Constraints on Long-Range Forces in De Sitter Space

Abstract: As explained by Weinberg long-ago, in Minkowski space, gauge invariance of scattering amplitudes in the soft limit leads to strong constraints on interacting gauge theories. Famous examples include an on-shell derivation of the Einstein equivalence principle and the absence of long-range forces mediated by massless particles with spin $>2$. In this talk I will describe the extension of this analysis to de Sitter (dS) space. The analogue of the Weinberg soft constraints in dS are "charge conservation identities" on the conformally invariant, late time Bunch-Davies wavefunction coefficients. Formally, these constraints correspond to a generalization of the analysis of CFTs with higher-spin symmetries by Maldacena-Zhiboedov to a class of non-unitary holographic "CFTs" dual to a dS bulk theory. I will explain how these identities allow us to place constraints (and in some cases prove strict no-go theorems) on interacting field theories of so-called "partially massless" (PM) gauge fields, including for the first time, constraints on PM fields coupled to Einstein gravity. Based on work to appear with Daniel Baumann, Kurt Hinterbichler, Austin Joyce, Hayden Lee, Jiajie Mei and Nathan Meurrens.