gravitinos

Gravitinos are hypothetical fermionic particles predicted by theories that combine supersymmetry with general relativity (supergravity). They are the fermionic superpartners of the graviton and carry spin 3/2. In a locally supersymmetric theory, the gravitino acts as the gauge field of local SUSY and acquires mass through the super-Higgs mechanism, with the goldstino providing the longitudinal component in the broken phase. The gravitino is described by the Rarita–Schwinger formalism.

The mass of the gravitino, m3/2, is set by the scale of supersymmetry breaking and the Planck mass. In simple gravity-mediated scenarios, m3/2 is typically in the 100 GeV to TeV range; in gauge-mediated SUSY breaking, gravitinos can be very light, from the eV to keV range, and are often the lightest supersymmetric particle (LSP). In other mediation schemes, the mass can take a wide range of values. The gravitino mass strongly influences its cosmological and collider phenomenology.

Interactions of the gravitino are suppressed by the Planck scale, making direct detection extremely challenging. Gravitino couplings occur through the supercurrent, leading to very weak interactions with Standard Model particles. If heavier than other superpartners, a gravitino can decay into SM particles and superpartners; if it is the LSP, it is effectively stable and signals in detectors depend on the properties of the next-to-lightest SUSY particle (NLSP).

Cosmology and phenomenology: gravitinos can be thermally produced in the early universe, with their abundance depending on the reheating temperature after inflation. A high production rate can conflict with Big Bang nucleosynthesis and dark matter constraints, a tension known as the gravitino problem. Depending on the mass and lifetime, gravitinos can be dark matter candidates or affect cosmology through NLSP decays. No direct detection has been achieved, but collider searches look for missing energy signatures and potential displaced decays in gravitino LSP scenarios.

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