22,087 research outputs found
Multigrid Monte Carlo with higher cycles in the Sine Gordon model
We study the dynamical critical behavior of multigrid Monte Carlo for the two
dimensional Sine Gordon model on lattices up to 128 x 128. Using piecewise
constant interpolation, we perform a W-cycle (gamma=2). We examine whether one
can reduce critical slowing down caused by decreasing acceptance rates on large
blocks by doing more work on coarser lattices. To this end, we choose a higher
cycle with gamma = 4. The results clearly demonstrate that critical slowing
down is not reduced in either case.Comment: 7 pages, 1 figure, whole paper including figure contained in ps-file,
DESY 93-00
Theoretical Analysis of Acceptance Rates in Multigrid Monte Carlo
We analyze the kinematics of multigrid Monte Carlo algorithms by
investigating acceptance rates for nonlocal Metropolis updates. With the help
of a simple criterion we can decide whether or not a multigrid algorithm will
have a chance to overcome critial slowing down for a given model. Our method is
introduced in the context of spin models. A multigrid Monte Carlo procedure for
nonabelian lattice gauge theory is described, and its kinematics is analyzed in
detail.Comment: 7 pages, no figures, (talk at LATTICE 92 in Amsterdam
Propagation of temporal entanglement
The equations that govern the temporal evolution of two photons in the
Schr{\"o}dinger picture are derived, taking into account the effects of loss,
group-velocity dispersion, temporal phase modulation, linear coupling among
different optical modes, and four-wave mixing. Inspired by the formalism, we
propose the concept of quantum temporal imaging, which uses dispersive elements
and temporal phase modulators to manipulate the temporal correlation of two
entangled photons. We also present the exact solution of a two-photon vector
soliton, in order to demonstrate the ease of use and intuitiveness of the
proposed formulation.Comment: 8 pages, 4 figure
Linear and non-linear theory of a parametric instability of hydrodynamic warps in Keplerian discs
We consider the stability of warping modes in Keplerian discs. We find them
to be parametrically unstable using two lines of attack, one based on
three-mode couplings and the other on Floquet theory. We confirm the existence
of the instability, and investigate its nonlinear development in three
dimensions, via numerical experiment. The most rapidly growing non-axisymmetric
disturbances are the most nearly axisymmetric (low m) ones. Finally, we offer a
simple, somewhat speculative model for the interaction of the parametric
instability with the warp. We apply this model to the masing disc in NGC 4258
and show that, provided the warp is not forced too strongly, parametric
instability can fix the amplitude of the warp.Comment: 14 pages, 6 figures, revised version with appendix added, to be
published in MNRA
Finite momentum condensation in a pumped microcavity
We calculate the absorption spectra of a semiconductor microcavity into which
a non-equilibrium exciton population has been pumped. We predict strong peaks
in the spectrum corresponding to collective modes analogous to the Cooper modes
in superconductors and fermionic atomic gases. These modes can become unstable,
leading to the formation of off-equilibrium quantum condensates. We calculate a
phase diagram for condensation, and show that the dominant instabilities can be
at a finite momentum. Thus we predict the formation of inhomogeneous
condensates, similar to Fulde-Ferrel-Larkin-Ovchinnikov states.Comment: 7 pages, 4 figures, updated to accepted versio
Storm severity detection (RF)
Measurement of lightning location data which occur together with continental thunderstorms and hurricanes was examined, and a second phase linear interferometer was deployed. Electrical emission originating from tropical storms in the Gulf of Mexico were monitored. The time span between hurricane ALLEN (10 August 1980) and hurricane ALICIA (18 August 1983) represents the longest period that the United States has gone without hurricane landfall. Both systems were active and data were acquired during the landfall period of hurricane ALICIA
Pensioner poverty over the next decade: what role for tax and benefit reform?
Recent falls in poverty amongst those aged 65 and over are unlikely to continue after 2007-08, even after the implementation of the proposals outlined in the Government's Pensions White Paper.
This report looks at the prospects for pensioner poverty in England over the next decade. The authors find that that the proportion of those aged 65 and over living in poverty is set to remain at its current level - around one-in-five - between 2007-08 and 2017-18. This is despite the overall increase in the generosity of state pensions arising from the Pensions White Paper, and the fact that younger cohorts are expected to have more private pension income and higher employment rates at older ages than those preceding them
Setting limits on Effective Field Theories: the case of Dark Matter
The usage of Effective Field Theories (EFT) for LHC new physics searches is
receiving increasing attention. It is thus important to clarify all the aspects
related with the applicability of the EFT formalism in the LHC environment,
where the large available energy can produce reactions that overcome the
maximal range of validity, i.e. the cutoff, of the theory. We show that this
does forbid to set rigorous limits on the EFT parameter space through a
modified version of the ordinary binned likelihood hypothesis test, which we
design and validate. Our limit-setting strategy can be carried on in its
full-fledged form by the LHC experimental collaborations, or performed
externally to the collaborations, through the Simplified Likelihood approach,
by relying on certain approximations. We apply it to the recent CMS mono-jet
analysis and derive limits on a Dark Matter (DM) EFT model. DM is selected as a
case study because the limited reach on the DM production EFT Wilson
coefficient and the structure of the theory suggests that the cutoff might be
dangerously low, well within the LHC reach. However our strategy can also be
applied to EFT's parametrising the indirect effects of heavy new physics in the
Electroweak and Higgs sectors
The stationary phase point method for transitional scattering: diffractive radio scintillation for pulsar
The stationary phase point (SPP) method in one-dimensional case is introduced
to treat the diffractive scintillation. From weak scattering, where the SPP
number N=1, to strong scattering (N1), via transitional scattering regime
(N2,3), we find that the modulation index of intensity experiences the
monotonically increasing from 0 to 1 with the scattering strength,
characterized by the ratio of Fresnel scale \rf to diffractive scale
\rdiff.Comment: Hanas Meeting paper, appear in ChJAA, 2006, 6, Su
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