Triple clasp formulas for $C_2$ webs

Abstract

Using the light ladder basis for Kuperberg's $C_2$ webs, we derive triple clasp formulas for idempotents projecting to the top summand in each tensor product of fundamental representations. We then find explicit formulas for the coefficients occurring in the clasps, by computing these coefficients as local intersection forms. Our formulas provide further evidence for Elias's clasp conjecture, which was given for type $A$ webs, and suggests how to generalize the conjecture to non-simply laced types.