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We report null results on a two year photometric search for outburst predictors in SS Cyg. Observations in Johnson V and Cousins I were obtained almost daily for multiple hours per night for two observing seasons. The accumulated data are put through various statistical and visual analysis techniques but fails to detect any outburst predictors. However, analysis of 102 years of AAVSO archival visual data led to the detection of a correlation between a long term quasi-periodic feature at around 1,000-2,000 days in length and an increase in outburst rate., Comment: Accepted in PASP, December 2007

In the minimal Standard Model, it is commonly believed that the Higgs mass cannot be too small, otherwise Top quark dynamics makes the Higgs potential unstable. Although this Higgs mass lower bound is relevant for current phenomenology, we show that the Higgs vacuum instability in fact does not exist and only appears when treating incorrectly the cut-off in the renormalization of a trivial theory. We also demonstrate how to calculate correctly the regulator-dependent Higgs mass lower bound., Comment: Plenary talk presented at Lattice2004(plenary), Fermilab, June 21-26, 2004; 7 pages, 10 figures

Some time ago, Svetitsky and Yaffe have argued that -- if the deconfinement phase transition of a (d+1)-dimensional Yang-Mills theory with gauge group G is second order -- it should be in the universality class of a d-dimensional spin model symmetric under the center of G. For d=3 these arguments have been confirmed numerically only in the SU(2) case with center Z(2), simply because all SU(N) Yang-Mills theories with N>=3 seem to have non-universal first order phase transitions. The symplectic groups Sp(N) also have the center Z(2) and provide another extension of SU(2) = Sp(1) to general N. Using lattice simulations, we find that the deconfinement phase transition of Sp(2) Yang-Mills theory is first order in 3+1 dimensions, while in 2+1 dimensions stronger fluctuations induce a second order transition. In agreement with the Svetitsky-Yaffe conjecture, for (2+1)-d Sp(2) Yang-Mills theory we find the universal critical behavior of the 2-d Ising model. For Sp(3) Yang-Mills theory the transition is first order both in 2+1 and in 3+1 dimensions. This suggests that the size of the gauge group -- and not the center symmetry -- determines the order of the deconfinement phase transition., Comment: 31 pages, 16 figures

We present numerical results for the deconfinement phase transition in Sp(2) and Sp(3) Yang-Mills theories in (2+1)-D and (3+1)-D. We then make a conjecture on the order of this phase transition in Yang-Mills theories with general Lie groups G = SU(N), SO(N), Sp(N) and with exceptional groups G = G(2), F(4), E(6), E(7), E(8)., Comment: Lattice2003(Topology and Confinement), 3 pages, 3 figures

Pure Yang-Mills theory has a finite-temperature phase transition, separating the confined and deconfined bulk phases. Svetitsky and Yaffe conjectured that if this phase transition is of second order, it belongs to the universality class of transitions for particular scalar field theories in one lower dimension. We examine Yang-Mills theory with the symplectic gauge groups Sp(N). We find new evidence supporting the Svetitsky-Yaffe conjecture and make our own conjecture as to which gauge theories have a universal second order deconfinement phase transition., Comment: 5 pages, 4 figures; Contribution to Confinement 2003, Tokyo, Japan, July 21-24, 2003

It is widely believed that, for a given Top mass, the Higgs mass has a lower bound: if m_Higgs is too small, the Higgs vacuum is unstable due to Top dynamics. From vacuum instability, the state-of-the-art calculation of the lower bound is close to the current experimental limit. Using non-perturbative simulations and large N calculations, we show that the vacuum is in fact never unstable. Instead, we investigate the existence of a new lower bound, based on the intrinsic cut-off of this trivial theory., Comment: 3 pages, 4 figures, uses espcrc2.sty, Lattice2003(higgs)

We study theories with the exceptional gauge group G(2). The 14 adjoint "gluons" of a G(2) gauge theory transform as {3}, {3bar} and {8} under the subgroup SU(3), and hence have the color quantum numbers of ordinary quarks, anti-quarks and gluons in QCD. Since G(2) has a trivial center, a "quark" in the {7} representation of G(2) can be screened by "gluons". As a result, in G(2) Yang-Mills theory the string between a pair of static "quarks" can break. In G(2) QCD there is a hybrid consisting of one "quark" and three "gluons". In supersymmetric G(2) Yang-Mills theory with a {14} Majorana "gluino" the chiral symmetry is Z(4)_\chi. Chiral symmetry breaking gives rise to distinct confined phases separated by confined-confined domain walls. A scalar Higgs field in the {7} representation breaks G(2) to SU(3) and allows us to interpolate between theories with exceptional and ordinary confinement. We also present strong coupling lattice calculations that reveal basic features of G(2) confinement. Just as in QCD, where dynamical quarks break the Z(3) symmetry explicitly, G(2) gauge theories confine even without a center. However, there is not necessarily a deconfinement phase transition at finite temperature., Comment: 34 pages, 2 figures

We discuss theories with the exceptional centerless gauge group G(2), paying attention to confinement and the pattern of chiral symmetry breaking. Exploiting the Higgs mechanism to break the symmetry down to SU(3), we also present how the familiar features of confinement and chiral symmetry breaking of SU(3) gauge theories reemerge. G(2) gauge theories show up as an unusual theoretical framework to study SU(3) gauge theories without the ``luxury'' of a center., Comment: 3 pages, 1 figure, Lattice2002 (Topology and Confinement)

We present the first set of quenched QCD measurements using the recently parametrized fixed-point Dirac operator D^FP. We also give a general and practical construction of covariant densities and conserved currents for chiral lattice actions. The measurements include (a) hadron spectroscopy, (b) corrections of small chiral deviations, (c) the renormalized quark condensate from finite-size scaling and, independently, spectroscopy, (d) the topological susceptibility, (e) small eigenvalue distributions and random matrix theory, and (f) local chirality of near-zero modes and instanton-dominance., Comment: 50 pages, 19 figures; misprints corrected, discussion on covariant densities extended, new appendix added

In this preliminary study, we examine the chiral properties of the parametrized Fixed-Point Dirac operator D^FP, see how to improve its chirality via the Overlap construction, measure the renormalized quark condensate Sigma and the topological susceptibility chi_t, and investigate local chirality of near zero modes of the Dirac operator. We also give a general construction of chiral currents and densities for chiral lattice actions., Comment: Lattice2001(chiral), based on a talk by T.J. and a poster by K.H., 6 pages

We have constructed a new fermion action which is an approximation to the (chirally symmetric) Fixed-Point action, containing the full Clifford algebra with couplings inside a hypercube and paths built from renormalization group inspired fat links. We present an exploratory study of the light hadron spectrum and the energy-momentum dispersion relation., Comment: Lattice2001(improvement), 3 pages, based on a talk by S.H; reference updated

We examine the role of the center Z(N) of the gauge group SU(N) in gauge theories. In this pedagogical article, we discuss, among other topics, the center symmetry and confinement and deconfinement in gauge theories and associated finite-temperature phase transitions. We also look at universal properties of domain walls separating distinct confined and deconfined bulk phases, including a description of how QCD color-flux strings can end on color-neutral domain walls, and unusual finite-volume dependence in which quarks in deconfined bulk phase seem to be "confined"., Comment: LaTex, 35 pages, 6 figures, uses sprocl.sty. To be published in the Festschrift in honor of B.L. Ioffe, "At the Frontier of Particle Physics/ Handbook of QCD", edited by M. Shifman

We report on an ongoing project to parametrize the Fixed-Point Dirac operator for massless quarks, using a very general construction which has arbitrarily many fermion offsets and gauge paths, the complete Clifford algebra and satisfies all required symmetries. Optimizing a specific construction with hypercubic fermion offsets, we present some preliminary results., Comment: Lattice 2000 (Improvement), 9 pages, based on a talk by K.H. and a poster by T.J. References added

The recently developed Meron-Cluster algorithm completely solves the exponentially difficult sign problem for a number of models previously inaccessible to numerical simulation. We use this algorithm in a high-precision study of a model of N=1 flavor of staggered fermions in (2+1)-dimensions with a four-fermion interaction. This model cannot be explored using standard algorithms. We find that the Z(2) chiral symmetry of this model is spontaneously broken at low temperatures and that the finite-temperature chiral phase transition is in the universality class of the 2-d Ising model, as expected., Comment: 18 pages, LaTex

We discuss the steps to construct Dirac operators which have arbitrary fermion offsets, gauge paths, a general structure in Dirac space and satisfy the basic symmetries (gauge symmetry, hermiticity condition, charge conjugation, hypercubic rotations and reflections) on the lattice. We give an extensive set of examples and offer help to add further structures., Comment: 19 pages, latex, maple code attached

Numerical simulations of numerous quantum systems suffer from the notorious sign problem. Important examples include QCD and other field theories at non-zero chemical potential, at non-zero vacuum angle, or with an odd number of flavors, as well as the Hubbard model for high-temperature superconductivity and quantum antiferromagnets in an external magnetic field. In all these cases standard simulation algorithms require an exponentially large statistics in large space-time volumes and are thus impossible to use in practice. Meron-cluster algorithms realize a general strategy to solve severe sign problems but must be constructed for each individual case. They lead to a complete solution of the sign problem in several of the above cases., Comment: 15 pages,LATTICE99

We examine a (3+1)-dimensional model of staggered lattice fermions with a four-fermion interaction and Z(2) chiral symmetry using the Hamiltonian formulation. This model cannot be simulated with standard fermion algorithms because those suffer from a very severe sign problem. We use a new fermion simulation technique - the meron-cluster algorithm - which solves the sign problem and leads to high-precision numerical data. We investigate the finite temperature chiral phase transition and verify that it is in the universality class of the 3-d Ising model using finite-size scaling., Comment: 21 pages, 6 figures

We have previously found analytically a very unusual and unexpected form of confinement in SU(3) Yang-Mills theory. This confinement occurs in the deconfined phase of the theory. The free energy of a single static test quark diverges, even though it is contained in deconfined bulk phase and there is no QCD string present. This phenomenon occurs in cylindrical volumes with a certain choice of spatial boundary conditions. We examine numerically an effective model for the Yang-Mills theory and, using a cluster algorithm, we observe this unusual confinement. We also find a new way to determine the interface tension of domain walls separating distinct bulk phases., Comment: LaTex, 14 pages, 4 figures

In the context of M-theory, Witten has argued that an intriguing phenomenon occurs, namely that QCD strings can end on domain walls. We present a simpler explanation of this effect using effective field theory to describe the behavior of the Polyakov loop and the gluino condensate in N = 1 supersymmetric QCD. We describe how domain walls separating distinct confined phases appear in this effective theory and how these interfaces are completely wet by a film of deconfined phase at the high-temperature phase transition. This gives the Polyakov loop a non-zero expectation value on the domain wall. Consequently, a static test quark which is close to the interface has a finite free energy and the string emanating from it can end on the wall., Comment: LATTICE98(hightemp), 3 pages, 2 figures

Complete wetting is a universal phenomenon associated with interfaces separating coexisting phases. For example, in the pure gluon theory, at $T_c$ an interface separating two distinct high-temperature deconfined phases splits into two confined-deconfined interfaces with a complete wetting layer of confined phase between them. In supersymmetric Yang-Mills theory, distinct confined phases may coexist with a Coulomb phase at zero temperature. In that case, the Coulomb phase may completely wet a confined-confined interface. Finally, at the high-temperature phase transition of gluons and gluinos, confined-confined interfaces are completely wet by the deconfined phase, and similarly, deconfined-deconfined interfaces are completely wet by the confined phase. For these various cases, we determine the interface profiles and the corresponding complete wetting critical exponents. The exponents depend on the range of the interface interactions and agree with those of corresponding condensed matter systems., Comment: 15 pages, 5 figures

As argued by Witten on the basis of M-theory, QCD strings can end on domain walls. We present an explanation of this effect in the framework of effective field theories for the Polyakov loop and the gluino condensate in N=1 supersymmetric QCD. The domain walls separating confined phases with different values of the gluino condensate are completely wet by a layer of deconfined phase at the high-temperature phase transition. As a consequence, even at low temperatures, the Polyakov loop has a non-vanishing expectation value on the domain wall. Thus, close to the wall, the free energy of a static quark is finite and the string emanating from it can end on the wall., Comment: 8 pages, 2 figures

In cylindrical volumes with C-periodic boundary conditions in the long direction, static quarks are confined even in the gluon plasma phase due to the presence of interfaces separating the three distinct high-temperature phases. An effective "string tension" is computed analytically using a dilute gas of interfaces. At T_c, the deconfined-deconfined interfaces are completely wet by the confined phase and the high-temperature "string tension" turns into the usual string tension below T_c. Finite size formulae are derived, which allow to extract interface and string tensions from the expectation value of a single Polyakov loop. A cluster algorithm is built for the 3-d three-state Potts model and an improved estimator for the Polyakov loop is constructed, based on the number of clusters wrapping around the C-periodic direction of the cluster., Comment: 3 pages, Latex, talk presented at Lattice '97, to appear in Nucl. Phys. B (Proc. Suppl.), uses espcrc2.sty

Due to the Gauss law, a single quark cannot exist in a periodic volume, while it can exist with C-periodic boundary conditions. In a C-periodic cylinder of cross section A = L_x L_y and length L_z >> L_x, L_y containing deconfined gluons, regions of different high temperature Z(3) phases are aligned along the z-direction, separated by deconfined- deconfined interfaces. In this geometry, the free energy of a single static quark diverges in proportion to L_z. Hence, paradoxically, the quark is confined, although the temperature T is larger than T_c. At T around T_c, the confined phase coexists with the three deconfined phases. The deconfined-deconfined interfaces can be completely or incompletely wet by the confined phase. The free energy of a quark behaves differently in these two cases. In contrast to claims in the literature, our results imply that deconfined-deconfined interfaces are not Euclidean artifacts, but have observable consequences in a system of hot gluons., Comment: 8 pages, Latex, no figures