Factorization of the identity R. Lechner Joint work with N. J. - PowerPoint PPT Presentation

Factorization of the identity R. Lechner Joint work with N. J. Laustsen and P. F. X. Müller J. Kepler University, Linz Bedlewo, July 19, 2016

Overview 1 Operators with large diagonal 2 Mixed-norm Hardy spaces H p ( H q )

Overview 1 Operators with large diagonal 2 Mixed-norm Hardy spaces H p ( H q )

� � � A description of the problem class • Let X be a Banach space and T : X → X a linear operator. Find conditions on X and T such that the identity Id on X factors through T i.e. Id X X � E �� P � ≤ C. E P � X X T • The problem has finite dimensional (quantitative) and infinite dimensional (qualitative) aspects. • Classical examples for X include: ℓ p (Pełczyński), ℓ ∞ (Lindenstrauss), L 1 (Enflo-Starbird), L p (Johnson-Maurey-Schechtman-Tzafriri), ℓ p n (Bourgain-Tzafriri). • Two parameters: L p ( L q ) , 1 < p, q < ∞ (Capon).

� � � A description of the problem class • Let X be a Banach space and T : X → X a linear operator. Find conditions on X and T such that the identity Id on X factors through T i.e. Id X X � E �� P � ≤ C. E P � X X T • The problem has finite dimensional (quantitative) and infinite dimensional (qualitative) aspects. • Classical examples for X include: ℓ p (Pełczyński), ℓ ∞ (Lindenstrauss), L 1 (Enflo-Starbird), L p (Johnson-Maurey-Schechtman-Tzafriri), ℓ p n (Bourgain-Tzafriri). • Two parameters: L p ( L q ) , 1 < p, q < ∞ (Capon).

� � � A description of the problem class • Let X be a Banach space and T : X → X a linear operator. Find conditions on X and T such that the identity Id on X factors through T i.e. Id X X � E �� P � ≤ C. E P � X X T • The problem has finite dimensional (quantitative) and infinite dimensional (qualitative) aspects. • Classical examples for X include: ℓ p (Pełczyński), ℓ ∞ (Lindenstrauss), L 1 (Enflo-Starbird), L p (Johnson-Maurey-Schechtman-Tzafriri), ℓ p n (Bourgain-Tzafriri). • Two parameters: L p ( L q ) , 1 < p, q < ∞ (Capon).

� � � A description of the problem class • Let X be a Banach space and T : X → X a linear operator. Find conditions on X and T such that the identity Id on X factors through T i.e. Id X X � E �� P � ≤ C. E P � X X T • The problem has finite dimensional (quantitative) and infinite dimensional (qualitative) aspects. • Classical examples for X include: ℓ p (Pełczyński), ℓ ∞ (Lindenstrauss), L 1 (Enflo-Starbird), L p (Johnson-Maurey-Schechtman-Tzafriri), ℓ p n (Bourgain-Tzafriri). • Two parameters: L p ( L q ) , 1 < p, q < ∞ (Capon).

� � � A description of the problem class • Let X be a Banach space and T : X → X a linear operator. Find conditions on X and T such that the identity Id on X factors through T i.e. Id X X � E �� P � ≤ C. E P � X X T • The problem has finite dimensional (quantitative) and infinite dimensional (qualitative) aspects. • Classical examples for X include: ℓ p (Pełczyński), ℓ ∞ (Lindenstrauss), L 1 (Enflo-Starbird), L p (Johnson-Maurey-Schechtman-Tzafriri), ℓ p n (Bourgain-Tzafriri). • Two parameters: L p ( L q ) , 1 < p, q < ∞ (Capon).

� � � A description of the problem class • Let X be a Banach space and T : X → X a linear operator. Find conditions on X and T such that the identity Id on X factors through T i.e. Id X X � E �� P � ≤ C. E P � X X T • The problem has finite dimensional (quantitative) and infinite dimensional (qualitative) aspects. • Classical examples for X include: ℓ p (Pełczyński), ℓ ∞ (Lindenstrauss), L 1 (Enflo-Starbird), L p (Johnson-Maurey-Schechtman-Tzafriri), ℓ p n (Bourgain-Tzafriri). • Two parameters: L p ( L q ) , 1 < p, q < ∞ (Capon).

� � � Operators with large diagonal • Let X be a Banach space and T : X → X a linear operator. n ∈ X ∗ be so • Suppose that X has an unconditional basis ( b n ) , and let b ∗ that � b n , b ∗ m � = 0 , m � = n , and � b n , b ∗ n � = 1 . • We say that T has large diagonal (relative to ( b n ) ) if inf n ∈ N |� Tb n , b ∗ n �| > 0 . • For many Banach spaces X we know that the identity factors through operators T with large diagonal, i.e. Id X X � E �� P � ≤ C. E P � X X T • X = ℓ p with the unit vector basis (Pełczyński) • X = L p (Andrew), X = L p ( L q ) (Capon) with the Haar basis

� � � Operators with large diagonal • Let X be a Banach space and T : X → X a linear operator. n ∈ X ∗ be so • Suppose that X has an unconditional basis ( b n ) , and let b ∗ that � b n , b ∗ m � = 0 , m � = n , and � b n , b ∗ n � = 1 . • We say that T has large diagonal (relative to ( b n ) ) if inf n ∈ N |� Tb n , b ∗ n �| > 0 . • For many Banach spaces X we know that the identity factors through operators T with large diagonal, i.e. Id X X � E �� P � ≤ C. E P � X X T • X = ℓ p with the unit vector basis (Pełczyński) • X = L p (Andrew), X = L p ( L q ) (Capon) with the Haar basis

� � � Operators with large diagonal • Let X be a Banach space and T : X → X a linear operator. n ∈ X ∗ be so • Suppose that X has an unconditional basis ( b n ) , and let b ∗ that � b n , b ∗ m � = 0 , m � = n , and � b n , b ∗ n � = 1 . • We say that T has large diagonal (relative to ( b n ) ) if inf n ∈ N |� Tb n , b ∗ n �| > 0 . • For many Banach spaces X we know that the identity factors through operators T with large diagonal, i.e. Id X X � E �� P � ≤ C. E P � X X T • X = ℓ p with the unit vector basis (Pełczyński) • X = L p (Andrew), X = L p ( L q ) (Capon) with the Haar basis

� � � Operators with large diagonal • Let X be a Banach space and T : X → X a linear operator. n ∈ X ∗ be so • Suppose that X has an unconditional basis ( b n ) , and let b ∗ that � b n , b ∗ m � = 0 , m � = n , and � b n , b ∗ n � = 1 . • We say that T has large diagonal (relative to ( b n ) ) if inf n ∈ N |� Tb n , b ∗ n �| > 0 . • For many Banach spaces X we know that the identity factors through operators T with large diagonal, i.e. Id X X � E �� P � ≤ C. E P � X X T • X = ℓ p with the unit vector basis (Pełczyński) • X = L p (Andrew), X = L p ( L q ) (Capon) with the Haar basis

� � � Operators with large diagonal • Let X be a Banach space and T : X → X a linear operator. n ∈ X ∗ be so • Suppose that X has an unconditional basis ( b n ) , and let b ∗ that � b n , b ∗ m � = 0 , m � = n , and � b n , b ∗ n � = 1 . • We say that T has large diagonal (relative to ( b n ) ) if inf n ∈ N |� Tb n , b ∗ n �| > 0 . • For many Banach spaces X we know that the identity factors through operators T with large diagonal, i.e. Id X X � E �� P � ≤ C. E P � X X T • X = ℓ p with the unit vector basis (Pełczyński) • X = L p (Andrew), X = L p ( L q ) (Capon) with the Haar basis

� � � Operators with large diagonal • Let X be a Banach space and T : X → X a linear operator. n ∈ X ∗ be so • Suppose that X has an unconditional basis ( b n ) , and let b ∗ that � b n , b ∗ m � = 0 , m � = n , and � b n , b ∗ n � = 1 . • We say that T has large diagonal (relative to ( b n ) ) if inf n ∈ N |� Tb n , b ∗ n �| > 0 . • For many Banach spaces X we know that the identity factors through operators T with large diagonal, i.e. Id X X � E �� P � ≤ C. E P � X X T • X = ℓ p with the unit vector basis (Pełczyński) • X = L p (Andrew), X = L p ( L q ) (Capon) with the Haar basis

� � � Operators with large diagonal • Let X be a Banach space and T : X → X a linear operator. n ∈ X ∗ be so • Suppose that X has an unconditional basis ( b n ) , and let b ∗ that � b n , b ∗ m � = 0 , m � = n , and � b n , b ∗ n � = 1 . • We say that T has large diagonal (relative to ( b n ) ) if inf n ∈ N |� Tb n , b ∗ n �| > 0 . • For many Banach spaces X we know that the identity factors through operators T with large diagonal, i.e. Id X X � E �� P � ≤ C. E P � X X T • X = ℓ p with the unit vector basis (Pełczyński) • X = L p (Andrew), X = L p ( L q ) (Capon) with the Haar basis

Can the identity operator on X be factored through each operator on X with large diagonal for all Banach spaces X with an unconditional basis? Answer: Theorem (N. J. Laustsen, R. L., P. F. X. Müller) There is an operator T on a Banach space X with an unconditional basis such that T has large diagonal, but the identity operator on X does not factor through T . Main ingredients for the proof: • X is Gowers’ space with an unconditional basis (Gowers–Maurey). • Fredholm theory. Theorem (N. J. Laustsen, R. L., P. F. X. Müller) The identity on mixed-norm Hardy spaces H p ( H q ) , 1 ≤ p, q < ∞ , factors through any operator T with large diagonal relative to the bi–parameter Haar basis. ( 1 < p, q < ∞ = Capon).