Renormalization group flows for gauge theories in axial gauges

Gauge theories in axial gauges are studied using Exact Renormalisation Group flows. We introduce a background field in the infrared regulator, but not in the gauge fixing, in contrast to the usual background field gauge. It is shown how heat-kernel methods can be used to obtain approximate solutions to the flow and the corresponding Ward identities. Expansion schemes are discussed, which are not applicable in covariant gauges. As an application, we derive the one-loop effective action for covariantly constant field strength, and the one-loop beta-function for arbitrary regulator

NMHDECAY: A Fortran Code for the Higgs Masses, Couplings and Decay Widths in the NMSSM

The Fortran code NMHDECAY computes the masses, couplings and decay widths of all Higgs bosons of the NMSSM in terms of its parameters at the electroweak (SUSY breaking) scale: the Yukawa couplings lambda and kappa, the soft trilinear terms A_lambda and A_kappa, and tan(beta) and mu_eff = lambda*. The computation of the spectrum includes leading two loop terms, electroweak corrections and propagator corrections. The computation of the decay widths is carried out as in HDECAY, but (for the moment) without three body decays. Each point in parameter space is checked against negative Higgs bosons searches at LEP, including unconventional channels relevant for the NMSSM. One version of the program uses generalized SLHA conventions for input and output.Comment: Typos corrected, references added, radiative corrections written out explicitely in new appendix

Escaping the Large Fine Tuning and Little Hierarchy Problems in the Next to Minimal Supersymmetric Model and h-> aa Decays

We demonstrate that the NMSSM can have small fine tuning and modest light stop mass while still evading all experimental constraints. For small tan(beta) [large tan(beta)], the relevant scenarios are such that there is always (often) a SM-like Higgs boson that decays to two lighter -- possibly much lighter -- pseudoscalar Higgses.Comment: 4 pages, 4 figures, revised to conform with PRL published versio

Many Light Higgs Bosons in the NMSSM

The next-to-minimal supersymmetric model with a light doublet-like CP-odd Higgs boson and small $\tan \beta$ can satisfy all experimental limits on Higgs bosons even with light superpartners. In these scenarios, the two lightest CP-even Higgs bosons, \hi and \hii, and the charged Higgs boson, \hp, can all be light enough to be produced at LEP and yet have decays that have not been looked for or are poorly constrained by existing collider experiments. The channel \hi\to \ai\ai (where \ai is the lightest CP-odd boson and has mass below $2m_b$) with \ai\to \tau^+\tau^- or $2j$ is still awaiting LEP constraints for \mhi>86\gev or 82\gev, respectively. LEP data may also contain \epem\to \hii\ai events where \hii\to Z\ai is the dominant decay, a channel that was never examined. Decays of the charged Higgs bosons are often dominated by H^\pm \to W^{\pm (\star)} \ai with \ai \to gg,c \bar c, \tau^+ \tau^-. This is a channel that has so far been ignored in the search for t\to \hp b decays at the Tevatron. A specialized analysis might reveal a signal. The light \ai might be within the reach of $B$ factories via \Upsilon\to \gamma \ai decays. We study typical mass ranges and branching ratios of Higgs bosons in this scenario and compare these scenarios where the \ai has a large doublet component to the more general scenarios with arbitrary singlet component for the \ai.Comment: 15 pages, 47 figure

Gauge invariance and background field formalism in the exact renormalisation group

We discuss gauge symmetry and Ward-Takahashi identities for Wilsonian flows in pure Yang-Mills theories. The background field formalism is used for the construction of a gauge invariant effective action. The symmetries of the effective action under gauge transformations for both the gauge field and the auxiliary background field are separately evaluated. We examine how the symmetry properties of the full theory are restored in the limit where the cut-off is removed.Comment: version to be published in PL

NMSSM Higgs Discovery at the LHC

We demonstrate that Higgs discovery at the LHC is possible in the context of the NMSSM even for those scenarios such that the only strongly produced Higgs boson is a very SM-like CP-even scalar which decays almost entirely to a pair of relatvely light CP-odd states. In combination with other search channels, we are on the verge of demonstrating that detection of at least one of the NMSSM Higgs bosons is guaranteed at the LHC for accumulated luminosity of $300 {\rm fb}^{-1}$.Comment: 8 pages, 1 figure, to appear in the Proceedings of the Les Houches Workshop 2003: ``Physics at TeV Colliders'

Phenomenology of the General NMSSM with Gauge Mediated Supersymmetry Breaking

We investigate various classes of Gauge Mediated Supersymmetry Breaking models and show that the Next-to-Minimal Supersymmetric Standard Model can solve the mu-problem in a phenomenologically acceptable way. These models include scenarios with singlet tadpole terms, which are phenomenologically viable, e.g., in the presence of a small Yukawa coupling <~ 10^{-5}. Scenarios with suppressed trilinear A-terms at the messenger scale lead naturally to light CP-odd scalars, which play the r\^ole of pseudo R-axions. A wide range of parameters of such models satisfies LEP constraints, with CP-even Higgs scalars below 114 GeV decaying dominantly into a pair of CP-odd scalars.Comment: 24 pages, 6 figures, typos corrected, reference adde

Global fit to Higgs signal strengths and couplings and implications for extended Higgs sectors

The most recent LHC data have provided a considerable improvement in the precision with which various Higgs production and decay channels have been measured. Using all available public results from ATLAS, CMS and the Tevatron, we derive for each final state the combined confidence level contours for the signal strengths in the (gluon fusion + ttH associated production) versus (vector boson fusion + VH associated production) space. These "combined signal strength ellipses" can be used in a simple, generic way to constrain a very wide class of New Physics models in which the couplings of the Higgs boson deviate from the Standard Model prediction. Here, we use them to constrain the reduced couplings of the Higgs boson to up-quarks, down-quarks/leptons and vector boson pairs. We also consider New Physics contributions to the loop-induced gluon-gluon and photon-photon couplings of the Higgs, as well as invisible/unseen decays. Finally, we apply our fits to some simple models with an extended Higgs sector, in particular to Two-Higgs-Doublet models of Type I and Type II, the Inert Doublet model, and the Georgi-Machacek triplet Higgs model.Comment: 31 pages, 15 figures; v2: fixed important factor of 2 missing in Eq. (1) (results unchanged), extended discussion in the next-to-last paragraph of Section 3, some references added; v3: appendices and references added, matches version accepted by PR

Mass Bounds for the Neutral Higgs Bosons in the Next-To-Minimal Supersymmetric Standard Model

In the Next--To--Minimal Supersymmetric Standard Model (NMSSM), the Higgs and neutralino/chargino sectors are strongly correlated by four common parameters at tree level. Therefore we analyze the experimental data from both the search for Higgs bosons as well as for neutralinos and charginos at LEP 100 in order to constrain the parameter space and the masses of the neutral Higgs particles in the NMSSM. We find that small singlet vacuum expectation values are ruled out, but a massless neutral Higgs scalar and pseudoscalar is not excluded for most of the parameter space of the NMSSM. Improved limits from the neutralino/chargino search at LEP 200, however, may lead to nonvanishing lower Higgs mass bounds.Comment: 9 pages, LATEX, 6 figures (not included). The complete paper (including figures) can be obtained via anonymous ftp at ftp://ftp.physik.uni-wuerzburg.de/pub/preprint/WUE-ITP-95-003.ps.g