1,867 research outputs found
Lattice study of infrared behaviour in SU(3) gauge theory with twelve massless flavours
We present details of a lattice study of infrared behaviour in SU(3) gauge
theory with twelve massless fermions in the fundamental representation. Using
the step-scaling method, we compute the coupling constant in this theory over a
large range of scale. The renormalisation scheme in this work is defined by the
ratio of Polyakov loops in the directions with different boundary conditions.
We closely examine systematic effects, and find that they are dominated by
errors arising from the continuum extrapolation. Our investigation suggests
that SU(3) gauge theory with twelve flavours contains an infrared fixed point.Comment: 29 pages, 15 figures, 4 tables. Minor revision. Published versio
Electromagnetic and spin polarisabilities in lattice QCD
We discuss the extraction of the electromagnetic and spin polarisabilities of
nucleons from lattice QCD. We show that the external field method can be used
to measure all the electromagnetic and spin polarisabilities including those of
charged particles. We then turn to the extrapolations required to connect such
calculations to experiment in the context of finite volume chiral perturbation
theory. We derive results relevant for lattice simulations of QCD,
partially-quenched QCD and quenched QCD. Our results for the polarisabilities
show a strong dependence on the lattice volume and quark masses, typically
differing from the infinite volume limit by ~10% for current lattice volumes
and quark masses.Comment: Minor change
Initial nucleon structure results with chiral quarks at the physical point
We report initial nucleon structure results computed on lattices with 2+1
dynamical M\"obius domain wall fermions at the physical point generated by the
RBC and UKQCD collaborations. At this stage, we evaluate only connected quark
contributions. In particular, we discuss the nucleon vector and axial-vector
form factors, nucleon axial charge and the isovector quark momentum fraction.
From currently available statistics, we estimate the stochastic accuracy of the
determination of and to be around 10%, and we expect to
reduce that to 5% within the next year. To reduce the computational cost of our
calculations, we extensively use acceleration techniques such as low-eigenmode
deflation and all-mode-averaging (AMA). We present a method for choosing
optimal AMA parameters.Comment: 7 pages, 11 figures; talk presented at the 32nd International
Symposium on Lattice Field Theory, 23-28 June, 2014, Columbia University, New
York, US
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
Rectangular Wilson Loops at Large N
This work is about pure Yang-Mills theory in four Euclidean dimensions with
gauge group SU(N). We study rectangular smeared Wilson loops on the lattice at
large N and relatively close to the large-N transition point in their
eigenvalue density. We show that the string tension can be extracted from these
loops but their dependence on shape differs from the asymptotic prediction of
effective string theory.Comment: 47 pages, 21 figures, 8 table
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