Can (Electric-Magnetic) Duality Be Gauged?

There exists a formulation of the Maxwell theory in terms of two vector potentials, one electric and one magnetic. The action is then manifestly invariant under electric-magnetic duality transformations, which are rotations in the two-dimensional internal space of the two potentials, and local. We ask the question: can duality be gauged? The only known and battled-tested method of accomplishing the gauging is the Noether procedure. In its decanted form, it amounts to turn on the coupling by deforming the abelian gauge group of the free theory, out of whose curvatures the action is built, into a non-abelian group which becomes the gauge group of the resulting theory. In this article, we show that the method cannot be successfully implemented for electric-magnetic duality. We thus conclude that, unless a radically new idea is introduced, electric-magnetic duality cannot be gauged. The implication of this result for supergravity is briefly discussed.Comment: Some minor typos correcte

Narrowband delay tolerant protocols for WSN applications. Characterization and selection guide

This article focuses on delay tolerant protocols for Wireless Sensor Network (WSN) applications, considering both established and new protocols. We obtained a comparison of their characteristics by implementing all of them on an original platform for network simulation, and by testing their behavior on a common test-bench. Thereafter, matching the requirements linked to each application with the performances achieved in the test-bench, allowed us to define an application oriented protocol selection guide

Dynamics over Signed Networks

A signed network is a network with each link associated with a positive or negative sign. Models for nodes interacting over such signed networks, where two different types of interactions take place along the positive and negative links, respectively, arise from various biological, social, political, and economic systems. As modifications to the conventional DeGroot dynamics for positive links, two basic types of negative interactions along negative links, namely the opposing rule and the repelling rule, have been proposed and studied in the literature. This paper reviews a few fundamental convergence results for such dynamics over deterministic or random signed networks under a unified algebraic-graphical method. We show that a systematic tool of studying node state evolution over signed networks can be obtained utilizing generalized Perron-Frobenius theory, graph theory, and elementary algebraic recursions.Comment: In press, SIAM Revie

First-Principles Modeling of Pt/LaAlO3/SrTiO3 Capacitors Under an External Bias Potential

We study the electrical properties of Pt/LaAlO3/SrTiO3 capacitors under the action of an external bias potential, using first-principles simulations performed at constrained electric displacement field. A complete set of band diagrams, together with the relevant electrical characteristics (capacitance and built-in fields), are determined as a function of LaAlO3 thickness and the applied potential.We find that the internal field in LaAlO3 monotonically decreases with increasing thickness; hence, the occurrence of spontaneous Zener tunneling is ruled out in this system.We discuss the implications of our results in the light of recent experimental observations on biased LaAlO3/SrTiO3 junctions involving metallic top electrodes.Comment: 5 pages, 4 figure

Illiquid Assets and Optimal Portfolio Choice

The presence of illiquid assets, such as human wealth or a family owned business, complicates the problem of portfolio choice. This paper is concerned with the problem of optimal asset allocation and consumption in a continuous time model when one asset cannot be traded. This illiquid asset, which depends on an uninsurable source of risk, provides a liquid dividend. In the case of human capital we can think about this dividend as labor income. The agent is endowed with a given amount of the illiquid asset and with some liquid wealth which can be allocated in a market where there is a risky and a riskless asset. The main point of the paper is that the optimal allocations to the two liquid assets and consumption will critically depend on the endowment and characteristics of the illiquid asset, in addition to the preferences and to the liquid holdings held by the agent. We provide what we believe to be the first analytical solution to this problem when the agent has power utility of consumption and terminal wealth. We also derive the value that the agent assigns to the illiquid asset. The risk adjusted valuation procedure we develop can be used to value both liquid and illiquid assets, as well as contingent claims on those assets.

New Evidence on the Link between Technological Change and Employment: Extending the Neo-Classical Paradigm

A burgeoning literature on "skill-biased" technological change (SBTC) reveals that investment in information and communications technology (ICT) is associated with workforce reductions and an increase in the demand for highly educated workers. Based on extensions of the neo-classical paradigm, researchers have also come to realize that the implementation of a new technology is often accompanied by organizational change. Two edited volumes by Marco Vivarelli, Mario Pianta, Pascal Petit, and Luc Soete provide important new evidence on the policy implications of these trends. We review these volumes and other recent studies and also provide new evidence on the relationship between technological change and organizational change, based on a comprehensive dataset of Italian manufacturing firms.