Celestial insights into the S-matrix bootstrap

TL;DR

This paper develops a Celestial amplitude framework for 2-2 scattering, deriving bounds on partial wave moments and revealing a new positivity linked to low spin dominance, with implications for scalar theories.

Contribution

It introduces crossing symmetric partial waves in Celestial variables, removes spurious singularities, and establishes novel bounds and positivity conditions related to low spin dominance.

Findings

Derived bounds on partial wave moments.

Identified a new positivity linked to spin-0 dominance.

Proved properties of Feynman blocks in Celestial variables.

Abstract

We consider 2-2 scattering in four spacetime dimensions in Celestial variables. Using the crossing symmetric dispersion relation (CSDR), we recast the Celestial amplitudes in terms of crossing symmetric partial waves. These partial waves have spurious singularities in the complex Celestial variable, which need to be removed in local theories. The locality constraints (null constraints) admit closed form expressions, which lead to novel bounds on partial wave moments. These bounds allow us to quantify the degree of low spin dominance(LSD) for scalar theories. We study a new kind of positivity that seems to be present in a wide class of theories. We prove that this positivity arises only in theories with a spin-0 dominance. The crossing symmetric partial waves with spurious singularities removed, dubbed as Feynman blocks, have remarkable properties in the Celestial variable, namely typically realness, in the sense of Geometric Function Theory (GFT). Using GFT techniques we derive non-projective bounds on Wilson coefficients in terms of partial wave moments.