3243998
Testing topology conserving gauge actions for Lattice QCD
We explore gauge actions for lattice QCD, which are constructed such that the occurrence of small plaquette values is strongly suppressed. Such actions orig inate from the admissibility condition in order to conserve the topological charge. The suppression of small plaquette values is expected to be advantageous for numerical studies in the e-regime and also for simulations with dynamical quarks. Performing simulations at a lattice spacing of about 0.1 fm, we present numerical results for the static potential, the physical scale r0, the stability of the topological charge history, the condition number of the kernel of the overlap operator and the acceptance rate against the step size in the local HMC algorithm.
8527236
Chiral properties of domain wall quarks in quenched QCD.
We investigate the chiral properties of quenched domain-wall QCD (DWQCD) at the lattice spacings ${a}^{\ensuremath{-}1}\ensuremath{\simeq}1$ and 2 GeV for both plaquette and renormalization-group (RG) improved gauge actions. In the case of the plaquette action we find that the quark mass defined through the axial Ward-Takahashi identity remains non-vanishing in the DWQCD chiral limit that the bare quark mass ${m}_{f}\ensuremath{\rightarrow}0$ and the length of the fifth dimension ${N}_{s}\ensuremath{\rightarrow}\ensuremath{\infty},$ indicating that chiral symmetry is not realized with quenched DWQCD up to ${a}^{\ensuremath{-}1}\ensuremath{\simeq}2$ GeV. The behavior is much improved for the RG-improved gauge action: while a nonvanishing quark mass remains in the chiral limit at ${a}^{\ensuremath{-}1}\ensuremath{\simeq}1$ GeV, the result at ${a}^{\ensuremath{-}1}\ensuremath{\simeq}2$ GeV is consistent with an exponentially vanishing quark mass in the DWQCD chiral limit, indicating the realization of exact chiral symmetry. An interpretation and implications are briefly discussed.
26599771
Sea quark effects on quarkonia
We study the effects of two dynamical sea quarks on the spectrum of heavy quarkonia. Within the non-relativistic approach to Lattice QCD we found sizeable changes to the hyperfine splitting, but we could not observe any changes for the fine structure. We also investigated the scaling behaviour of our results for several different lattice spacings.
14619672
Chiral zero modes on the Domain Wall model in (4+1)-dimensions
We investigate an original domain-wall model in 4+1 dimensions numerically in the presence of U(1) dynamical gauge field only in an extra dimension, corresponding to a weak coupling limit of four-dimensional physical gauge coupling. Using a quenched approximation we carry out a numerical simulation for this model at ${\ensuremath{\beta}}_{s}{(=1/g}_{s}^{2})=$ 0.29 (``symmetric'' phase) and 0.5 (``broken'' phase), where ${g}_{s}$ is the gauge coupling constant of the extra dimension. In the broken phase, we found that there exists a critical value of a domain-wall mass ${m}_{0}^{c}$ which separates a region with a fermionic zero mode on the domain wall from the one without it in the same case of (2+1)-dimensional model. On the other hand, in the symmetric phase, our numerical data suggest that the chiral zero modes disappear in the infinite limit of four-dimensional volume. From these results it seems difficult to construct the U(1) lattice chiral gauge theory via an original domain-wall formulation.
5379081
Scaling test of fermion actions in the Schwinger model
Abstract We discuss the scaling behaviour of different fermion actions in dynamical simulations of the 2-dimensional massive Schwinger model. We have chosen Wilson, hypercube, twisted mass and overlap fermion actions. As physical observables, the pion mass and the scalar condensate are computed for the above mentioned actions at a number of coupling values and fermion masses. We also discuss possibilities to simulate overlap fermions dynamically avoiding problems with low-lying eigenvalues of the overlap kernel.
125708608
Walking signals in $N_f=8$ QCD on the lattice
10281433
Evaluation of test structures for the novel n + -in-p pixel and strip sensors for very high radiation environments
Abstract Radiation-tolerant n + -in-p silicon sensors were developed for use in very high radiation environments. Novel n + -in-p silicon strip and pixel sensors and test structures were fabricated, tested and evaluated, in order to understand the designs implemented. The resistance between the n + implants (interstrip resistance), the electric potential of the p-stop, and the punch-through-protection (PTP) onset voltage were measured before and as a function of fluence after irradiation. The technology computer-aided design (TCAD) simulations were used to understand the radiation damage and fluence dependence of the structures. The decrease in the interstrip resistance is a consequence of increased leakage current. The decrease in the electric potential of the p-stop results from a build-up of positive charge in the silicon–silicon oxide interface. The decrease and subsequent increase in the PTP onset voltages results from the interface charge build-up and an increase in acceptor states.