Electroweak Model Research Articles

Prospects for precision measurements in nuclear decay in the LHC era

Precision measurements in nuclear β decay offer a sensitive window to search for new physics beyond the standard electroweak model. Searches for new physics are also a strong motivation for experiments carried out at the high energy frontier. It is instructive to confront results from the low energy and the high energy frontiers in order to look for possible complementarities. This paper reviews the constraints on new physics obtained from nuclear and neutron decays and compares them to those from other semi‐leptonic processes and from the LHC. The sensitivity requirements of new precision experiments in β decay, to impact the search for new physics at the light of current and projected LHC results, are updated. Experimental developments in nuclear and neutron β decay are discussed with emphasis on their projected goals to improve the limits on exotic weak couplings.

Classification of finite reparametrization symmetry groups in the three-Higgs-doublet model

Symmetries play a crucial role in electroweak symmetry breaking models with non-minimal Higgs content. Within each class of these models, it is desirable to know which symmetry groups can be implemented via the scalar sector. In N-Higgs-doublet models, this classification problem was solved only for N=2 doublets. Very recently, we suggested a method to classify all realizable finite symmetry groups of Higgs-family transformations in the three-Higgs-doublet model (3HDM). Here, we present this classification in all detail together with an introduction to the theory of solvable groups, which play the key role in our derivation. We also consider generalized-CP symmetries, and discuss the interplay between Higgs-family symmetries and CP-conservation. In particular, we prove that presence of the ℤ4 symmetry guarantees the explicit CP-conservation of the potential. This work completes classification of finite reparametrization symmetry groups in 3HDM.

Explaining the Higgs decays at the LHC with an extended electroweak model

We show that the observed enhancement in the diphoton decays of the recently discovered new boson at the LHC, which we assume to be a Higgs boson, can be naturally explained by a new doublet of charged vector bosons from extended electroweak models with SU(3) C ⊗SU(3) L ⊗U(1) X symmetry. These models are also rather economical in explaining the measured signal strengths, within the current experimental errors, demanding fewer assumptions and less parameters tuning. Our results show a good agreement between the theoretical expected sensitivity to a 126–125 GeV Higgs boson, and the experimental significance observed in the diphoton channel at the 8 TeV LHC. Effects of an invisible decay channel for the Higgs boson are also taken into account, in order to anticipate a possible confirmation of deficits in the branching ratios into ZZ ∗, WW ∗, bottom quarks, and tau leptons.

Anomalous Higgs interactions in gauge-Higgs unification

We discuss anomalous Higgs interactions in the scenario of gauge-Higgs unification. In the scenario Higgs originates from higher dimensional gauge field and has a physical meaning as AB phase or Wilson loop. As its inevitable consequence, physical observables are expected to be periodic in the Higgs field. In particular, the Yukawa coupling is expected to show some periodic and non-linear behavior as the function of the Higgs VEV. For a specific choice of the VEV, the Yukawa coupling of KK zero mode fermion even vanishes. On the other hand, the Yukawa coupling is originally provided by gauge interaction, which is linear in the Higgs field. We discuss how such two apparent contradiction about the non-linearity of the Yukawa coupling can be reconciled and at the same time how these two "pictures" give different predictions in the simplest framework of the scenario: SU(3) electroweak model in 5-dimensional flat space-time with orbifolding. The deviation of the Yukawa coupling from the standard model prediction is also calculated for arbitrary VEV. We study "$H$-parity", which guarantees the stability of the Higgs for a specific choice of the VEV. Also discussed is the Higgs interaction with $W^\pm$ and $Z^0$. It turns out that in our framework of flat space-time the interaction does not show deviation from the standard model prediction, except for the specific case of the VEV.

Interpretation of Neutrino–Matter Interactions at Low Energies as Contraction of Gauge Group of Electroweak Model

Interpretation of Neutrino–Matter Interactions at Low Energies as Contraction of Gauge Group of Electroweak Model

Strongly Coupled Models with a Higgs-like Boson

Considering the one-loop calculation of the oblique S and T parameters, we have presented a study of the viability of strongly-coupled scenarios of electroweak symmetry breaking with a light Higgs-like boson. The calculation has been done by using an effective Lagrangian, being short-distance constraints and dispersive relations the main ingredients of the estimation. Contrary to a widely spread believe, we have demonstrated that strongly coupled electroweak models with massive resonances are not in conflict with experimental constraints on these parameters and the recently observed Higgs-like resonance. So there is room for these models, but they are stringently constrained. The vector and axial-vector states should be heavy enough (with masses above the TeV scale), the mass splitting between them is highly preferred to be small and the Higgs-like scalar should have a WW coupling close to the Standard Model one. It is important to stress that these conclusions do not depend critically on the inclusion of the second Weinberg sum rule.

S3model for lepton mass matrices with nearly minimal texture

We propose a simple extension of the electroweak standard model based on the discrete ${S}_{3}$ symmetry that is capable of realizing a nearly minimal Fritzsch-type texture for the Dirac mass matrices of both charged leptons and neutrinos. This is achieved with the aid of additional ${Z}_{5}$ and ${Z}_{3}$ symmetries, one of which can be embedded in $U(1{)}_{B\ensuremath{-}L}$. Five complex scalar singlet fields are introduced in addition to the standard model with right-handed neutrinos. Although more general, the modified texture of the model retains the successful features of the minimal texture without fine-tuning; namely, it accommodates the masses and mixing of the leptonic sector and relates the emergence of large leptonic mixing angles with the seesaw mechanism. For large deviations of the minimal texture, both quasidegenerate spectrum or inverted hierarchy are allowed for neutrino masses.

Tests of the standard electroweak model at the energy frontier

In this review, tests of standard electroweak (EW) theory at the highest available energies as a precursor to the Large Hadron Collider (LHC) era are summarized. The primary focus is on the published results (as of March 2010) from proton-antiproton collisions at $\sqrt{s}=1.96\text{ }\text{ }\mathrm{TeV}$ at the Fermilab Tevatron collected using the CDF and D0 detectors. After presenting an overview of the EW sector of the standard model, a summary of experimental tests of EW theory as of March 2010 is provided. These include gauge boson properties and self-couplings, tests of EW physics from the top-quark sector, and searches for the Higgs boson.

PARTICLE PHYSICS FROM ALMOST-COMMUTATIVE SPACETIMES

Our aim in this review paper is to present the applications of Connes' noncommutative geometry to elementary particle physics. Whereas the existing literature is mostly focused on a mathematical audience, in this paper we introduce the ideas and concepts from noncommutative geometry using physicists' terminology, gearing towards the predictions that can be derived from the noncommutative description. Focusing on a light package of noncommutative geometry (so-called "almost-commutative manifolds"), we shall introduce in steps: electrodynamics, the electroweak model, culminating in the full Standard Model. We hope that our approach helps in understanding the role noncommutative geometry could play in describing particle physics models, eventually unifying them with Einstein's (geometrical) theory of gravity.

Contraction of electroweak model and neutrino

The electroweak model, which lepton sector correspond to the contracted gauge group SU(2; j) × U(1), j → 0, whereas boson and quark sectors are standard one, is suggested. The field space of the model is fibered under contraction in such a way that neutrino fields are in the fiber and all other fields are in the base. Properties of the fibered field space are understood in context of semi-Riemannian geometry. This model describes in a natural manner why neutrinos so rarely interact with matter, as well as why neutrino cross section increase with the energy. Dimensionfull parameter of the model is interpreted as neutrino energy. Dimensionless contraction parameter j at low energy is connected with the Fermi constant of weak interactions and is approximated as j2 ≈ 10−5.

Origins of mass

Abstract Newtonian mechanics posited mass as a primary quality of matter, incapable of further elucidation. We now see Newtonian mass as an emergent property. That mass-concept is tremendously useful in the approximate description of baryon-dominated matter at low energy — that is, the standard “matter” of everyday life, and of most of science and engineering — but it originates in a highly contingent and non-trivial way from more basic concepts. Most of the mass of standard matter, by far, arises dynamically, from back-reaction of the color gluon fields of quantum chromodynamics (QCD). Additional quantitatively small, though physically crucial, contributions come from the intrinsic masses of elementary quanta (electrons and quarks). The equations for massless particles support extra symmetries — specifically scale, chiral, and gauge symmetries. The consistency of the standard model relies on a high degree of underlying gauge and chiral symmetry, so the observed non-zero masses of many elementary particles (W and Z bosons, quarks, and leptons) requires spontaneous symmetry breaking. Superconductivity is a prototype for spontaneous symmetry breaking and for mass-generation, since photons acquire mass inside superconductors. A conceptually similar but more intricate form of all-pervasive (i.e. cosmic) superconductivity, in the context of the electroweak standard model, gives us a successful, economical account of W and Z boson masses. It also allows a phenomenologically successful, though profligate, accommodation of quark and lepton masses. The new cosmic superconductivity, when implemented in a straightforward, minimal way, suggests the existence of a remarkable new particle, the so-called Higgs particle. The mass of the Higgs particle itself is not explained in the theory, but appears as a free parameter. Earlier results suggested, and recent observations at the Large Hadron Collider (LHC) may indicate, the actual existence of the Higgs particle, with mass m H ≈ 125 GeV. In addition to consolidating our understanding of the origin of mass, a Higgs particle with m H ≈ 125 GeV could provide an important clue to the future, as it is consistent with expectations from supersymmetry.

Precision correlation measurements in nuclear β decay

Precision measurements in nuclear β decay provide a sensitive means of searching for new physics beyond the standard electroweak model. This paper reviews the status of selected precision measurements of correlation observables in nuclear and neutron β decay and discusses the prospects and future plans.

Spontaneous SU(2) symmetry violation in the SU(2) L × SU(2) R × SU(4) electroweak model

A new approach to EW composite scalars is developed, starting from the fundamental gauge interaction on high scale. The latter is assumed to have the group structure $SU(2)_L \times SU(2)_R\times SU(4)$ where SU(4) is the Pati-Salam color-lepton group. The topological EW vacuum filled by instantons is explicitly constructed and the resulting equations for fermion masses exhibit spontaneous SU(2) flavor symmetry violation with possibility of very large mass ratios.

Contraction of electroweak model can explain the interactions neutrinos with matter

The very rare interactions neutrinos with matter and the dependence of the corresponding cross-section on neutrinos energy are explained as contraction of the gauge group of the Electroweak Model already at the level of classical gauge fields. Small contraction parameter is connected with the universal Fermi constant of weak interactions and neutrino energy as \(^2 (s) = \sqrt {G_{F^S } }\).

Zpscalar dark matter from multi-Higgs-doublet models

In many models, stability of dark matter particles is protected by a conserved Z_2 quantum number. However dark matter can be stabilized by other discrete symmetry groups, and examples of such models with custom-tailored field content have been proposed. Here we show that electroweak symmetry breaking models with N Higgs doublets can readily accommodate scalar dark matter candidates stabilized by groups Z_p with any $p \le 2^{N-1}$, leading to a variety of kinds of microscopic dynamics in the dark sector. We give examples in which semi-annihilation or multiple semi-annihilation processes are allowed or forbidden, which can be especially interesting in the case of asymmetric dark matter.

Effective theory of a dynamically broken electroweak Standard Model at NLO

We consider the Standard Model as an effective theory at the weak scale $v$ of a generic new strong interaction that dynamically breaks electroweak symmetry at the energy scale $\Lambda\sim $ (few) TeV. Assuming only the minimal field content with the Standard Model fermions and gauge bosons, but without a light Higgs particle, we construct the complete Lagrangian through next-to-leading order, that is, including terms of order $v^2/\Lambda^2$. The systematics behind this expansion is clarified. Although similar to chiral perturbation theory, it is not governed by the dimension of operators alone, but depends in an essential way on the loop expansion. Power-counting formulas are derived that indicate the classes of operators required at the next-to-leading order. The complete set of operators at leading and next-to-leading order is then listed, based on the restrictions implied by the Standard-Model gauge symmetries. We recover the well-known operators discussed in the literature in connection with the electroweak chiral Lagrangian and in similar contexts, but we collect a complete and systematic list of all terms through order $v^2/\Lambda^2$. This includes some operators not discussed in explicit terms before. We also show that a few of the previously considered operators can be eliminated via the equations of motion. As another important result we confirm the known list of dimension-6 operators in the Standard Model with an elementary Higgs doublet, essentially as a special case of our scenario.

THE THIRD TYPE OF FERMION MIXING IN THE LEPTON AND QUARK INTERACTIONS WITH LEPTOQUARKS

The low-energy manifestations of a minimal extension of the electroweak standard model based on the quark–lepton symmetry SU(4)V ⊗SU(2)L ⊗GR of the Pati–Salam-type are analyzed. Given this symmetry the third type of mixing in the interactions of the SU(4)V leptoquarks with quarks and leptons is shown to be required. An additional arbitrariness of the mixing parameters could allow, in principle, to decrease noticeably the lower bound on the vector leptoquark mass originated from the low-energy rare processes, strongly suppressed in the standard model.

The size of the weak bosons

We study the hypothesis that the bosons are composite systems, which have a size of the order of 10−17 cm. The electromagnetic self-energies of the weak bosons lead to specific departures from the standard elektroweak model, in agreement with observation. Above the energy of 1 TeV the standard electroweak model breaks down completely.

Direct detection of leptophilic dark matter in a model with radiative neutrino masses

We consider an electroweak scale model for dark matter (DM) and radiative neutrino mass generation. Despite the leptophilic nature of DM with no direct couplings to quarks and gluons, scattering with nuclei is induced at the 1-loop level through photon exchange. Effectively, there are charge-charge, dipole-charge, and dipole-dipole interactions. We investigate the parameter space consistent with constraints from neutrino masses and mixing, charged lepton-flavor violation, perturbativity, and the thermal production of the correct DM abundance, and calculate the expected event rate in DM direct detection experiments. We show that current data from XENON100 start to constrain certain regions of the allowed parameter space, whereas future data from XENON1T has the potential to significantly probe the model.

The Higgs boson resonance width from a chiral Higgs–Yukawa model on the lattice

The Higgs boson is a central part of the electroweak theory and is crucial to generate masses for quarks, leptons and the weak gauge bosons. We use a 4-dimensional Euclidean lattice formulation of the Higgs–Yukawa sector of the electroweak model to compute physical quantities in the path integral approach which is evaluated by means of Monte Carlo simulations thus allowing for fully non-perturbative calculations. The chiral symmetry of the model is incorporated by using the Neuberger overlap Dirac operator. The here considered Higgs–Yukawa model does not involve the weak gauge bosons and furthermore, only a degenerate doublet of top- and bottom quarks are incorporated. The goal of this work is to study the resonance properties of the Higgs boson and its sensitivity to the strength of the quartic self-coupling.