25,940 research outputs found
Quantum integrable system with two color components in two dimensions
The Davey-Stewartson 1(DS1) system[9] is an integrable model in two
dimensions. A quantum DS1 system with 2 colour-components in two dimensions has
been formulated. This two-dimensional problem has been reduced to two
one-dimensional many-body problems with 2 colour-components. The solutions of
the two-dimensional problem under consideration has been constructed from the
resulting problems in one dimensions. For latters with the -function
interactions and being solved by the Bethe ansatz, we introduce symmetrical and
antisymmetrical Young operators of the permutation group and obtain the exact
solutions for the quantum DS1 system. The application of the solusions is
discussed.Comment: 14 pages, LaTeX fil
Loop algorithm for Heisenberg models with biquadratic interaction and phase transitions in two dimensions
We present a new algorithm for quantum Monte Carlo simulation based on global
updating with loops. While various theoretical predictions are confirmed in one
dimension, we find, for S=1 systems on a square lattice with an
antiferromagnetic biquadratic interaction, that the intermediate phase between
the antiferromagnetic and the ferromagnetic phases is disordered and that the
two phase transitions are both of the first order in contrast to the
one-dimensional case. It is strongly suggested that the transition points
coincide those at which the algorithm changes qualitatively.Comment: 4 pages including 4 figures, to appear in JPS
Relaxation of a Single Knotted Ring Polymer
The relaxation of a single knotted ring polymer is studied by Brownian
dynamics simulations. The relaxation rate lambda_q for the wave number q is
estimated by the least square fit of the equilibrium time-displaced correlation
function to a double exponential decay at long times. The relaxation rate
distribution of a single ring polymer with the trefoil knot appears to behave
as lambda_q=A(1/N^)x for q=1 and lambda_q=A'(q/N)^x' for q=2 and 3, where
x=2.61, x'=2.02 and A>A'. The wave number q of the slowest relaxation rate for
each N is given by q=2 for small values of N, while it is given by q=1 for
large values of N. This crossover corresponds to the change of the structure of
the ring polymer caused by the localization of the knotted part to a part of
the ring polymer.Comment: 13 pages, 5 figures, uses jpsj2.cl
Tidal Stabilization of Rigidly Rotating, Fully Relativistic Neutron Stars
It is shown analytically that an external tidal gravitational field increases
the secular stability of a fully general relativistic, rigidly rotating neutron
star that is near marginal stability, protecting it against gravitational
collapse. This stabilization is shown to result from the simple fact that the
energy required to raise a tide on such a star, divided by the
square of the tide's quadrupole moment , is a decreasing function of the
star's radius , (where, as changes, the
star's structure is changed in accord with the star's fundamental mode of
radial oscillation). If were positive, the tidal
coupling would destabilize the star. As an application, a rigidly rotating,
marginally secularly stable neutron star in an inspiraling binary system will
be protected against secular collapse, and against dynamical collapse, by tidal
interaction with its companion. The ``local-asymptotic-rest-frame'' tools used
in the analysis are somewhat unusual and may be powerful in other studies of
neutron stars and black holes interacting with an external environment. As a
byproduct of the analysis, in an appendix the influence of tidal interactions
on mass-energy conservation is elucidated.Comment: Revtex, 10 pages, 2 figures; accepted for publication in Physical
Review D. Revisions: Appendix rewritten to clarify how, in Newtonian
gravitation theory, ambiguity in localization of energy makes interaction
energy ambiguous but leaves work done on star by tidal gravity unambiguous.
New footnote 1 and Refs. [11] and [19
Increased Yield of ttbb at Hadron Colliders in Low-Energy Supersymmetry
Light bottom squarks and gluinos have been invoked to explain the b quark
pair production excess at the Tevatron. We investigate the associated
production of ttbb at hadron colliders in this scenario, and find that the
rates for this process are enhanced over the Standard Model prediction. If
light gluinos exist, it may be possible to detect them at the Tevatron, and
they could easily be observed at the LHC.Comment: 5p, references added, version accepted to PR
Meaningful characterisation of perturbative theoretical uncertainties
We consider the problem of assigning a meaningful degree of belief to
uncertainty estimates of perturbative series. We analyse the assumptions which
are implicit in the conventional estimates made using renormalisation scale
variations. We then formulate a Bayesian model that, given equivalent initial
hypotheses, allows one to characterise a perturbative theoretical uncertainty
in a rigorous way in terms of a credibility interval for the remainder of the
series. We compare its outcome to the conventional uncertainty estimates in the
simple case of the calculation of QCD corrections to the e+e- -> hadrons
process. We find comparable results, but with important conceptual differences.
This work represents a first step in the direction of a more comprehensive and
rigorous handling of theoretical uncertainties in perturbative calculations
used in high energy phenomenology.Comment: 28 pages, 5 figures. Language modified in order to make it more
'bayesian'. No change in results. Version published in JHE
Binary Neutron Stars in General Relativity: Quasi-Equilibrium Models
We perform fully relativistic calculations of binary neutron stars in
quasi-equilibrium circular orbits. We integrate Einstein's equations together
with the relativistic equation of hydrostatic equilibrium to solve the initial
value problem for equal-mass binaries of arbitrary separation. We construct
sequences of constant rest mass and identify the innermost stable circular
orbit and its angular velocity. We find that the quasi-equilibrium maximum
allowed mass of a neutron star in a close binary is slightly larger than in
isolation.Comment: 4 pages, 3 figures, RevTe
Microscopic Modeling of the Growth of Order in an Alloy: Nucleated and Continuous Ordering
We study the early-stages of ordering in using a model Hamiltonian
derived from the effective medium theory of cohesion in metals: an approach
providing a microscopic description of interatomic interactions in alloys. Our
simulations show a crossover from a nucleated growth regime to a region where
the ordering does not follow any simple growth laws. This mirrors the
experimental observations in . The kinetics of growth, obtained from
the simulations, is in semi-quantitative agreement with experiments. The
real-space structures observed in our simulations offer some insight into the
nature of early-stage kineticsComment: 13 pages, Revtex, 3 postscript figures in a second file
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