Supergravity from the Bottom Up
Tony Gherghetta, Wenqi Ke

TL;DR
This paper uses on-shell methods to construct and analyze effective theories involving massive spin-3/2 fermions, revealing that consistent theories up to high energy scales necessarily include supergravity interactions.
Contribution
It demonstrates that bottom-up amplitude methods recover supergravity features and establish the uniqueness of broken supergravity as the effective theory for massive spin-3/2 fermions.
Findings
Adding a spin-2 graviton interaction yields a Planck-scale unitarity cutoff.
Interactions with only spin 0 and 1 do not produce a high-energy valid effective theory.
Unitarity up to the Planck scale requires coupling to two massive spin-1 states in certain cases.
Abstract
We employ on-shell methods to construct scattering amplitudes and derive effective theories involving massive spin-3/2 fermions interacting with spin 0, 1 and 2 bosons. The four-point massive amplitudes are constructed using an all-line-transverse momentum shift, assuming that in the massless limit, three-point interactions are smooth and the Ward identity is satisfied. For a Majorana spin-3/2 fermion with mass , we show that interactions with only spin 0 and massive spin-1 bosons do not lead to an effective theory valid up to a cutoff that is independent of particle masses. Instead, adding an interaction with a spin-2 graviton gives rise to four-point amplitudes with a Planck scale unitarity cutoff that reproduces well-known results from supergravity, such as -term breaking with a complex scalar and -term breaking with an additional massive…
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Taxonomy
TopicsCosmology and Gravitation Theories · Geophysics and Gravity Measurements · Planetary Science and Exploration
