Séance Séminaire

Séminaire Gaston Darboux

Subgroup distortion in hyperbolic groups

Given a finitely generated group, any finite generating set defines a natural metric on the group, called the word metric. The distortion function of a subgroup measures the extent to which the intrinsic word metric of the subgroup differs from the metric induced by the ambient group. Ol'shanskii showed that there are almost no restrictions on which functions arise as distortion functions of subgroups of finitely presented groups. This prompts one to ask what happens if the ambient group has some particularly nice geometry, for example, if it is hyperbolic. I will survey which functions are known to be distortion functions of subgroups of hyperbolic groups. I will then describe joint work with Tim Riley which adds to this list.