arXiv subjects
Publications and source records attributed to Istvan Montvay.
The spectrum of N=1 supersymmetric Yang-Mills theory, calculated on the lattice, is presented. The masses have been determined on three different lattice spacings and extrapolated towards vanishing gluino mass. We present the extrapolation to the continuum limit which is consistent with the formation of degenerate supermultiplets.
The spectrum of the lightest bound states in N=1 supersymmetric Yang-Mills theory with SU(2) gauge group, calculated on the lattice, is presented. The masses have first been extrapolated towards vanishing gluino mass and then to the continuum limit. The final picture is consistent with the formation of degenerate supermultiplets.
Recently a new method to set the scale in lattice gauge theories, based on the gradient flow generated by the Wilson action, has been proposed, and the systematic errors of the new scales t0 and w0 have been investigated by various groups. The Wilson flow provides also an interesting alternative smoothing procedure in particular useful for the measurement of the topological charge as a pure gluonic observable. We show the viability of this method for N=1 supersymmetric Yang-Mills theory by analysing the configurations produced by the DESY-Muenster collaboration. For increasing flow time the topological charge quickly approaches near-integer values. The topological susceptibility has been measured for different fermion masses and its value is observed to approach zero in the chiral limit. Finally, the relation between the scale defined by the Wilson flow and the topological charge has been investigated, demonstrating a correlation between these two quantities.
We summarise the latest results of our collaboration concerning N=1 supersymmetric Yang-Mills theory in four dimensions on the lattice. We investigate the expected formation of supersymmetric multiplets of the lightest particles and the behaviour of the topological susceptibility approaching the supersymmetric limit of the theory.
Numerical simulations of supersymmetric theories on the lattice are intricate and challenging with respect to their theoretical foundations and algorithmic realisation. Nevertheless, the simulations of a four-dimensional supersymmetric gauge theory have made considerable improvements over the recent years. In this contribution we summarise the results of our collaboration concerning the mass spectrum of this theory. The investigation of systematic errors allows now a more precise estimate concerning the expected formation of supersymmetric multiplets of the lightest particles. These multiplets contain flavour singlet mesons, glueballs, and an additional fermionic state.
We present the current results of our simulations of N=1 supersymmetric Yang-Mills theory on a lattice. The masses of the gluino-glue particle, the a-eta-prime, the a-f0 meson, and the scalar glueball are obtained at finer lattice spacing than before, and extrapolations towards vanishing gluino mass are made. The calculations employ different levels of stout smearing. The statistical accuracy as well as the control of finite size effects and lattice artefacts are better than in previous investigations. Taking the statistical and systematic uncertainties into account, the extrapolations towards vanishing gluino mass of the masses of the fermionic and bosonic states in our present calculations are consistent with the formation of degenerate supermultiplets.
Exploratory simulations of four-nucleon interactions are performed taking into account the dynamical effects of internal nucleon loops. The four-nucleon interactions in the isoscalar and isovector channels are described by Yukawa interactions with auxiliary scalar fields. The nucleon mass and the average field lengths of the scalar fields are determined as a function of nucleon hopping parameter and Yukawa coupling strengths. There are no problems with "exceptional configurations" at strong couplings which make quenched simulations unreliable.
Supersymmetric Yang-Mills theory is in several respects different from QCD and pure Yang-Mills theory. Therefore, a reinvestigation of the scales, at which finite size effects and lattice artifacts become relevant, is necessary. Both, finite size effects and lattice artifacts, induce a breaking of supersymmetry. In view of the unexpected mass gap between bosonic and fermionic particles an estimation of these effects is essential.
The spectrum of particles in supersymmetric Yang-Mills theory is expected to contain a spin 1/2 bound state of gluons and gluinos, the gluino-glue particle. We study the mass of this particle in softly broken supersymmetric Yang-Mills theory on a lattice by means of numerical simulations. The main focus is the estimation of finite size effects. We extrapolate the mass first to the infinite volume and then to the limit of a vanishing gluino mass. The results indicate that finite size effects are tolerable on lattices of moderate size, and that remaining deviations from supersymmetry are probably due to finite lattice spacing effects.
We present an exploratory study of chiral effective theories of nuclei with methods adopted from lattice quantum chromodynamics (QCD). We show that the simulations in the Euclidean path integral approach are feasible and that we can determine the energy of the two nucleon state. This opens up the possibility to determine in future simulations nucleon phase shifts by varying the parameters and the simulated volumes. The physical cut-off of the theory is realised by blocking of the lattice fields. By keeping the block size fixed in physical units the lattice cut-off (i.e. the lattice spacing) can be freely changed. This offers an effective way for controlling lattice artefacts.
The spectrum of supersymmetric Yang-Mills theory presented so far shows an unexpected gap between the bosonic and fermionic masses. This finding was in contradiction with the basic requirements of supersymmetry. In this work we will present new results indicating that the mass gap is reduced at a smaller lattice spacing. Hence lattice artifacts are the most likely explanation for it. These new results have been obtained at a larger beta value and on a larger lattice.
We discuss the computation of the kaon and D meson masses in the N_f = 2+1+1 twisted mass lattice QCD setup, where explicit heavy flavor and parity breaking occurs at finite lattice spacing. We present three methods suitable in this context and verify their consistency.
We discuss the computation of the mass of the K and D mesons within the framework of N_f = 2+1+1 twisted mass lattice QCD from a technical point of view. These quantities are essential, already at the level of generating gauge configurations, being obvious candidates to tune the strange and charm quark masses to their physical values. In particular, we address the problems related to the twisted mass flavor and parity symmetry breaking, which arise when considering a non-degenerate (c,s) doublet. We propose and verify the consistency of three methods to extract the K and D meson masses in this framework.
We present results of lattice QCD simulations with mass-degenerate up and down and mass-split strange and charm (N_f = 2+1+1) dynamical quarks using Wilson twisted mass fermions at maximal twist. The tuning of the strange and charm quark masses is performed at two values of the lattice spacing a~0.078 fm and a~0.086 fm with lattice sizes ranging from L~1.9 fm to L~2.8 fm. We measure with high statistical precision the light pseudoscalar mass m_PS and decay constant f_PS in a range 270 < m_PS < 510 MeV and determine the low energy parameters f_0, l_3 and l_4 of SU(2) chiral perturbation theory. We use the two values of the lattice spacing, several lattice sizes as well as different values of the light, strange and charm quark masses to explore the systematic effects. A first study of discretisation effects in light-quark observables and a comparison to N_f=2 results are performed.
The advantages of using Multi-Step corrections for simulations of lattice gauge theories with dynamical fermions will be discussed. This technique is suited for algorithms based on the Multi-Boson representation of the dynamical fermions as well as for the Hybrid Monte-Carlo (HMC) algorithm and variants of the latter, like the Polynomial-HMC. Especially the latter has the power to deal with an odd number of fermion fields--an essential feature necessary for realistic QCD-simulations with up-, down-, and strange-quarks. In particular, we will discuss the application of the multi-step (actually two-step) correction technique to a PHMC updating algorithm for twisted-mass Wilson fermions with non-degenerate fermion masses, as it was used in recent dynamical simulations for N_f=2+1+1 fermion flavors.
We present preliminary results of a study of the supersymmetric (SUSY) Ward identities (WIs) for the N=1 SU(2) SUSY Yang-Mills theory in the context of one-loop lattice perturbation theory. The supersymmetry on the lattice is explicitly broken by the gluino mass and the lattice artifacts. However, the renormalization of the supercurrent can be carried out in a scheme that restores the nominal continuum WIs. The perturbative calculation of the renormalization constants and mixing coefficients for the local supercurrent is presented.
We report on a lattice study of two-color QCD with adjoint staggered fermions at high density. We find that the model has no early onset and we report on results for diquark condensation, from simulations with and without a diquark source term.
We study the global symmetries of SU(2) gauge theory with N flavors of staggered fermions in the presence of a chemical potential. We motivate the special interest of the case N=1 (staggered) with fermions in the adjoint representation of the gauge group. We present results from numerical simulations with both hybrid Monte Carlo and the Two-Step Multi-Bosonic algorithm.