3 research outputs found
Lattice QCD with open boundary conditions and twisted-mass reweighting
Lattice QCD simulations at small lattice spacings and quark masses close to
their physical values are technically challenging. In particular, the
simulations can get trapped in the topological charge sectors of field space or
may run into instabilities triggered by accidental near-zero modes of the
lattice Dirac operator. As already noted in ref. [1], the first problem is
bypassed if open boundary conditions are imposed in the time direction, while
the second can potentially be overcome through twisted-mass determinant
reweighting [2]. In this paper, we show that twisted-mass reweighting works out
as expected in QCD with open boundary conditions and 2+1 flavours of O(a)
improved Wilson quarks. Further algorithmic improvements are tested as well and
a few physical quantities are computed for illustration.Comment: Plain TeX source, 27 pages, 7 figure
Lattice QCD without topology barriers
As the continuum limit is approached, lattice QCD simulations tend to get
trapped in the topological charge sectors of field space and may consequently
give biased results in practice. We propose to bypass this problem by imposing
open (Neumann) boundary conditions on the gauge field in the time direction.
The topological charge can then flow in and out of the lattice, while many
properties of the theory (the hadron spectrum, for example) are not affected.
Extensive simulations of the SU(3) gauge theory, using the HMC and the closely
related SMD algorithm, confirm the absence of topology barriers if these
boundary conditions are chosen. Moreover, the calculated autocorrelation times
are found to scale approximately like the square of the inverse lattice
spacing, thus supporting the conjecture that the HMC algorithm is in the
universality class of the Langevin equation.Comment: Plain TeX source, 26 pages, 4 figures include
Master-field simulations of O(a)-improved lattice QCD: Algorithms, stability and exactness
Plain TeX source, 35 pages, 6 figures; v2: minor text corrections;
v3: reference added; v4: corrected 2 typos; v5: published versionIn master-field simulations of lattice QCD, the expectation values of interest are obtained from a single or at most a few representative gauge-field configurations on very large lattices. If the light quarks are included, the generation of these fields using standard techniques is however challenging in view of various algorithmic instabilities and precision issues. Ways to overcome these problems are described here for the case of the O(α)-improved Wilson formulation of lattice QCD and the viability of the proposed measures is then checked in extensive simulations of the theory with
flavours of quarks