394 research outputs found
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
High Statistics Analysis using Anisotropic Clover Lattices: (IV) Volume Dependence of Light Hadron Masses
The volume dependence of the octet baryon masses and relations among them are
explored with Lattice QCD. Calculations are performed with n_f=2+1 clover
fermion discretization in four lattice volumes, with spatial extent L ~ 2.0,
2.5, 3.0 and 3.9 fm, with an anisotropic lattice spacing of b_s ~ 0.123 fm in
the spatial direction, and b_t = b_s/3.5 in the time direction, and at a pion
mass of m_pi ~ 390 MeV. The typical precision of the ground-state baryon mass
determination is ~0.2%, enabling a precise exploration of the volume dependence
of the masses, the Gell-Mann--Okubo mass relation, and of other mass
combinations. A comparison of the volume dependence with the predictions of
heavy baryon chiral perturbation theory is performed in both the SU(2)_L X
SU(2)_R and SU(3)_L X SU(3)_R expansions. Predictions of the three-flavor
expansion for the hadron masses are found to describe the observed volume
dependences reasonably well. Further, the Delta-N-pi axial coupling constant is
extracted from the volume dependence of the nucleon mass in the two-flavor
expansion, with only small modifications in the three-flavor expansion from the
inclusion of kaons and etas. At a given value of m_pi L, the finite-volume
contributions to the nucleon mass are predicted to be significantly smaller at
m_pi ~ 140 MeV than at m_pi ~ 390 MeV due to a coefficient that scales as ~
m_pi^3. This is relevant for the design of future ensembles of lattice
gauge-field configurations. Finally, the volume dependence of the pion and kaon
masses are analyzed with two-flavor and three-flavor chiral perturbation
theory.Comment: 34 pages, 45 figure
Meson and baryon spectrum for QCD with two light dynamical quarks
We present results of meson and baryon spectroscopy using the Chirally
Improved Dirac operator on lattices of size 16**3 x 32 with two mass-degenerate
light sea quarks. Three ensembles with pion masses of 322(5), 470(4) and 525(7)
MeV and lattice spacings close to 0.15 fm are investigated. Results on ground
and excited states for several channels are given, including spin two mesons
and hadrons with strange valence quarks. The analysis of the states is done
with the variational method, including two kinds of Gaussian sources and
derivative sources. We obtain several ground states fairly precisely and find
radial excitations in various channels. Excited baryon results seem to suffer
from finite size effects, in particular at small pion masses. We discuss the
possible appearance of scattering states in various channels, considering
masses and eigenvectors. Partially quenched results in the scalar channel
suggest the presence of a 2-particle state, however, in most channels we cannot
identify them. Where available, we compare our results to results of quenched
simulations using the same action.Comment: 27 pages, 29 figures, 11 table
Search for Fermion Actions on Hyperdiamond Lattices
Fermions moving in a two-dimensional honeycomb lattice (graphene) have, at
low energies, chiral symmetry. Generalizing this construction to four
dimensions potentially provides fermions with chiral symmetry and only the
minimal fermion doubling demanded by the Nielsen-Ninomiya no-go theorem. The
practical usefulness of such fermions hinges on whether the action has a
necessary set of discrete symmetries of the lattice. If this is the case, one
avoids the generation of dimension three and four operators which require fine
tuning. We construct hyperdiamond lattice actions with enough symmetries to
exclude fine tuning; however, they produce multiple doublings. The limit where
the actions exhibit minimal doubling does not possess the requisite symmetry.Comment: 4 pages, 1 figur
RANK/RANKL/OPG pathway: genetic associations with stress fracture period prevalence in elite athletes
Context: The RANK/RANKL/OPG signalling pathway is important in the regulation of bone turnover, with single nucleotide polymorphisms (SNPs) in genes within this pathway associated with bone phenotypic adaptations.
Objective: To determine whether four SNPs associated with genes in the RANK/RANKL/OPG signalling pathway were associated with stress fracture injury in elite athletes.
Design, Participants, and Methods: Radiologically confirmed stress fracture history was reported in 518 elite athletes, forming the Stress Fracture Elite Athlete (SFEA) cohort. Data were analysed for the whole group, and were sub-stratified into male and cases of multiple stress fracture group. Genotypes were determined using proprietary fluorescence-based competitive allele-specific PCR assays.
Results: SNPs rs3018362 (RANK) and rs1021188 (RANKL) were associated with stress fracture injury (p<0.05). 8.1% of stress fracture group and 2.8% of the non-stress fracture group were homozygote for the rare allele of rs1021188. Allele frequency, heterozygotes and homozygotes for the rare allele of rs3018362 were associated with stress fracture period prevalence (p<0.05). Analysis of the male only group showed 8.2% of rs1021188 rare allele homozygotes to have suffered a stress fracture while 2.5% of the non-stress fracture group were homozygous. In cases of multiple stress fractures, homozygotes for the rare allele of rs1021188, and individuals possessing at least one copy of the rare allele of rs4355801 (OPG) were shown to be associated with stress fracture injury (p<0.05).
Conclusions: The data support an association between SNPs in the RANK/RANKL/OPG signalling pathway and the development of stress fracture injury. The association of rs3018362 (RANK) and rs1021188 (RANKL) with stress fracture injury susceptibility supports their role in the maintenance of bone health, and offers potential targets for therapeutic interventions
Hadron Structure on the Lattice
A few chosen nucleon properties are described from a lattice QCD perspective:
the nucleon sigma term and the scalar strangeness in the nucleon; the vector
form factors in the nucleon, including the vector strangeness contribution, as
well as parity breaking effects like the anapole and electric dipole moment;
and finally the axial and tensor charges of the nucleon. The status of the
lattice calculations is presented and their potential impact on phenomenology
is discussed.Comment: 17 pages, 9 figures; proceedings of the Conclusive Symposium of the
Collaborative Research Center 443 "Many-body structure of strongly
interacting systems", Mainz, February 23-25, 201
Patient Acceptability of the Yorkshire Dialysis Decision Aid (YoDDA) Booklet: A Prospective Non-Randomized Comparison Study Across 6 Predialysis Services
Background: Patients are satisfied with their kidney care but want more support in making dialysis choices. Predialysis leaflets vary across services, with few being sufficient to enable patients’ informed decision making. We describe the acceptability of a patient decision aid and feasibility of evaluating its effectiveness within usual predialysis practice. Methods: Prospective non-randomized comparison design, Usual Care or Usual Care Plus Yorkshire Dialysis Decision Aid Booklet (+YoDDA), in 6 referral centers (Yorkshire-Humber, UK) for patients with sustained deterioration of kidney function. Consenting (C) patients completed questionnaires after predialysis consultation (T1), and 6 weeks later (T2). Measures assessed YoDDA’s utility to support patients’ decisions and integration within usual care. Results: Usual Care (n = 105) and +YoDDA (n = 84) participant characteristics were similar: male (62%), white (94%), age (mean = 62.6; standard deviation [SD] 14.4), kidney disease severity (glomerular filtration rate [eGFR] mean = 14.7; SD 3.7); decisional conflict was <25; choice-preference for home versus hospital dialysis approximately 50:50. Patients valued receiving YoDDA, reading it on their own (96%), and sharing it with family (72%). +YoDDA participants had higher scores for understanding kidney disease, reasoning about options, feeling in control, sharing their decision with family. Study engagement varied by center (estimated range 14 – 49%; mean 45%); participants varied in completion of decision quality measures. Conclusions: Receiving YoDDA as part of predialysis education was valued and useful to patients with worsening kidney disease. Integrating YoDDA actively within predialysis programs will meet clinical guidelines and patient need to support dialysis decision making in the context of patients’ lifestyle
Symmetries and Interactions from Lattice QCD
Precision experimental tests of the Standard Model of particle physics (SM)
are one of our best hopes for discovering what new physics lies beyond the SM
(BSM). Key in the search for new physics is the connection between theory and
experiment. Forging this connection for searches involving low-energy hadronic
or nuclear environments requires the use of a non-perturbative theoretical
tool, lattice QCD. We present two recent lattice QCD calculations by the CalLat
collaboration relevant for new physics searches: the nucleon axial coupling,
, whose precise value as predicted by the SM could help point to new
physics contributions to the so-called "neutron lifetime puzzle", and hadronic
matrix elements of short-ranged operators relevant for neutrinoless double beta
decay searches.Comment: Plenary talk presented CIPANP2018. 11 pages, 3 figure
UK Renal Research Strategy
This is the first published UK Renal Research Strategy compiled by professional and patient stakeholders across the renal community to provide guidance and evidence to funders, policy makers and those helping to create and support the next generation of researchers. Two rounds of widely based consultation with contributions from major renal stakeholders, patients, clinicians, multi-disciplinary teams, researchers and funders contributed to the strategic vision and aims. The strategy calls for action and implementation of the strategy will be reviewed and monitored by an Implementation Board
Neutrinoless double beta decay from lattice QCD
While the discovery of non-zero neutrino masses is one of the most important accomplishments by physicists in the past century, it is still unknown how and in what form these masses arise. Lepton number-violating neutrinoless double beta decay is a natural consequence of Majorana neutrinos and many BSM theories, and many experimental efforts are involved in the search for these processes. Understanding how neutrinoless double beta decay would manifest in nuclear environments is key for understanding any observed signals. In these proceedings we present an overview of a set of one- and two-body matrix elements relevant for experimental searches for neutrinoless double beta decay, describe the role of lattice QCD calculations, and present preliminary lattice QCD results
- …