Joel Giedt

Dark Matter, Constrained Minimal Supersymmetric Standard Model, and Lattice QCD

Recent lattice measurements have given accurate estimates of the light and strange quark condensates in the proton. We use these new results to signi#12;cantly improve the dark matter predictions in a set of benchmark models that represent di#11;erent scenarios in the constrained minimal supersymmetric standard model (CMSSM). Because the predicted cross sections are at least an order of magnitude smaller than previously suggested, our results have signi#12;cant consequences for dark matter searches.

Phase diagram of SU(2) with 2 flavors of dynamical adjoint quarks

We report on numerical simulations of SU(2) lattice gauge theory with two flavors of light dynamical quarks in the adjoint of the gauge group. The dynamics of this theory is thought to be very different from QCD?the theory exhibiting conformal or near conformal behavior in the infrared. We make a high resolution survey of the phase diagram of this model in the plane of the bare coupling and quark mass on lattices of size 83 ? 16. Our simulations reveal a line of first order phase transitions extending from ? = 0 to ? = ?c ~ 2.0. For ??>??c the phase boundary is no longer first order but continues as the locus of minimum meson mass. For ??>??c we observe the pion and rho masses along the phase boundary to be light, independent of bare coupling and approximately degenerate. We discuss possible interpretations of these observations and corresponding continuum limits.

Detection of center vortices in the lattice Yang-Mills vacuum

We discuss the implementation of the {open_quotes}direct{close_quotes} maximal center gauge (a gauge which maximizes the lattice average of the squared-modulus of the trace of link variables), and its use in identifying Z{sub 2} center vortices in Yang-Mills vacuum configurations generated by lattice Monte Carlo calculations. We find that center vortices identified in the vacuum state account for the full asymptotic string tension. Scaling of vortex densities with lattice coupling, change in vortex size with cooling, and sensitivity to Gribov copies are discussed. Preliminary evidence is presented, on small lattices, for center dominance in SU(3) lattice gauge theory. {copyright} {ital 1998} {ital The American Physical Society}

Dark Matter, the MCSSM and lattice QCD

Recent lattice measurements have given accurate estimates of the light and strange quark condensates in the proton. We use these new results to signi#12;cantly improve the dark matter predictions in a set of benchmark models that represent di#11;erent scenarios in the constrained minimal supersymmetric standard model (CMSSM). Because the predicted cross sections are at least an order of magnitude smaller than previously suggested, our results have signi#12;cant consequences for dark matter searches.

Non-positive fermion determinants in lattice supersymmetry

Abstract We find that fermion determinants are not generally positive in a recent class of constructions with explicit lattice supersymmetry. These involve an orbifold of supersymmetric matrix models, and have as their target (continuum) theory (2,2) 2-dimensional super-Yang–Mills. The fermion determinant is shown to be identically zero for all boson configurations due to the existence of a zeromode fermion inherited from the “mother theory”. Once this eigenvalue is factored out, the fermion determinant generically has arbitrary complex phase. We discuss the implications of this result for simulation of the models.

DECONSTRUCTION AND OTHER APPROACHES TO SUPERSYMMETRIC LATTICE FIELD THEORIES

This paper contains both a review of recent approaches to supersymmetric lattice field theories and some new results on the deconstruction approach. The essential reason for the complex phase problem of the fermion determinant is shown to be derivative interactions that are not present in the continuum. These irrelevant operators violate the self-conjugacy of the fermion action that is present in the continuum. It is explained why this complex phase problem does not disappear in the continuum limit. The fermion determinant suppression of various branches of the classical moduli space is explored, and found to be supportive of previous claims regarding the continuum limit.

Massive neutrinos and (heterotic) string theory

String theories in principle address the origin and values of the quark and lepton masses. Perhaps the small values of neutrino masses could be explained generically in string theory even if it is more difficult to calculate individual values, or perhaps some string constructions could be favored by generating small neutrino masses. We examine this issue in the context of the well-known three-family standard-like

Perturbative renormalization of lattice N = 4 super Yang-Mills theory

{Z}_{3}

Vortex structure vs. monopole dominance in Abelian-projected gauge theory

heterotic orbifolds, where the theory is well enough known to construct the corresponding operators allowed by string selection rules, and analyze the D- and F-flatness conditions. Surprisingly, we find that a simple seesaw mechanism does not arise. It is not clear whether this is a property of this construction, or of orbifolds more generally, or of string theory itself. Extended seesaw mechanisms may be allowed; more analysis will be needed to settle that issue. We briefly speculate on their form if allowed and on the possibility of alternatives, such as small Dirac masses and triplet seesaws. The smallness of neutrino masses may be a powerful probe of string constructions in general. We also find further evidence that there are only 20 inequivalent models in this class, which affects the counting of string vacua.

MCRG Minimal Walking Technicolor

We consider