We define the triangulated category of relative singularities of a closed subscheme in
a scheme. When the closed subscheme is a Cartier divisor, we consider matrix
factorizations of the related section of a line bundle, and their analogues
with locally free sheaves replaced by coherent ones. The appropriate exotic
derived category of coherent matrix factorizations is then identified with
the triangulated category of relative singularities, while the similar exotic
derived category of locally free matrix factorizations is its full subcategory.
The latter category is identified with the kernel of the direct image functor
corresponding to the closed embedding of the zero locus and acting between the
conventional (absolute) triangulated categories of singularities. Similar results are
obtained for matrix factorizations of infinite rank; and two different “large”
versions of the triangulated category of relative singularities, corresponding to
the approaches of Orlov and Krause, are identified in the case of a Cartier
divisor. A version of the Thomason–Trobaugh–Neeman localization theorem
is proven for coherent matrix factorizations and disproven for locally free
matrix factorizations of finite rank. Contravariant (coherent) and covariant
(quasicoherent) versions of the Serre–Grothendieck duality theorems for matrix
factorizations are established, and pull-backs and push-forwards of matrix
factorizations are discussed at length. A number of general results about
derived categories of the second kind for curved differential graded modules
(CDG-modules) over quasicoherent CDG-algebras are proven on the way.
Hochschild (co)homology of matrix factorization categories are discussed in an
appendix.
Keywords
matrix factorizations, relative singularities of Cartier
divisors, triangulated categories of singularities, derived
categories of the second kind, coderived categories, direct
and inverse images, covariant Serre–Grothendieck duality,
localization theory
Department of Algebraic
Geometry
Steklov Mathematical Institute of the Russian Academy of
Sciences
Gubkina str., 8
Moscow
119991
Russia
and Laboratory of Algebraic Geometry
Higher School of Economics
7 Vavilova str.
Moscow
117312
Russia
Mathematics Department
Technion – Israel Institute of Technology
32000 Haifa
Israel
and Sector of Algebra and Number Theory
Institute for Information Transmission Problems
Moscow
127994
Russia
and Laboratory of Algebraic Geometry
National Research University Higher School of Economics
Moscow
117312
Russia