Sparse polynomial equations and other enumerative problems whose Galois groups are wreath products

We introduce a new technique to prove connectivity of subsets of covering spaces (so called inductive connectivity), and apply it to Galois theory of problems of enumerative geometry. As a model example, consider the problem of permuting the roots of a complex polynomial $$f(x) = c_0 + c_1 x^{d_1} + \cdots + c_k x^{d_k}$$ f ( x ) = c 0 + c 1 x d 1 + ⋯ + c k x d k by varying its coefficients. If the GCD of the exponents is d, then the polynomial admits the change of variable $$y=x^d$$ y = x d , and its roots split into necklaces of length d. At best we can expect to permute these necklaces, i.e. the Galois group of f equals the wreath product of the symmetric group over $$d_k/d$$ d k / d elements and $${\mathbb {Z}}/d{\mathbb {Z}}$$ Z / d Z . We study the multidimensional generalization of this equality: the Galois group of a general system of polynomial equations equals the expected wreath product for a large class of systems, but in general this expected equality fails, making the problem of describing such Galois groups unexpectedly rich.

Generating wreath products of symmetric and alternating groups

We show that the wreath product of two finite symmetric or alternating groups is 2-generated.

Embeddings in matrix wreath products of algebras

We use matrix wreath products to show that (1) every countable dimensional nonsingular algebra is embeddable in a finitely generated nonsingular algebra, (2) for every infinite dimensional finitely generated PI-algebra [Formula: see text] there exists an epimorphism [Formula: see text], where [Formula: see text] and the algebra [Formula: see text] is not representable by matrices over a commutative algebra. If the algebra [Formula: see text] is commutative, then [Formula: see text] satisfies the ACC on two-sided ideals as in the recent examples of Greenfeld and Rowen.

Group graded Morita equivalences for wreath products

"Starting with group graded Morita equivalences, we obtain Morita equivalences for tensor products and wreath products."