Let A be a commutative ring, B a commutative A-algebra and M a complex of B-modules. We begin by constructing the square SqB/A M , which is also a complex of B-modules. The squaring operation is a quadratic functor, and its construction requires differential graded (DG) algebras. If there exists an isomorphism ρ : M ≃ −→ SqB/A M then the pair (M,ρ) is called a rigid complex over B relative to A...

We already know that the noncommutative N-graded Noetherian algebras resemble commutative local rings in many respects. also have important property every minimal acyclic complex of finitely generated graded free modules is totally acyclic, and we want to generalize such properties algebra. By generalizing conclusions about combining what algebras, identify a class with acyclic. discuss how rel...

We prove a conjecture of A. S. Buch concerning the structure constants of the Grothendieck ring of a flag variety with respect to its basis of Schubert structure sheaves. For this, we show that the coefficients in this basis of the structure sheaf of any subvariety with rational singularities, have alternating signs. Equivalently, the class of the dualizing sheaf of such a subvariety is a nonne...

Gross and Hopkins have proved that in chromatic stable homotopy, Spanier-Whitehead duality nearly coincides with Brown-Comenetz duality. Our goal is to give a conceptual interpretation for this phenomenon in terms of the Gorenstein condition for maps of ring spectra in the sense of [5] We describe a general notion of Brown-Comenetz dualizing module for a map of ring spectra and show that in thi...

We study the arithmetic self-intersection number of the dualizing sheaf on arithmetic surfaces with respect to morphisms of a particular kind. We obtain upper bounds for the arithmetic self-intersection number of the dualizing sheaf on minimal regular models of the modular curves associated with congruence subgroups Γ0(N) with square free level, as well as for the modular curves X(N) and the Fe...

Let D be a division algebra over a base field k. The homological transcendence degree of D, denoted by HtrD, is defined to be the injective dimension of the algebra D⊗k D ◦. We show that Htr has several useful properties which the classical transcendence degree has. We extend some results of Resco, Rosenberg, Schofield and Stafford, and compute Htr for several classes of division algebras. The ...

Let D be a division algebra over a base field k. The homological transcendence degree of D, denoted by HtrD, is defined to be the injective dimension of the algebra D⊗k D ◦. We show that Htr has several useful properties which the classical transcendence degree has. We extend some results of Resco, Rosenberg, Schofield and Stafford, and compute Htr for several classes of division algebras. The ...