An exact algorithm for three-flavor QCD with $O(a)$-improved Wilson fermions

Simulations of odd flavors QCD can be performed in the framework of the hybrid Monte Carlo algorithm where the inverse of the fermion matrix is approximated by a polynomial. In this exploratory study we perform three flavors QCD simulations. We make a comparison of the hybrid Monte Carlo algorithm and the R-algorithm which also simulates odd flavors systems but has step-size errors. We find that results from our hybrid Monte Carlo algorithm are in agreement with those from th...

We apply a recent proposal to speed up the Hybrid-Monte-Carlo simulation of systems with dynamical fermions to two flavor QCD with clover-improvement. For our smallest quark masses we see a speed-up of more than a factor of two compared with the standard algorithm.

We give a detailed description of the so-called Polynomial Hybrid Monte Carlo (PHMC) algorithm. The effects of the correction factor, which is introduced to render the algorithm exact, are discussed, stressing their relevance for the statistical fluctuations and (almost) zero mode contributions to physical observables. We also investigate rounding-error effects and propose several ways to reduce memory requirements.

Some results of test runs on a $6^3\times 12$ lattice with Wilson quarks and gauge group SU(2) for a previously proposed fermion algorithm by A. Slavnov are presented.

We present simulation details and results for the light hadron spectrum in N f = 2 + 1 lattice QCD with the nonperturbatively O(a)-improved Wilson quark action and the Iwasaki gauge action. Simulations are carried out at a lattice spacing of 0.09 fm on a (2.9fm)^3 box using the PACS-CS computer. We employ the Luscher's domain-decomposed HMC algorithm with several improvements to reduce the degenerate up-down quark mass toward the physical value. So far the resulting pseudosca...

We compare the Hybrid Monte Carlo (HMC) and the Kramers equation algorithms for simulations of QCD with two flavors of dynamical Wilson fermions and gauge group $SU(2)$. The results for the performance of both algorithms are obtained on $6^312$, $12^4$ and $16^4$ lattices at a pion to $\rho$ meson mass ratio of $m_\pi/m_\rho \approx 0.9$. We find that the Kramers equation algorithm gives an equally good performance as the HMC algorithm. We demonstrate that the classical equat...

We consider recent progress in algorithms for generating gauge field configurations that include the dynamical effects of light fermions. We survey what has been achieved in recent state-of-the-art computations, and examine the trade-offs between performance and control of systematic errors. We briefly review the use of polynomial and rational approximations in Hybrid Monte Carlo algorithms, and some of the theory of on-shell chiral fermions on the lattice. This provides a th...

We compare the performance of the PHMC algorithm with the one of the HMC algorithm in practical simulations of lattice QCD. We show that the PHMC algorithm can lead to an acceleration of numerical simulations. It is demonstrated that the PHMC algorithm generates configurations carrying small isolated eigenvalues of the lattice Dirac operator and hence leads to a sampling of configuration space that is different from that of the HMC algorithm.

We explore the region of small sea quark masses below $m_{PS}/m_V=0.5$ in two-flavor QCD using a mean-field improved clover quark action and an RG-improved gauge action at $a \simeq 0.2$ fm on $12^3 \times 24$ and $16^3 \times 24$ lattices. We find that instability of the standard BiCGStab algorithm at small quark masses can be mostly removed by the BiCGStab(DS-$L$) algorithm, which employs $L$-th minimal residual polynomials with a dynamical selection of $L$. We also find si...

We present an update of our study of the phase diagram of two-flavour QCD at zero baryon density with dynamical $O(a)$ improved Wilson quarks. All simulations are done on lattices with a temporal extent of $N_t=16$ and spatial extent $L=32,48$ and 64, ensuring that discretisation effects are small and finite size effects can be controlled. In the approach to the chiral limit we currently have three scans with pion masses between 540 and 200 MeV. In this proceedings article th...