53 research outputs found
The Aoki phase for N_f=2 Wilson fermions revisited
We report on a numerical reinvestigation of the Aoki phase in full lattice
QCD with two flavors of unimproved Wilson fermions. For zero temperature the
Aoki phase can be confirmed at inverse coupling and ,
but not at and . At non-zero temperature the Aoki phase
was found to exist also at .Comment: 3 pages LaTex, 5 figures. Parallel talk at Lattice2003(Theory
Reply to "Comment on `Lattice determination of Sigma - Lambda mixing' "
In this Reply, we respond to the above Comment. Our computation [Phys. Rev. D
91 (2015) 074512] only took into account pure QCD effects, arising from quark
mass differences, so it is not surprising that there are discrepancies in
isospin splittings and in the Sigma - Lambda mixing angle. We expect that these
discrepancies will be smaller in a full calculation incorporating QED effects.Comment: 5 page
Determination of the strange nucleon form factors
The strange contribution to the electric and magnetic form factors of the
nucleon is determined at a range of discrete values of up to
GeV. This is done by combining recent lattice QCD results for the
electromagnetic form factors of the octet baryons with experimental
determinations of those quantities. The most precise result is a small negative
value for the strange magnetic moment: . At
larger values of both the electric and magnetic form factors are
consistent with zero to within -sigma
Distribution Amplitudes of Pseudoscalar Mesons
We present results for the first two moments of the distribution amplitudes
of pseudoscalar mesons. Using two flavors of non-perturbatively improved clover
fermions and non-perturbative renormalization of the matrix elements we perform
both chiral and continuum extrapolations and compare with recent results from
models and experiments.Comment: 7 pages, 4 figures, based on presentation at Lattice 200
Charge Symmetry Violation in the Electromagnetic Form Factors of the Proton
Experimental tests of QCD through its predictions for the strange-quark
content of the proton have been drastically restricted by our lack of knowledge
of the violation of charge symmetry (CSV). We find unexpectedly tiny CSV in the
proton's electromagnetic form factors by performing the first extraction of
these quantities based on an analysis of lattice QCD data. The resulting values
are an order of magnitude smaller than current bounds on proton strangeness
from parity violating electron-proton scattering experiments. This result paves
the way for a new generation of experimental measurements of the proton's
strange form factors to challenge the predictions of QCD
Oceanic events and biotic effects of the Cenomanian-Turonian anoxic event
a b s t r a c t Profound biotic changes accompanied the late Cenomanian d 13 C excursion and OAE2 in planktic foraminifera in the Tarfaya Basin of Morocco. Planktic foraminifera experienced a severe turnover, though no mass extinction, beginning with the rapid d 13 C excursion and accelerating with the influx of oxic bottom waters during the first peak and trough of the excursion. Species extinctions equaled the number of evolving species, though only the disaster opportunists Guembelitria and Hedbergella thrived along with a low oxygen tolerant benthic assemblage. The succeeding d 13 C plateau and organic-rich black shale deposition marks the anoxic event and maximum biotic stress accompanied by a prolonged drop in diversity to just two species, the dominant (80-90%) low oxygen tolerant Heterohelix moremani and surface dweller Hedbergella planispira. After the anoxic event other species returned, but remained rare and sporadically present well into the lower Turonian, whereas Heterohelix moremani remained the single dominant species. The OAE2 biotic turnover suggests that the stress to calcareous plankton was related to changes in the watermass stratification, intensity of upwelling, nutrient flux and oxic levels in the water column driven by changes in climate and oceanic circulation. Results presented here demonstrate a 4-stage pattern of biotic response to the onset, duration, and recovery of OAE2 that is observed widely across the Tethys and its bordering epicontinental seas. Published by Elsevier Ltd
Isospin splittings in the decuplet baryon spectrum from dynamical QCD+QED
We report a new analysis of the isospin splittings within the decuplet baryon spectrum. Our numerical results are based upon five ensembles of dynamical QCD+QED lattices. The analysis is carried out within a flavour-breaking expansion which encodes the effects of breaking the quark masses and electromagnetic charges away from an approximate SU(3) symmetric point. The results display total isospin splittings within the approximate SU(2) multiplets that are compatible with phenomenological estimates. Further, new insight is gained into these splittings by separating the contributions arising from strong and electromagnetic effects. We also present an update of earlier results on the octet baryon spectrum
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