Constraints on spin-3/2 and excited spin-1/2 fermions coming from the leptonic Z0-partial width

We consider effective interactions among excited spin-1/2 and spin-3/2 leptons with the usual ones. Assuming that these new leptons are lighter than the Z0, we study the constraints on their masses and compositeness scale coming from the leptonic Z0 partial width.

On discrete symmetries of the multi-boson KP hierarchies

We show that the multi-boson KP hierarchies possess a class of discrete symmetries linking them to discrete Toda systems. These discrete symmetries are generated by the similarity transformation of the corresponding Lax operator. This establishes a canonical nature of the discrete transformations. The spectral equation, which defines both the lattice system and the corresponding Lax operator, plays a key role in determining pertinent symmetry structure. We also introduce the concept of the square root lattice leading to a family of new pseudo-differential operators with covariance under additional Bäcklund transformations.

Glueballs in peripheral heavy-ion collisions

We estimate the cross-section for glueball production in peripheral heavy-ion collisions through two-photon and double-Pomeron exchange, at energies that will be available at RHIC and LHC. Glueballs will be produced at large rates, opening the possibility to study decays with very small branching ratios. In particular, we discuss the possibility of observing the subprocess γγ(PP) → G → γγ.

Rindler and Minkowski particles relationship revisited

We show that the emission of a Minkowski particle by a general class of scalar sources as described by inertial observers corresponds to either the emission or the absorption of a Rindler particle as described by uniformly accelerated observers. Our results are discussed in connection with the current controversy whether uniformly accelerated detectors radiate.

Toda lattice field theories, discrete W algebras, Toda lattice hierarchies and quantum groups

In analogy with the Liouville case we study the sl3 Toda theory on the lattice and define the relevant quadratic algebra and out of it we recover the discrete W3 algebra. We define an integrable system with respect to the latter and establish the relation with the Toda lattice hierarchy. We compute the relevant continuum limits. Finally we find the quantum version of the quadratic algebra.

Compatibility of a model for the QCD-Pomeron and chiral-symmetry breaking phenomenologies

The phenomenology of a QCD-Pomeron model based on the exchange of a pair of non-perturbative gluons, i.e. gluon fields with a finite correlation length in the vacuum, is studied in comparison with the phenomenology of QCD chiral symmetry breaking, based on non-perturbative solutions of Schwinger-Dyson equations for the quark propagator including these non-perturbative gluon effects. We show that these models are incompatible, and point out some possibles origins of this problem.

Local actions with electric and magnetic sources

Superstring field theory was recently used to derive a covariant action for a self-dual five-form field strength. This action is shown to be a ten-dimensional version of the McClain-Wu-Yu action. By coupling to D-branes, it can be generalized in the presence of sources. In four dimensions, this gives a local Maxwell action with electric and magnetic sources.

Probing SU(2) symmetry breaking in the nucleon sea

Investigation of invariant cross-sections for production of K*- and K*0, in the fragmentation region of the proton, in p - p and γ - p reactions, gives a direct and unambiguous probe to the symmetry breaking of the nucleon sea. Based on existing data, we clearly found a large asymmetry of the sea. Our result is in excellent agreement with NA51 measurement, signaling lack of any nuclear effect. The measurement can be carried out in a single experimental set up. The ratio K*-/K*0 is equivalent to ū/d̄, with easy access to the x-dependence of the asymmetry. The observed asymmetry from available experimental data is used to improve the valon-recombination model. © 1997 Elsevier Science B.V.

Infrared finite solutions for the gluon propagator and the QCD vacuum energy

Nonperturbative infrared finite solutions for the gluon polarization tensor have been found, and the possibility that gluons may have a dynamically generated mass is supported by recent Monte Carlo simulation on the lattice. These solutions differ among themselves, due to different approximations performed when solving the Schwinger-Dyson equations for the gluon polarization tensor. Only approximations that minimize energy are meaningful, and, according to this, we compute an effective potential for composite operators as a function of these solutions in order to distinguish which one is selected by the vacuum. © 1997 Elsevier Science B.V.

Bounds on contact interactions from LEP1 data and high-Q2 HERA events

A contact four-fermion interaction between light quarks and electrons has been evoked as a possible explanation for the excess of events observed by HERA at high-Q2. We explore the 1-loop effects of such interaction in Γ(Z0 → e+e-) measured at LEP and impose strong bounds on the lower limit of the effective scale. Our results are able to discard some of the contact interactions as possible explanation for the HERA events. © 1997 Elsevier Science B.V.

A simple action for a free fractional spin particle

By studying classical realizations of the sl(2, R-fraktur sign) algebra in a two dimensional phase space (q,π), we have derived a continuous family of new actions for free fractional spin particles in 2 + 1 dimensions. For the case of light-like spin vector (SμSμ = 0), the action is remarkably simple. We show the appearence of the Zitterbewegung in the solutions of the equations of motion, and relate the actions to others in the literature at classical level. © 1997 Elsevier Science B.V.

Limits on anomalous top couplings from Z pole physics

We obtain constraints on possible anomalous interactions of the top quark with the electroweak vector bosons arising from the precision measurements at the Z pole. In the framework of SU(2)L ⊕ U(1)Y chiral Lagrangians, we examine all effective CP-conserving operators of dimension five which induce fermionic currents involving the top quark. We constrain the magnitudes of these anomalous interactions by evaluating their one-loop contributions to the Z pole physics. Our analysis shows that the operators that contribute to the LEP observables get bounds close to the theoretical expectation for their anomalous couplings. We also show that those which break the SU(2)C custodial symmetry are more strongly bounded. © 1997 Elsevier Science B.V.

Triple gauge boson production and dynamical symmetry breaking at the Next Linear Collider

We study in a model independent way the role of a techniomega resonance in the process e+e-→ W+W-Z at the Next Linear Collider. © 1998 Elsevier Science B.V.

Dispersion relations and the spin polarizabilities of the nucleon

A forward dispersion calculation is implemented for the spin polarizabilities γ1, ⋯, γ4 of the proton and the neutron. These polarizabilities are related to the spin structure of the nucleon at low energies and are structure-constants of the Compton scattering amplitude at script O sign(ω3). In the absence of a direct experimental measurement of these quantities, a dispersion calculation serves the purpose of constraining the model building, and of comparing with recent calculations in heavy baryon chiral perturbation theory. © 1998 Elsevier Science B.V.

Conformal compensators and manifest type IIB S-duality

Using the conformal compensator superfields of N = 2 D = 4 supergravity, the Type IIB S-duality transformations are expressed as a linear rotation which mixes the compensator and matter superfields. The classical superspace action for D = 4 compactifications of Type IIB supergravity is manifestly invariant under this transformation. Furthermore, the introduction of conformal compensators allows a Fradkin-Tseytlin term to be added to the manifestly SL(2,Z)-covariant sigma model action of Townsend and Cederwall. © 1998 Published by Elsevier Science B.V.