We study the set vol(M, G) of volumes of all representations ρ : π1M → G, where M is a closed oriented 3-manifold and G is either Iso+H 3 or Isoe SL2(R).By various methods, including relations between the volume of representations and the Chern-Simons invariants of flat connections, and recent results of surfaces in 3-manifolds, we prove that any 3-manifold M with positive Gromov simplicial volume has a finite cover M with vol( M, Iso+H 3 ) = {0}, and that any non-geometric 3-manifold M containing at least one Seifert piece has a finite cover M with vol( M, Isoe SL2(R)) = {0}.We also find 3-manifolds M with positive simplicial volume but vol(M, Iso+H 3 ) = {0}, and non-trivial graph manifolds M with vol(M, Isoe SL2(R)) = {0}, proving that it is in general necessary to pass to some finite covering to guarantee that vol(M, G) = {0}.Besides we determine vol(M, G) when M supports the Seifert geometry.
ContentsDefinition 4.9. Let M be an orientable closed irreducible mixed 3-manifold containing no essential Klein bottles. Let J 0 be a JSJ piece, T 0 be a JSJ torus adjacent to J 0 and ζ 0 be a slope on T 0 . A partial PW subsurface j : R M is said to be virtually bounded by ζ 0 outside J 0 if the boundary ∂R of R is non-empty, covering ζ 0 under j, and if the interiorR of R misses J 0 under j. In this case, the carrier chunk X(R) ⊂ M of R is the unique minimal chunk that contains R, and the carrier boundary of X(R) is the component T 0 ⊂ ∂X(R).Definition 4.10. We say that a partial PW subsurface j : R M is parallel cutting if, for every JSJ torus T ⊂ M , all components of j −1 (T ) in R cover the same slope of T .
Virtual existence of partial PW subsurfacesTheorem 4.11. Let M be an orientable closed irreducible mixed 3-manifold containing no essential Klein bottles. Let ζ 0 be a slope on a JSJ torus T 0 adjacent to a JSJ piece J 0 . Then, for some finite coverM of M together with an elevation (J 0 ,T 0 ,ζ 0 ) of the triple (J 0 , T 0 , ζ 0 ),
Pierre Derbez I2M UMR 7373