# Ground state as initial state

In document Explicit Exchange Interaction and Decoherence Dynamics in One-Dimensional Quantum Systems (Page 81-86)

(Cω)n.

We will always take t smaller than 1/10n so that the last summation is bounded by 4(n−1)(1 + 1/5n)n−2 <4ne1/5 <5n. This implies

Vol(tEm+Dm)>Dnm+nt Dmn−1·Em−5n2t2(Cω)n. Now, the choice t= 10n1 (Dn−1m ·Em)((Cω)n)−1 gives by substituting

1 20

(Dmn−1·Em)2

(Cω)n 6Vol(Em+Dm)−Dmn 6Vol(α)−Dmn

(and we have indeed t 6 10n1 by Lemma 7.4), whence Theorem 7.1. Of course, the

constant 20 is certainly not optimal.

(7.5) Corollary. If α ∈ENS, then the divisorial Zariski decompositionα =N(α) +hαi is such that

n−1i ·N(α) = 0.

Proof. By replacing α with α+δc1(H), one sees that it is sufficient to consider the case where α is big. Then the orthogonality estimate implies

m)(Dmn−1)·(µm)Em=Dmn−1·(µm)m)Em

6Dmn−1·Em 6C(Vol(α)−Dnm)1/2.

Sincehαn−1i= lim(µm)(Dmn−1),N(α) = lim(µm)Em and limDmn = Vol(α), we get the

desired conclusion in the limit.

### 8. Dual of the pseudo-effective cone

We consider here the Serre duality pairing

(8.1) H1,1(X,R)×Hn−1,n−1(X,R)−→R, (α, β)7−→α·β = Z

X

α∧β.

When restricted to real vector subspaces generated by integral classes, it defines a perfect pairing

(8.2) NSR×NSn−1,n−1R (X)−→R

where NSR ⊂H1,1(X,R) and NSn−1,n−1R (X)⊂Hn−1,n−1(X,R). Next, we introduce the concept of mobile curves.

64 J.-P. Demailly Applications of Pluripotential theory to Algebraic Geometry

(8.3) Definition. Let X be a smooth projective variety.

(a) One definesNE(X)⊂NSn−1,n−1R (X) to be the convex cone generated by cohomology classes of all effective curves in Hn−1,n−1(X,R).

(b) We say that C is a mobile curve if C = Ct0 is a member of an analytic family {Ct}t∈S such that S

t∈SCt = X and, as such, is a reduced irreducible 1-cycle. We define the mobile coneME(X), to be the convex cone generated by all mobile curves.

(c) If X is projective, we say that an effective 1-cycle C is a strongly mobile if we have C =µ(Ae1∩ · · · ∩Aen−1)

for suitable very ample divisors Aej on X, wheree µ: Xe →X is a modification. We let MEs(X) be the convex cone generated by all strongly mobile effective 1-cycles (notice that by taking Aej general enough these classes can be represented by reduced irreducible curves; also, by Hironaka, one could just restrict oneself to compositions of blow-ups with smooth centers).

Clearly, we have

(8.4) MEs(X)⊂ME(X)⊂NE(X)⊂NSn−1,n−1R (X).

Another simple observation is:

(8.5) Proposition. One has α·C >0 whenever {α} ∈Eand {C} ∈ME(X). In other words ENS =E∩NSR(X) is contained in the dual cone (ME(X)).

Proof. If the class {α} is represented by a closed positive current T and C = Ct0 belongs to a covering family (Ct)t∈S, it is easy to see that T|Ct is locally well defined and nonnegative as soon asCt is not contained in the set of poles of a local potential ϕof T. However, this occurs only when t belongs to a pluripolar set P ⊂S, hence fort ∈SrP we have

α·C = Z

Ct

T|Ct >0.

The following statement was first proved in [BDPP04].

(8.6) Theorem. If X is projective, the cones ENS = Eff(X) and MEs(X)are dual with respect to Serre duality, and we have MEs(X) = ME(X).

In other words, a line bundle L is pseudo-effective if (and only if) L·C > 0 for all mobile curves, i.e., L· C > 0 for every very generic curve C (not contained in a countable union of algebraic subvarieties). In fact, by definition of MEs(X), it is enough to consider only those curves C which are images of generic complete intersection of very ample divisors on some varietyXe, under a modificationµ: Xe →X. By a standard blowing-up argument, it also follows that a line bundleL on a normal Moishezon variety is pseudo-effective if and only if L·C >0 for every mobile curve C.

Chapter II, Approximation of currents and intersection theory 65

Proof. By (8.5) we have ENS ⊂ (ME(X)) and (8.4) implies (ME(X)) ⊂ (MEs(X)), therefore

(8.7) ENS⊂(MEs(X)).

If we show that ENS = (MEs(X)), we get at the same time (MEs(X)) = (ME(X)), and therefore by biduality (Hahn-Banach theorem) we will infer MEs(X) = ME(X).

Now, if the inclusion were strict in (8.7), there would be an element α ∈ ∂ENS on the boundary of ENS which is in the interior of MEs(X).

E

ENS

M

(MNS)

NSR(X) H1,1(X,R) Hn−1,n−1(X,R)

MNS

M

α−εω αα+δω ω

Γ

NNSn−1(X)

Let ω = c1(H) be an ample class. Since α ∈ ∂ENS, the class α+δω is big for every δ > 0, and since α ∈((MEs(X))) we still have α−εω ∈(MEs(X)) for ε >0 small.

Therefore

(8.8) α·Γ>εω·Γ

for every strongly mobile curve Γ, and therefore for every Γ∈MEs(X). We are going to contradict (8.8). Since α+δω is big, we have an approximate Zariski decomposition

µδ(α+δω) =Eδ+Dδ.

We pick Γ = (µδ)(Dδn−1)∈MEs(X). By the Hovanskii-Teissier concavity inequality ω·Γ>(ωn)1/n(Dδn)(n−1)/n.

On the other hand

α·Γ =α·(µδ)(Dn−1δ )

δα·Dn−1δδ(α+δω)·Dδn−1

= (Eδ+Dδ)·Dn−1δ = Dδn+Dδn−1·Eδ. By the orthogonality estimate, we find

α·Γ

ω·Γ 6 Dδn+ 20(Cω)n(Vol(α+δω)−Dnδ)1/2

n)1/n(Dδn)(n−1)/n

6C(Dδn)1/n+C′′(Vol(α+δω)−Dnδ)1/2 (Dδn)(n−1)/n .

66 J.-P. Demailly Applications of Pluripotential theory to Algebraic Geometry

However, since α ∈∂ENS, the class α cannot be big so

δ→0limDnδ = Vol(α) = 0.

We can also takeDδ to approximate Vol(α+δω) in such a way that (Vol(α+δω)−Dδn)1/2 tends to 0 much faster than Dnδ. Notice that Dnδnωn, so in fact it is enough to take

Vol(α+δω)−Dδn2n,

which gives (α·Γ)/(ω·Γ)6(C+C′′)δ. This contradicts (8.8) for δ small.

### Asymptotic cohomology functionals and Monge-Amp` ere operators

The goal of this chapter is to show that there are strong relations between certain Monge-Amp`ere integrals appearing in holomorphic Morse inequalities, and asymptotic cohomology estimates for tensor powers of holomorphic line bundles. Especially, we prove that these relations hold without restriction for projective surfaces, and in the special case of the volume, i.e. of asymptotic 0-cohomology, for all projective manifolds. These results can be seen as a partial converse to the Andreotti-Grauert vanishing theorem.

### 0. Introduction and main definitions

Throughout this chapter, X denotes a compact complex manifold, n= dimCX its complex dimension and L → X a holomorphic line bundle. In order to estimate the growth of cohomology groups, it is interesting to consider appropriate “asymptotic co-homology functions”. Following partly notation and concepts introduced by A. K¨uronya [K¨ur06, FKL07], we introduce

(0.1) Definition. LetX be a compact complex manifold and letL→X be a holomorphic line bundle.

(a) The q-th asymptotic cohomology functional is defined as bhq(X, L) := lim sup

k→+∞

n!

knhq(X, L⊗k).

(b) The q-th asymptotic holomorphic Morse sum of L is bh≤q(X, L) := lim sup

k→+∞

n!

kn X

06j6q

(−1)q−jhj(X, L⊗k).

When the lim sup’s are limits, we have the obvious relation bh≤q(X, L) = X

06j6q

(−1)q−jbhj(X, L).

68 J.-P. Demailly Applications of Pluripotential theory to Algebraic Geometry

Clearly, Definition 0.1 can also be given for a Q-line bundle L or a Q-divisor D, and in the case q = 0 one gets by (II 6.5) what is called the volume of L (see also [DEL00], [Bck02], [Laz04]):

(0.2) Vol(X, L) :=bh0(X, L) = lim sup

k→+∞

n!

knh0(X, L⊗k).

### 1. Extension of the functionals to real cohomology classes

We are going to show that the bhq functional induces a continuous map (1.1) DNSR(X)∋α 7→bhqDNS(X, α),

which is defined on the “divisorial N´eron-Severi space” DNSR(X) ⊂ HBC1,1(X,R), i.e.

the vector space spanned by real linear combinations of classes of divisors in the real Bott-Chern cohomology group of bidegree (1,1). Here HBCp,q(X,C) is defined as the quo-tient of d-closed (p, q)-forms by∂∂-exact (p, q)-forms, and there is a natural conjugation HBCp,q(X,C) → HBCq,p(X,C) which allows us to speak of real classes when q = p. Notice that HBCp,q(X,C) coincides with the usual Dolbeault cohomology group Hp,q(X,C) when X is K¨ahler, and that DNSR(X) coincides with the usual N´eron-Severi space

(1.2) NSR(X) =R⊗Q H2(X,Q)∩H1,1(X,C)

whenX is projective (the inclusion can be strict in general, e.g. on complex 2-tori which only have indefinite integral (1,1)-classes, cf. [BL04]).

For α ∈NSR(X) (resp.α ∈DNSR(X)), we set bhqNS(X, α)

resp. bhqDNS(X, α)

= lim sup

k→+∞,k1c1(L)→α

n!

knhq(X, L)

= inf

ε>0, k0>0 sup

k>k0,kk1c1(L)−αk

n!

knhq(X, L).

(1.3)

when the pair (k, L) runs overN×Pic(X), resp. over N×PicD(X) where PicD(X)⊂ Pic(X) is the subgroup generated by “divisorial line bundles”, i.e. line bundles of the form OX(D). Similar definitions can be given for the Morse sum functionals bh6qNS(X, α) and bh6qDNS(X, α). Clearly bh6qDNS(X, α) 6 bh6qNS(X, α) on DNSR(X), but we do not know at this point whether this is always an equality. From the very definition, bhqNS , bh6NSq (and likewise bhqDNS , bh6qDNS) are upper semi-continuous functions which are positively homogeneous of degree n, namely

(1.4) bhqNS(X, λα) =λnbhqNS(X, α)

for allα ∈NSR(X) and all λ>0. Notice thatbhqNS(X, α) andbh6NSq(X, α) are always finite thanks to holomorphic Morse inequalities (see below).

(1.5) Proposition.

In document Explicit Exchange Interaction and Decoherence Dynamics in One-Dimensional Quantum Systems (Page 81-86)