Asymptotics of the quantum invariants for surgeries on the figure 8 knot
We investigate the Reshetikhin--Turaev invariants associated to SU(2) for the 3-manifolds M obtained by doing any rational surgery along the figure 8 knot. In particular, we express these invariants in terms of certain complex double contour integrals. These integral formulae allow us to propose a formula for the leading asymptotics of the invariants in the limit of large quantum level. We analyze this expression using the saddle point method. We construct a certain surjection from the set of stationary points for the relevant phase functions onto the space of conjugacy classes of nonabelian SL(2,C)-representations of the fundamental group of M and prove that the values of these phase functions at the relevant stationary points equal the classical Chern--Simons invariants of the corresponding flat SU(2)-connections. Our findings are in agreement with the asymptotic expansion conjecture. Moreover, we calculate the leading asymptotics of the colored Jones polynomial of the figure 8 knot following R. Kashaev. This leads to a slightly finer asymptotic description of the invariant than predicted by the volume conjecture of Kashaev and H. Murakami and J. Murakami.