531 research outputs found
Beyond the Standard Model with Precision Nucleon Matrix Elements on the Lattice
Precision measurements of nucleons provide constraints on the Standard Model
and can discern the signatures predicted for particles beyond the Standard
Model (BSM). Knowing the Standard Model inputs to nucleon matrix elements will
be necessary to constrain the couplings of dark matter candidates such as the
neutralino, to relate the neutron electric dipole moment to the CP-violating
theta parameter, or to search for new TeV-scale particles though non-
interactions in neutron beta decay. However, these matrix elements derive from
the properties of quantum chromodynamics (QCD) at low energies, where
perturbative treatments fail. Using lattice gauge theory, we can
nonperturbatively calculate the QCD path integral on a supercomputer. In this
proceeding, I will discuss a few representative areas in which lattice QCD
(LQCD) can contribute to the search for BSM physics, emphasizing suppressed
operators in neutron decay, and outline prospects for future development.Comment: 3 pages, 2 figures, talk presented at the 19th Particles and Nuclei
International Conference (PANIC 2011), Massachusetts Institute of Technology,
Cambridge, MA, USA, July 24-29, 201
Charmed spectroscopy from a nonperturbatively determined relativistic heavy quark action in full QCD
We present a preliminary calculation of the charmed meson spectrum using the
2+1 flavor domain wall fermion lattice configurations currently being generated
by the RBC and UKQCD collaborations. The calculation is performed using the
3-parameter, relativistic heavy quark action with nonperturbatively determined
coefficients. We will also demonstrate a step-scaling procedure for determining
these coefficients nonperturbatively using a series of quenched, gauge field
ensembles generated for three different lattice spacings.Comment: Proceeding for 24th International Symposium on Lattice Field Theory
(Lattice 2006), Tucson, Arizona, 23-28 Jul 200
Nucleon structure in lattice QCD with dynamical domain-wall fermions quarks
We report RBC and RBC/UKQCD lattice QCD numerical calculations of nucleon
electroweak matrix elements with dynamical domain-wall fermions (DWF) quarks.
The first, RBC, set of dynamical DWF ensembles employs two degenerate flavors
of DWF quarks and the DBW2 gauge action. Three sea quark mass values of 0.04,
0.03 and 0.02 in lattice units are used with about 200 gauge configurations
each. The lattice cutoff is about 1.7 GeV and the spatial volume is about (1.9
fm)^3. Despite the small volume, the ratio of the isovector vector and axial
charges g_A/g_V and that of structure function moments _{u-d}/_{Delta u -
Delta d} are in agreement with experiment, and show only very mild quark mass
dependence. The second, RBC/UK, set of ensembles employs one strange and two
degenerate (up and down) dynamical DWF quarks and Iwasaki gauge action. The
strange quark mass is set at 0.04, and three up/down mass values of 0.03, 0.02
and 0.01 in lattice units are used. The lattice cutoff is about 1.6 GeV and the
spatial volume is about (3.0 fm)^3. Even with preliminary statistics of 25-30
gauge configurations, the ratios g_A/g_V and _{u-d}/_{Delta u - Delta d}
are consistent with experiment and show only very mild quark mass dependence.
Another structure function moment, d_1, though yet to be renormalized, appears
small in both sets.Comment: 7 pages, 4 figures, talk presented at Lattice 2006, Tucson, Arizona,
to be published in PoS(LAT2006)118; replaced Figure 3 with the pion mass
squared in GeV^2 unit and corrected a minor error in the abstract in number
of gauge configuration
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