A mixing operator TT for which the tuple (T,T2)(T, T^2) is not disjoint transitive.

Using a result from ergodic Ramsey theory, we answer a question posed by Bes, Martin, Peris and Shkarin by showing a mixing operator $T$ on a Hilbert space such that the tuple $(T, T^2)$ is not disjoint transitive

Recurrence in Linear Dynamics

A bounded and linear operator is said to be hypercyclic if there exists a vector such that its orbit under the action of the operator is dense. The first example of a hypercyclic operator on a Banach space was given in 1969 by Rolewicz who showed that if B is the unweighted unilateral backward shift on l 2 , then λB is hypercyclic if and only if |λ| > 1. Among its features, we can mention for example that finite-dimensional spaces cannot support hypercyclic operators, proved by Kitai. On the other hand, several people have shown in different contexts, in the Hilbert space frame, that the set of hypercyclic vectors for a hypercyclic operator is a Gδ dense set. This thesis is divided into four chapters. In the first one, we give some preliminaries by mentioning some definitions and known results that will be of great help later. In chapter 2, we introduce a refinement of the notion of hypercyclicity, relative to the set N(U, V ) = {n ∈ N : T −nU ∩ V 6= ∅} when belonging to a certain collection F of subsets of N, namely a bounded and linear operator T is called F-operator if N(U, V ) ∈ F, for any pair of non-empty open sets U, V in X. First, we do an analysis of the hierarchy established between F-operators, whenever F covers those families mostly studied in Ramsey theory. Second, we investigate which kind of properties of density can have the sets N(x, U) = {n ∈ N : T nx ∈ U} and N(U, V ) for a given hypercyclic operator, and classify the hypercyclic operators accordingly to these properties. In chapter three, we introduce the following notion: an operator T on X satisfies property PF if for any U non-empty open set in X, there exists x ∈ X such that N(x, U) ∈ F. Let BD the collection of sets in N with positive upper Banach density. We generalize the main result of a paper due to Costakis and Parissis using a strong result of Bergelson and Mccutcheon in the vein of Szemerédi’s theorem, leading us to a characterization of those operators satisfying property PBD. It turns out that operators having property PBD satisfy a kind of recurrence described in terms of essential idempotents of βN (the Stone-Čech compactification of N). We will discuss the case of weighted backward shifts satisfying property PBD. On the other hand, as a consequence we obtain a characterization of reiteratively hypercyclic operators, i.e. operators for which there exists x ∈ X such that for any U non-empty open set in X, the set N(x, U) ∈ BD. The fourth chapter focuses on a refinement of the notion of disjoint hypercyclicity. We extend a result of Bès, Martin, Peris and Shkarin by stating: Bw is F-weighted backward shift if and only if (Bw, . . . , Br w) is d-F, for any r ∈ N, where F runs along some filters containing strictly the family of cofi- nite sets, which are frequently used in Ramsey theory. On the other hand, we point out that this phenomenon does not occur beyond the weighted shift frame by showing a mixing linear operator T on a Hilbert space such that the tuple (T, T2 ) is not d-syndetic. We also, investigate the relationship between reiteratively hypercyclic operators and d-F tuples, for filters F contained in the family of syndetic sets. Finally, we examine conditions to impose in order to get reiterative hypercyclicity from syndeticity in the weighted shift frame.Puig De Dios, Y. (2014). Recurrence in Linear Dynamics [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/48473TESI

Strong transitivity properties for operators

[EN] Given a Furstenberg family F of subsets of N, an operator T on a topological vector space X is called F-transitive provided for each non-empty open subsets U, V of X the set {n is an element of Z(+) : T-n (U) boolean AND V not equal empty set} belongs to We classify the topologically transitive operators with a hierarchy of F-transitive subclasses by considering families F that are determined by various notions of largeness and density in Z(+). (C) 2018 Elsevier Inc. All rights reserved.The first, the second, and the third authors were partially supported by MINECO, Project MTM2016-75963-P. The third author was also supported by Generalitat Valenciana, Project PROMETEO/2017/102. We want to thank the referee whose careful comments produced an improvement in the presentation of the paper.Bès, JP.; Menet, Q.; Peris Manguillot, A.; Puig-De Dios, Y. (2019). Strong transitivity properties for operators. Journal of Differential Equations. 266(2-3):1313-1337. https://doi.org/10.1016/j.jde.2018.07.076S131313372662-

Symmetric tensor powers of graphs

The symmetric tensor power of graphs is introduced and its fundamental properties are explored. A wide range of intriguing phenomena occur when one considers symmetric tensor powers of familiar graphs. A host of open questions are presented, hoping to spur future research