Rigidity of spherical codes

TL;DR

This paper investigates the rigidity of spherical codes, revealing that many known packings are jammed while others, especially in higher dimensions, are not, leading to new configurations that surpass previous records.

Contribution

It systematically studies the rigidity of spherical codes, identifies which configurations are jammed, and introduces new configurations in high dimensions that improve existing records.

Findings

Coxeter-Todd lattice is locally jammed but not globally jammed.

Many packings in 4-12 dimensions are jammed.

New kissing configurations in 25-31 dimensions surpass 1982 records.

Abstract

A packing of spherical caps on the surface of a sphere (that is, a spherical code) is called rigid or jammed if it is isolated within the space of packings. In other words, aside from applying a global isometry, the packing cannot be deformed. In this paper, we systematically study the rigidity of spherical codes, particularly kissing configurations. One surprise is that the kissing configuration of the Coxeter-Todd lattice is not jammed, despite being locally jammed (each individual cap is held in place if its neighbors are fixed); in this respect, the Coxeter-Todd lattice is analogous to the face-centered cubic lattice in three dimensions. By contrast, we find that many other packings have jammed kissing configurations, including the Barnes-Wall lattice and all of the best kissing configurations known in four through twelve dimensions. Jamming seems to become much less common for large kissing configurations in higher dimensions, and in particular it fails for the best kissing configurations known in 25 through 31 dimensions. Motivated by this phenomenon, we find new kissing configurations in these dimensions, which improve on the records set in 1982 by the laminated lattices.