Some notes on the inverse problem for braids

Abstract

The Kontsevich integral $Z$ associates to each braid $b$ (or more generally knot $k$) invariants $Z_i(b)$ lying in finite dimensional vector spaces, for $i = 0, 1, 2, ...$. These values are not yet known, except in special cases. The inverse problem is that of determining $b$ from its invariants $Z_i(b)$. In this paper we study the case of braids on two strands, which is already sufficient to produce interesting and unexpected mathematics. In particular, we find connections with number theory, numerical analysis and field theory in physics. However, we will carry this study out with an eye to the more general case of braids on $n$ strands. We expect that solving the inverse problem even for $n=3$ will present real difficulties. Most of the concepts in this paper also apply to knots, but to simplify the exposition we will rarely mention this. The organisation and bulk of the writing of this paper predates its most significant results. We hope later to present better and develop further these results.