A Gravitino Distance Conjecture

We conjecture that in $\mathcal{N}=1$ supersymmetric 4d string vacua with non-vanishing gravitino mass, the limit $m_{3/2}\rightarrow 0$ is at infinite distance. In particular one can write $M_{\text{tower}} \simeq m_{3/2}^\delta$ so that as the gravitino mass goes to zero, a tower of KK states as well as emergent strings become tensionless. This conjecture may be motivated from the Weak Gravity Conjecture as applied to strings and membranes and implies in turn the AdS distance conjecture. We test this proposal in classical 4d type IIA orientifold vacua in which one obtains a range of values $\tfrac13 \le \delta \le 1$. The parameter $\delta$ is related to the scale decoupling exponent in AdS vacua and to the $\alpha$ exponent in the SDC for the type IIA complex structure. We present a general analysis of the gravitino mass in the limits of moduli space in terms of limiting Mixed Hodge Structures and study in some detail the case of two moduli F-theory settings, which yield a lower bound $\delta>1/4$. The conjecture has important phenomenological implications. In particular we argue that low-energy supersymmetry of order 1 TeV is only obtained if there is a tower of KK states at an intermediate scale, of order $10^8\text{-}10^{13}$ GeV. One also has an upper bound for the Hubble constant upon inflation $H\lesssim m_{3/2}^\delta M^{(1-\delta)}_{\text{P}}$