Bounds on warped extra dimensions from a Standard Model-like Higgs boson

We point out that the discovery of a light Higgs boson in the γγ, ZZ, and WW   decay channels at the LHC, with cross sections not far from the predictions of the Standard Model, would have profound implications for the parameters of warped extra-dimension models with a brane-localized Higgs sector. Due to loop effects of Kaluza–Klein particles, these models predict a significant reduction of the Higgs production cross section via gluon–gluon fusion, combined with an enhancement of the ratio Br(h→γγ)/Br(h→ZZ)$\mathrm{Br}(h\to \gamma \gamma )/\mathrm{Br}(h\to ZZ)$ in large parts of parameter space. LHC measurements of these decays will probe Kaluza–Klein masses up to the 10 TeV range, exceeding by far the reach for direct production.     

Higgs boson emission in very rare decays of an extra vector boson

We explore the phenomenological structure of E ₆-inspired grand unified group with the gauge group SU(3)_c×SU(2)_L×U(1)_Y×U(1), the emphasis being laid upon its implications for Higgs boson observation. In particular, we discuss the probability for the mass eigenstate Z ₂ to decay into a Higgs particle and a bound state composed of heavy quarks. Constraints on and relations between the Z ₂ and Higgs masses are presented.     

Reweighing the evidence for a light Higgs boson in dileptonic W boson decays

We reconsider observables for discovering and measuring the mass of a Higgs boson via its dileptonic decays h → W W* → ?ν?ν. We define an observable generalizing the transverse mass that takes into account the fact that one of the intermediate W bosons is likely to be on shell. We compare this new variable with existing ones and argue that it gives a significant improvement for discovery in the region mh < 2 mW.     

Vector boson decays of the Higgs boson

We derive the width of the Higgs boson into vector bosons. General formulas are derived both for the on–shell decay as well for the off–shell decays, and , where . For the off-shell decays the width of the decaying vector boson is properly included. The formulas are valid both for the Standard Model as well as for arbitrary extensions. As an example we study in detail the gauge-invariant effective Lagrangian models where we can have sizable enhancements over the Standard Model that could be observed at LEP. Received: 31 July 1998 / Revised version: 23 September 1998 / Published online: 6 November 1998     

Search for Higgs scalars in upsilon decays

We have searched for the decay of ?'s into a monochromatic photon accompanied by other particles as a signal for the reaction ?→γ+Higgs. Two different methods are presented both with null result. While we are not sensitive to the branching ratios predicted by the standard model with a minimal Higgs content, we can put limits on the possible values of the lowest Higgs mass and the ratio of the vacuum expectation values for more complex models. Our results are also of interest with respect to the ξ(2.2) being a Higgs in the context of such models.     

Limits on a light Higgs boson

We reexamine the bounds on a very light Higgs boson (φ) coming from limits on the decays K→π+φ and B→φ+X. We show that, if there are only three families, m_φ>2m_τ, and that regardless of the number of families M_φ>360 MeV.     

Higgs boson searches via dileptonic bottomonium decays

We explore the pseudoscalar ηb${\eta }_b$ and the scalar χ_b0${\chi }_{b0}$ decays into ?⁺?⁻${?}^{+}{?}^{-}$ to probe whether it is possible to probe the Higgs sectors beyond that of the Standard Model. We, in particular, focus on the Minimal Supersymmetric Standard Model, and determine the effects of its Higgs bosons on the aforementioned bottomonium decays into lepton pairs. We find that the dileptonic branchings of the bottomonia can be sizeable for a relatively light Higgs sector.     

Searching for a light Higgs boson

The Lindé-Weinberg bound [1] on the mass of the Higgs boson does not apply if one of the fermions of the standard model is very massive [2] or in non-standard models with multiple Higgs particles [1]. We consider both the standard model and a common extension thereof to two or more Higgs doublets. If the Higgs responsible for lepton masses is very light, one reliable method for indirectly detecting it would be a more careful measurement of g − 2 for the muon. More direct is the search for Higgs particles detected in association with τ pairs in existing or defunct e⁺e⁻ colliders operating well below the Z mass. We analyze both methods in detail, and find that data from several existing colliders could eliminate large portions of parameter space - or, perhaps, find the Higgs boson.     

The Higgs in large extra dimensions

Transverse (submillimeter) and longitudinal (TeV) extra dimensions can help in dealing with the Higgs hierarchy problem. On the one hand large transverse dimensions can lower the fundamental scale of quantum gravity from the Planck scale to the TeV range. On the other hand longitudinal dimensions can provide genuine extra-dimensional symmetries (higher dimensional gauge symmetry and/or supersymmetry) to protect the Higgs mass against ultraviolet sensitivity. In this article we review recent developments along these directions. To cite this article: K. Benakli, M. Quirós, C. R. Physique 4 (2003).     

Six-quark decays of the Higgs boson in supersymmetry with R-parity violation

Both electroweak precision measurements and simple supersymmetric extensions of the standard model prefer a mass of the Higgs boson less than the experimental lower limit (on a standard-model-like Higgs boson) of 114 GeV. We show that supersymmetric models with R parity violation and baryon-number violation have a significant range of parameter space in which the Higgs boson dominantly decays to six jets. These decays are much more weakly constrained by current CERN LEP analyses and would allow for a Higgs boson mass near that of the Z. In general, lighter scalar quark and other superpartner masses are allowed. The Higgs boson would potentially be discovered at hadron colliders via the appearance of new displaced vertices.     

Double production of vector quarkonia in exclusive Higgs boson decays

Partial widths with respect to the exclusive decays of Standard Model Higgs bosons to pairs of vector quarkonia, H → J/ψJ/ψ, H → YY, H → J/ψϕ, and H → J/ψY, were calculated with allowance for relativistic corrections associated with the internal motion of quarks in qarkonia.     

FCNC top quark decays in extra dimensions

The flavor changing neutral top quark decay t→cX is computed, where X is a neutral standard model particle, in an extended model with a single extra dimension. The cases for the photon, X=γ, and a standard model Higgs boson, X=H, are analyzed in detail in a non-linear R_ξ gauge. We find that the branching ratios can be enhanced by the dynamics originating in the extra dimension. In the limit where 1/R≫m_t, we have found Br(t→cγ)≃10^-10 for 1/R = 0.5 TeV. For the decay t→cH, we have found Br(t→cH)≃10^-10 for a low Higgs mass value. The branching ratios go to zero when 1/R→∞.