Regular Holomorphic Functions On Complex Banach Lattices

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Regular Holomorphic Functions on ComplexBanach LatticesRay RyanNational University of Ireland GalwayWorkshop on Infinite Dimensional AnalysisBuenos Aires 20141 / 21

1. Holomorphy — some of the historyIHilbert (1909): Holomorphic functions on CN defined locallyby monomial expansions:Xf(z) cα (z a)αα2 / 21

1. Holomorphy — some of the historyIHilbert (1909): Holomorphic functions on CN defined locallyby monomial expansions:Xf(z) cα (z a)ααIFréchet, Gâteaux, Michael, Taylor,. . . : Power series ofhomogeneous polynomials:Xf(z) Pn (z a)nin a neighbourhood of a.Pn : (bounded) n-homogeneous polynomials.2 / 21

1. Holomorphy — some of the historyIHilbert (1909): Holomorphic functions on CN defined locallyby monomial expansions:Xf(z) cα (z a)ααIFréchet, Gâteaux, Michael, Taylor,. . . : Power series ofhomogeneous polynomials:Xf(z) Pn (z a)nIin a neighbourhood of a.Pn : (bounded) n-homogeneous polynomials.Grothendieck, Nachbin, Gupta (1950’s and 60’s): Duality interms of nuclear functions/tensor products: 0P(n E 0 ) PN (n E)(subject to AP)2 / 21

IBoland, Dineen (1970’s): Holomorphic functions on nuclearlocally convex spaces. For suitable nuclear spaces withbasis, the monomials are a basis for the space of holomorphicfunctions.3 / 21

IBoland, Dineen (1970’s): Holomorphic functions on nuclearlocally convex spaces. For suitable nuclear spaces withbasis, the monomials are a basis for the space of holomorphicfunctions.IMatos, Nachbin (1980’s and 90’s): Monomial expansions forholomorphic functions on a Banach space with unconditionalbasis.Hν (E): the space of holomorphic functions representablelocally by unconditionally convergent monomial expansions.3 / 21

IBoland, Dineen (1970’s): Holomorphic functions on nuclearlocally convex spaces. For suitable nuclear spaces withbasis, the monomials are a basis for the space of holomorphicfunctions.IMatos, Nachbin (1980’s and 90’s): Monomial expansions forholomorphic functions on a Banach space with unconditionalbasis.Hν (E): the space of holomorphic functions representablelocally by unconditionally convergent monomial expansions.IDefant, Dı́az, Garcı́a, Kalton, Maestre (2001 and 2005)proved Dineen’s conjecture: if E is a Banach space and n 2,then P(n E) has an unconditional basis if and only if E is finitedimensional.3 / 21

2. The Matos-Nachbin Holomorphy TypeE: a Banach space with unconditional Schauder basis (ej ).Every P P(n E) has a monomial expansion:XP(z) A(z, . . . , z), z zj ejjP(z) Xcα z α α nBut this expansion is only conditionally convergent in general.4 / 21

2. The Matos-Nachbin Holomorphy TypeE: a Banach space with unconditional Schauder basis (ej ).Every P P(n E) has a monomial expansion:XP(z) A(z, . . . , z), z zj ejjP(z) Xcα z α α nBut this expansion is only conditionally convergent in general.Pν (n E): the subspace of polynomials for which the monomialexpansion is unconditionally convergent at every point.4 / 21

If P Pν (n E), thenP̃(z) : X cα zα α nalso belongs to Pν (n E). A norm is defined on Pν (n E) byν(P) : kP̃k supX cα zα : kzk 6 1Pν (n E) is a Banach space with this norm.5 / 21

If P Pν (n E), thenXP̃(z) : cα zα α nalso belongs to Pν (n E). A norm is defined on Pν (n E) byν(P) : kP̃k supX cα zα : kzk 6 1Pν (n E) is a Banach space with this norm.PN (n E) Pν (n E) P(n E)Extreme cases:1. E c0 : Pν (n E) PN (n E)2. E 1 : Pν (n E) P(n E)(with equivalent norms in each case.)5 / 21

Holomorphic functions.In the complex case, we have a holomorphy type:for P Pν (n E) and z E, 1 νd̂k P(z) 6 4n kzkn k ν(P)k!6 / 21

Holomorphic functions.In the complex case, we have a holomorphy type:for P Pν (n E) and z E, 1 νd̂k P(z) 6 4n kzkn k ν(P)k!Theorem (Matos-Nachbin): A holomorphic function f on adomain U E belongs to Hν (U) if and only if f is representablelocally in U by unconditionally pointwise convergent monomialexpansions.6 / 21

Matos-Nachbin (1992):E a complex Banach space with an unconditional basis. Let U be aReinhardt domain in E containing 0.the following are equivalent:1. U is the domain of convergence of a multiple power seriesaround 0.2. U is modularly decreasing and logarithmically convex.3. U is the domain of existence of some f Hν (()U).4. U is a domain of ν-holomorphy.5. U is a domain of holomorphy.6. U is pseudo-convex.7 / 21

3. RegularityRiesz spaces (vector lattices):A real vector space E with a compatible lattice structure:x, y E x y,x yFor every x E,x x x wherex x 0,x ( x) 0Absolute values: x : x ( x) x x Normed Lattice: Riesz space with a norm satisfyingk x k kxkDedekind complete: every order bounded set has a supremum.8 / 21

Regular operatorsAn operator T : E F between Riesz spaces is regular if it can bewritten as the difference of two positive operators.9 / 21

Regular operatorsAn operator T : E F between Riesz spaces is regular if it can bewritten as the difference of two positive operators.If F is Dedekind complete, then regularity of an operator T isequivalent to order boundedness and in this case, the spaceLr (E; F) of regular operators is a Dedekind complete Riesz space. T (x) sup{ T (y) : y 6 x} for x E T (x) 6 T ( x ) xOrder dual:E Lr (E; R)9 / 21

Banach Lattices10 / 21

Banach Lattices1. Regular operators are bounded (Automatic continuity ofpositive operators.)10 / 21

Banach Lattices1. Regular operators are bounded (Automatic continuity ofpositive operators.)2. The space of regular operators is a Banach lattice with theregular norm:kT kr : k T k10 / 21

Banach Lattices1. Regular operators are bounded (Automatic continuity ofpositive operators.)2. The space of regular operators is a Banach lattice with theregular norm:kT kr : k T k3. E E 0 , the Banach dual, with equality of norms.10 / 21

Banach Lattices1. Regular operators are bounded (Automatic continuity ofpositive operators.)2. The space of regular operators is a Banach lattice with theregular norm:kT kr : k T k3. E E 0 , the Banach dual, with equality of norms.4. Principal ideals: for u 0, the principal idealEu : {x E : x 6 ku for some k N}with norm given by the Minkowski functional of the orderinterval [ u, u] is an AM-space with unit. It is latticeisometric to a C(K) space.Eu C(K)10 / 21

Regular polynomials on Banach latticesMultilinear forms:A L(n E1 , E2 , . . . , En ) is positive ifA(x1 , . . . , xn ) 0for all x1 , . . . , xn 0and A is regular if it is the difference of two positive forms.11 / 21

Regular polynomials on Banach latticesMultilinear forms:A L(n E1 , E2 , . . . , En ) is positive ifA(x1 , . . . , xn ) 0for all x1 , . . . , xn 0and A is regular if it is the difference of two positive forms.Lr (n E1 , . . . , En ): the Banach lattice of regular n-linear forms withthe regular norm. Lr (E1 , Lr (n 1 E2 , . . . , En ))Lr (n E1 , . . . , En ) 11 / 21

Regular polynomials on Banach latticesMultilinear forms:A L(n E1 , E2 , . . . , En ) is positive ifA(x1 , . . . , xn ) 0for all x1 , . . . , xn 0and A is regular if it is the difference of two positive forms.Lr (n E1 , . . . , En ): the Banach lattice of regular n-linear forms withthe regular norm. Lr (E1 , Lr (n 1 E2 , . . . , En ))Lr (n E1 , . . . , En ) Homogeneous polynomials:The n-homogeneous polynomial P Â is positive if A is positive.Pr (n E): the Banach lattice of regular n-homogeneous polynomialswith the regular normkPkr : k P k11 / 21

If P P(n E) is positive, then1. P(x) 0 for every x 0.2. P is monotone on the positive cone:if 0 6 x 6 ythenP(x) 6 P(y)12 / 21

If P P(n E) is positive, then1. P(x) 0 for every x 0.2. P is monotone on the positive cone:if 0 6 x 6 ythenP(x) 6 P(y)But for n 3, these conditions are not sufficient to ensure P 0.12 / 21

If P P(n E) is positive, then1. P(x) 0 for every x 0.2. P is monotone on the positive cone:if 0 6 x 6 ythenP(x) 6 P(y)But for n 3, these conditions are not sufficient to ensure P 0.Absolute value: P(x) 6 P ( x ) x E P is the smallest positive n-homogeneous polynomial satisfyingthis.12 / 21

Every Banach space with a 1-unconditional basis is a Banachlattice,P where the lattice operations are defined coordinatewise: ifx xj ej , thenX x xj ejj13 / 21

Every Banach space with a 1-unconditional basis is a Banachlattice,P where the lattice operations are defined coordinatewise: ifx xj ej , thenX x xj ejjGrecu–Ryan (2004): If E is a Banach space with a1-unconditional basis, thenPν (n E) Pr (n E)with equality of norms.13 / 21

4. Tensor Products14 / 21

4. Tensor ProductsThe Fremlin Tensor Product (1972)For (archimedean) Riesz spaces E and F, the Fremlin tensorproduct E F linearizes regular bilinear forms on E F.14 / 21

4. Tensor ProductsThe Fremlin Tensor Product (1972)For (archimedean) Riesz spaces E and F, the Fremlin tensorproduct E F linearizes regular bilinear forms on E F.The Fremlin-Wittstock Banach Lattice Tensor Products π F and E ε F: Banach lattice versions of the projective andE injective Banach space tensor products.14 / 21

4. Tensor ProductsThe Fremlin Tensor Product (1972)For (archimedean) Riesz spaces E and F, the Fremlin tensorproduct E F linearizes regular bilinear forms on E F.The Fremlin-Wittstock Banach Lattice Tensor Products π F and E ε F: Banach lattice versions of the projective andE injective Banach space tensor products.Perez-Villanueva (2005):None of Grothendieck’s 14 natural tensor norms are Banach latticenorms.14 / 21

4. Tensor ProductsThe Fremlin Tensor Product (1972)For (archimedean) Riesz spaces E and F, the Fremlin tensorproduct E F linearizes regular bilinear forms on E F.The Fremlin-Wittstock Banach Lattice Tensor Products π F and E ε F: Banach lattice versions of the projective andE injective Banach space tensor products.Perez-Villanueva (2005):None of Grothendieck’s 14 natural tensor norms are Banach latticenorms.Labuschagne (2004): If E and F are Banach lattices and α is areasonable crossnorm on E F, then there is a reasonable α F is a Banach lattice withcrossnorm α on E F such that E respect to the ordering induced by the α -closure of the Fremlincone of E F.14 / 21

Regular multilinear forms on C(K) spaces15 / 21

Regular multilinear forms on C(K) spaces π C(L) C(K) ε C(L)C(K) with equality of norms.15 / 21

Regular multilinear forms on C(K) spaces π C(L) C(K) ε C(L)C(K) with equality of norms.Theorem (Fremlin): Every regular multilinear form on a productof C(K) spaces is integral.15 / 21

Regular multilinear forms on C(K) spaces π C(L) C(K) ε C(L)C(K) with equality of norms.Theorem (Fremlin): Every regular multilinear form on a productof C(K) spaces is integral.Linearizing regular polynomialsLoane (2007) : Construction of a symmetric n-fold Fremlintensor product satisfying O 0E Pr (n E)n, π ,sfor Banach lattices E.15 / 21

5. Complex Banach LatticesMittelmeyer-Wolff (1974) Axiomatization:E a complex vector space, with a function m : E R , satisfying1. m(λx) λ m(x);2. m(m(m(x) m(y)) m(x y)) m(x) m(y) m(x y);3. m(m(y) km(x)) m(y) km(x) k 0 implies x 0;4. E is the R-linear span of m(E).This structure is called a Complex Riesz Space. E is thealgebraic complexification of the real vector space ER m(E) andthis space has a vector lattice structure with m as absolute value.16 / 21

The Krivine Functional Calculus for Banach LatticesFix x1 , . . . , xn E.Let Cn be the vector lattice of all continuous, positivelyhomogeneous real functions on Rn , withkfk sup{ f(t1 , . . . , tn ) : t1 · · · tn 1}17 / 21

The Krivine Functional Calculus for Banach LatticesFix x1 , . . . , xn E.Let Cn be the vector lattice of all continuous, positivelyhomogeneous real functions on Rn , withkfk sup{ f(t1 , . . . , tn ) : t1 · · · tn 1}There exists a unique mapτ : Cn EsatisfyingIτ(tj ) xj for each j 1, . . . , n.Iτ is linear and preserves the lattice operations.Ikτ(f)k 6 kfk x1 · · · xn .17 / 21

Complex Banach Lattices:For z x iy EC , the modulus is defined byq z x 2 y 2 sup x cos θ y sin θ06θ62πEC is a Banach space with the normkzk k z k18 / 21

6. Regular HolomorphyLet E be a complex Banach lattice. The spaces of regularhomogeneous polynomials form a holomorphy type, with acorresponding space Hr (U) of regular holomorphic functions foreach domain U in E.19 / 21

6. Regular HolomorphyLet E be a complex Banach lattice. The spaces of regularhomogeneous polynomials form a holomorphy type, with acorresponding space Hr (U) of regular holomorphic functions foreach domain U in E.PDefinition: A power series n Pn of n-homogeneouspolynomials on E is regularly convergent at z E if each Pn isregular andX Pn ( z ) n19 / 21

6. Regular HolomorphyLet E be a complex Banach lattice. The spaces of regularhomogeneous polynomials form a holomorphy type, with acorresponding space Hr (U) of regular holomorphic functions foreach domain U in E.PDefinition: A power series n Pn of n-homogeneouspolynomials on E is regularly convergent at z E if each Pn isregular andX Pn ( z ) nTheorem: f H(U) is a regular holomorphic function if andonly if f is representable locally in U by regularly pointwiseconvergent power series.19 / 21

Properties of the domain of regular convergencePLet n Pn be a power series whose terms are all regular. Let Dbe the set of points at which the series is regularly convergent.20 / 21

Properties of the domain of regular convergencePLet n Pn be a power series whose terms are all regular. Let Dbe the set of points at which the series is regularly convergent.D is a solid set: if z D and w 6 z , then w D.20 / 21

Properties of the domain of regular convergencePLet n Pn be a power series whose terms are all regular. Let Dbe the set of points at which the series is regularly convergent.D is a solid set: if z D and w 6 z , then w D.The finite dimensional case:When E Ck , the domain of convergence is logarithmicallyconvex:if z, w D, then z θ w 1 θ D for every θ (0, 1)20 / 21

A Hölder Inequality for homogeneous polynomials:Let P be a regular homogeneous polynomial on the (real orcomplex) Banach lattice E and let a, b be positive elements of E.Then θ 1 θP(aθ b1 θ ) 6 P (a) P (b)for every θ (0, 1).Proof:P restricts to a regular polynomial on the principal ideal generatedby u a b.By Fremlin’s theorem, P is an integral polynomial on En C(K).Apply the Hölder inequality.21 / 21

A Hölder Inequality for homogeneous polynomials:Let P be a regular homogeneous polynomial on the (real orcomplex) Banach lattice E and let a, b be positive elements of E.Then θ 1 θP(aθ b1 θ ) 6 P (a) P (b)for every θ (0, 1).Proof:P restricts to a regular polynomial on the principal ideal generatedby u a b.By Fremlin’s theorem, P is an integral polynomial on En C(K).Apply the Hölder inequality.Corollary: The domain of regular convergence of a power seriesof regular homogeneous polynomials is logarithmically convex.21 / 21

terms of nuclear functions/tensor products: P(nE0) P N(nE) 0 (subject to AP) 2/21. I Boland, Dineen (1970’s): Holomorphic functions on nuclear locally convex spaces. For suitable nuclear spaces with basis, the mono

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