Some new results on an old controversy: is perturbation theory the correct asymptotic expansion in nonabelian models?

Several years ago it was found that perturbation theory for two-dimensional O(N) models depends on boundary conditions even after the infinite volume limit has been taken termwise, provided $N>2$. There ensued a discussion whether the boundary conditions introduced to show this phenomenon were somehow anomalous and there was a class of `reasonable' boundary conditions not suffering from this ambiguity. Here we present the results of some computations that may be interpreted as giving some support for the correctness of perturbation theory with conventional boundary conditions; however the fundamental underlying question of the correctness of perturbation theory in these models and in particular the perturbative $\beta$ function remain challenging problems of mathematical physics.Comment: 4 pages, 3 figure

Unsecured cloud object storage: a primer on prevalence & mitigation techniques

Cloud storage services are gaining popularity due to their flexibility, elasticity, and support to a growing need of data storage at a very accessible price, around $0.02 per GigaByte (GB) each month. Thus, more and more companies and users are relying on cloud providers to store their files. This project will study the four main cloud storage providers: Amazon Web Services (AWS), Google Cloud, IBM Cloud and Microsoft's Azure. After understanding how each cloud provider works, a scanning tool was developed to search all four providers for public objects. To make sure companies and administrators understand the utility of the tool, privacy settings and permissions are commented, also commenting how and why previous data leakage occurred. The tool has been tested and the results obtained show that there is a lot of sensitive data available to the public. With the help of the developed tool, penetration testers can help companies by making sure that no sensitive data is publicly available

La información como problema observacional

El concepto de informacion, antes que designar una magnitud observable, implica un modelo de cognicion que presupone una doble fractura ontologica: entre el sujeto y el mundo, de un lado, y entre conocimiento y accion, del otro. Una aproximacion genealogica a la idea de informacion como encrucijada a la vez epistemologica y cognitiva pone de relieve la centralidad de la teoria de la observacion en la resolucion de sus contradicciones. La naturaleza recursiva de la observación inherente a la logica informacional hace especialmente pertinente la reflexion constructivista como parte ineludible de una revision epistemologica de los conceptos de informacion y comunicacion.By attempting to fix an observable magnitude, the concept of information involves a cognitive model that enables a double ontological rupture: between subject and world, on one side, and between cognition and action, on the other side. A genealogical approach to information as a simultaneously epistemological and cognitive crossroad highlights the centrality of observation theory in the resolution of its contradictions. The recursive nature of observation inherent to informational logics makes constructivist assumptions especially relevant as a key contribution for an epistemological revision of the ideas of information and communication

Explicit tensor network representation for the ground states of string-net models

The structure of string-net lattice models, relevant as examples of topological phases, leads to a remarkably simple way of expressing their ground states as a tensor network constructed from the basic data of the underlying tensor categories. The construction highlights the importance of the fat lattice to understand these models.Comment: 5 pages, pdf figure

A hierarchy of topological tensor network states

We present a hierarchy of quantum many-body states among which many examples of topological order can be identified by construction. We define these states in terms of a general, basis-independent framework of tensor networks based on the algebraic setting of finite-dimensional Hopf C*-algebras. At the top of the hierarchy we identify ground states of new topological lattice models extending Kitaev's quantum double models [26]. For these states we exhibit the mechanism responsible for their non-zero topological entanglement entropy by constructing a renormalization group flow. Furthermore it is shown that those states of the hierarchy associated with Kitaev's original quantum double models are related to each other by the condensation of topological charges. We conjecture that charge condensation is the physical mechanism underlying the hierarchy in general.Comment: 61 page

Perturbation theory for O(3) topological charge correlators

To check the consistency of positivity requirements for the two-point correlation function of the topological charge density, which were identified in a previous paper, we are computing perturbatively this two-point correlation function in the two-dimensional O(3) model. We find that at the one-loop level these requirements are fulfilled.Comment: v1: 27 pages, 7 figures; v2: 28 pages, 8 figures, matches published versio

Reflections on the development of agro-food economics

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Experience, Identity and Social Complexity: Notes for a Constructivist Perspective on Media System

El texto considera los puntos débiles de la descripción luhmanniana del sistema de los media a la luz de la intersección entre estudios culturales y pensamiento sistémico y argumenta la relevancia del código interés/nointerés en los acoplamientos operacioThis paper considers the weak points of luhmann s description of the mass media system, in the light of the intersection between cultural studies and systemic thinking, as well as showing the relevance of the interest/non-interest code in the operationa