Regge

Regge refers to Tullio Regge, an Italian theoretical physicist whose work has had a lasting impact on both high-energy physics and numerical relativity. Two major concepts bear his name: Regge theory in particle physics and Regge calculus in general relativity.

Regge theory is a framework for understanding the analytic structure of scattering amplitudes in the strong interaction. It introduces complex angular momentum and Regge poles, leading to Regge trajectories that relate the spin of hadrons to their squared masses. The idea is that families of particles lie on nearly linear trajectories, alpha(t), and that high-energy scattering can be described by the exchange of these trajectories rather than individual particles. Regge theory helped explain patterns in the hadron spectrum and the energy dependence of scattering at high energies and small momentum transfer, long before quantum chromodynamics provided a complete picture. It also influenced later developments in string theory and the dual resonance model, where hadronic states map to vibrational modes of strings.

Regge calculus is a discrete approach to general relativity introduced by Regge. In this formalism, spacetime is approximated by a simplicial lattice composed of flat simplices, with curvature concentrated on lower-dimensional hinges. The fundamental variables are edge lengths, and the theory yields a piecewise-linear approximation to Einstein’s equations. Regge calculus has found use in numerical relativity for simulating curved spacetimes and in various approaches to quantum gravity, including spin foam models and lattice gravity.