Distinguishing the higgs boson from the dilaton at the large hadron collider

It is likely that the LHC will observe a color- and charge-neutral scalar whose decays are consistent with those of the standard model (SM) Higgs boson. The Higgs interpretation of such a discovery is not the only possibility. For example, electroweak symmetry breaking could be triggered by a spontaneously broken, nearly conformal sector. The spectrum of states at the electroweak scale would then contain a narrow scalar resonance, the pseudo-Goldstone boson of conformal symmetry breaking, with Higgs-boson-like properties. If the conformal sector is strongly coupled, this pseudodilaton may be the only new state accessible at high energy colliders. We discuss the prospects for distinguishing this mode from a minimal Higgs boson at the LHC and ILC. The main discriminants between the two scenarios are (i) cubic self-interactions and (ii) a potential enhancement of couplings to massless SM gauge bosons.     

Integrating out the standard Higgs field in the path integral

We integrate out the Higgs boson in the electroweak standard model at one loop and construct a low-energy effective Lagrangian assuming that the Higgs mass is much larger than the gauge-boson masses. Instead of applying diagrammatical techniques, we integrate out the Higgs boson directly in the path integral, which turns out to be much simpler. By using the background-field method and the Stueckelberg formalism, we directly find a manifestly gauge-invariant result. The heavy-Higgs effects on fermionic couplings are derived, too. At one loop the log M_H terms of the heavy-Higgs limit of the electroweak standard model coincide with the UV-divergent terms in the gauged non-linear σ-model, but vertex functions differ in addition by finite constant terms. Finally, the leading Higgs effects to some physical processes are calculated from the effective Lagrangian.     

The holographic composite Higgs

Theories where the Higgs boson is a composite particle elegantly solve the hierarchy problem. This idea has been recently investigated in the framework of 5-dimensional warped models that, according to the AdS/CFT correspondence, have a 4-dimensional holographic interpretation in terms of strongly coupled field theories. We present a minimal model in which the Higgs arises as a pseudo-Goldstone boson and the electroweak symmetry is dynamically broken. This model can successfully solve the flavor problem and pass all the electroweak precision tests. To cite this article: R. Contino, A. Pomarol, C. R. Physique 8 (2007).     

Indirect bounds on heavy scalar masses of the two-Higgs-doublet model in light of recent Higgs boson searches

We study an upper bound on masses of additional scalar bosons from the electroweak precision data and theoretical constraints such as perturbative unitarity and vacuum stability in the two-Higgs-doublet model taking account of recent Higgs boson search results. If the mass of the Standard-Model-like Higgs boson is rather heavy and is outside the allowed region by the electroweak precision data, such a discrepancy should be compensated by contributions from the additional scalar bosons. We show the upper bound on masses of the additional scalar bosons to be about 2 (1) TeV for the mass of the Standard-Model-like Higgs boson to be 240 (500) GeV.     

Leading Electroweak Corrections to the Neutral Higgs Boson Production at the Fermilab Tevatron

We calculate the leading electroweak corrections to the light neutral Higgs boson production via qq → WH at the Fermilab Tevatron in both the standard model and the minimal supersymmetric model, which arise from the top-quark and Higgs boson loop diagrams. We found that the leading electroweak corrections can exceed the QCD corrections for favorable values of the parameters in the MSSM, but such corrections are only about -2%~-4% in the SM, which are much smaller than the QCD corrections. For the mass region of 90 < mh, < 120 GeV, the leading electroweak corrections can reach -20% for large tan β, and these corrections may be observable at a high luminosity Tevatron; at the least, new constraints on the tan β can be established.     

Associate Higgs and gauge boson production at hadron colliders in a model with vector resonances

Motivated by new models of dynamical electroweak symmetry breaking that predict a light composite Higgs boson, we build an effective Lagrangian which describes the standard model (with a light Higgs) and vector resonances. We compute the cross section for the associate production of a Higgs and a gauge boson. For some values of model parameters we find that the cross section is significantly enhanced with respect to the standard model. This enhancement is similar at the LHC (large hadron collider) and the Tevatron for the same range of resonance mass. PACS 12.60.Nz     

Inflation,LHC and the Higgs boson

After the Higgs boson has been discovered, the Standard Model of particle physics became a confirmed theory, potentially valid up to the Planck scale and allowing one to trace the evolution of the Universe from the inflationary stage till the present days. We discuss the relation between the results from the LHC and the inflationary cosmology. We overview the Higgs inflation, and its relation to the possible metastability of the electroweak vacuum. A short overview of the bounds on the metastability of the electroweak vacuum in the models with inflation not related to the Higgs boson is presented.     

General electroweak mixing models and extended gauge theories

General electroweak mixing schemes containing an arbitrary number of weak bosons and agreeing with the predictions of the standard model for neutrino scattering and polarized electron scattering in the low energy approximation are analyzed using the propagator matrix formalism. The mean charged boson mass is bounded while the mean neutral boson mass is unbounded and determined as a function of the mean charged one. Under a special assumption on the electroweak mixing parameters the four fermion interaction agrees with the one of extended gauge theories and the mean boson masses agree with the boson masses of the standard model.     

Update of the global electroweak fit and constraints on two-Higgs-doublet models

We present an update of the global fit of the Standard Model electroweak sector to latest experimental results. We include new kinematic top quark and W boson mass measurements from the LHC, a \(\sin \!^2\theta ^{\ell }_{\mathrm{eff}}\) result from the Tevatron, and a new evaluation of the hadronic contribution to \(\alpha (M_Z^2)\). We present tests of the internal consistency of the electroweak Standard Model and updated numerical predictions of key observables. The electroweak data combined with measurements of the Higgs boson coupling strengths and flavour physics observables are used to constrain parameters of two-Higgs-doublet models.     

Modified Yang-Mills Theory and Electroweak Interactions

Since the Higgs boson of the standard electroweak model has not been detecteddespite many experimental attempts, nonstandard electroweak models notincluding the Higgs boson may be worthy of consideration; one of them isproposed here. This new model of electroweak interactions is based on theYang-Mills theory completed by a nontrivial condition at infinity for theYang-Mills potentials corresponding to the zero-field intensities. It is shown thatwithin the framework of this model the three vector potentials of the Yang-Millstheory allow one to describe both the Maxwell electromagnetic interactions andthe Fermi weak interactions and to obtain the known value of the Z ⁰ boson mass.     

Top Quark,Heavy Fermions and the Composite Higgs Boson

We study the properties of heavy fermions in the vector-like representation of the electroweak gauge group SU(2)_W×U(1)_Y with Yukawa couplings to the standard model Higgs boson. Applying the renormalization group analysis, we discuss the effects of heavy fermions to the vacuum stability bound and the triviality bound on the mass of the Higgs boson. We also discuss the interesting possibility that the Higgs particle is composed of the top quark and heavy fermions. The bound on the composite Higgs mass is estimated using the method of Bardeen, Hill and Lindner (Phys. Rev. D 41 (1990) 1647), 150 GeV ≤ m_H ≤ 450 GeV.     

Renormalization-group improved calculation of top-quark production near threshold

The top-quark cross section close to threshold in e(+)e(-) annihilation is computed including the summation of logarithms of the velocity at next-to-next-to-leading-logarithmic order in QCD. The remaining theoretical uncertainty in the normalization of the total cross section is at the few-percent level, an order of magnitude smaller than in previous next-to-next-to-leading order calculations. This uncertainty is smaller than the effects of a light standard-model Higgs boson.     

Discovery of the Higgs boson by the ATLAS and CMS experiments at the LHC

The Standard Model (SM) Higgs boson was predicted by theorists in the 1960s during the development of the electroweak theory. Prior to the startup of the CERN Large Hadron Collider (LHC), experimental searches found no evidence of the Higgs boson. In July 2012, the ATLAS and CMS experiments at the LHC reported the discovery of a new boson in their searches for the SM Higgs boson. Subsequent experimental studies have revealed the spin-0 nature of this new boson and found its couplings to SM particles consistent to those of a Higgs boson. These measurements confirmed the newly discovered boson is indeed a Higgs boson. More measurements will be performed to compare the properties of the Higgs boson with the SM predictions.     

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.     

On the semi-classical vacuum structure of the electroweak interaction

It is shown that in the semi-classical approximation of the electroweak sector of the standard model the moduli space of vacua can be identified with the first de Rham cohomology group of space–time. This gives a slightly different physical interpretation of the occurrence of the well-known Ahoronov–Bohm effect. Moreover, when charge conjugation is taken into account, the existence of a non-trivial ground state of the Higgs boson is shown to be equivalent to the triviality of the electroweak gauge bundle. As a consequence, the gauge bundle of the electromagnetic interaction must also be trivial. Though derived at “tree level” the results presented here may also have some consequences for quantizing, e.g., electromagnetism on an arbitrary curved space–time.     

First-order electroweak phase transition powered by additional F-term loop effects in an extended supersymmetric Higgs sector

We investigate the one-loop effect of new charged scalar bosons on the Higgs potential at finite temperatures in the supersymmetric standard model with four Higgs doublet chiral superfields as well as a pair of charged singlet chiral superfields. In this model, the mass of the lightest Higgs boson h is determined only by the D-term in the Higgs potential at the tree-level, while the triple Higgs boson coupling for hhh can receive a significant radiative correction due to nondecoupling one-loop contributions of the additional charged scalar bosons. We find that the same nondecoupling mechanism can also contribute to realize stronger first order electroweak phase transition than that in the minimal supersymmetric standard model, which is definitely required for a successful scenario of electroweak baryogenesis. Therefore, this model can be a new candidate for a model in which the baryon asymmetry of the Universe is explained at the electroweak scale.     

Spontaneously broken Lorentz invariance from the dynamics of a heavy sterile neutrino

A relativistic theory for neutrino superluminality is presented (in principle, the same mechanism applies also to other fermions). The theory involves the standard-model particles and one additional heavy sterile neutrino with an energy-scale close to or above the electroweak one, all particles propagating in the usual 3 + 1 spacetime dimensions. Lorentz violation results from spontaneous symmetry breaking in the sterile-neutrino sector. The theory tries, as far as possible, to be consistent with the existing experimental data from neutrino physics and to keep the number of assumptions minimal. There are clear experimental predictions which can be tested.     

Remarks on Higgs inflation

We discuss models where the Higgs boson of the electroweak standard model plays the role of the inflaton. We focus on the question of the violation of perturbative unitarity due to the coupling of the Higgs boson either to the Ricci scalar or to the Einstein tensor and discuss the background dependence of the unitarity bounds. Our conclusion is that the simplest model which restricts itself to the standard model Higgs boson without introducing further degrees of freedom has a serious problem. However, in the asymptotically safe gravity scenario, the Higgs boson of the standard model could be the inflaton and no physics beyond the standard model is required to explain both inflation and the spontaneous breaking of the electroweak symmetry of the standard model.     

On mass-shell renormalizability of the massive Yang-Mills theory

Renormalizable theory of electroweak interactions without scalar particles can be constructed by the modifying the Standard Model. One should remove all terms with the scalar field from the Lagrangian in the unitary gauge. The resulting electroweak theory without the Higgs particle is on mass-shell renormalizable and unitary. Thus the experimental non-observation of the Higgs boson will not mean a problem for the concept of renormalizability in quantum field theory but will confirm the scalar free theory.