Georgia Institute of Technology College of Sciences

The talk involves an explicit formula for the Chern class on K_3(F), F=number field, givenin terms of the cyclic quantum dilogarithm on the Bloch group of F. Such a formula constructsexcplicitly units in number fields, given a complete hyperbolic 3-manifold, and a complex root ofunity, and those units fit in the asymptotic expansion of quantum knot invariants. The existence ofsuch a formula was conjectured 4 years ago by Zagier (and abstractly follows from Voevodsky's work),and the final solution to the problem was given in recent joint work of the speaker with FrankCalegari and Don Zagier. The key ingredient to the concrete formula is a special function, thecyclic quantum dilogarithm, from a physics 1993 paper of Kashaev and others. The connection of thisformula with physics, and with the Quantum Modular Form Conjecture of Zagier continues with jointwork with Tudor Dimofte. But this is the topic of another talk.