Computing monodromy via continuation methods on random Riemann surfaces

We consider a Riemann surface X defined by a polynomial f (x, y) of degree d, whose coefficients are chosen randomly. Hence, we can suppose that X is smooth, that the discriminant delta(x) of f has d(d - 1) simple roots, Delta, and that delta(0) not equal 0, i.e. the corresponding fiber has d distinct points {y(1), ..., y(d)}. When we lift a loop 0 is an element of gamma subset of C - Delta by a continuation method, we get d paths in X connecting {y(1), ..., y(d)}, hence defining a permutation of that set. This is called monodromy. Here we present experimentations in Maple to get statistics on the distribution of transpositions corresponding to loops around each point of Delta. Multiplying families of "neighbor" transpositions, we construct permutations and the subgroups of the symmetric group they generate. This allows us to establish and study experimentally two conjectures on the distribution of these transpositions and on transitivity of the generated subgroups. Assuming that these two conjectures are true, we develop tools allowing fast probabilistic algorithms for absolute multivariate polynomial factorization, under the hypothesis that the factors behave like random polynomials whose coefficients follow uniform distributions. (C) 2010 Elsevier B.V. All rights reserved.