English

On Fuchs's additive intersection problem for the hyperbolic metric

Complex Variables 2026-03-18 v1

Abstract

For hyperbolic domains D1,D2{zC:z<R}D_1,D_2\subset \{z\in\mathbb C:|z|<R\} and zD1D2z\in D_1\cap D_2, we consider the ratio λD1D2(z)λD1(z)+λD2(z). \frac{\lambda_{D_1\cap D_2}(z)} {\lambda_{D_1}(z)+\lambda_{D_2}(z)}. We solve a problem of W. H. J. Fuchs by proving that the supremum of this ratio is ++\infty when D1D_1 and D2D_2 range over all hyperbolic domains. If D1D_1 and D2D_2 are further assumed to be simply connected, then the supremum is 11. We also show that the infimum of this ratio is 12\frac12 in both settings, and that the value 12\frac12 is attained if and only if D1=D2D_1=D_2.

Cite

@article{arxiv.2603.16676,
  title  = {On Fuchs's additive intersection problem for the hyperbolic metric},
  author = {Yixin He and Quanyu Tang},
  journal= {arXiv preprint arXiv:2603.16676},
  year   = {2026}
}

Comments

14 pages. Comments and suggestions are welcome

R2 v1 2026-07-01T11:24:26.446Z