6 research outputs found
Electromagnetic corrections to pseudoscalar decay constants
The effects of electromagnetic interactions on pseudoscalar decay constants
are investigated. Using a compact QED and QCD action we are able to resolve
differences of about 0.1 MeV. We obtain the preliminary results f_pi^0-f_pi^+/-
=0.09(3) MeV and f_D^0-f_D^+/- =0.79(11) MeV for light and charmed pseudoscalar
decay constants on a N_f=2 nonperturbatively improved Sheikholeslami-Wohlert
ensemble.Comment: 7 pages, 3 figures. Talk presented at the XXIX International
Symposium on Lattice Field Theory, Lattice2011, Squaw Valley, Lake Tahoe,
California, July 201
<x>_{u-d} from lattice QCD at nearly physical quark masses
We determine the second Mellin moment of the isovector quark parton
distribution function _{u-d} from lattice QCD with N_f=2 sea quark flavours,
employing the non-perturbatively improved Wilson-Sheikholeslami-Wohlert action
at a pseudoscalar mass of 157(6) MeV. The result is converted
non-perturbatively to the RI'-MOM scheme and then perturbatively to the MSbar
scheme at a scale mu = 2 GeV. As the quark mass is reduced we find the lattice
prediction to approach the value extracted from experiments.Comment: 4 pages, 3 figures, v2: minor updates including journal ref
QPACE 2 and Domain Decomposition on the Intel Xeon Phi
We give an overview of QPACE 2, which is a custom-designed supercomputer
based on Intel Xeon Phi processors, developed in a collaboration of Regensburg
University and Eurotech. We give some general recommendations for how to write
high-performance code for the Xeon Phi and then discuss our implementation of a
domain-decomposition-based solver and present a number of benchmarks.Comment: plenary talk at Lattice 2014, to appear in the conference proceedings
PoS(LATTICE2014), 15 pages, 9 figure
Strong contribution to octet baryon mass splittings
We calculate the contribution to the mass splittings in baryonic
isospin multiplets using SU(3) chiral perturbation theory and lattice QCD.
Fitting isospin-averaged perturbation theory functions to PACS-CS and
QCDSF-UKQCD Collaboration lattice simulations of octet baryon masses, and using
the physical light quark mass ratio as input, allows ,
and to be evaluated from the
full SU(3) theory. The resulting values for each mass splitting are consistent
with the experimental values after allowing for electromagnetic corrections. In
the case of the nucleon, we find , with the
dominant uncertainty arising from the error in
QCD spectroscopy and quark mass renormalisation in external magnetic fields with Wilson fermions
Brandt BB, Bali G, Endrödi G, Glaessle B. QCD spectroscopy and quark mass renormalisation in external magnetic fields with Wilson fermions. In: Proceedings of The 33rd International Symposium on Lattice Field Theory — PoS(LATTICE 2015). Trieste, Italy: Sissa Medialab; 2016: 265
Isospin breaking in octet baryon mass splittings
Using an SU(3) flavour symmetry breaking expansion in the quark mass, we determine the QCD component of the nucleon, Sigma and Xi mass splittings of the baryon octet due to up-down (and strange) quark mass differences in terms of the kaon mass splitting. Provided the average quark mass is kept constant, the expansion coefficients in our procedure can be determined from computationally cheaper simulations with mass degenerate sea quarks and partially quenched valence quarks. Both the linear and quadratic terms in the SU(3) flavour symmetry breaking expansion are considered; it is found that the quadratic terms only change the result by a few percent, indicating that the expansion is highly convergent