1,231 research outputs found
Polynomial loss of memory for maps of the interval with a neutral fixed point
We give an example of a sequential dynamical system consisting of
intermittent-type maps which exhibits loss of memory with a polynomial rate of
decay. A uniform bound holds for the upper rate of memory loss. The maps may be
chosen in any sequence, and the bound holds for all compositions.Comment: 16 page
Multi-Pion Systems in Lattice QCD and the Three-Pion Interaction
The ground-state energies of 2, 3, 4 and 5 \pi^+'s in a spatial volume V (2.5
fm)^3 are computed with lattice QCD. By eliminating the leading contribution
from three-\pi^+ interactions, particular combinations of these n-\pi^+
ground-state energies provide precise extractions of the \pi^+\pi^+ scattering
length in agreement with that obtained from calculations involving only two
\pi^+'s. The three-\pi^+ interaction can be isolated by forming other
combinations of the n-\pi^+ ground-state energies. We find a result that is
consistent with a repulsive three-\pi^+ interaction for m_\pi < 352 MeV.Comment: 4 pages, 5 figure
High Statistics Analysis using Anisotropic Clover Lattices: (I) Single Hadron Correlation Functions
We present the results of high-statistics calculations of correlation
functions generated with single-baryon interpolating operators on an ensemble
of dynamical anisotropic gauge-field configurations generated by the Hadron
Spectrum Collaboration using a tadpole-improved clover fermion action and
Symanzik-improved gauge action. A total of 292,500 sets of measurements are
made using 1194 gauge configurations of size 20^3 x 128 with an anisotropy
parameter \xi= b_s/b_t = 3.5, a spatial lattice spacing of b_s=0.1227\pm 0.0008
fm, and pion mass of m_\pi ~ 390 MeV. Ground state baryon masses are extracted
with fully quantified uncertainties that are at or below the ~0.2%-level in
lattice units. The lowest-lying negative-parity states are also extracted
albeit with a somewhat lower level of precision. In the case of the nucleon,
this negative-parity state is above the N\pi threshold and, therefore, the
isospin-1/2 \pi N s-wave scattering phase-shift can be extracted using
Luescher's method. The disconnected contributions to this process are included
indirectly in the gauge-field configurations and do not require additional
calculations. The signal-to-noise ratio in the various correlation functions is
explored and is found to degrade exponentially faster than naive expectations
on many time-slices. This is due to backward propagating states arising from
the anti-periodic boundary conditions imposed on the quark-propagators in the
time-direction. We explore how best to distribute computational resources
between configuration generation and propagator measurements in order to
optimize the extraction of single baryon observables
The K+K+ Scattering Length from Lattice QCD
The K+K+ scattering length is calculated in fully-dynamical lattice QCD with
domain-wall valence quarks on the MILC asqtad-improved gauge configurations
with rooted staggered sea quarks. Three-flavor mixed-action chiral perturbation
theory at next-to-leading order, which includes the leading effects of the
finite lattice spacing, is used to extrapolate the results of the lattice
calculation to the physical value of m_{K+}/f_{K+}. We find m_{K+} a_{K+K+} =
-0.352 +- 0.016, where the statistical and systematic errors have been combined
in quadrature.Comment: 17 pages, 12 figures. NPLQCD collaboratio
Precise Determination of the I=2 pipi Scattering Length from Mixed-Action Lattice QCD
The I=2 pipi scattering length is calculated in fully-dynamical lattice QCD
with domain-wall valence quarks on the asqtad-improved coarse MILC
configurations (with fourth-rooted staggered sea quarks) at four light-quark
masses. Two- and three-flavor mixed-action chiral perturbation theory at
next-to-leading order is used to perform the chiral and continuum
extrapolations. At the physical charged pion mass, we find m_pi a_pipi(I=2) =
-0.04330 +- 0.00042, where the error bar combines the statistical and
systematic uncertainties in quadrature.Comment: 20 pages, 7 figure
SU(2) Low-Energy Constants from Mixed-Action Lattice QCD
An analysis of the pion mass and pion decay constant is performed using
mixed-action Lattice QCD calculations with domain-wall valence quarks on
ensembles of rooted, staggered n_f = 2+1 MILC configurations. Calculations were
performed at two lattice spacings of b~0.125 fm and b~0.09 fm, at two strange
quark masses, multiple light quark masses, and a number of lattice volumes. The
ratios of light quark to strange quark masses are in the range 0.1 <= m_l / m_s
<= 0.6, while pion masses are in the range 235 < m_\pi < 680 MeV. A two-flavor
chiral perturbation theory analysis of the Lattice QCD calculations constrains
the Gasser-Leutwyler coefficients bar{l}_3 and bar{l}_4 to be bar{l}_3 =
4.04(40)(+73-55) and bar{l}_4 = 4.30(51)(+84-60). All systematic effects in the
calculations are explored, including those from the finite lattice space-time
volume, the finite lattice spacing, and the finite fifth dimension in the
domain-wall quark action. A consistency is demonstrated between a chiral
perturbation theory analysis at fixed lattice spacing combined with a leading
order continuum extrapolation, and the mixed-action chiral perturbation theory
analysis which explicitly includes the leading order discretization effects.
Chiral corrections to the pion decay constant are found to give f_\pi / f =
1.062(26)(+42-40) where f is the decay constant in the chiral limit. The most
recent scale setting by the MILC Collaboration yields a postdiction of f_\pi =
128.2(3.6)(+4.4-6.0)(+1.2-3.3) MeV at the physical pion mass.Comment: 28 pages, 9 figures; version 2 accepted for publication in PR
Human and Canine Pulmonary Blastomycosis, North Carolina, 2001–2002
We investigated a cluster of blastomycosis in 8 humans and 4 dogs in a rural North Carolina community. Delayed diagnosis, difficulty isolating Blastomyces dermatitidis in nature, and lack of a sensitive and specific test to assess exposure make outbreaks of this disease difficult to study
Finite-volume effects and the electromagnetic contributions to kaon and pion masses
We report on the MILC Collaboration calculation of electromagnetic effects on
light pseudoscalar mesons. The simulations employ asqtad staggered dynamical
quarks in QCD plus quenched photons, with lattice spacings varying from 0.12 to
0.06 fm. Finite volume corrections for the MILC realization of lattice
electrodynamics have been calculated in chiral perturbation theory and applied
to the lattice data. These corrections differ from those calculated by Hayakawa
and Uno because our treatment of zero modes differs from theirs. Updated
results for the corrections to "Dashen's theorem" are presented.Comment: 7 pages, 2 figures. Presented at Lattice 2014, Columbia University,
June 23-28, 201
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