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Register a new userPhysics results from dynamical overlap fermion simulations
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Authors
Shoji Hashimoto
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I summarize the physics results obtained from large-scale dynamical overlap fermion simulations by the JLQCD and TWQCD collaborations. The numerical simulations are performed at a fixed global topological sector; the physics results in the theta-vacuum is reconstructed by correcting the finite volume effect, for which the measurement of the topological susceptibility is crucial. Physics applications we studied so far include a calculation of chiral condensate, pion mass, decay constant, form factors, as well as (vector and axial-vector) vacuum polarization functions and nucleon sigma term.
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We apply the Hybrid Monte Carlo method to the simulation of overlap fermions. We give the fermionic force for the molecular dynamics update. We present early results on a small dynamical chiral ensemble.
We present results of a hybrid Monte-Carlo algorithm for dynamical, $n_f=2$, four-dimensional QCD with overlap fermions. The fermionic force requires careful treatment, when changing topological sectors. The pion mass dependence of the topological susceptibility is studied on $6^4$ and $12cdot 6^3$ lattices. The results are transformed into physical units.
We present simulation results for the 2-flavour Schwinger model with dynamical overlap fermions. In particular we apply the overlap hypercube operator at seven light fermion masses. In each case we collect sizable statistics in the topological sectors 0 and 1. Since the chiral condensate Sigma vanishes in the chiral limit, we observe densities for the microscopic Dirac spectrum, which have not been addressed yet by Random Matrix Theory (RMT). Nevertheless, by confronting the averages of the lowest eigenvalues in different topological sectors with chiral RMT in unitary ensemble we obtain -- for the very light fermion masses -- values for Sigma that follow closely the analytical predictions in the continuum.
We report meson spectra obtained by using valence overlap fermion propagators generated on a background of 2+1 flavor domain wall fermion gauge configurations on 16^3 X 32, 24^3 X 64 and 32^3 X 64 lattices. We use many-to-all correlators with Z3 grid source and low eigenmode substitution which is efficient in reducing errors for the hadron correlators. The preliminary results on meson spectrum, a0 correlators, and charmonium hyperfine splitting for three sea quark masses are reported here.
We take a new approach to determine the scale parameter $r_0$, the physical masses of strange and charm quarks through a global fit which incorporates continuum extrapolation, chiral extrapolation and quark mass interpolation to the lattice data. The charmonium and charm-strange meson spectrum are calculated with overlap valence quarks on $2+1$-flavor domain-wall fermion gauge configurations generated by the RBC and UKQCD Collaboration. We use the masses of $D_s$, $D_s^*$ and $J/psi$ as inputs and obtain $m_c^{overline{rm MS}}(2,{rm GeV})=1.110(24),{rm GeV}$, $m_s^{overline{rm MS}}(2,{rm GeV})=0.104(9),{rm GeV}$ and $r_0=0.458(11),{rm fm}$. Subsequently, the hyperfine-splitting of charmonium and $f_{D_s}$ are predicted to be $112(5),{rm MeV}$ and $254(5),{rm MeV}$, respectively.
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