A translator gets distracted by every rustle in the hall, and a one-hour meeting stretches into two. A single wrong intonation changes the meaning beyond recognition. That's roughly how a particle with spin 3/2—the gravitino — behaves. It cannot exist in isolation: its "speech" must be perfectly coordinated with its surroundings, or the whole structure falls apart.
The author of the paper takes a long-standing argument to its conclusion: a massless gravitino must be part of supergravity — a theory where every particle has a superpartner. This is not a guess but a strict requirement. Otherwise, scattering amplitudes (mathematical descriptions of collisions) cannot be decomposed into consistent parts. And it gets even more demanding: for massive particles in theories with extended supersymmetry, the rules become stricter. For instance, vector bosons (force carriers) must interact according to Lie algebras — the same ones that govern symmetries in particle physics. Gravitational interaction even drags graviphotons, hypothetical partners of the graviton, into the game.
In the final part, the author shows that gravitino scattering in supergravity with unbroken symmetry 𝒩≥4 fully reconstructs the super-Higgs mechanism — the process that gives the gravitino its mass. So the translator doesn't just listen to the hall; they reconstruct the entire scene from the rustles. Theories where such a mechanism is impossible are simply unviable — the gravitino in them "stays silent," and nature rejects them.
as written by the authors arXiv:2608.04080v1
I study constraints from consistent complex factorisation of $$2\rightarrow 2$$ scattering amplitudes in $$4d$$ and their relationship with supersymmetry. I complete the argument demonstrating that a massless helicity-$$3/2$$ particle must be a gravitino in a theory of supergravity and derive the structure and couplings of massive supermultiplets from first principles. For massive BPS particles in theories with extended supersymmetry, further constraints on the couplings are derived from consistent factorisation of massive superamplitudes. Among these is the requirement that BPS vector bosons must have couplings conforming to Lie algebra structure constants or generalised Chern-Simons terms. The gravitational coupling is shown to participate and draws the graviphotons into the Lie algebra. All $$2\rightarrow 2$$ tree-level amplitudes of massive particles with spin $$s\leq 1$$ are calculated in (super)gravity using on-shell methods and the double copy. These are assembled and decomposed into (super)amplitudes with varying amounts of supersymmetry. Finally, I study scattering of BPS gravitinos with unbroken $$\mathcal{N}\geq 4$$ supergravity and show that consistent factorisation leads to the full reconstruction of the super-Higgs mechanism. This argument completely determines the perturbative structure of all $$\mathcal{N}=4$$ Minkowski vacua of gauged maximal supergravity. Gravitinos in theories not admitting a super-Higgs mechanism are ruled-out.
The gravitino is the superpartner of the graviton, the particle that carries gravity. If the gravitino exists, detecting it would be direct proof of supersymmetry.
In Robert Wilson's novel "Spin," alien technology manipulates time — much like supersymmetry links particles and their partners into a unified scheme.