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Register a new userSpectrum of 4d N=1 SYM on the lattice with light dynamical Wilson gluinos
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We perform Monte Carlo investigations of the 4d ${cal N}=1$ supersymmetric Yang-Mills (SYM) theory on the lattice with dynamical gluinos in the adjoint representation of the SU(2) gauge group. Our aim is to determine the mass spectrum of the low-lying bound states which is expected to be organised in supermultiplets in the infinite volume continuum limit. For this purpose we perform simulations on large lattices, up to an extension $L/r_0 simeq 6$ where $r_0 simeq 0.5 rm fm$ is the Sommer scale parameter. We apply improved lattice actions: tree-level improved Symanzik (tlSym) gauge action and in the later runs a Stout-smeared Wilson fermion action. The gauge configuration samples are prepared by the Two-Step Polynomial Hybrid Monte Carlo (TS-PHMC) update algorithm.
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The lattice provides a powerful tool to non-perturbatively investigate strongly coupled supersymmetric Yang-Mills (SYM) theories. The pure SU(2) SYM theory with one supercharge is simulated on large lattices with small Majorana gluino masses down to about $am_{tilde g}=0.068$ with lattice spacing $asimeq 0.125$ fm. The gluino dynamics is simulated by the Two-Step Multi-Boson (TSMB) and the Two-Step Polynomial Hybrid Monte Carlo (TS-PHMC) algorithms. Supersymmetry (SUSY) is broken explicitly by the lattice and the Wilson term and softly by the presence of a non-vanishing gluino mass. However, the recovery of SUSY is expected in the infinite volume continuum limit by tuning the bare parameters to the SUSY point in the parameter space. This scenario is studied by the determination of the low-energy mass spectrum and by means of lattice SUSY Ward-Identities (WIs).
We present preliminary results for the light harden spectrum in $N_f=2+1$ lattice QCD obtained with the nonperturbatively $O(a)$-improved Wilson quark action and the Iwasaki gauge action. Simulations are carried out at $beta=1.90$ on a $32^3 times 64$ lattice using the PACS-CS computer. We employ Luschers domain-decomposed HMC algorithm to reduce the up-down quark masses toward the physical value. The pseudoscalar meson masses range from 730 MeV down to 210 MeV. We compare the light harden spectrum extrapolated to the physical point with the experimental values.
We report on a lattice simulation result for four-dimensional {cal N}=1 SU(2) super Yang-Mills theory with the dynamical overlap gluino. We study the spectrum of the overlap Dirac operator at three different gluino masses m=0.2, 0.1 and 0.05 with the Iwasaki action on a 8^3 times 16 lattice. We find that the lowest eigenvalue distributions are in good agreement with the prediction from the random matrix theory. Moreover the mass dependence of the condensate is almost constant, which gives a clean chiral limit. Our results for the gluino condensate in the chiral limit is < bar{psi} psi > r_0^3 = 0.63(12), where r_0 is the Sommer scale.
We report on a numerical simulation with 2+1 dynamical flavors of overlap fermions. We calculate pseudo-scalar masses and decay constants on a $16^3times 48 times (0.11 {rm fm})^4$ lattice at five different up and down quark masses and two strange quark masses. The lightest pion mass corresponds to $approx 310$ MeV. We also study the validity of the chiral perturbation theory using the results of the numerical simulation with two dynamical flavors and conclude that the one-loop formulae cannot be directly applied in the strange quark mass region. We therefore extrapolate our 2+1-flavor results to the chiral limit by fitting the data to the two-loop formulae of the chiral perturbation theory.
The electromagnetic form factors provide important insight into the internal structure of the nucleon and continue to be of major interest for experiment and phenomenology. For an intermediate range of momenta the form factors can be calculated on the lattice. However, the reliability of the results is limited by systematic errors mostly due to the required extrapolation to physical quark masses. Chiral effective field theories predict a rather strong quark mass dependence in a range which was yet inaccessible for lattice simulations. We give an update on recent results from the QCDSF collaboration using gauge configurations with dynamical Nf=2, non-perturbatively O(a)-improved Wilson fermions at pion masses as low as 350 MeV.
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