Abstract: Bions are multiple fractional instanton configurations with zero instanton charge playing important roles in quantum field theories on a compactified space with a twisted boundary condition. We classify fractional instantons and bions in the SU(N) principal chiral model on (Formula presented.) with twisted boundary conditions. We find that fractional instantons are global vortices wrapping around S1 with their U(1) moduli twisted along S1, that carry 1/N instanton (baryon) numbers for the (Formula presented.) symmetric twisted boundary condition and irrational instanton numbers for generic boundary condition. We work out neutral and charged bions for the SU(3) case with the (Formula presented.) symmetric twisted boundary condition. We also find for generic boundary conditions that only the simplest neutral bions have zero instanton charges but instanton charges are not canceled out for charged bions. A correspondence between fractional instantons and bions in the SU(N) principal chiral model and those in Yang-Mills theory is given through a non-Abelian Josephson junction.
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