10,478 research outputs found
Mixed action computations on fine dynamical lattices
We report on our first experiences in simulating Neuberger valence fermions
on CLS configurations with light sea quark masses and small lattice
spacings. Valence quark masses are considered that allow to explore the
matching to (partially quenched) chiral perturbation theory both in the
- and -regimes. The setup is discussed, and first results are
presented for spectral observables.Comment: 7 pages. Presented at the XXVII International Symposium on Lattice
Field Theory, July 26-31, 2009, Peking University, Beijing, Chin
Flavour symmetry restoration and kaon weak matrix elements in quenched twisted mass QCD
We simulate two variants of quenched twisted mass QCD (tmQCD), with
degenerate Wilson quarks of masses equal to or heavier than half the strange
quark mass. We use Ward identities in order to measure the twist angles of the
theory and thus check the quality of the tuning of mass parameters to a physics
condition which stays constant as the lattice spacing is varied. Flavour
symmetry breaking in tmQCD is studied in a framework of two fully twisted and
two standard Wilson quark flavours, tuned to be degenerate in the continuum.
Comparing pseudoscalar masses, obtained from connected quark diagrams made of
tmQCD and/or standard Wilson quark propagators, we confirm that flavour
symmetry breaking effects, which are at most 5%, decrease as we approach the
continuum limit. We also compute the pseudoscalar decay constant in the
continuum limit, with reduced systematics. As a consequence of improved tuning
of the mass parameters at , we reanalyse our previous
results. Our main phenomenological findings are and .Comment: 41 pages, figures included, one reference added. Final version as
accepted for publication on Nucl.Phys.
A precise determination of in quenched QCD
The parameter is computed in quenched lattice QCD with Wilson twisted
mass fermions. Two variants of tmQCD are used; in both of them the relevant
four-fermion operator is renormalised multiplicatively. The
renormalisation adopted is non-perturbative, with a Schroedinger functional
renormalisation condition. Renormalisation group running is also
non-perturbative, up to very high energy scales. In one of the two tmQCD
frameworks the computations have been performed at the physical -meson mass,
thus eliminating the need of mass extrapolations. Simulations have been
performed at several lattice spacings and the continuum limit was reached by
combining results from both tmQCD regularisations. Finite volume effects have
been partially checked and turned out to be small. Exploratory studies have
also been performed with non-degenerate valence flavours. The final result for
the RGI bag parameter, with all sources of uncertainty (except quenching) under
control, is .Comment: 54 pages, 11 figure
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