Results for the Green's function theory
are compared with those obtained with mean-field theory (MFT). We find
significant differences between these approaches.Comment: to appear in Europ.J.Phys.B, 13 pages, 9 figure
Dielectric screening of surface states in a topological insulator
Hexagonal warping provides an anisotropy to the dispersion curves of the
helical Dirac fermions that exist at the surface of a topological insulator. A
sub-dominant quadratic in momentum term leads to an asymmetry between
conduction and valence band. A gap can also be opened through magnetic doping.
We show how these various modifications to the Dirac spectrum change the
polarization function of the surface states and employ our results to discuss
their effect on the plasmons. In the long wavelength limit, the plasmon
dispersion retains its square root dependence on its momentum,
, but its slope is modified and it can acquire a weak
dependence on the direction of . Further, we find the existence
of several plasmon branches, one which is damped for all values of
, and extract the plasmon scattering rate for a representative
case.Comment: 11 pages, 8 figure
Spin Alignment of Heavy Meson Revisited
Using heavy quark effective theory a factorized form for inclusive production
rate of a heavy meson can be obtained, in which the nonperturbative effect
related to the heavy meson can be characterized by matrix elements defined in
the heavy quark effective theory. Using this factorization, predictions for the
full spin density matrix of a spin-1 and spin-2 meson can be obtained and they
are characterized only by one coefficient representing the nonperturbative
effect. Predictions for spin-1 heavy meson are compared with experiment
performed at colliders in the energy range from GeV to
GeV, a complete agreement is found for - and -meson.
There are distinct differences from the existing approach and they are
discussed.Comment: 6 pages, Talk given at 3rd Circum-Pan-Pacific Symposium on "High
Energy Spin Physics", Beijing, China, 8-13, 200
A Model of Heat Conduction
We define a deterministic ``scattering'' model for heat conduction which is
continuous in space, and which has a Boltzmann type flavor, obtained by a
closure based on memory loss between collisions. We prove that this model has,
for stochastic driving forces at the boundary, close to Maxwellians, a unique
non-equilibrium steady state
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