ZZ and Zgamma still haven't found what they are looking for

TL;DR

This paper investigates the leading deviations from the Standard Model in neutral diboson processes at high energies, using effective field theory and fundamental principles like unitarity and causality to constrain new physics effects.

Contribution

It identifies key dimension-8 operators affecting neutral diboson processes and derives positivity bounds on their coefficients from fundamental physical principles.

Findings

Identification of dominant dimension-8 operators in neutral diboson processes

Derivation of positivity constraints on operator coefficients

Analysis of symmetries and selection rules for new physics contributions

Abstract

Neutral diboson processes are precise probes of the Standard Model (SM) of particle physics, which entail high sensitivity to new physics effects. We identify in terms of dimension-8 effective operators the leading departures from the SM that survive in neutral diboson processes at high-energy, and which interfere with the unsuppressed SM helicity contributions. We describe symmetries and selections rules that single out those operators, both for weakly and strongly coupled physics beyond the SM. Finally, we show that unitarity and causality enforce, via dispersion relations, positivity constraints on the coefficients of these effective operators, reducing the parameter space which is theoretically allowed.