Unjamming of Granular Packings as a Constraint Satisfaction Problem: Evidence for a Growing Static Length Scale in Frictionless Packings

An outstanding question in the physics of soft jammed packings concerns the nature of the correlations that arise near the unjamming transition. In this work, we treat unjamming as a constraint satisfaction problem and demonstrate that a static correlation function, which probes sensitivity to boundary conditions,exhibits a diverging correlation length as the packing is decompressed. This length scale is related to isostaticity, and has been connected earlier to the existence of soft modes in isostatic packings. The form of the correlation function is remarkably similar to one predicted in the mosaic theory of the glass transition, and we relate the nature of the growing correlations to the entropy of packings.