Heavy Higgs production and decay via e+e−→Z0H0→bbˉZ0Z0e^+e^-\to Z^0 H^0 \to b\bar bZ^0Z^0 and irreducible backgrounds at Next Linear Colliders

The complete matrix element for e^+e^-\ar b\bar bZ^0Z^0 has been computed at tree--level and applied to $Z^0H^0$--production followed by Z^0\ar b\bar b and H^0\ar Z^0Z^0, including all the irreducible background, at Next Linear Colliders. We find that, assuming flavour identification of the $Z^0$--decay products, this channel, together with e^+e^-\ar b\bar bW^+W^- in which Z^0H^0\ar (b\bar b)(W^+W^-), can be important for the study of the parameters of the Standard Model Higgs boson over the heavy mass range 2M_{Z^0}\Ord M_{H^0}\Ord 2{m_t}.Comment: 24 pages, LaTeX (uses Feynman), 7 figures (.ps files or hardcopies of figs.2-7 available upon request

Composite Higgs Search at the LHC

The Higgs boson production cross-sections and decay rates depend, within the Standard Model (SM), on a single unknown parameter, the Higgs mass. In composite Higgs models where the Higgs boson emerges as a pseudo-Goldstone boson from a strongly-interacting sector, additional parameters control the Higgs properties which then deviate from the SM ones. These deviations modify the LEP and Tevatron exclusion bounds and significantly affect the searches for the Higgs boson at the LHC. In some cases, all the Higgs couplings are reduced, which results in deterioration of the Higgs searches but the deviations of the Higgs couplings can also allow for an enhancement of the gluon-fusion production channel, leading to higher statistical significances. The search in the H to gamma gamma channel can also be substantially improved due to an enhancement of the branching fraction for the decay of the Higgs boson into a pair of photons.Comment: 32 pages, 16 figure

Discourses of conflict and collaboration and institutional context in the implementation of forest conservation policies in Soria, Spain

This article examines the emergence of conflict and collaboration in the implementation of forest conservation policies in Soria, Spain. We draw insights from discursive institutionalism and use a comparative case study approach to analyse and compare a situation of social conflict over the Natural Park declaration in the Sierra de Urbión, and a civil society led collaborative process to develop management plans for the “Sierra de Cabrejas” in Soria. The implementation of the EU Habitats Directive generated different outcomes in these two cases, which unfolded in the context of the same nature conservation legislation and national and provincial administrative structures but differed in terms of types of forests involved, property rights arrangements and forest use histories. We critically examine the influence of the institutional context and dominant discourses on the emergence of outcomes: conflict emerged where local institutions and discourses were threatened by the EU directive, while collaboration was possible where local institutions and counter-discourses were weak. We find that the institutional context plays an important part in determining local discourses in the implementation of forest conservation policies. Yet local counter-discourses have limited influence in the implementation and policy processes in the face of contestation by the discourses of regional civil servants conservation activists

Predictions for Higgs production at the Tevatron and the associated uncertainties

We update the theoretical predictions for the production cross sections of the Standard Model Higgs boson at the Fermilab Tevatron collider, focusing on the two main search channels, the gluon-gluon fusion mechanism $gg \to H$ and the Higgs-strahlung processes $q \bar q \to VH$ with $V=W/Z$, including all relevant higher order QCD and electroweak corrections in perturbation theory. We then estimate the various uncertainties affecting these predictions: the scale uncertainties which are viewed as a measure of the unknown higher order effects, the uncertainties from the parton distribution functions and the related errors on the strong coupling constant, as well as the uncertainties due to the use of an effective theory approach in the determination of the radiative corrections in the $gg \to H$ process at next-to-next-to-leading order. We find that while the cross sections are well under control in the Higgs--strahlung processes, the theoretical uncertainties are rather large in the case of the gluon-gluon fusion channel, possibly shifting the central values of the next-to-next-to-leading order cross sections by more than $\approx 40$. These uncertainties are thus significantly larger than the $\approx 10$ error assumed by the CDF and D0 experiments in their recent analysis that has excluded the Higgs mass range $M_H=$162-166 GeV at the 95% confidence level. These exclusion limits should be, therefore, reconsidered in the light of these large theoretical uncertainties.Comment: 40 pages, 12 figures. A few typos are corrected and some updated numbers are provide

Intermediate mass standard model Higgs boson at the proposed CERN LEP⊗\otimesLHC epep collider

The production of the \sm\ Higgs $\phi$ with intermediate mass at the proposed CERN LEP$\otimes$LHC $ep$ collider in $\gamma q(\bar q)\rightarrow W^\pm\phi q'(\bar q')$, $\gamma q(\bar q)\rightarrow Z^0\phi q(\bar q)$ and $g\gamma\rightarrow q\bar q\phi$ events is studied. This is done for all possible (massive) flavours of the quarks $q(q')$ and using photons generated via Compton back--scattering of laser light. We study signatures in which the Higgs decays to $b\bar b$--pairs and the electroweak vector bosons $W^\pm$ and $Z^0$ decay either hadronically or leptonically. All possible backgrounds to these signals are also computed. Flavour identification on $b$--jets is assumed. Explicit formulae for the helicity amplitudes of the above processes are given.Comment: 31 pages, Latex, 8 figures uuencoded, revised version, significant changes in the discussion of the results, in tables and figure

A cyclic universe with colour fields

The topology of the universe is discussed in relation to the singularity problem. We explore the possibility that the initial state of the universe might have had a structure with 3-Klein bottle topology, which would lead to a model of a nonsingular oscillating (cyclic) universe with a well-defined boundary condition. The same topology is assumed to be intrinsic to the nature of the hypothetical primitive constituents of matter (usually called preons) giving rise to the observed variety of elementary particles. Some phenomenological implications of this approach are also discussed.Comment: 21 pages, 9 figures; v.4: final versio

Search for the standard model Higgs boson produced in association with a top-quark pair in pp collisions at the LHC

This is the pre-print version of the final published paper that is available from the link below.A search for the standard model Higgs boson produced in association with a top-quark pair is presented using data samples corresponding to an integrated luminosity of 5.0 fb-1 (5.1 fb-1) collected in pp collisions at the center-of-mass energy of 7TeV (8TeV). Events are considered where the top-quark pair decays to either one lepton+jets (tt→lvqq’bb) or dileptons [tt→l(+)vl(-)vbb], l being an electron or a muon. The search is optimized for the decay mode H → bb. The largest background to the ttH signal is top-quark pair production with additional jets. Artificial neural networks are used to discriminate between signal and background events. Combining the results from the 7TeV and 8TeV samples, the observed (expected) limit on the cross section for Higgs boson production in association with top quark pairs for a Higgs boson mass of 125 GeV is 5.8 (5.2) times the standard model expectatio

NMSSM Higgs Benchmarks Near 125 GeV

The recent LHC indications of a SM-like Higgs boson near 125 GeV are consistent not only with the Standard Model (SM) but also with Supersymmetry (SUSY). However naturalness arguments disfavour the Minimal Supersymmetric Standard Model (MSSM). We consider the Next-to-Minimal Supersymmetric Standard Model (NMSSM) with a SM-like Higgs boson near 125 GeV involving relatively light stops and gluinos below 1 TeV in order to satisfy naturalness requirements. We are careful to ensure that the chosen values of couplings do not become non perturbative below the grand unification (GUT) scale, although we also examine how these limits may be extended by the addition of extra matter to the NMSSM at the two-loop level. We then propose four sets of benchmark points corresponding to the SM-like Higgs boson being the lightest or the second lightest Higgs state in the NMSSM or the NMSSM-with-extra-matter. With the aid of these benchmark points we discuss how the NMSSM Higgs boson near 125 GeV may be distinguished from the SM Higgs boson in future LHC searches.Comment: 40 pages, 1 figure; Minor changes and further references include