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arXiv · 2606.28245

Spinor-helicity formalism for continuous-spin particles

Thomas Basile·Xavier Bekaert·Felipe Figueroa·Evgeny Skvortsov
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Abstract

We propose a new formulation of continuous-spin particles (CSP) with the help of a single two-component spinor to build asymptotic states. This formulation allows to write down amplitudes in a straightforward way, similar to the massless spinor-helicity approach. The helicity states naturally emerge upon decomposing into components of a fixed homogeneity degree. We show that CSP amplitudes can be understood as the infinite-spin limit of amplitudes of massive particles and, similarly to the scattering of black holes, a certain universal factor exponentiates. In analogy with the recent discovery of collinear amplitudes in self-dual theories, we find nontrivial CSP collinear amplitudes where the collinear fractions are constrained by the dimensionful parameter characterising the various continuous-spin particles.

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Thomas Basile, Xavier Bekaert, Felipe Figueroa, Evgeny Skvortsov. 2026-06-26. Spinor-helicity formalism for continuous-spin particles. https://arxiv.org/abs/2606.28245

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