Probing composite gravity in colliders

We explore scenarios in which the graviton is not a fundamental degree of freedom at short distances but merely emerges as an effective degree of freedom at long distances. In general, the scale of such graviton “compositeness,” ${\Lambda }_g$, can only be probed by measuring gravitational forces at short distances, which becomes increasingly difficult and eventually impossible as the distance is reduced. Here, however, we point out that if supersymmetry is an underlying symmetry, the gravitino can be used as an alternative probe to place a limit on ${\Lambda }_g$ in a collider environment, by demonstrating that there is a model-independent relation, ${\Lambda }_g\gtrsim m_{3/2}$. In other words, the gravitino knows that gravity is standard at least down to its Compton wavelength, so this can also be viewed as a test of general relativity possible at very short distances. If composite gravity is found first at some ${\Lambda }_g$, this would imply a model-independent upper bound on $m_{3/2}$.

Figure 1

Diagrams representing (a) corrections to the cosmological constant, (b) corrections to the gravitational mass, and (c) corrections to the inertial mass. A solid line represents a heavy matter particle, and a double wavy line represents a graviton.

Figure 2

The ${\tilde{\chi }}_{\mathbf{p}}{\tilde{\chi }}_{\mathbf{0}}\to {\tilde{\chi }}_{\mathbf{0}}{\tilde{\chi }}_{\mathbf{p}}$ scattering via the $t$-channel $W_{\mu }^3$ exchange.