23,439 research outputs found
Modulational instability of nonlinear polarization mode coupling in microresonators
We investigate frequency comb generation in the presence of polarization
effects induced by nonlinear mode coupling in microresonator devices. A set of
coupled temporal Lugiato-Lefever equations are derived to model the propagation
dynamics, and an in-depth study is made of the modulational instability of
their multistable homogeneous steady-state solutions. It is shown that new
kinds of instabilities can occur for co-propagating fields that interact
through nonlinear cross-phase modulation. These instabilities display
properties that differ from their scalar counterpart, and are shown to result
in the generation of new types of incoherently coupled frequency comb states.Comment: 8 pages, 7 figure
Finite-Temperature Phase Structure of Lattice QCD with the Wilson Quark Action for Two and Four Flavors
We present further analyses of the finite-temperature phase structure of
lattice QCD with the Wilson quark action based on spontaneous breakdown of
parity-flavor symmetry. Results are reported on (i) an explicit demonstration
of spontaneous breakdown of parity-flavor symmetry beyond the critical line,
(ii) phase structure and order of chiral transition for the case of
flavors, and (iii) approach toward the continuum limit.Comment: Poster presented at LATTICE96(finite temperature); 4 pages, Latex,
uses espcrc2 and epsf, seven ps figures include
The pion charge radius from charged pion electroproduction
We analyze a low-energy theorem of threshold pion electroproduction which
allows one to determine the charge radius of the pion. We show that at the same
order where the radius appears, pion loops induce a correction to the momentum
dependence of the longitudinal dipole amplitude . This
model-independent correction amounts to an increase of the pion charge radius
squared from the electroproduction data by about 0.26~fm. It sheds light on
the apparent discrepancy between the recent determination of the pion radius
from electroproduction data and the one based on pion-electron scattering.Comment: 3 pp, REVTeX, uses eps
Finite Temperature QCD with Wilson Quarks: A Study with a Renormalization Group Improved Gauge Action
Finite temperature transition in lattice QCD with degenerate Wilson quarks is
investigated on an lattice, using a renormalization group improved
gauge action. We find the following for the case:
1) The transition is smooth for a wide range of the quark mass.
2) The chiral transition is continuous.
3) The chiral condensation well satisfies a scaling relation with the
critical exponents of the 3 dimensional spin model. For , we find
that the chiral transition is of first order.Comment: 4 pages (6 figures), Postscript file, Contribution to Lattice 95
proceeding
A Classification of random Dirac fermions
We present a detailed classification of random Dirac hamiltonians in two
spatial dimensions based on the implementation of discrete symmetries. Our
classification is slightly finer than that of random matrices, and contains
thirteen classes. We also extend this classification to non-hermitian
hamiltonians with and without Dirac structure.Comment: 15 pages, version2: typos in the table of classes are correcte
Phase structure of QCD for general number of flavors
We investigate and elucidate the phase structure of QCD for general number of
flavors with Wilson quarks, varying from 2 up to 300. Based on
numerical results combined with the result of the perturbation theory we
propose the following picture: When , there is only a trivial fixed
point and therefore the theory in the continuum limit is trivial. On the other
hand, when , there is a non-trivial fixed point and therefore
the theory is non-trivial with anomalous dimensions, however, without quark
confinement. Theories which satisfy both quark confinement and spontaneous
chiral symmetry breaking in the continuum limit exist only for . We
also discuss the structure of the deconfining phase at finite temperatures for
the small number of flavors such as and 3, through a systematic study
of it for general number of flavors.Comment: LaTeX, 7 pages, 10 PS figures, Talk presented at LATTICE96(poster)
and LATTICE96(finite temperature
Comparison of finite-size-scaling functions for 3d O(N) spin models to QCD
We calculate numerically universal finite-size-scaling functions of the
magnetization for the three-dimensional O(4) and O(2) spin models. The approach
of these functions to the infinite-volume scaling functions is studied in
detail on the critical and pseudocritical lines. For this purpose we determine
the pseudocritical line in two different ways. We find that the asymptotic form
of the finite-size-scaling functions is already reached at small values of the
scaling variable. A comparison with QCD lattice data for two flavours of
staggered fermions shows a similar finite-size behaviour which is compatible
with that of the spin models.Comment: Lattice2001(hightemp), 3 pages, 5 figures, acknowledgements
completed, minor typographical errors correcte
Heavy-Light Semileptonic Decays in Staggered Chiral Perturbation Theory
We calculate the form factors for the semileptonic decays of heavy-light
pseudoscalar mesons in partially quenched staggered chiral perturbation theory
(\schpt), working to leading order in , where is the heavy quark
mass. We take the light meson in the final state to be a pseudoscalar
corresponding to the exact chiral symmetry of staggered quarks. The treatment
assumes the validity of the standard prescription for representing the
staggered ``fourth root trick'' within \schpt by insertions of factors of 1/4
for each sea quark loop. Our calculation is based on an existing partially
quenched continuum chiral perturbation theory calculation with degenerate sea
quarks by Becirevic, Prelovsek and Zupan, which we generalize to the staggered
(and non-degenerate) case. As a by-product, we obtain the continuum partially
quenched results with non-degenerate sea quarks. We analyze the effects of
non-leading chiral terms, and find a relation among the coefficients governing
the analytic valence mass dependence at this order. Our results are useful in
analyzing lattice computations of form factors and when the
light quarks are simulated with the staggered action.Comment: 53 pages, 8 figures, v2: Minor correction to the section on finite
volume effects, and typos fixed. Version to be published in Phys. Rev.
Thermodynamics with 3 and 2+1 Flavors of Improved Staggered Quarks
We present preliminary results from exploring the phase diagram of finite
temperature QCD with three degenerate flavors and with two light flavors and
the mass of the third held approximately at the strange quark mass. We use an
order Symanzik improved gauge action and an order
improved staggered quark action. The improved staggered
action leads to a dispersion relation with diminished lattice artifacts, and
hence better thermodynamic properties. It decreases the flavor symmetry
breaking of staggered quarks substantially, and we estimate that at the
transition temperature for an to lattice {\em all} pions will
be lighter than the lightest kaon. Preliminary results on lattices with
, 6 and 8 are presented.Comment: 3 pages, 6 figures, contribution to Lattice2001(hightemp) August
19--24, 2001, Berlin, German
Observing mergers of non-spinning black-hole binaries
Advances in the field of numerical relativity now make it possible to
calculate the final, most powerful merger phase of binary black-hole
coalescence for generic binaries. The state of the art has advanced well beyond
the equal-mass case into the unequal-mass and spinning regions of parameter
space. We present a study of the nonspinning portion of parameter space,
primarily using an analytic waveform model tuned to available numerical data,
with an emphasis on observational implications. We investigate the impact of
varied mass ratio on merger signal-to-noise ratios (SNRs) for several
detectors, and compare our results with expectations from the test-mass limit.
We note a striking similarity of the waveform phasing of the merger waveform
across the available mass ratios. Motivated by this, we calculate the match
between our 1:1 (equal mass) and 4:1 mass-ratio waveforms during the merger as
a function of location on the source sky, using a new formalism for the match
that accounts for higher harmonics. This is an indicator of the amount of
degeneracy in mass ratio for mergers of moderate-mass-ratio systems.Comment: 13 pages, 11 figures, submitted to Phys. Rev.
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