E.N. Argyres

Stable calculations for unstable particles: Restoring gauge invariance

We discuss theoretical and phenomenological aspects of the use of boson propagators with energy-dependent widths in predictions for high-energy scattering processes. In general, gauge invariance is violated in such calculations. We discuss several approaches to restore gauge invariance, necessary for a reliable result. The most promising method is the addition of the relevant parts of the fermionic corrections, which fulfills all Ward identities. The numerical difference between this and other approaches is studied. A number of recommendations are given for LEP2 computations.

Amplitude estimates for multi-Higgs production at high energies

Abstract We present a number of exact and asymptotic results concerning the perturbative tree-level amplitudes for the decay of an off-shell scalar into a large number of on-shell scalars. These results are useful in the discussion of whether or not perturbative unitarity will be violated at sufficiently high energies and/or multiplicities.

One-loop corrections to three-vector-boson vertices in the standard model

Abstract We study the one-loop corrections to the three-boson vertices γW + W − and ZW + W − , and we present expressions for the dipole Δκ V and quadrupole ΔQ V form factors as a function of Q 2 , m top and m Higgs , where Q μ is half of the four-momentum carried by the neutral bosons. We also discuss the relevance of our results to future experiments, where reactions of the type ƒ R ƒ R → W + W − at high Q 2 will be analysed and we show that (I) it might be possible, given a good experimental sensitivity, to extract valuable informations for the mass of the top quark and (II) that any measured value of Δκ V above 10 −2 will be a signal of new physics.

Cross-section estimates for multi-Higgs production at high energies

Abstract We present lower limits on the cross-section for the process q q → H ∗ → nH as predicted by tree-level perturbation theory in the Minimal Standard Model. Emphasis is on high multiplicity n of the final state. Both the bound on the matrix element and the phase-space are treated essentially exactly, which makes our limit on the unitarity-respecting behaviour of this cross-section rigorous to leading order in the quark-Higgs Yukawa coupling.

Multiscalar production amplitudes beyond threshold

Abstract We present exact tree-order amplitudes for H ∗ → n H , for final states containing one or two particles with non-zero three-momentum, for various interaction potentials. We show that there are potentials leading to tree amplitudes that satisfy unitary, not only at threshold but also in the above kinematical configurations and probably beyond. As a by-product, we also calculated 2 → n tree amplitudes at threshold and show that for the unbroken ifφ4 theory they vanish for n ⩾ 4, for the standard Model Higgs they vanish for n ⪖ 3 and for a model potential, respecting tree-order unitarity, for n even and n ⩾ 4. Finally, we calculate the imaginary part of the one-loop 1 → n amplitude in both symmetric and spontaneously broken φ4 theory.

Hadron and jet production at collider energies in perturbative QCD

Abstract Large p T production of hadrons and jets at collider and ISR energies is studied in conventional perturbative QCD. Recently determined gluon and other parton distributions are used and higher order [ O ( α 3 S )] perturbative corrections ( K -factors) are taken into account. Good description of the data is found. The possible role of gluinos and other particles of supersymmetric theories is briefly discussed.

On amplitude zeros at threshold

Abstract The occurence of zeros of A (2→n) amplitudes at threshold in scalar theories is studied. We find a differential equation for the scalar potential, which incorporates all known cases where the A (2→n) amplitudes at threshold vanish for all sufficiently large n, in all space-time dimensions, d⩾1. This equation is related to the reflectionless potentials of quantum mechanics and to integrable theories in 1+1 dimensions. As an application, we find that the sine-Gordon potential and its hyperbolic version, the sinh-Gordon potential, also have amplitude zeros at threshold, scA(2→n) =0, for n⩾4 and d⩾2, independently of the mass and the coupling constant.

W+W−γ production as a test of three-boson couplings at LEP II

Abstract The reaction e + e − → W + W − γ is considered, for CM energies up to 2 TeV. Anomalous three-boson couplings κ γ and κ z are also included, and the sensitivity of the process on these deviations is studied.

Multiscalar amplitudes to all orders in perturbation theory

Abstract A method for calculating loop amplitudes at the multiboson threshold is presented, based on Feynman-diagram techniques. We explicitly calculate the one-loop amplitudes in both φ 4 -symmetric and broken symmetry cases, using dimensional regularization. We argue that, to all orders in the perturbation expansion, the unitarity-violating behaviour of the tree-order amplitudes persists.

Intermittency, Kadanoff scaling and hadronization

Abstract We show that Kadanoff scaling near the critical point of the Feynman-Wilson fluid leads to intermittency in the rapidity-space. A minimum rapidity interval δ 0 , below which intermittency disappears, naturally emerges and its magnitude is evaluated. We argue that the characteristic pattern of the factorial moments, when compared with data, especially in relativistic ion collisions, may signal a higher-order phase transition related to the quark-gluon plasma hadronization.