How light can the Higgs be?

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

Excitations of the static quark-antiquark system in several gauge theories

The spectrum of gluons in the presence of a static quark-antiquark pair is studied using Monte Carlo simulations on anisotropic space-time lattices. For very small quark-antiquark separations R, the level orderings and approximate degeneracies disagree with the expectations from an effective string theory. As the quark-antiquark separation R increases, a dramatic rearrangement of the energies occurs, and above 2 fm, all of the levels studied show behavior consistent with an effective string description. The energy spacings are nearly pi/R, but a tantalizing fine structure remains. In addition to 4-dimensional SU(3) gauge theory, results from 3-dimensional SU(2) and compact U(1) gauge theories are also presented.Comment: 12 pages, 4 figures, talk presented at the International Conference on Color Confinement and Hadrons in Quantum Chromodynamics (Confinement 2003), RIKEN, July 21-24, 200

The QCD String Spectrum and Conformal Field Theory

The low energy excitation spectrum of the critical Wilson surface is discussed between the roughening transition and the continuum limit of lattice QCD. The fine structure of the spectrum is interpreted within the framework of two-dimensional conformal field theory.Comment: Lattice2001 (confinement),3 pages,1 figure,uses espcrc2.st

QCD String Spectrum 2002

Results from a comprehensive new analysis on the excitation spectrum of the QCD string are presented. A rapid onset of string formation is observed in the spectrum on a length scale of 2 fm, with Dirichlet boundary conditions. The crossover from the short distance spectrum towards string excitations and an observed fine structure in the 1--3 fm range are related to effective string theory. The deficiencies of the Nambu-Goto bosonic string model in describing the observed spectrum are briefly discussed.Comment: Lattice2002(topology), 3 pages, 2 figure

Effects of Nitrogen Photoabsorption Cross Section Resolution on Minor Species Vertical Profiles in Titan's Upper Atmosphere

The significant variations in both measured and modeled densities of minor species in Titan's atmosphere call for the evaluation of possible influencing factors in photochemical modeling. The effect of nitrogen photoabsorption cross section selection on the modeled vertical profiles of minor species is analyzed here, with particular focus on C2H6 and HCN. Our results show a clear impact of cross sections used on all neutral and ion species studied. Affected species include neutrals and ions that are not primary photochemical products, including species that do not even contain nitrogen. The results indicate that photochemical models that employ low-resolution cross sections may significantly miscalculate the vertical profiles of minor species. Such differences are expected to have important implications for Titan's overall atmospheric structure and chemistry.NASA Outer Planet Research program NNH12ZDA001NInstitute for Computational Engineering and Sciences (ICES

The Casimir Energy Paradox of the QCD String

It is widely thought that the early onset of the asymptotic Casimir energy with unit conformal charge signals bosonic string formation of the confining flux connecting a static quark-antiquark pair in QCD. This is observed on a scale where most of the string eigenmodes do not exist and the few stable modes above the ground state are displaced. Hints for the resolution of this paradox are suggested.Comment: Lattice2003(topology