Standard Electroweak Research Articles

Embedding Brans-Dicke gravity into electroweak theory

We argue that a version of the four dimensional Brans-Dicke theory can be embedded in the standard flat spacetime electroweak theory. The embedding involves a change of variables that separates the isospin from the hypercharge in the electroweak theory.

Kertész Line and Embedded Monopoles in QCD

We propose a new class of defects in QCD which can be viewed as embedded monopoles made of quark and gluon fields. These objects are explicitly gauge invariant and they closely resemble the Nambu monopoles in the standard electroweak model. We argue that the "embedded QCD monopoles" are proliferating in the quark-gluon plasma phase while in the low-temperature hadronic phase the spatial proliferation of these objects is suppressed. At realistic quark masses and zero chemical potential the hadronic and quark-gluon phases are generally believed to be connected by a smooth crossover across which all thermodynamic quantities are nonsingular. We argue that these QCD phases are separated by a well-defined boundary-known as the Kertész line in condensed matter systems-associated with the onset of the proliferation of the embedded QCD monopoles in the quark-gluon plasma phase.

Muon g – 2: a theoretical review

Recent developments in the theory of the muon anomalous magnetic moment are reviewed. The Standard Model contributions, including QED, electroweak, and hadronic parts, are summarized.

The experimental status of Higgs Sector of the Standard Electroweak Model at the end of the LEP-SLC era

A method is proposed to calculate the confidence level for agreement of data with the Higgs sector of the Standard Model (SM). This is done by combining information from direct and indirect Higgs Boson searches. Good agreement with the SM is found for $m_H \simeq 120$ GeV using the observables most sensitive to m H : A l and m W . In particular, quantum corrections, as predicted by the SM, are observed with a statistical significance of forty-four standard deviations. However, apparent deviations from the SM of 3.7 $\sigma$ and 2.8 $\sigma$ are found for the Z $\nu \overline{\nu}$ and right-handed Zb $\overline{{\rm b}}$ couplings respectively. The maximum confidence level for agreement with the SM of the entire data set considered is $\simeq 0.006$ for $m_H \simeq 180$ GeV. The reason why confidence levels about an order of magnitude higher than this have been claimed for global fits to similar data sets is explained.

Radiatively generatedνeoscillations: General analysis, textures, and models

We study the consequences of assuming that the mass scale ${\ensuremath{\Delta}}_{\ensuremath{\bigodot}}$ corresponding to the solar neutrino oscillations and mixing angle ${U}_{e3}$ corresponding to the electron neutrino oscillation at CHOOZ are radiatively generated through the standard electroweak gauge interactions. All the leptonic mass matrices having zero ${\ensuremath{\Delta}}_{\ensuremath{\bigodot}}$ and ${U}_{e3}$ at a high scale lead to a unique low energy value for the ${\ensuremath{\Delta}}_{\ensuremath{\bigodot}}$ which is determined by the (known) size of the radiative corrections, solar and the atmospheric mixing angle and the Majorana mass of the neutrino observed in neutrinoless double beta decay. This prediction leads to the following consequences. (i) The MSSM radiative corrections generate only the dark side of the solar neutrino solutions. (ii) The inverted mass hierarchy $(m,\ensuremath{-}m,0)$ at the high scale fails in generating the LMA solution but it can lead to the LOW or vacuum solutions. (iii) The ${\ensuremath{\Delta}}_{\ensuremath{\bigodot}}$ generated in models with maximal solar mixing at a high scale is zero to the lowest order in the radiative parameter. It tends to get suppressed as a result of this and lies in the vacuum region. We discuss specific textures which can lead to the LMA solution in the present framework and provide a gauge theoretical realization of this in the context of the seesaw model.

Spin geometry and grand unification

Gravitation becomes unified with quantum mechanics when we recognize that the spacetime tetrads and the matter fields of Fermions are the integral and half-integral spin representations of theEinstein group, E, the global extension of the Poincare group to a curved spacetimeM. There are8 fundamental spinor representations of theE group, interchanged byP, T, andC: the degree-one maps of spin space overM. Tensor products of2 spinor fields buildClifford vectors or 1 forms, e.g. the spacetime tetrads. It takes tensor products of all8 spinor fields to build a natural 4 form; in particular, ourE-invariant Lagrangian density Open image in new window . We propose a simple form for Open image in new window : the8-spinor factorization of theMaurer-Cartan 4-form, Ω4. Thespin connections Ωα step off the conjoined left and right internalgl (2, ℂ) phase increments over aspacetime incrementeα. Our actionSg measures the covering number of the spinor phases over spacetimeM∪DJ; theDJ aresingular domains or caustics, whereJ=1, 2, and 3 chiral pairs of spin waves cross. Here, the massive Dirac equations emerge to govern the mass scattering that keep the “null zig-zags” of a bispinor particle confined to a timelike worldtube. We identify the coupled envelopes of 1, 2, and 3 chiral bispinor pairs as the leptons, mesons, and hadrons, respectively. These source topologically —nontrivialgl (2,C) phase distributions in the far-field region, which appear aseffective vector potentials. Their vorticities are thespin curvatures, whose Hermitian parts —thegravitational curvatures —specify how our spacetime manifoldM must expand and curve to accommodate such anholonomic differentials. The anti-Hermitian parts reproduce the standard electroweak and strong fields, together with their actions.

MASS AND COUPLING CONSTANT LIMITS FROM CONVERGENCE CONDITIONS ON THE EFFECTIVE CHARGE IN QED

The massless fermion limit of QED is discussed. For on-shell renormalization the high energy behavior fixes no lower limit on the mass of the lightest fermion if the fine structure constant α is allowed to vary. The choice of an arbitrary (spacelike) subtraction point does, however, fix a lower limit on the mass of the lightest fermion, for any subtraction scale μ, if the effective charge α eff (μ) respects both quantum mechanical superposition and renormalization scale invariance. Limits on the values of α or the electron mass are obtained within the Standard Electroweak Model by requiring convergence of α eff (MZ).

Gauge independent effective potential and the Higgs boson mass bound

We introduce the Vilkovisky-DeWitt formalism for deriving the lower bound of the Higgs boson mass. We illustrate the formalism with a simplified version of the Standard Electroweak Model, where all charged boson fields as well as the bottom-quark field are disregarded. The effective potential obtained in this approach is gauge independent. We derive from the effective potential the mass bound of the Higgs boson. The result is compared to its counterpart obtained from the ordinary effective potential.

Gamma‐Ray Bursts from Baryon Decay in Neutron Stars

The standard unbroken electroweak theory is known to erase baryon number. The baryon number symmetry can be restored in the core of a neutron star as its density diverges via gravitational instability due to a binary merger event. We argue that for certain double Higgs models with discrete symmetries, this process may result in an expanding self-sustained burning front which would convert the entire neutron matter into radiation. This process would release ~10^{54} ergs in electromagnetic radiation over ~10^{-4} sec, with negligible baryonic contamination. The resulting fireball would have all the properties necessary to produce a gamma-ray burst as a result of its interaction with ambient interstellar gas. The subsequent Higgs decay would produce a millisecond burst of ~10^{52} ergs in ~100 GeV neutrinos which might be observable. The above mechanism may have also caused electroweak baryogenesis in the early universe, giving rise to the observed matter-antimatter asymmetry today.

High temperature dimensional reduction and parity violation

The effective super-renormalizable 3-dimensional Lagrangian, describing the high temperature limit of chiral gauge theories, has more symmetry than the original 4d Lagrangian: parity violation is absent. Parity violation appears in the 3d theory only through higher-dimensional operators. We compute the coefficients of dominant P-odd operators in the Standard Electroweak theory and discuss their implications. We also clarify the parametric accuracy obtained with dimensional reduction.

The role of M in precision studies of the standard model

Recent calculations have significantly decreased the scheme and residual scale dependence of basic radiative corrections of the Standard Electroweak Model. This leads to a theoretically accurate prediction of the W-boson mass M(W), as well as a reduced upper bound for the Higgs boson mass M(H). The implications of a precise M(W) measurement on the M(H) estimate are emphasized.

Anomalous four-fermion processes in electron-positron collisions

This paper studies the electroweak production of all possible four-fermion collisions with non-standard triple gauge boson couplings. All CP conserving couplings are considered. It is an extension of the methods and strategy, which were recently used for the Standard Model electroweak production of four-fermion final states. Since the fermions are taken to be massless the matrix elements can be evaluated efficiently, but certain phase space cuts have to be imposed to avoid singularities. Experimental cuts are of a similar nature. With the help of the constructed event generator a number of illustrative results is obtained for W-pair production. These show on one hand the distortions of the Standard Model angular distributions caused by either off-shell effects or initial state radiation. On the other hand, also the modifications of distributions due to anomalous couplings are presented, considering either signal diagrams or all diagrams.

Decay of Z into two light Higgs bosons.

If the standard electroweak gauge model is extended to include two or more Higgs doublets, there may be a neutral Higgs boson h which is light (with a mass of say 10 GeV) but the hZZ coupling is suppressed so that it has so far escaped experimental detection. However, the effective hhZZ coupling is generally unsuppressed; hence, the decay of Z into two light Higgs bosons plus a fermion-antifermion pair may have an observable branching fraction, especially if h decays invisibly as, for example, in the recently proposed doublet Majoron model.

The Standard Model

An introduction to the Standard Electroweak Model is given. The three sectors of the Model are briefly reviewed. Some of the topics discussed are symmetries, the number of families, top quark, Higgs boson, CP violation and baryon asymmetry of the universe. I also give a list of some open questions in physics.

Neutrino magnetic moment and the process νe → νeγ

The contribution of a neutrino magnetic moment μ ν to the cross section of the process νe − → νe − γ has been calculated and compared with the Standard Electroweak one. The radiative process allows to reach low enough values of Q 2 without the need to operate at very small energies of recoil electrons. Regions in the phase space which are more favourable to set bounds on μ ν are suggested.

New supersymmetric option for two Higgs doublets.

If the standard electroweak gauge model is embedded in a larger theory which is supersymmetric and the latter breaks down to the former at some mass scale, then the reduced Higgs potential at the electroweak mass scale may differ from that of the well-known minimal supersymmetric extension. Specifically, if the larger theory is based on $\rm {SU(2)_L \times SU(2)_R \times U(1)}$, an interesting alternative exists for two Higgs doublets.

Relaxation of Baryon Number in the Standard Electroweak Model

The presence of many topologically distinct vacua is an essential ingredient of the baryon-number nonconservation in the standard electroweak model. t'Hoofe) showed that the baryon-number violation takes place at zero temperature via quantum tunneling (instanton) transitions between the topologically inequivalent vacua and the amplitude is exponentially suppressed by the WKB factor exp (-27[/(12). Since the SU(2) gauge coupling constant (12 is very small, the instanton processes are completely negligible. On the other hand, it has been suggested) that diffusion over potential barriers interpolating between neighbouring vacua may occur at much larger rate. Recently, several authors3) have calculated the rate for thermal transitions using the sphaleron solution of Klinkhamer and Manton) which corresponds to a saddle-point field configuration connecting the neighbouring vacua. They found that the baryonnumber violation is unsuppressed around temperature T ~ O(lOO)Ge V. This being the case, the baryon-number asymmetry of the universe, produced, e.g., at GUT scale, might be substantially affected by the sphaleron-induced processes at the electroweak scale. In the above picture, the difference of fermion free energies LlF between the neighbouring vacua is crucial for producing net changes id the baryon number of the universe (see Eq. (20)). Cohen, Dugan and Manohar) have claimed that the rate of the net baryon-number change is exponentially small although there are unsuppressed fluctuations in the baryon number at high temperatures. In their analysis, they have argued that there is no change in the fermion free energy when the system goes over the potential barrier. The purpose of this paper is to calculate carefully effects of the fermion fields on the potential of Higgs and gauge field-and obtain the fermion free energy in the static background fields of arbitrary topological charges. We discuss the relaxation of the net baryon number, using the Langer-Afflech theory.6) We assume that the system of quarks and leptons is in thermal equilibrium, while a collective excitation mode of the Higgs and gauge fields relevant to the baryon number violation produces inequilibrium transitions along the way developed in Ref. 6). These physical assumptions lead to a conclusion different from Cohen et al.)

LATEST RESULTS FROM THE UA2 EXPERIMENT

The decays W → e ν, Z → e + e - have been studied using the UA2 detector at the CERN [Formula: see text] Collider. Measurements of the Standard Model parameters from a sample of 251 W decays and 39 Z decays are compared with expectations of the Standard Electroweak Model. An upper limit on the number of light neutrino species is deduced from the cross — section ratio σ( W → e ν)/σ( Z → e + e -). A signal of the hadronic decay mode, [Formula: see text], is observed above the background of QCD produced di-jets.

Comment on "Commutator of the Quark Mass Matrices in the Standard Electroweak Model and a Measure of MaximalCPNonconservation."

Comment on "Commutator of the Quark Mass Matrices in the Standard Electroweak Model and a Measure of Maximal<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>CP</mml:mi></mml:math>Nonconservation."

Comment on "Commutator of the quark mass matrices in the standard electroweak model and a measure of maximal CP nonconservation"

Received 18 August 1986DOI:https://doi.org/10.1103/PhysRevLett.57.2874©1986 American Physical Society