Isoperimetric profiles and random walks on some groups defined by piecewise actions

We study the isoperimetric and spectral profiles of certain families of finitely generated groups defined via actions on labelled Schreier graphs and simple gluing of such. In one of our simplest constructions—the pocket-extension of a group G —this leads to the study of certain finitely generated subgroups of the full permutation group S ( G ∪ { ∗ } ) . Some sharp estimates are obtained while many challenging questions remain.