ALPs, the on-shell way

Bertuzzo, Enrico; Grojean, Christophe; Salla, Gabriel M.

Preprint

PUBDB-2023-03958

ALPs, the on-shell way

Bertuzzo, E. ; Grojean, C.DESY* ; Salla, G. M. (Corresponding author)

2023

[10.3204/PUBDB-2023-03958]

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Please use a persistent id in citations: doi:10.3204/PUBDB-2023-03958

Report No.: CERN-TH-2023-202; DESY-23-090; HU-EP-23/21; arXiv:2311.16253

Abstract: We study how the coupling between axion-like particles (ALPs) and matter can be obtained at the level of on-shell scattering amplitudes. We identify three conditions that allow us to compute amplitudes that correspond to shift-symmetric Lagrangians, at the level of operators with dimension 5 or higher, and we discuss how they relate and extend the Adler's zero condition. These conditions are necessary to reduce the number of coefficients consistent with the little-group scaling to the one expected from the Lagrangian approach. We also show how our formalism easily explains that the dimension-5 interaction involving one ALP and two massless spin-1 bosons receive corrections from higher order operators only when the ALP has a non-vanishing mass. As a direct application of our results, we perform a phenomenological study of the inelastic scattering $\ell^+\ell^- \to \phi h$ (with $\ell^\pm$ two charged leptons, $\phi$ the ALP and $h$ the Higgs boson) for which, as a result of the structure of the 3-point and 4-point amplitudes, dimension-7 operators can dominate over the dimension-5 ones well before the energy reaches the cutoff of the theory.

Keyword(s): dimension, 5 ; operator, higher-order ; scattering amplitude, on-shell ; lepton ; axion-like particles ; inelastic scattering ; scaling ; Higgs particle ; structure