39 research outputs found
Implications of for high-energy observation
Absorption of high-energy over electrons above the W boson
production threshold is reexamined. It is pointed out that, in the case of
photon emissions along the direction of incident high-energy , the
kinematically allowed average energy carried by the final state hard photon can
be of the incident energy above the W boson production
threshold. The differential energy spectrum for the final state hard photon is
calculated. We also discuss implications of our results for the prospective
search of high-energy through this final state hard photon.Comment: 9 pages, 3 figures, RevTe
Topological transition in a two-dimensional model of liquid crystal
Simulations of nematic-isotropic transition of liquid crystals in two
dimensions are performed using an O(2) vector model characterised by non linear
nearest neighbour spin interaction governed by the fourth Legendre polynomial
. The system is studied through standard Finite-Size Scaling and
conformal rescaling of density profiles of correlation functions. A topological
transition between a paramagnetic phase at high temperature and a critical
phase at low temperature is observed. The low temperature limit is discussed in
the spin wave approximation and confirms the numerical results
Magnetization Process of the Classical Heisenberg Model on the Shastry-Sutherland Lattice
We investigate classical Heisenberg spins on the Shastry-Sutherland lattice
and under an external magnetic field. A detailed study is carried out both
analytically and numerically by means of classical Monte-Carlo simulations.
Magnetization pseudo-plateaux are observed around 1/3 of the saturation
magnetization for a range of values of the magnetic couplings. We show that the
existence of the pseudo-plateau is due to an entropic selection of a particular
collinear state. A phase diagram that shows the domains of existence of those
pseudo-plateaux in the plane is obtained.Comment: 9 pages, 11 figure
Charge Transport in the Dense Two-Dimensional Coulomb Gas
The dynamics of a globally neutral system of diffusing Coulomb charges in two
dimensions, driven by an applied electric field, is studied in a wide
temperature range around the Berezinskii-Kosterlitz-Thouless transition. I
argue that the commonly accepted ``free particle drift'' mechanism of charge
transport in this system is limited to relatively low particle densities. For
higher densities, I propose a modified picture involving collective ``partner
transfer'' between bound pairs. The new picture provides a natural explanation
for recent experimental and numerical findings which deviate from standard
theory. It also clarifies the origin of dynamical scaling in this context.Comment: 4 pages, RevTeX, 2 eps figures included; some typos corrected, final
version to be published in Phys. Rev. Let
Probing d-wave pairing correlations in the pseudogap regime of the cuprate superconductors via low-energy states near impurities
The issue of probing the pseudogap regime of the cuprate superconductors,
specifically with regard to the existence and nature of superconducting pairing
correlations of d-wave symmetry, is explored theoretically. It is shown that if
the d-wave correlations believed to describe the superconducting state persist
into the pseudogap regime, but with pair-potential phase-fluctuations that
destroy their long-range nature, then the low-energy quasiparticle states
observed near extended impurities in the truly superconducting state should
also persist as resonances in the pseudogap regime. The scattering of
quasiparticles by these phase-fluctuations broadens what was (in the
superconducting state) a sharp peak in the single-particle spectral function at
low energy, as we demonstrate within the context of a simple model. This peak
and its broadening is, in principle, accessible via scanning tunneling
spectroscopy near extended impurities in the pseudogap regime. If so, such
experiments would provide a probe of the extent to which d-wave superconducting
correlations persist upon entering the pseudogap regime, thus providing a
stringent diagnostic of the phase-fluctuation scenario.Comment: 8 pages, 2 figure
Internal Modes and Magnon Scattering on Topological Solitons in 2d Easy-Axis Ferromagnets
We study the magnon modes in the presence of a topological soliton in a 2d
Heisenberg easy-axis ferromagnet. The problem of magnon scattering on the
soliton with arbitrary relation between the soliton radius R and the "magnetic
length" Delta_0 is investigated for partial modes with different values of the
azimuthal quantum numbers m. Truly local modes are shown to be present for all
values of m, when the soliton radius is enough large. The eigenfrequencies of
such internal modes are calculated analytically on limiting case of a large
soliton radius and numerically for arbitrary soliton radius. It is demonstrated
that the model of an isotropic magnet, which admits an exact analytical
investigation, is not adequate even for the limit of small radius solitons,
R<<Delta_0: there exists a local mode with nonzero frequency. We use the data
about local modes to derive the effective equation of soliton motion; this
equation has the usual Newtonian form in contrast to the case of the easy-plane
ferromagnet. The effective mass of the soliton is found.Comment: 33 pages (REVTeX), 12 figures (EPS
Cosmic Ray Diffusion from the Galactic Spiral Arms, Iron Meteorites, and a possible climatic connection?
We construct a Galactic cosmic ray (CR) diffusion model while considering
that CR sources reside predominantly in the Galactic spiral arms. We find that
the CR flux (CRF) reaching the solar system should periodically increase each
crossing of a Galactic spiral arm. We search for this signal in the CR exposure
age record of Iron meteorites and confirm this prediction. We then check the
hypothesis that climate, and in particular the temperature, is affected by the
CRF to the extent that glaciations can be induced or completely hindered by
possible climatic variations. We find that although the geological evidence for
the occurrence of IAEs in the past Eon is not unequivocal, it appears to have a
nontrivial correlation with the spiral arm crossings--agreeing in period and
phase. Thus, a better timing study of glaciations could either confirm this
result as an explanation to the occurrence of IAEs or refute a CRF climatic
connection.Comment: 4 Journal pages, 2 figures, revtex4. Appearing today in Phys Rev Let
Measurement of high order current correlators
The feasibility of measuring high-order current correlators by means of a
linear detector is analyzed. Two different types of measurements are
considered: measurement of fluctuation power spectrum and measurement of
unequal-time current correlators at fixed points in time. In both cases,
formally exact expressions in terms of Keldysh time-ordered electron current
operators are derived for the detector output. An explicit time ordering is
found for the current correlators under the expectation operator used in
measurements of high order unequal-time current correlators. The situation when
a detector measures current correlators at different points of a conductor is
considered.Comment: 27 page