We study relations among characteristic classes of smooth manifold bundles with highly-connected fibers. For bundles with fiber the connected sum of g copies of a product of spheres S d × S d and odd d , we find numerous algebraic relations among so-called "generalized Miller-Morita-Mumford classes". For all g > 1, we show that these infinitely many classes are algebraically generated by a finite subset.Our results contrast with the fact that there are no algebraic relations among these classes in a range of cohomological degrees that grows linearly with g, according to recent homological stability results. In the case of surface bundles (d = 1), our approach recovers some previously known results about the structure of the classical "tautological ring", as introduced by Mumford, using only the tools of algebraic topology. 55R40; 57R22, 55T10
IntroductionLet M be a 2d -dimensional closed oriented smooth manifold. We denote by Diff M the topological group of orientation-preserving diffeomorphisms of M . The bar construction can be used to construct the space BDiff(M) that classifies bundles with fiber M . For any characteristic class of vector bundles p ∈ H * +2d (BSO 2d ; Q), we will define a generalized Miller-Morita-Mumford class (or just kappa class) κ p ∈ H * (BDiff(M); Q). These are the simplest examples of characteristic classes of bundles 1 with fiber M and structure group Diff M .We are mainly interested in the case where the fiber is #g S d × S d , the connected sum of g copies of S d × S d . More generally, we let the fiber to be a highly-connected manifold (see Definition 2.5) of genus g and dimension 2d , denoted M 2d g or M g . Recall that H * (BSO 2d ; Q) = Q[p 1 , . . . , p d−1 , e], where p i is the Pontryagin class of degree 4i and e is the Euler class of degree 2d . Let S ⊂ H * (BSO 2d ; Q) consist of the monomials 1 A geometric example of such a bundle is a proper submersion f : E → B of smooth, oriented manifolds that has M as its fiber.arXiv:1310.6804v3 [math.AT]