The anomalous 3-boson couplings as an implication of the Higgs sector

We discuss the possible new electroweak interactions which may be generated by the Higgs sector at the scale of theZ mass. For this purpose, we give a set ofSU(2)×U(1) gauge invariant operators constructed in terms ofW, Z, γ and Higgs fields which in the unitary gauge describe all possible γWW andZWW anomalous couplings. The dimension of these operators varies from 6 to 12. This fact allows us to consider various scenaria for the manifestations of the New Physics. We conclude that the underlying dynamics induced by the Higgs sector can be tested through a model-independent amplitude analysis of gauge boson pair production at LEP2 and future colliders.     

Possible test of the weak boson self-coupling below theW + W −-threshold

The weak boson self-coupling contributes to the decayZ ⁰→W ^± X ^?. It is argued how this contribution provides a possible, though experimentally difficult test of the gauge type nature of the electroweak interactions below theW ⁺ W ^? threshold.     

Sphalerons on orbifolds

In this work, we study the electroweak sphalerons in a 5D background, where the fifth dimension lies on an interval. We consider two specific cases: flat space-time and the anti-de Sitter space-time compactified on S ¹/Z ₂. In our work, we take the SU(2) gauge–Higgs model, where the gauge fields reside in the 5D bulk; but the Higgs doublet is confined in one brane. We find that the results in this model are close to those of the 4D Standard Model (SM). The existence of the warp effect, as well as the heaviness of the gauge Kaluza–Klein modes make the results extremely close to the SM ones.     

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.     

A numerical estimate of the upper limit for the Higgs boson mass

TheSU (2) Higgs model with a scalar doublet field is studied by Monte Carlo calculations on 12⁴ and 16⁴ lattices. The gauge coupling is chosen to be similar in magnitude to the physical value in the standard model. The numerical results at large scalar self-coupling imply an upper limitm _H /m _W ?9 for the ratio of the Higgs boson mass to the W-mass.     

A minimalSU(2)×U(1)×U(1) electroweak model with mirror fermions

We present a minimal extension of the standard electroweak model, which accommodates mirror fermions, based onSU(2)×U(1)×U(1). Mirror mixing happens through sterile neutrino states and induces radiative mixing for charged leptons. Quarks and mirror quarks are not mixed with each other, consistent with the suppression of flavour changing neutral currents. Higgs sector, fermion masses and neutral currents are discussed. In this scheme there can be a secondZ boson as light as 0.2TeV.     

Stringy origin of Tevatron Wjj anomaly

The invariant mass distribution of dijets produced in association with W bosons, recently observed by the CDF Collaboration at Tevatron, reveals an excess in the dijet mass range 120-160 GeV/c², 3σ beyond Standard Model expectations. We show that such an excess is a generic feature of low mass string theory, due to the production and decay of a leptophobic Z^′, a singlet partner of SU(3) gluons coupled primarily to the U(1) baryon number. In this framework, U(1) and SU(3) appear as subgroups of U(3) associated with open strings ending on a stack of 3 D-branes. In addition, a minimal model contains two other stacks to accommodate the electro-weak SU(2)⊂U(2) and the hypercharge U(1). Of the three U(1) gauge bosons, the two heavy Z^′ and Z^″ receive masses through the Green-Schwarz mechanism. For a given Z^′ mass, the model is quite constrained. Fine tuning three of its free parameters is just sufficient to simultaneously ensure: a small Z-Z^′ mixing in accord with the stringent LEP data on the Z mass; very small (less than 1%) branching ratio into leptons; and a large hierarchy between Z^″ and Z^′ masses. The heavier neutral gauge boson Z^″ is within the reach of LHC.     

Anomalously interacting new extra vector bosons and their first LHC constraints

In this review phenomenological consequences of the Standard Model extension by means of new spin-1 chiral fields with the internal quantum numbers of the electroweak Higgs doublets are summarized. The prospects for resonance production and detection of the chiral vector Z* and W*^± bosons at the LHC energies are considered on the basis of quantitative simulations within the CompHEP/CalcHEP package. The Z* boson can be observed as a Breit-Wigner resonance peak in the invariant dilepton mass distributions in the same way as the well-known extra gauge Z?? bosons. However, the Z* bosons have unique signatures in transverse momentum, angular and pseudorapidity distributions of the final leptons, which allow one to distinguish them from other heavy neutral resonances. In 2010, with 40 pb^?1 of the LHC proton-proton data at the energy 7 TeV, the ATLAS detector was used to search for narrow resonances in the invariant mass spectrum of e ⁺ e ^? and ??⁺??^? final states and high-mass charged states decaying to a charged lepton and a neutrino. No statistically significant excess above the Standard Model expectation was observed. The exclusion mass limits of 1.15 and 1.35 TeV/c ² were obtained for the chiral neutral Z* and charged W* bosons, respectively. These are the first direct limits on the W* and Z* boson production. Based on the above, a novel strategy for the chiral boson search in the LHC dijet data is discussed. For almost all currently considered exotic models the relevant signal is expected in the central dijet rapidity region y _1,2 ? 0 and |y ₁ ? y ₂| ? 0. On the contrary, the chiral bosons do not contribute to this region but produce an excess of dijet events far away from it. In particular, for these bosons the appropriate kinematical restrictions lead to a dip in the centrality ratio distribution over the dijet invariant mass instead of a bump expected in the most exotic models.     

Study of single weak boson production in electron-positron scattering

The studies of the week boson production in electron-positron scattering are reviewed. At the lowest order of the Weinberg-Salam gauge theory, the cross sections for the various processes of the single weak boson production are computed by paying an attention on the gauge invariance at the high energies, or by calculating all the relevant Feynman diagrams, some of which have been neglected in the studies so far. A formulation is presented to compute the cross sections for the various processes,e ⁺ e ^?→WUD, whereW is the weak boson,WUD stands for \(W^ + \bar U D\) , or \(W^ - U \bar D\) , andU(D) represents the up (down) state of theSU(2) _L doublet. Also the upper bound of the contributions from the single weak boson production via the two photon process is estimated by using the real photon approximation.     

Electroweak vacuum stability in classically conformal $$$$ extension of the standard model

We consider the minimal U(1)\(_{B-L}\) extension of the standard model (SM) with the classically conformal invariance, where an anomaly-free U(1)\(_{B-L}\) gauge symmetry is introduced along with three generations of right-handed neutrinos and a U(1)\(_{B-L}\) Higgs field. Because of the classically conformal symmetry, all dimensional parameters are forbidden. The \(B-L\) gauge symmetry is radiatively broken through the Coleman–Weinberg mechanism, generating the mass for the \(U(1)_{B-L}\) gauge boson (\(Z^\prime \) boson) and the right-handed neutrinos. Through a small negative coupling between the SM Higgs doublet and the \(B-L\) Higgs field, the negative mass term for the SM Higgs doublet is generated and the electroweak symmetry is broken. In this model context, we investigate the electroweak vacuum instability problem in the SM. It is well known that in the classically conformal U(1)\(_{B-L}\) extension of the SM, the electroweak vacuum remains unstable in the renormalization group analysis at the one-loop level. In this paper, we extend the analysis to the two-loop level, and perform parameter scans. We identify a parameter region which not only solve the vacuum instability problem, but also satisfy the recent ATLAS and CMS bounds from search for \(Z^\prime \) boson resonance at the LHC Run-2. Considering self-energy corrections to the SM Higgs doublet through the right-handed neutrinos and the \(Z^\prime \) boson, we derive the naturalness bound on the model parameters to realize the electroweak scale without fine-tunings.     

The Higgs-photon-Z boson coupling revisited

We analyze the coupling of CP-even and CP-odd Higgs bosons to a photon and a Z boson in extensions, of the Standard Model. In particular, we study in detail the effect of charged Higgs bosons in two-Higgs doublet models;. and the contribution of SUSY particle loops in the minimal supersymmetric extension of the Standard Model: The Higgs-γZ coupling can be measured in the decayZ → γ+Higgs ate ⁺ e ^? colliders running on theZ resonance, or in the reverse process Higgs →Zγ with the Higgs boson produced at LHC. We show that a measurement of this coupling with a precision at the percent level, which could be the case at futuree ⁺ e ^? colliders, would allow to distinguish between the lightest SUSY and standard Higgs bosons in large areas of the parameter space.     

Deep inelastic production of charged vector bosons at HERA energies

We discuss the production of gauge bosons in polarized and unpolarized deep inelastice P-scattering in the context of the standard modelSU(3)×SU(2)×U(1) of the strong and electroweak interactions. We present results for the total and the differential cross sections as functions of the parameters of the outgoing lepton for energies available at HERA in the near future. Besides the γ-exchange diagrams we also have included the contributions ofW- andZ-exchange. We find that they cannot be neglected especially for the processe ^? P→v _e W ^? X.     

Three-body decays of Higgs bosons at LEP2 and application to a hidden fermiophobic Higgs

We study the decays of Higgs bosons to a lighter Higgs boson and a virtual gauge boson in the context of the non-supersymmetric two-Higgs doublet model (2HDM). We consider the phenomenological impact at LEP2 and find that such decays, when open, may be dominant in regions of parameter space and thus affect current Higgs boson search techniques. Three-body decays would be a way of producing light neutral Higgs bosons which have so far escaped detection at LEP due to suppressed couplings to the Z, and are of particular importance in the 2HDM (Model I) which allows both a light fermiophobic Higgs and a light charged scalar.     

Direct search for the Standard Model Higgs boson

For twelve years, LEP revolutionized the knowledge of electroweak symmetry breaking within the standard model, and the direct discovery of the Higgs boson would have been the crowning achievement. Searches at the Z resonance and above the W⁺W⁻ threshold allowed an unambiguous lower limit on the mass of the standard model Higgs boson to set be at 114.1 GeV·c⁻². After years of efforts to push the LEP performance far beyond the design limits, hints of what could be the first signs of the existence of a 115 GeV·c⁻² Higgs boson appeared in June 2000, were confirmed in September, and were then confirmed again in November. An additional six-month period of LEP operation was enough to provide a definite answer, with an opportunity to make a fundamental discovery of prime importance. To cite this article: P. Janot, M. Kado, C. R. Physique 3 (2002) 1193–1202.     

New physics contribution to neutral trilinear gauge boson couplings

We study the one-loop new physics effects to the CP even triple neutral gauge boson vertices γ ^⋆ γ Z, γ ^⋆ Z Z, Z ^⋆ Z γ and Z ^⋆ ZZ in the context of Little Higgs models. We compute the contribution of the additional fermions in Little Higgs models in the framework of direct product groups where [SU(2)×U(1)]² gauge symmetry is embedded in SU(5) global symmetry and also in the framework of the simple group where SU(N)×U(1) gauge symmetry breaks down to SU(2) _L ×U(1). We calculate the contribution of the fermions to these couplings when T parity is invoked. In addition, we re-examine the MSSM contribution at the chosen point of SPS1a′ and compare with the SM and Little Higgs models.     

Nonperturbative contribution to the fermion propagator and dynamical electroweak symmetry breaking

We examine the field-theoretical contribution of fermion-antifermion condensates arising from a weak-SU(2) doublet of condensing fermions to electroweak vacuum polarization functions. For the custodial-SU(2) case of equal condensates and masses, we find that the condensate contributions to vacuum polarization functions uphold the electroweak signature relationm _w=m _zcosθ_w, and that these contributions are decoupled entirely from oblique radiative corrections. If only the upper member of the doublet forms a fermion-antifermion condensate, the relationm _w=m _zcosθ_w is again upheld in the limit that the mass of the lower member of the doublet is small compared to that of the upper member. For this case, the upper-member's fermion-antifermion condensate is shown to enter oblique radiative corrections. In the absense of an explicit Higgs mechanism, identification of this doublet with (t, b) is shown to be excluded by present empirical bounds onS, T, andU parameters. Further phenomenological consequences of fermion-antifermion condensate contributions to theW-Z mass matrix are discussed, both in the absense and in the presence of an explicit Higgs mechanism.     

Spontaneous Symmetry Breaking in Presence of Electric and Magnetic Charges

Starting with the definition of quaternion gauge theory, we have undertaken the study of SU(2) _e ×SU(2) _m ×U(1) _e ×U(1) _m in terms of the simultaneous existence of electric and magnetic charges along with their Yang-Mills counterparts. As such, we have developed the gauge theory in terms of four coupling constants associated with four-gauge symmetry SU(2) _e ×SU(2) _m ×U(1) _e ×U(1) _m . Accordingly, we have made an attempt to obtain the abelian and non-Abelian gauge structures for the particles carrying simultaneously the electric and magnetic charges (namely dyons). Starting from the Lagrangian density of two SU(2)×U(1) gauge theories responsible for the existence of electric and magnetic charges, we have discussed the consistent theory of spontaneous symmetry breaking and Higgs mechanism in order to generate the masses. From the symmetry breaking, we have generated the two electromagnetic fields, the two massive vector W ^± and Z ⁰ bosons fields and the Higgs scalar fields.     

Induced Higgs couplings to neutral bosons in e+e− collisions

We calculate induced couplings of the type HV_γ in the standard model, where H is a Higgs meson and V is a virtual or real neutral gauge boson (Z⁰ or photon). Numerous applications are given for e⁺e^? collisions and various Higgs meson decays. The calculated rates are in general somewhat too low to make these processed an attractive way to search for the Higgs boson. However, once it has been found, it is argued that these processes should be studied experimentally since the induced couplings probe the structure of the gauge theory in an interesting way. In particular, it may be possible to infer the existence of one or more heavy fermion generations (of mass ?m_Z) by observing their virtual effects in radiative decays into Higgs particles. We also briefly treat the related coupling HV_γ with V a heavy quarkonium vector state.     

Higgs as a pseudo-Goldstone boson, the mu problem and gauge-mediated supersymmetry breaking

We study the interplay between the spontaneous breaking of a global symmetry of the Higgs sector and gauge-mediated supersymmetry breaking, in the framework of a supersymmetric model with global SU(3) symmetry. In addition to solving the supersymmetric flavor problem and alleviating the little hierarchy problem, this scenario automatically triggers the breaking of the global symmetry and provides an elegant solution to the μ/Bμ problem of gauge mediation. We study in detail the processes of global symmetry and electroweak symmetry breaking, including the contributions of the top/stop and gauge-Higgs sectors to the one-loop effective potential of the pseudo-Goldstone Higgs boson. While the joint effect of supersymmetry and of the global symmetry allows in principle the electroweak symmetry to be broken with little fine-tuning, the simplest version of the model fails to bring the Higgs mass above the LEP bound due to a suppressed tree-level quartic coupling. To cure this problem, we consider the possibility of additional SU(3)-breaking contributions to the Higgs potential, which results in a moderate fine-tuning. The model predicts a rather low messenger scale, a small tanβ value, a light Higgs boson with Standard Model-like properties, and heavy higgsinos.     

Has a fermiophobic Higgs boson been detected at the LHC?

We show that, in the present inclusive searches for the Higgs boson at the LHC, a fermiophobic Higgs mimics the standard-model-like Higgs if its mass is around 125 GeV. For that mass the order-of-magnitude reduction of fermiophobic Higgs production cross sections is compensated by a corresponding increase in the Higgs branching fraction into γγ  , while the WW^?$W{W}^{?}$, ZZ^?$Z{Z}^{?}$, Zγ signal yields are predicted to be somewhat smaller. The excess seen in the ATLAS and CMS fermiophobic Higgs boson searches in the γγ channel, including the exclusive vector-boson-fusion analysis, could point to a fermiophobic rather than a standard-model Higgs boson. If the Higgs boson will turn out to be fermiophobic, many of our present ideas of new physics should be revised.