Odd Koschorke classes

We introduce odd Koschorke classes in odd K-theory by using degeneracy loci of self-adjoint Fredholm operators. These classes are characteristic classes analogous to the even Koschorke classes in even K-theory. We study two aspects of these classes: their role as obstruction classes and their realization as characteristic classes with real coefficients for odd twisted K-theory. On the even side, we introduce generalized Koschorke classes indexed by arbitrary partitions via Cibotaru's notion of a quasi-manifold. These classes form a $\mathbb{C}$-basis of $H^*(\mathrm{Fred}_0;\mathbb{C})$ and recover the usual Koschorke classes for rectangular partitions. Finally, by analogy with the correspondence between even Koschorke classes and singular vectors for a representation of the Virasoro algebra, we state a result for a representation of a super-Virasoro algebra: each singular vector has a unique finite expansion in terms of generalized Koschorke classes and generalized odd Koschorke classes.