Towards the effective potential of the littlest Higgs model

We compute the relevant parameters of the combined Higgs and φ scalar effective potential in the littlest Higgs (LH) model. These parameters are obtained as the sum of two kinds of contributions. The first one is the one-loop radiative corrections coming from fermions and gauge bosons. The second one is obtained at tree level from the higher-order effective operators needed for the ultraviolet completion of the model. Finally, we analyze the restrictions that the requirement of reproducing the standard electroweak symmetry breaking of the SM set on the LH model parameters.     

SU(5) effective potential including Higgs loop contribution and bounds for the Higgs masses

We refine the calculation of the SU(5) effective potential including Higgs and radiative contributions in the one-loop level. We give the mass spectrum and from this and the stability of the symmetry breaking pattern we derive bounds for the Higgs masses and inequalities between the Higgs couplings and the gauge coupling.     

Little Higgs models and single top production at the LHC

We investigate the corrections of the “littlest” Higgs (LH) model and the SU(3) simple group model to single top production at the CERN Large Hadron Collider (LHC). We find that the new gauge bosons W_H ^± predicted by the LH model can generate significant contributions to single top production via the s-channel process. The correction terms for the tree-level Wqq’ couplings coming from the SU(3) simple group model can give large contributions to the cross sections of the t-channel single top production process. We expect that the effects of the LH model and the SU(3) simple group model on single top production can be detected at the LHC experiments.     

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.     

Charged Higgs boson in the economical 3-3-1 model

The SU(3) _C ⊗ SU(3) _L ⊗ U(1) _X gauge model with two Higgs triplets (the economical 3-3-1 model) is presented. The minimal Higgs potential is considered in detail, and new Higgs bosons with the mass proportional to the bilepton mass are predicted. In the effective approximation, the charged Higgs bosons H ₂ ^± are scalar bileptons, while the neutral scalar bosons H ⁰ and H ₁ ⁰ do not carry a lepton number. The couplings of the charged Higgs bosons to leptons and quarks are given. We show that Yukawa couplings of H ₂ ^± to ordinary leptons and quarks are lepton-number violating. The pair production of H ₂ ^± at high-energy e ⁺ e ⁻ colliders with the polarization of the e ⁺, e ⁻ beams is studied in detail. A numerical evaluation shows that, if the Higgs mass is not too heavy, then the reaction can give an observable cross section in future colliders at a high degree of polarization. The reaction e ⁺ e ⁻ → H ₂ ^± W ^∓ is also examined. We show that the production cross sections of H ₂ ^± W ^∓ are very small, much below the pair production of H ₂ ^± , and, therefore, the associated production of H ₂ ^± and W ^∓ is, in general, not expected to lead to easily observable signals in the e ⁺ e ⁻ annihilation. The text was submitted by the authors in English.     

A novel approach to confront electroweak data and theory

A novel approach to study electroweak physics at one-loop level in generic SU(2)_L×U(1)_Y theories is introduced. It separates the 1-loop corrections into two pieces: process specific ones from vertex and box contributions, and universal ones from contributions to the gauge boson propagators. The latter are parametrized in terms of four effective form factors $\bar e^2 (q^2 ), \bar s^2 (q^2 ), \bar g_Z^2 (q^2 )$ and $\bar g_W^2 (q^2 )$ corresponding to the γγ, γZ,ZZ andWW propagators. Under the assumption that only the Standard Model contributes to the process specific corrections, the magnitudes of the four form factors are determined atq ²=0 and atq ²=m _Z ² by fitting to all available precision experiments. These values are then compared systematically with predictions of SU(2)_L×U(1)_Y theories. In all fits α _s (m _Z ) and $\bar \alpha (m_Z^2 )$ are treated as external parameters in order to keep the interpretation as flexible as possible. The treatment of the electroweak data is presented in detail together with the relevant theoretical formulae used to interpret the data. No deviation from the Standard Model has been identified. Ranges of the top quark and Higgs boson masses are derived as functions of α _s (m _Z ) and $\bar \alpha (m_Z^2 )$ . Also discussed are consequences of the recent precision measurement of the left-right asymmetry at SLC as well as the impact of a top quark mass and an improvedW mass measurement.     

Electroweak baryon number violation at finite temperature

We consider baryon and lepton number violating processes in the electroweak theory induced by gauge and Higgs fields passing the sphaleron solution at finite temperature. We show that for temperatures larger than 19 GeV the anomalous baryon and lepton number violating processes are suppressed by the Boltzmann factor exp (?βE _sp), whereE _sp is the sphaleron energy, rather than by the instanton tunneling factor exp (?8π²/g ²). We caculate the rate of baryon and lepton number violating processes at finite temperature and determine the freezing temperature of the anomalous processes in the early universe as a function of the Higgs mass. We compare the freezing temperature with the critical temperature of the electroweak phase transition infered from the one-loop finite-temperature effective potential. We obtain a critical Higgs mass of the order of 100 GeV, slightly depending on the top mass and the magnitude of the pre-exponential factor in the rate of theB non-conservation, above which the anomalous processes are certainly in equilibrium after the electroweak phase transition. Assuming that the temperature-dependence of the sphaleron energy is given by that found from the one-loop finitetemperature effective potential, this critical Higgs mass is lowered to a value of the order of 50 GeV.     

Possible heavy solitons in the strongly coupled Higgs sector

In a presumed dynamically broken, minimally coupled SU(2) model, a natural Higgs mass of order 1 TeV marks the onset of a strongly interacting Higgs sector probably rich in resonance structure and inaccessible to perturbation theory. In the spirit of the chiral dynamics approach to low-energy hadron physics, the heavy Higgs sector is here assumed to be well described up to one-loop effects by an SO(4) non-linear σ-model of the Skyrme type. Taken as an effective zeroth-order lagrangian, the latter is shown to admit two varieties of finite-energy, three-dimensional localized solitons which may exist in nature. They are given by the S³ → S³ Chern-Pontryagin maps and the S³ → S² twisted toroid Hopf maps, respectively. Upper and lower bounds on the masses of the hedgehog and twisted ring with kink-number one are found to lie in the few TeV range. By a topological theorem of Finkelstein et al., both types of solitons provide classical analogues of superheavy fermion states. The connection between these solitons with other extended objects predicted by Nambu and Huang, and their possible experimental signatures are sketched. Finally, the extension of our results to the more realistic SU(2) × U(1) Weinberg-Salam model is discussed.     

MSSM Higgs sector at the one-loop level

This work provides an elementary introduction to the Higgs sector renormalisation within the Minimal Supersymmetric Standard Model (MSSM) framework. The main aim of the paper is to clarify some technical details that are usually omitted in the existing literature. The MSSM tree-level relation m _h ² + m _H ² = m _A ² + m _Z ² is renormalised using the standard technique of direct computation of the relevant one-loop Feynman diagrams. The calculation is performed within the unitary gauge and the definition of the renormalised parameters is briefly reviewed. The expected cancellation of ultraviolet divergences is explicitly checked and the well-known leading-log term is recovered. All the necessary ingredients of the computations are summarized in the appendices which makes the work more self-contained.     

Prospects for the measurement of the structure of the coupling of a Higgs boson to weak gauge bosons in weak boson fusion with the ATLAS detector

The prospects for the measurement of the tensor structure of the vertex between a standard model Higgs boson and two weak gauge bosons using the distribution of the azimuthal angles between the two tagging jets in the weak boson fusion channel are studied in a Monte Carlo analysis using the fast simulation of the ATLAS detector. The decay channels H→τ⁺τ^-→ll+4ν, H→τ⁺τ^-→lh+3ν at m_H=120 GeV and H→W⁺W^-→llνν at m_H=160 GeV are used in the analysis. For a standard model Higgs boson it is found that purely anomalous couplings are expected to be excluded at a confidence level corresponding to 2σ or more at m_H=120 GeV and more than 5σ at m_H=160 GeV from 30 fb^-1 of data. With a value of 1 roughly reproducing the standard model cross section for a purely anomalous coupling, the standard deviation in a measurement of a contribution of a CP even anomalous coupling in addition to the standard model coupling is estimated to be 0.20 at m_H=120 GeV and 0.09 at m_H=160 GeV.     

Electric dipole moment and chromoelectric dipole moment of the top quark inSU(3)C×SU(3)L×U(1)X model

We show that inSU(3) _C ×SU(3) _L ×U(1) _X model, the leading contribution to the electric and chromolelectric dipole moment of the top quark is due to the one-loop diagrams which come from exchanging the charged and neutral Higgs bosons. The dipole moments are typically of the order of 10^?19 e-cm and 10^?19 g-cm respectively, for the values of relative phases of the vev's such that CP violation is maximal. From an experimental point of view, theq ² dependence of dipole moment form factors is given.     

Gauge symmetry breaking in compact multiply connected manifolds

In a multiply connected manifold, M₄⊗S₃/Z², we compute at one-loop level the gauge symmetry breaking due to Wilson loops. For an SU(3) model without matter fields a non-trivial vacuum, which breaks the gauge symmetry has lower energy.     

SANCnews: Sector 4f,charged current

In this paper we describe the implementation of the charged current decays of the type t→bl⁺ν_l(γ) in the framework of the SANC system. All calculations are done taking into account the one-loop electroweak correction in the standard model. The emphasis of this paper is on the presentation of numerical results. Various distributions are produced by means of a Monte Carlo integrator and event generator. Comparison with the results of the CompHEP and PYTHIA packages are presented for the Born and hard photon contributions. The validity of the cascade approximation at one-loop level is also studied. PACS 14.65.Ha; 12.15.-y; 12.15.Lk     

Lattice (Φ 4)4 effective potential giving spontaneous symmetry breaking and the role of the Higgs mass

We present a critical reappraisal of the available results on the broken phase ofλ(Φ ⁴)₄ theory, as obtained from rigorous formal analyses and from lattice calculations. All the existing evidence is compatible with Spontaneous Symmetry Breaking but dictates a trivially free shifted field that becomes controlled by a quadratic hamiltonian in the continuum limit. As recently pointed out, this implies that the simple one-loop effective potential should become effectively exact. Moreover, the usual naive assumption that the Higgs mass-squaredm _h ² is proportional to its “renormalized” self-couplingλ _R is not valid outside perturbation theory: the appropriate continuum limit hasm _h finite and vanishingλ _R . A Monte Carlo lattice computation of theλ(Φ ⁴)₄ effective potential, both in the single-component and in theO(2)-symmetric cases, is shown to agree very well with the one-loop prediction. Moreover, its perturbative leading-log improvement (based on the concept ofλ _R ) fails to reproduce the Monte Carlo data. These results, while supporting in a new fashion the peculiar “triviality” of theλ(Φ ⁴)₄ theory, also imply that, outside perturbation theory, the magnitude of the Higgs mass does not give a measure of the observable interactions in the scalar sector of the standard model.     

Threshold effects in SUSY and non-SUSY GUTs

We discuss recent contributions on threshold effects in grand unfiied theories including minimal SUSY SU (5), non-SUSY modifications of the grand desert in SU(5) and SO(10), and SO(10) with single intermediate symmetires. Consequences of theorems on vanishing GUT-scale corrections to sin² θ_w in SO(10) with SU(2) _L XSU(2) _R XSU(4) _c (g_2l =g_2R ) intermediate symmetry are discussed and vanishing corrections on the inter-mediate scale are explicitly demonstrated where predictions are more precise. Threshold and higher dimensional operator effects in SUSY SU(5) recently derived by a number of authors are presented.     

Chromomagnetic dipole moment of the top quark revisited

We study the complete one-loop contributions to the chromagnetic dipole moment Δκ of the top quark in the standard model, two Higgs doublet models, topcolor assisted technicolor models, 331 models and extended models with a single extra dimension. We find that the SM predicts Δκ=-0.056 and the predictions of the other models are also consistent with the constraints imposed on Δκ by low-energy precision measurements.     

The weak mixing angle and unification mass in supersymmetric SU(5)

We consider the predictions for the weak mixing angle θ_W and the scale M of unification in a supersymmetric extension of SU(5), with particular emphasis on the sensitivity to the number of Higgs multiplets. In the one-loop approximation, we also calculate the ratio m_b/m_τ. We discuss generally the effects of an intermediate threshold between the weak interaction scale and M and estimate the sensitivity of θ_W and M to the scale of supersymmetry breaking.The evolution of the coupling constants of the supersymmetric SU(3) ? SU(2) ? U(1) effective gauge theory is described and the two-loop corrections to θ_{W and M} are calculated.     

Higgs charged bosons and the problem of solar neutrinos

For a model with the SU(2)L×SU(2)_R×U(1)_{B−L} gauge group, the passage of neutrino flux through a substance is studied. It is shown that Higgs charged physical bosons can considerably change the potential of neutrino interaction with the solar substance. An analytical expression for the survival probability of left-handed electron neutrinos is derived in the two-flavor approximation. Yanka Kupala Grodno State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 32–37, January, 2000.     

Higgs Boson Decay into Two Gluons and a <Emphasis Type="Italic">Z</Emphasis> Boson

Results for the one-loop calculation of the decay width Γ(H→ggZ) in the standard model with Higgs boson masses in the range 115 GeV<m _H <2m _W are presented. We find that among all the helicity amplitudes contributing to the width only those for which the gluons have the same polarization and the Z is longitudinally polarized contribute in any significant way. The calculation includes all contributions from the second and third generations, and kinematic cuts to enhance the H→ggZ signal. Compared to the width of H→gg, we find Γ(H→ggZ)/Γ(H→gg)≲10⁻⁴.     

Variation of fundamental constants in space and time: Theory and observations

Review of recent works devoted to the temporal and spatialvariation of the fundamental constants and dependence of the fundamentalconstants on the gravitational potential (violation of local position invariance) is presented. We discuss the variation of the fine structure constant α=e²/ħc, strong interaction andfundamental masses (Higgs vacuum), e.g. the electron-to-proton mass ratioμ=m_e/M_p or X_e=m_e/Λ_QCD and X_q=m_q/Λ_QCD.We also present new results from Big Bang nucleosynthesisand Oklo natural nuclear reactor data and propose new measurements of enhanced effects in atoms, nuclei and molecules, both in quasar and laboratory spectra.