Gauge boson/Higgs boson unification: The Higgs bosons as superpartners of massive gauge bosons

The N = 4 supergravity theories with local SO(4) invariance are formulated in superspace. The gauged SO(4) theory with two coupling constants (g₁, g₂) is shown to reduce to three inequivalent models: g₁ = g₂ with negative cosmological constant, g₁ = ?g₂ with positive cosmological constant, and g₁ = 0, g₂ ≠ 0 which is a particular case of the Freedman-Schwarz gauged SU(2) ? SU(2) model. The Higgs effect in the vector-scalar sector of the gauged N = 5 supergravity is analyzed.     

Doubly charged Higgs bosons

We explore through two simple models, the first in which scalars are treated as fundamental and the second in which they are composite objects, the possibility that representations containing doubly charged scalars may participate in the spontaneous breakdown of the SU(2) × U(1) symmetry of electroweak interactions. We show that such exotic Higgs bosons may posses unsuppressed coupling to pairs of gauge vector bosons and comment on the observability of these charged Higgs bosons through the Cahn-Dawson mechanism in high-energy hadron colliders.     

Forests, groves and Higgs bosons

We determine the gauge invariance classes of tree level Feynman diagrams in spontaneously broken gauge theories, providing a proof for the formalism of gauge and flavor flips. We find new gauge invariance classes in theories with a nonlinearly realized scalar sector. In unitarity gauge, the same gauge invariance classes correspond to a decomposition of the scattering amplitude into pieces that satisfy the relevant Ward identities individually. In theories with a linearly realized scalar sector in gauge, no additional non-trivial gauge invariance classes exist compared to the unbroken case.Received: 2 June 2003, Revised: 21 July 2003, Published online: 5 September 2003     

Higgs bosons at the LHC

The investigation of the dynamics responsible for electroweak symmetry breaking is one of the prime tasks of the experiments at the CERN Large Hadron Collider (LHC). In this article, the potential of the ATLAS and CMS experiments for the discovery of a standard model Higgs boson and for Higgs bosons in the minimal supersymmetric extension is summarized. Emphasis is put on those studies which have been performed recently by the experimental collaborations using a realistic simulation of the detector performance. This includes a discussion of the search for Higgs bosons using the vector boson-fusion mode, a discussion on the measurement of Higgs boson parameters as well as a detailed review of the MSSM sector for different benchmark scenarios.     

Heavy Higgs bosons at LEP

Production of a heavy Weinberg-Salam-type neutral Higgs boson at LEP energies is considered. We conclude that the Higgs is unlikely to be detected at LEP if its mass is greater than 150 GeV.     

Production of very massive Higgs bosons

We compare Higgs boson production mechanisms at multi-TeV hadronic colliders. In addition to the previously investigated processes gluon + gluon → H and $\text{q}\text{q}\text{→ V}{}^1\text{→}\text{VH}\text{(}\text{V}\text{=}\text{W, Z}\text{)}$, we consider Higgs boson formation by pairs of virtual W's or Z's, a process analogous to two-photon collisions in e⁺e^? scattering. The Higgs production process $\text{W}{}^1\text{W}{}^1\text{→}\text{H}$ is dominated by longitudinal W's and is the most important mechanism for M_H > 6 M_W, if the top quark mass is about 30 GeV.     

Strangephilic Higgs bosons in the MSSM

We suggest a new CPX-derived scenario for the search for strangephilic MSSM Higgs bosons at the Tevatron and the LHC, in which all neutral and charged Higgs bosons decay predominantly into pairs of strange quarks and into a strange and a charm quark, respectively. The proposed scenario is realized within a particular region of the MSSM parameter space and requires large values of tan?β, where threshold radiative corrections are significant to render the effective strange-quark Yukawa coupling dominant. Experimental searches for neutral Higgs bosons based on the identification of b-quark jets or τ leptons may miss a strangephilic Higgs boson and its existence could be inferred indirectly by searching for hadronically decaying charged Higgs bosons. Potential strategies and experimental challenges to search for strangephilic Higgs bosons at the Tevatron and the LHC are discussed.     

Higgs bosons in nonlinearly realized supersymmetry

Using the formatlism developed by Samuel and Wess a general form of the Higgs potential in nonlinearly realized supersymmetric extention of the Standard Model in curved space is constructed. In flat space limit we derive bounds for Higgs boson masses and mass relations. Comparisons to the linear supersymmetric models MSSM and NMSSM are made.     

Higgs bosons and matter-antimatter oscillations in GUTS

The presence of Higgs bosons of diquark and dilepton types at intermediate mass scales in GUTs is analysed in connection with the possible generation of neutron-antineutron and hydrogen-antihydrogen oscillations. Their renormalization effects on the calculation of the parameters sin²θ_w and m_b/m_τ are investigated in SU(5) and in an SO(10) version with a left-right symmetric breaking chain. In correspondence with suitable combination of higgses, we find solutions in SU(5) for n_G=3 and reasonable values of sin²θ_w, m_b/m_τ and proton lifetime τ_p, which allow detectable $\text{n}\text{-}\text{n}$, but undetectable $\text{H}\text{-}\text{H}$ transitions. Solutions of this type, but with higher τ_p, are also found in a particular scheme of SO(10), where the intermediate mass is at the scale M_R at which the left-right symmetry is broken and is of order 10²×m_w. This modifies then conclusions of analyses of SO(10) models, where either no diquarks and dileptons or only a specific set of them are taken into account.An extension of our analysis to supersymmetric versions of SU(5) and SO(10) does not produce acceptable solutions.     

Experimental signatures of fermiophobic Higgs bosons

The most general Two Higgs Doublet Model potential without explicit CP violation depends on 10 real independent parameters. Excluding spontaneous CP violation results in two 7 parameter models. Although both models give rise to 5 scalar particles and 2 mixing angles, the resulting phenomenology of the scalar sectors is different. If flavour changing neutral currents at tree level are to be avoided, one has, in both cases, four alternative ways of introducing the fermion couplings. In one of these models the mixing angle of the CP even sector can be chosen in such a way that the fermion couplings to the lightest scalar Higgs boson vanishes. At the same time it is possible to suppress the fermion couplings to the charged and pseudo-scalar Higgs bosons by appropriately choosing the mixing angle of the CP odd sector. We investigate the phenomenology of both models in the fermiophobic limit and present the different branching ratios for the decays of the scalar particles. We use the present experimental results from the LEP collider to constrain the models. Received: 21 July 1999 / Revised version: 6 September 1999 / Published online: 3 November 1999     

Light Higgs bosons in phenomenological NMSSM

We consider scenarios in the next-to-minimal supersymmetric model (NMSSM) where the CP-odd and charged Higgs bosons are very light. As we demonstrate, these can be obtained as simple deformations of existing phenomenological MSSM benchmarks scenarios with parameters defined at the weak scale. This offers a direct and meaningful comparison to the MSSM case. Applying a wide set of up-to-date constraints from both high-energy collider and flavor physics, the Higgs boson masses and couplings are studied in viable parts of parameter space. The LHC phenomenology of the light Higgs scenario for neutral and charged Higgs boson searches is discussed.     

Gauge bosons at zero and finite temperature

Gauge theories of the Yang–Mills type are the single most important building block of the standard model of particle physics and beyond. They are an integral part of the strong and weak interactions, and in their Abelian version of electromagnetism. Since Yang–Mills theories are gauge theories their elementary particles, the gauge bosons, cannot be described without fixing a gauge. Therefore, to obtain their properties a quantized and gauge-fixed setting is necessary.