Abstract:The minimal supersymmetric standard model, and extensions, have stringent upper bounds on the mass of the lightest Higgs boson if perturbativity up to the Planck scale is assumed. We argue that these bounds are softened tremendously if the Higgs is charged under an asymptotically free gauge group. We present a model with an additional SU(2) gauge group which easily produces Higgs masses above 200 GeV while avoiding electroweak constraints. If one allows some fine-tuning of the high-scale value of the gauge coupling, Higgs masses greater than 350 GeV are achieved. Unification of couplings is predicted to similar accuracy as in the minimal supersymmetric standard model with only small deviations at the two-loop level.

We present new techniques for finding anomaly-free sets of fermions. Although the anomaly cancellation conditions typically include cubic equations with integer variables that cannot be solved in general, we prove by construction that any chiral set of fermions can be embedded in a larger set of fermions which is chiral and anomaly-free. Applying these techniques to extensions of the standard model, we find anomaly-free models that have arbitrary quark and lepton charges under an additional U͑1͒ gauge group.

Twin Higgs models are economical extensions of the Standard Model that stabilize the electroweak scale. In these theories the Higgs field is a pseudo Nambu-Goldstone boson that is protected against radiative corrections up to scales of order 5 TeV by a discrete parity symmetry. We construct, for the first time, a class of composite twin Higgs models based on confining QCD-like dynamics. These theories naturally incoporate a custodial isospin symmetry and predict a rich spectrum of particles with masses of order a TeV that will be accessible at the LHC.

We investigate the cosmological signatures of instantons mediating tunneling between de Sitter minima. For generic potentials the Coleman-de Luccia instanton does not necessarily exist; when it does not, the instanton which contributes to the decay rate is the trivial constant solution, known as the Hawking-Moss instanton. With the aid of a toy model we interpret this solution and describe the resulting cosmology. In neither the Coleman-de Luccia nor Hawking-Moss case can the resulting cosmology be closed. An observation of significant positive curvature would therefore rule out the possibility that our universe arose from any transition from a neighboring minimum in the string-theory landscape.

The LEP-II bound on the light Higgs mass rules out the vast majority of parameter space left to the Minimal Supersymmetric Standard Model (MSSM) with weakscale soft-masses. This suggests the importance of exploring extensions of the MSSM with non-minimal Higgs physics. In this article, we explore a theory with an additional singlet superfield and an extended gauge sector. The theory has a number of novel features compared to both the MSSM and Next-to-MSSM, including easily realizing a light CP-even Higgs mass consistent with LEP-II limits, tan β 1, and a lightest Higgs which is charged. These features are achieved while remaining consistent with perturbative unification and without large stop-masses. Discovery modes at the Tevatron and LHC are discussed.

We present a measurement of the Hubble constant based on Cepheid distances to 27 galaxies within 20 Mpc. We take the Cepheid data from published measurements by the Hubble Telescope Key Project on the Distance ScaleWe calibrate the Cepheid period-luminosity (PL) relation with data from (H 0 KP). over 700 Cepheids in the LMC obtained by the OGLE collaboration ; we assume an LMC distance modulus of 18.50 mag kpc). Using this PL calibration, we obtain new distances to the (d LMC \ 50.1 galaxies. We correct the redshifts of these galaxies for peculiar velocities using two distinct veloc-H 0 KP ity Ðeld models : the phenomenological model of Tonry et al. and a model based on the IRAS density Ðeld and linear gravitational instability theory. We combine the Cepheid distances with the corrected redshifts for the 27 galaxies to derive the Hubble constant. The results are km s~1 H 0 , H 0 \ 85^5 Mpc~1 (random error) at 95% conÐdence when the IRAS model is used, and 92^5 km s~1 Mpc~1 when the phenomenological model is used. The IRAS model is a better Ðt to the data, and the Hubble constant it returns is more reliable. Systematic error stems mainly from LMC distance uncertainty, which is not directly addressed by this paper. Our value of is signiÐcantly larger than that quoted by H 0 the km s~1 Mpc~1. Cepheid recalibration explains D30% of this di †erence, and H 0 KP, H 0 \ 71^6 velocity Ðeld analysis accounts for D70%. We discuss in detail possible reasons for this discrepancy and future studies needed to resolve it.

In the Minimal Supersymmetric Standard Model (the MSSM), the electroweak symmetry is restored as supersymmetry-breaking terms are turned off. We describe a generic extension of the MSSM where the electroweak symmetry is broken in the supersymmetric limit. We call this limit the "sEWSB" phase, short for supersymmetric electroweak symmetry breaking. We define this phase in an effective field theory that only contains the MSSM degrees of freedom. The sEWSB vacua naturally have an inverted scalar spectrum, where the heaviest CP-even Higgs state has Standard Model-like couplings to the massive vector bosons; experimental constraints in the scalar Higgs sector are more easily satisfied than in the MSSM.

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