Structural aspects of extremal functions in the Krzyż conjecture

Abstract

Extremal functions for the $n$th coefficient in the Krzyż conjecture are atomic singular inner functions with at most $n$ atoms. This paper gives a lower bound on the number of atoms $N$ of the form $N\geq cn$, marking progress toward proving the expected $N=n$. Furthermore, we prove new formulas for extremal functions using variational techniques. Using these results and several other methods, we establish new conditions on extremal functions which are equivalent to the Krzyż conjecture being true. We also characterize the possible analytic invariants of extremal functions.