Counting Yang-Mills Dyons with Index Theorems

TL;DR

This paper uses index theorems to count supersymmetric bound states of BPS monopoles and dyons in N=4 and N=2 Yang-Mills theories, revealing larger degeneracies than expected.

Contribution

It extends the counting of BPS bound states to generic Coulombic vacua with multiple Higgs fields, providing new insights into dyon degeneracies.

Findings

Number of magnetic bound states matches electromagnetic duality predictions.

Degeneracy of dyons exceeds single supermultiplet expectations.

Counting applies to generic electric charges in N=4 and N=2 theories.

Abstract

We count the supersymmetric bound states of many distinct BPS monopoles in N=4 Yang-Mills theories and in pure N=2 Yang-Mills theories. The novelty here is that we work in generic Coulombic vacua where more than one adjoint Higgs fields are turned on. The number of purely magnetic bound states is again found to be consistent with the electromagnetic duality of the N=4 SU(n) theory, as expected. We also count dyons of generic electric charges, which correspond to 1/4 BPS dyons in N=4 theories and 1/2 BPS dyons in N=2 theories. Surprisingly, the degeneracy of dyons is typically much larger than would be accounted for by a single supermultiplet of appropriate angular momentum, implying many supermutiplets of the same charge and the same mass.