2,085 research outputs found
Hadron Mass Extraction from Lattice QCD
The extraction of quantities from lattice QCD calculations at realistic quark
masses is of considerable importance. Whilst physical quark masses are some way
off, the recent advances in the calculation of hadron masses within full QCD
now invite improved extrapolation methods. We show that, provided the correct
chiral behaviour of QCD is respected in the extrapolation to realistic quark
masses, one can indeed obtain a fairly reliable determination of masses, the
sigma commutator and the J parameter. We summarise these findings by presenting
the nonanalytic behaviour of nucleon and rho masses in the standard Edinburgh
plot.Comment: Talk presented by S. V. Wright at the Workshop on Lattice Hadron
Physics (LHP2001), Cairns, Australia, 9-18 July 2001, 8 pages, requires
espcrc2.sty (included
Incorporating Chiral Symmetry in Extrapolations of Octet Baryon Magnetic Moments
We explore methods of extrapolating lattice calculations of hadronic
observables to the physical regime, while respecting the constraints of chiral
symmetry and heavy quark effective theory. In particular, we extrapolate
lattice results for magnetic moments of the spin-1/2 baryon octet to the
physical pion mass and compare with experimental measurements. The success
previously reported for extrapolations of the nucleon magnetic moments carries
over to the Sigma baryons. A study of the residual discrepancies in the Xi
baryon moments suggests that it is important to have new simulation data with a
more realistic strange quark mass.Comment: 9 pages, 4 figure
Non-static brane probes, topological charges and calibrations
In this thesis we consider probe branes in 10- and 11-dimensional supergravity backgrounds. Firstly, we consider probing a class of 11-dimensional backgrounds with giant gravitons. These backgrounds arise from lifting solutions of 4-dimensional U(1)(^4) and 7-dimensional U(1)(^2) gauged supergravities. We find that giant gravitons degenerate to massless particles exist in arbitrary lifted backgrounds, and furthermore both these objects are degenerate to massive charged particles probing the associated lower-dimensional gauged supergravity solutions. We then move on to consider superalgebras for M2- and M5-brane probes in general 11-dimensional supersymmetric backgrounds. We derive the form of the topological charges which appear in the super translation part of the algebra. These charges are given by the integral (over the spatial world-volume of the brane) of certain closed forms constructed from Killing spinors and background fields. The super- translation algebra allows us to derive BPS bounds on the energy/momentum of probe branes in these general supersymmetric backgrounds. These bounds can be interpreted as generalized calibration bounds for these branes. We then use a similar procedure in type IIB supergravity to construct a calibration bound for a giant graviton in AdS(^5) x S(^5). As a by-product of this construction, we find a number of differential and algebraic relations satisfied by p-forms constructed from Killing spinors in type IIB supergravity. These relations are valid for the most general supersymmetric backgrounds. We then show that the calibration bound which we have constructed is saturated by a large class of general giant gravitons in AdS(^5) x S(^5), which are defined via holomorphic surfaces in C(^1)'(^2) x C(^3). Moreover, dual giant gravitons also saturate the calibration bound. We find that both these branes minimize "energy minus momentum" in their homology class
Convergence of chiral effective field theory
We formulate the expansion for the mass of the nucleon as a function of pion
mass within chiral perturbation theory using a number of different ultra-violet
regularisation schemes; including dimensional regularisation and various
finite-ranged regulators. Leading and next-to-leading order non-analytic
contributions are included through the standard one-loop Feynman graphs. In
addition to the physical nucleon mass, the expansion is constrained by recent,
extremely accurate, lattice QCD data obtained with two flavors of dynamical
quarks. The extent to which different regulators can describe the chiral
expansion is examined, while varying the range of quark mass over which the
expansions are matched. Renormalised chiral expansion parameters are recovered
from each regularisation prescription and compared. We find that the
finite-range regulators produce consistent, model-independent results over a
wide range of quark mass sufficient to solve the chiral extrapolation problem
in lattice QCD.Comment: 13 pages, 13 figures; To appear in Progress in Particle and Nuclear
Physics; presented at Erice School on Quarks in Hadrons and Nuclei, September
200
Chiral Extrapolation of Hadronic Observables
One of the great challenges of lattice QCD is to produce unambiguous
predictions for the properties of physical hadrons. We review recent progress
with respect to a major barrier to achieving this goal, namely the fact that
computation time currently limits us to large quark mass. Using insights from
the study of the lattice data itself, together with the general constraints of
chiral symmetry, we demonstrate that it is possible to extrapolate accurately
and in an essentially model independent manner from the mass region where
calculations will be performed within the next five years to the chiral limit.Comment: Lattice2002(plenary) Invited presentation at The XX Int. Symposium on
Lattice Field Theory, Lattice 2002, MIT Boston, June 24--29, 200
A model realisation of the Jaffe-Wilczek correlation for pentaquarks
We discuss a realisation of the pentaquark structure proposed by Jaffe and
Wilczek within a simple quark model with colour-spin contact interactions and
coloured harmonic confinement, which accurately describes the
splitting. In this model spatially compact diquarks are formed in the
pentaquark but no such compact object exists in the nucleon. The colour-spin
attraction brings the Jaffe-Wilczek-like state down to a low mass, compatible
with the experimental observation and below that of the naive ground state with
all -waves. We find, however, that although these trends are maintained, the
extreme effects observed do not survive the required ``smearing'' of the delta
function contact interaction. We also demonstrate the weakness of the
``schematic'' approximation when applied to a system containing a -wave. An
estimate of the anti-charmed pentaquark mass is made which is in line with the
Jaffe-Wilczek prediction and significantly less than the value reported by the
H1 collaboration.Comment: 10 pages, uses psfra
UK policy statements on testosterone deficiency
To address widespread media and scientific concerns over the appropriate treatment of TDS with Testosterone Therapy (T Therapy), the Executive Committee of the British Society for Sexual Medicine developed eight consensus statements, based on current scientific evidence to address these controversial issues. These statements were in no-way designed to replace the published evidence-based guidelines on the subject developed by various professional organisations, but to provide specific answers to several current controversial issues. This review examined evidence from Medline, EMBASE and Cochrane searches on HG, T Therapy and cardiovascular safety from May 2005 to May 2015, which revealed 1714 articles, with 52 clinical trials and 32 placebo-controlled randomised controlled trials. The task force developed the following eight key statements
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