Showing papers on "Gauge boson published in 1986"

Physics at LEP

Abstract: In this contribution I have given a brief survey of some of the most interesting new particle searches which can be performed at LEP. Particular emphasis has been given to the particles (Higgs bosons, supersymmetry) whose existence is motivated by attempts to understand the masses of the elementary particles. There are many other aspects to LEP physics, such as precision measurements on the Z0 peak, toponium, QCD studies, and looking at the reaction e+e− → W+W−. However, I think that these few examples are sufficient to show that LEP physics will be very interesting, to Jack and to the rest of us.

Observables in low-energy superstring models

Abstract: We compile phenomenological constraints on the minimal low-energy effective theory which can be obtained from the superstring by Calabi-Yau compactification. Mixing with the single additional neutral gauge boson in this model reduces the mass of the conventional Z0, Field vacuum expectation values are constrained by the experimental upper bound on this shift. Then, requiring the sneutrino mass squared to be positive constrains the scale of supersymmetry breaking more than do lower bounds on the masses of new charged particles and of sparticles. More model-dependent constraints follow from the “naturalness” requirement that observables do not depend sensitively on input parameters. We find a preference for the second neutral gauge boson to weigh ≲320 GeV, $m_{\tilde g} \mathbin{\lower.3ex\hbox{$\buildrel<\over{\smash{\scriptstyle\sim}\vphantom{_x}}$}} 250$ GeV and $m_{\tilde q} \mathbin{\lower.3ex\hbox{$\buildrel<\over{\smash{\scriptstyle\sim}\vphantom{_x}}$}} 500$ GeV. Dynamical generation of the gauge hi...

On the 1‐Loop Renormalization of the Electroweak Standard Model and its Application to Leptonic Processes

Abstract: A renormalization scheme for the electroweak standard model is presented in which the electric charge and the masses of the gauge bosons, Higgs particle and fermions are used as physical parameters. The photon is treated such that quantum electrodynamics is contained as a simple substructure. Field renormalization respecting the gauge symmetry gives finite propagators and vertex functions. The Ward identities between the Green functions of the unphysical sector allow a renormalization that maintains the simple pole structure of the propagators in the t'Hooft-Feynman gauge. We give a complete list of self energies and all renormalization constants also in the unphysical Higgs and ghost sector. Explicit results are given for the renormalized self energies, vertex functions and boxes that enter the evaluation of 1-loop radiative corrections to fermionic processes. We calculate the 1-loop radiative corrections to purely leptonic reactions like $\mu$ decay, $ u \mu \mu e$ scattering and $\mu$ pair production in $e^+ e^−$ annihilation. A test of the standard model is performed by comparing these low energy data with the results of the $p \bar{p}$ collider experiments for the W and Z boson masses.

Gauge invariance and unitarity in higher-derivative quantum gravity

Abstract: The question of unitarity is examined in the renormalizable, ``higher-derivative'' theory of quantum gravity. It is pointed out that the presence of a massive spin-2 ghost in the bare propagator is inconclusive, since this excitation is unstable. In the presence of unstable particles, expansions using bare propagators are impossible---modified expansions with dressed propagators that exhibit the complex nature of the unstable pole must be employed. It is found, however, that the position of the complex poles in the dressed propagator is explicitly gauge dependent. It turns out that this is a specifically gravitational effect; it does not occur in gauge theories with an internal-symmetry gauge group. On the other hand, a physical S matrix between in and out states containing only transverse, massless gravitons and physical massless matter fields is shown to be gauge independent. It then follows by a standard, albeit formal, argument that the contribution of all gauge-variant poles to its intermediate states must cancel. The physical S matrix should therefore, be unitary. In this development, the standard rules of quantum field theory are followed throughout; no ad hoc modifications, such as the Lee-Wick prescription, are ever invoked.

Extra Gauge Bosons in E(6)

Abstract: Recent developments in superstring theories have renewed interest in E/sub 6/ as the group for grand unification. E/sub 6/ has rank 6, two more than the standard model, so that an E/sub 6/ grand unified theory can have extra gauge bosons. For example, it can have extra low-energy Z-italic's. If there is just one extra Z-italic at low energy, it can be a mixture of the two extra U(1)'s present in E/sub 6/. We parametrize this mixing by an angle t-italich-italice-italict-italica-italic. We consider the effects of Z-italic(t-italich-italice-italict-italica-italic) in neutral currents, putting limits on its mass. In addition, we consider the branching ratios, Drell-Yan production, and forward-backward asymmetries for Z-italic(t-italich-italice-italict-italica-italic). Another possibility is that, in addition to one extra Z-italic, there is an extra SU(2) present in the low-energy theory. It is SU(2)/sub I-italic/, the SU(2) which commutes with the electromagnetic charge. We consider the effects of the W-italic/sub I-italic/, which are electromagnetically neutral, in production of exotic particles and other rare processes, particularly flavor-changing neutral currents.

Canonical quantization of a two-dimensional model with anomalous breaking of gauge invariance

Abstract: We investigate in detail the operator quantum dynamics of a two-dimensional model exhibiting anomalous breaking of gauge invariance. The equal-time algebra is systematically obtained by using the Dirac-bracket formalism for constrained systems. For certain values of the regularization parameter the system is shown to undergo drastic changes. For the value of the parameter corresponding to the chiral Schwinger model no operator solutions are found to exist.

Skyrmions with ρ and ω Mesons as Dynamical Gauge Bosons

Abstract: We extend the Skyrme model to incorporate the vector mesons $\ensuremath{\rho}$ and $\ensuremath{\omega}$ in a way consistent with the non-Abelian anomalies of QCD and vector-meson dominance. The vector mesons are treated as composite gauge bosons of a hidden ${\mathrm{SU}(2)}_{V}\ensuremath{\bigotimes}\mathrm{U}(1)$ symmetry. We investigate the bulk properties of hedgehog-type Skyrme solitons in the baryon number $B=1$ sector of this model.

Spontaneous Symmetry Breakdown in the Abelian Higgs Model

Abstract: For the abelian Higgs model we introduce a new gauge invariant observable which in Landau gauge is $$\phi (x)\bar \phi (y)$$ . In three or more dimensions this observable is used to show that the global gauge symmetry is spontaneously broken in the lattice theory for a suitable range of parameters. This observable also provides a gauge invariant order parameter for the phase transition in this model.

Theory and Detection of Magnetic Monopoles in Gauge Theories

Abstract: These lecture notes discusses the developments both in the theoretical understanding of the physics and mathematics of magnetic monopoles as well as the ways in which they can be detected experimentally.The subject has now become highly interdisciplinary and recent monopole meetings have attracted participants from low temperature physics at one extreme to cosmology at the other.

Quantum Dynamics of Chiral Fermions in a Model With Anomalous Breaking of Gauge Invariance

Abstract: We study the quantum dynamics of chiral fermion fields minimally coupled to a gauge field. The model, originally proposed by Jackiw and Rajaraman, is known to exhibit the anomalous breaking of gauge invariance, which leads to the appearance of an arbitrary parameter a. Both functional and operator techniques are used to obtain the two-point fermion Green's functions for ag1 and a=1. In both cases clustering holds, and the theory contains asymptotically free fermions. The quantum equation of motion for the field tensor resembles formally that of the Proca theory, but with a dynamically generated mass and a nonconserved source. It is found that for a=1 the generating functional cannot be written in terms of a manifestly Lorentz-invariant Lagrangian.

The Constants of Nature

Abstract: Apart from gravity, all physics phenomena can be described by the standard gauge-theory framework of modern particle physics: quantum chromodynamics and the electroweak gauge theory. At least eighteen parameters are needed to adjust theory and experiments. A further reduction of the parameters requires theoretical considerations reaching beyond the standard model.

Magnetic Monopoles and Charged States in Four-dimensional, Abelian Lattice Gauge Theories

Abstract: We construct physical states of arbitrary magnetic charge for the U(1)4 lattice gauge theory and electrically charged states for the four-dimensional, noncompact Abelian Higgs model, or spinor QED, in the massless QED phase of these models. We discuss the infraparticle structure of monopoles and charged particles and show that, in the continuum limit (if it exists), the Lorentz group cannot be implemented unitarily on charged sectors.

Phenomenology of exotic particles in E 6 theories

Abstract: We explore the properties of the exotic fermions as well as the additional gauge boson(s) and Higgs scalars present in E/sub 6/ grand unified theories resulting from superstrings. Special attention has been paid to the decay modes of these new particles and their production mechanisms at existing accelerators and those under construction.

Massive, unitary, renormalizable Yang-Mills theory without Higgs bosons.

Abstract: We present a variant of the Stueckelberg formalism for Yang-Mills theory where the Stueckelberg scalar field is eliminated in favor of the gauge potential. Normally this leads to nonpolynomial interactions. However, we point out that it is possible to pick a gauge where the nonpolynomiality disappears and the resulting theory is power-counting renormalizable and unitary. This procedure allows one to construct an electroweak model without the Higgs boson.