The ring of global sections of a differential scheme

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1 The ring of global sections of a differential scheme Dmitry Trushin The Einstein Institute of Mathematics The Hebrew University of Jerusalem January 2012 Dmitry Trushin () The ring of global sections January, / 10

2 Affine schemes All rings are associative, commutative, and with an identity Dmitry Trushin () The ring of global sections January, / 10

3 Affine schemes All rings are associative, commutative, and with an identity Affine varieties over K Reduced finitely generated K-algebras X A n K K[X ] Max B B Dmitry Trushin () The ring of global sections January, / 10

4 Affine schemes All rings are associative, commutative, and with an identity Affine varieties over K Reduced finitely generated K-algebras X A n K K[X ] Max B B R a ring (Spec R, O R ) a locally ringed space Dmitry Trushin () The ring of global sections January, / 10

5 Affine schemes All rings are associative, commutative, and with an identity Affine varieties over K X A n K Reduced finitely generated K-algebras K[X ] Max B B R a ring (Spec R, O R ) a locally ringed space Definition ϕ: Spec R q R q and ϕ(q) R q ϕ is regular at p if for all q U ϕ(q) = a/b in R q O R (U) = regular functions in U X = Spec R Dmitry Trushin () The ring of global sections January, / 10

6 Affine differential scheme A differential ring is a ring R with = {δ 1,..., δ m }, δ i δ j = δ j δ i Dmitry Trushin () The ring of global sections January, / 10

7 Affine differential scheme A differential ring is a ring R with = {δ 1,..., δ m }, δ i δ j = δ j δ i Affine -varieties over K X A n K Max B Reduced -finitely generated K-algebras K{X } B Dmitry Trushin () The ring of global sections January, / 10

8 Affine differential scheme A differential ring is a ring R with = {δ 1,..., δ m }, δ i δ j = δ j δ i Affine -varieties over K X A n K Max B Reduced -finitely generated K-algebras K{X } B R a ring (Spec R, O R ) a locally ringed space Dmitry Trushin () The ring of global sections January, / 10

9 Affine differential scheme A differential ring is a ring R with = {δ 1,..., δ m }, δ i δ j = δ j δ i Affine -varieties over K X A n K Max B Reduced -finitely generated K-algebras K{X } B R a ring (Spec R, O R ) a locally ringed space (cannot use Spec R) Dmitry Trushin () The ring of global sections January, / 10

10 Affine differential scheme A differential ring is a ring R with = {δ 1,..., δ m }, δ i δ j = δ j δ i Affine -varieties over K X A n K Max B Reduced -finitely generated K-algebras K{X } B R a ring (Spec R, O R ) a locally ringed space (cannot use Spec R) Definition ϕ: Spec R q R q and ϕ(q) R q ϕ is regular at p if for all q U ϕ(q) = a/b in R q O R (U) = regular functions in U X = Spec R Dmitry Trushin () The ring of global sections January, / 10

11 The problem Commutative case Differential case Set R = O R (Spec R) Set R = O R (Spec R) ι: R R ι: R R Dmitry Trushin () The ring of global sections January, / 10

12 The problem Commutative case Differential case Set R = O R (Spec R) Set R = O R (Spec R) ι: R R ι: R R always isomorphism not necessarily injective not necessarily surjective Dmitry Trushin () The ring of global sections January, / 10

13 The problem Commutative case Differential case Set R = O R (Spec R) Set R = O R (Spec R) ι: R R ι: R R always isomorphism not necessarily injective not necessarily surjective Conjecture (Jerald Kovacic) The map ι : Spec R Spec R q ι 1 (q) is a homeomorphism. Dmitry Trushin () The ring of global sections January, / 10

14 Reduced schemes Commutative case Differential case ϕ: Spec R q k(q) ϕ: Spec R q k(q) ϕ(q) = a/b in k(q) and O R (U) = regular functions in U Dmitry Trushin () The ring of global sections January, / 10

15 Reduced schemes Commutative case Differential case ϕ: Spec R q k(q) ϕ: Spec R q k(q) ϕ(q) = a/b in k(q) and O R (U) = regular functions in U Set R = O R (Spec R) Set R = O R (Spec R) ι r : R R Dmitry Trushin () The ring of global sections January, / 10

16 Reduced schemes Commutative case Differential case ϕ: Spec R q k(q) ϕ: Spec R q k(q) ϕ(q) = a/b in k(q) and O R (U) = regular functions in U Set R = O R (Spec R) Set R = O R (Spec R) ι r : R R Theorem ι r : R D R. Then ι r : Spec D Spec R is a homeomorphism. Dmitry Trushin () The ring of global sections January, / 10

17 Reduced schemes Commutative case Differential case ϕ: Spec R q k(q) ϕ: Spec R q k(q) ϕ(q) = a/b in k(q) and O R (U) = regular functions in U Set R = O R (Spec R) Set R = O R (Spec R) ι r : R R Theorem ι r : R D R. Then ι r : Spec D Spec R is a homeomorphism. Corollary The mapping ι r : Spec R Spec R is a homeomorphism. Dmitry Trushin () The ring of global sections January, / 10

18 Keigher rings Definition (Keigher ring) I R is a -ideal r(i ) is a -ideal. Dmitry Trushin () The ring of global sections January, / 10

19 Keigher rings Definition (Keigher ring) I R is a -ideal r(i ) is a -ideal. R is a Ritt algebra (Q R) R is a Keigher ring. Dmitry Trushin () The ring of global sections January, / 10

20 Keigher rings Definition (Keigher ring) I R is a -ideal r(i ) is a -ideal. R is a Ritt algebra (Q R) R is a Keigher ring. Theorem R is a Keigher ring, and we are given ι: R D R. Then ι : Spec D Spec R is a homeomorphism. Dmitry Trushin () The ring of global sections January, / 10

21 Keigher rings Definition (Keigher ring) I R is a -ideal r(i ) is a -ideal. R is a Ritt algebra (Q R) R is a Keigher ring. Theorem R is a Keigher ring, and we are given ι: R D R. Then ι : Spec D Spec R is a homeomorphism. Corollary R is a Keigher ring. Then ι : Spec R Spec R is a homeomorphism. Dmitry Trushin () The ring of global sections January, / 10

22 Improvement Ehud Hrushovski: R to be a Keigher ring is a very strong condition Dmitry Trushin () The ring of global sections January, / 10

23 Improvement Ehud Hrushovski: R to be a Keigher ring is a very strong condition Theorem R is a differential ring such that nil R is differential and we are given ι: R D R. Then is a homeomorphism. ι : Spec D Spec R Dmitry Trushin () The ring of global sections January, / 10

24 Improvement Ehud Hrushovski: R to be a Keigher ring is a very strong condition Theorem R is a differential ring such that nil R is differential and we are given ι: R D R. Then is a homeomorphism. Corollary ι : Spec D Spec R R is a differential ring such that nil R is differential. Then is a homeomorphism. ι : Spec R Spec R Dmitry Trushin () The ring of global sections January, / 10

25 Iterative derivations Definition Let δ = {δ k } k 0, δ k : R R: 1) δ 0 (x) = x 3) δ k (ab) = µ+ν=k δµ (a)δ ν (b) 2) δ k (a + b) = δ k (a) + δ k (b) 4) δ k δ m = ( ) k+m k δ k+m Dmitry Trushin () The ring of global sections January, / 10

26 Iterative derivations Definition Let δ = {δ k } k 0, δ k : R R: 1) δ 0 (x) = x 3) δ k (ab) = µ+ν=k δµ (a)δ ν (b) 2) δ k (a + b) = δ k (a) + δ k (b) 4) δ k δ m = ( ) k+m k δ k+m A differential ring R is a ring with = {δ 1,..., δ m }, δ i are iterative derivations, and δ i δ j = δ j δ i. Dmitry Trushin () The ring of global sections January, / 10

27 Iterative derivations Definition Let δ = {δ k } k 0, δ k : R R: 1) δ 0 (x) = x 3) δ k (ab) = µ+ν=k δµ (a)δ ν (b) 2) δ k (a + b) = δ k (a) + δ k (b) 4) δ k δ m = ( ) k+m k δ k+m A differential ring R is a ring with = {δ 1,..., δ m }, δ i are iterative derivations, and δ i δ j = δ j δ i. Definition ϕ: Spec R q R q and ϕ(q) R q ϕ is regular at p if for all q U ϕ(q) = a/b in R q O R (U) = regular functions in U X = Spec R Dmitry Trushin () The ring of global sections January, / 10

28 Iterative case Set R = O R (Spec R). Dmitry Trushin () The ring of global sections January, / 10

29 Iterative case Set R = O R (Spec R). Theorem R is a differential ring with iterative derivations and ι: R D R. Then is a homeomorphism. ι : Spec D Spec R Dmitry Trushin () The ring of global sections January, / 10

30 Iterative case Set R = O R (Spec R). Theorem R is a differential ring with iterative derivations and ι: R D R. Then ι : Spec D Spec R is a homeomorphism. Corollary R is a differential ring with iterative derivations. Then ι : Spec R Spec R is a homeomorphism. Dmitry Trushin () The ring of global sections January, / 10

31 The structure sheaf R ι R X ι X p p Dmitry Trushin () The ring of global sections January, / 10

32 The structure sheaf R ι R X ι X p p Question Does O R coincide with O R? Dmitry Trushin () The ring of global sections January, / 10

33 The structure sheaf R ι R X ι X p p Question Does O R coincide with O R? O R, p could contain more nilpotent elements than O R,p Dmitry Trushin () The ring of global sections January, / 10

34 The structure sheaf R ι R X ι X p p Question Does O R coincide with O R? O R, p could contain more nilpotent elements than O R,p Fact If R is reduced. Then O R = O R. Dmitry Trushin () The ring of global sections January, / 10

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