Lines of minima and Teichmuller geodesics

Abstract

For two measured laminations $ν^+$ and $ν^-$ that fill up a hyperbolizable surface $S$ and for $t \in (-\infty, \infty)$, let $L_t$ be the unique hyperbolic surface that minimizes the length function $e^t l(ν^+) + e^{-t} l(ν^-)$ on Teichmuller space. We characterize the curves that are short in $L_t$ and estimate their lengths. We find that the short curves coincide with the curves that are short in the surface $G_t$ on the Teichmuller geodesic whose horizontal and vertical foliations are respectively, $e^t ν^+$ and $e^{-t} ν^-$. By deriving additional information about the twists of $ν^+$ and $ν^-$ around the short curves, we estimate the Teichmuller distance between $L_t$ and $G_t$. We deduce that this distance can be arbitrarily large, but that if $S$ is a once-punctured torus or four-times-punctured sphere, the distance is bounded independently of $t$.