8,918 research outputs found
Numerical Exploration of the RI/MOM Scheme Gauge Dependence
The gauge dependence of some fermion bilinear RI/MOM renormalization
constants is studied by comparing data which have been gauge-fixed in two
different realizations of the Landau gauge and in a generic covariant gauge.
The very good agreement between the various sets of results and the theory
indicates that the numerical uncertainty induced by the lattice gauge-fixing
procedure is below the statistical errors of our data sample which is of the
order of (1-1.5)%.Comment: 3 pages, 2 figures, Lattice2002(theoretical
Relaxation time of -reversal chains and other chromosome shuffles
We prove tight bounds on the relaxation time of the so-called -reversal
chain, which was introduced by R. Durrett as a stochastic model for the
evolution of chromosome chains. The process is described as follows. We have
distinct letters on the vertices of the -cycle ( mod
); at each step, a connected subset of the graph is chosen uniformly at
random among all those of length at most , and the current permutation is
shuffled by reversing the order of the letters over that subset. We show that
the relaxation time , defined as the inverse of the spectral gap of
the associated Markov generator, satisfies . Our results can be interpreted as strong evidence for a
conjecture of R. Durrett predicting a similar behavior for the mixing time of
the chain.Comment: Published at http://dx.doi.org/10.1214/105051606000000295 in the
Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute
of Mathematical Statistics (http://www.imstat.org
The quest for three-color entanglement: experimental investigation of new multipartite quantum correlations
We experimentally investigate quadrature correlations between pump, signal,
and idler fields in an above-threshold optical parametric oscillator. We
observe new quantum correlations among the pump and signal or idler beams, as
well as among the pump and a combined quadrature of signal and idler beams. A
further investigation of unforeseen classical noise observed in this system is
presented, which hinders the observation of the recently predicted tripartite
entanglement. In spite of this noise, current results approach the limit
required to demonstrate three-color entanglement.Comment: 10 pages, 5 figures, submitted to Opt. Expres
Effects of finite volume on the KL-KS mass difference
Phenomena that involve two or more on-shell particles are particularly sensitive to the effects of finite volume and require special treatment when computed using lattice QCD. In this paper we generalize the results of LĂŒscher and Lellouch and LĂŒscher, which determine the leading-order effects of finite volume on the two-particle spectrum and two-particle decay amplitudes to determine the finite-volume effects in the second-order mixing of the K0 and K0ÂŻ states. We extend the methods of Kim, Sachrajda, and Sharpe to provide a direct, uniform treatment of these three, related, finite-volume corrections. In particular, the leading, finite-volume corrections to the KL-KS mass difference ÎMK and the CP-violating parameter ΔK are determined, including the potentially large effects which can arise from the near degeneracy of the kaon mass and the energy of a finite-volume, two-pion state
Electromagnetic corrections to leptonic decay rates of charged pseudoscalar mesons: finite-volume effects
In Carrasco et al. we have recently proposed a method to calculate
electromagnetic corrections to leptonic decay widths of pseudoscalar mesons.
The method is based on the observation that the infrared divergent
contributions (that appear at intermediate stages of the calculation and that
cancel in physical quantities thanks to the Bloch-Nordsieck mechanism) are
universal, i.e. depend on the charge and the mass of the meson but not on its
internal structure. In this talk we perform a detailed analysis of the
finite-volume effects associated with our method. In particular we show that
also the leading finite-volume effects are universal and perform an
analytical calculation of the finite-volume leptonic decay rate for a
point-like meson
Finite-Volume QED Corrections to Decay Amplitudes in Lattice QCD
We demonstrate that the leading and next-to-leading finite-volume effects in
the evaluation of leptonic decay widths of pseudoscalar mesons at
are universal, i.e. they are independent of the structure of the meson. This is
analogous to a similar result for the spectrum but with some fundamental
differences, most notably the presence of infrared divergences in decay
amplitudes. The leading non-universal, structure-dependent terms are of
(compared to the leading non-universal corrections in the
spectrum). We calculate the universal finite-volume effects, which requires an
extension of previously developed techniques to include a dependence on an
external three-momentum (in our case, the momentum of the final state lepton).
The result can be included in the strategy proposed in
Ref.\,\cite{Carrasco:2015xwa} for using lattice simulations to compute the
decay widths at , with the remaining finite-volume effects starting
at order . The methods developed in this paper can be generalised to
other decay processes, most notably to semileptonic decays, and hence open the
possibility of a new era in precision flavour physics
Leading isospin-breaking corrections to pion, kaon and charmed-meson masses with Twisted-Mass fermions
We present a lattice computation of the isospin-breaking corrections to
pseudoscalar meson masses using the gauge configurations produced by the
European Twisted Mass collaboration with dynamical quarks at
three values of the lattice spacing ( and fm)
with pion masses in the range MeV. The strange and
charm quark masses are tuned at their physical values. We adopt the RM123
method based on the combined expansion of the path integral in powers of the
- and -quark mass difference () and of the
electromagnetic coupling . Within the quenched QED approximation,
which neglects the effects of the sea-quark charges, and after the
extrapolations to the physical pion mass and to the continuum and infinite
volume limits, we provide results for the pion, kaon and (for the first time)
charmed-meson mass splittings, for the prescription-dependent parameters
, \epsilon_\gamma(\overline{MS}, 2~\mbox{GeV}),
\epsilon_{K^0}(\overline{MS}, 2~\mbox{GeV}), related to the violations of the
Dashen's theorem, and for the light quark mass difference (\widehat{m}_d -
\widehat{m}_u)(\overline{MS}, 2~\mbox{GeV}).Comment: 47 pages, 20 figures, 4 tables; comments on QED and QCD splitting
prescriptions added; version to appear in PR
Relaxation times of kinetically constrained spin models with glassy dynamics
We analyze the density and size dependence of the relaxation time for
kinetically constrained spin systems. These have been proposed as models for
strong or fragile glasses and for systems undergoing jamming transitions. For
the one (FA1f) or two (FA2f) spin facilitated Fredrickson-Andersen model at any
density and for the Knight model below the critical density at which
the glass transition occurs, we show that the persistence and the spin-spin
time auto-correlation functions decay exponentially. This excludes the
stretched exponential relaxation which was derived by numerical simulations.
For FA2f in , we also prove a super-Arrhenius scaling of the form
. For FA1f in = we
rigorously prove the power law scalings recently derived in \cite{JMS} while in
we obtain upper and lower bounds consistent with findings therein.
Our results are based on a novel multi-scale approach which allows to analyze
in presence of kinetic constraints and to connect time-scales and
dynamical heterogeneities. The techniques are flexible enough to allow a
variety of constraints and can also be applied to conservative stochastic
lattice gases in presence of kinetic constraints.Comment: 4 page
Constraining Fundamental Physics with Future CMB Experiments
The Planck experiment will soon provide a very accurate measurement of Cosmic
Microwave Background anisotropies. This will let cosmologists determine most of
the cosmological parameters with unprecedented accuracy. Future experiments
will improve and complement the Planck data with better angular resolution and
better polarization sensitivity. This unexplored region of the CMB power
spectrum contains information on many parameters of interest, including
neutrino mass, the number of relativistic particles at recombination, the
primordial Helium abundance and the injection of additional ionizing photons by
dark matter self-annihilation. We review the imprint of each parameter on the
CMB and forecast the constraints achievable by future experiments by performing
a Monte Carlo analysis on synthetic realizations of simulated data. We find
that next generation satellite missions such as CMBPol could provide valuable
constraints with a precision close to that expected in current and near future
laboratory experiments. Finally, we discuss the implications of this
intersection between cosmology and fundamental physics.Comment: 11 pages, 14 figure
- âŠ