Lodha, Yash2017-07-102017-07-102017-07-10201710.1142/S0218196717500151https://infoscience.epfl.ch/handle/20.500.14299/139128WOS:000402741300003The Tarski number of a nonamenable group is the smallest number of pieces needed for a paradoxical decomposition of the group. Nonamenable groups of piecewise projective homeomorphisms were introduced in [N. Monod, Groups of piecewise projective homeomorphisms, Proc. Natl. Acad. Sci. 110(12) (2013) 4524-4527], and nonamenable finitely presented groups of piecewise projective homeomorphisms were introduced in [Y. Lodha and J. T. Moore, A finitely presented non amenable group of piecewise projective homeomorphisms, Groups, Geom. Dyn. 10(1) (2016) 177-200]. These groups do not contain non-abelian free subgroups. In this paper, we prove that the Tarski number of all groups in both families is at most 25. In particular, we demonstrate the existence of a paradoxical decomposition with 25 pieces. Our argument also applies to any group of piecewise projective homeomorphisms that contains as a subgroup the group of piecewise PSL2(Z) homeomorphisms of R with rational breakpoints and an affine map that is a not an integer translation.AmenableTarski numberfinitely presentedfree grouppiecewiseprojectivetorsion freetext::journal::journal article::research article