The dynamical gluon mass in the massless bound-state formalism

We describe the phenomenon of dynamical gluon mass generation within the massless bound-state formalism, which constitutes the general framework for the systematic implementation of the Schwinger mechanism in non-Abelian gauge theories. The main ingredient of this formalism is the dynamical formation of bound states with vanishing mass, which gives rise to effective vertices containing massless poles; these vertices, in turn, trigger the Schwinger mechanism, and allow for the gauge-invariant generation of an effective gluon mass. In this particular approach, the gluon mass is directly related to quantities that are intrinsic to the bound-state formation itself, such as the "transition amplitude" and the corresponding "bound-state wave-function". Specifically, a set of powerful relations discussed in the text, allows one to determine the dynamical evolution of the gluon mass through a Bethe-Salpeter equation, which controls the dynamics of the relevant wave-function. In addition, it is possible to demonstrate that the massless bound-state formalism is equivalent to the standard approach based on Schwinger-Dyson equations, thus establishing a formal connection between two different nonperturbative formalisms.Comment: 12 pages, 8 figures. Talk presented at the QCD-TNT-III-From quarks and gluons to hadronic matter: A bridge too far? 2-6 September, 2013 - ECT* Trento, Ital

The Minimal Quiver Standard Model

This paper discusses the minimal quiver gauge theory embedding of the standard model that could arise from brane world type string theory constructions. It is based on the low energy effective field theory of D-branes in the perturbative regime. The model differs from the standard model by the addition of one extra massive gauge boson, and contains only one additional parameter to the standard model: the mass of this new particle. The coupling of this new particle to the standard model is uniquely determined by input from the standard model and consistency conditions of perturbative string theory. We also study some aspects of the phenomenology of this model and bounds on its possible observation at the Large Hadron Collider.Comment: 4 pages, 1 figure. v2: minor correction, added reference. v3: added references. Typos fixed. Improved discussio

What are the prospects for privatizing infrastructure? Lessons from U. S. roads and solid waste

Infrastructure (Economics) ; Roads

Bank ratings: what determines their quality?

This paper examines the quality of credit ratings assigned to banks by the three largest rating agencies. We interpret credit ratings as relative assessments of creditworthiness, and define a new ordinal metric of rating error based on banks' expected default frequencies. Our results suggest that on average large banks receive more positive bank ratings, particularly from the agency to which the bank provides substantial securitization business. These competitive distortions are economically significant and contribute to perpetuate the existence of ‘too-big-to-fail' banks. We also show that, overall, differential risk weights recommended by the Basel accords for investment grade banks bear no significant relationship to empirical default probabilities. — Harald Hau, Sam Langfield and David Marques-Ibane

Formal Modelling and Safety Analysis of an Avionic Functional Architecture with Alloy

International audienceWe propose an approach based on Alloy to formally model and assess a system architecture with respect to system-level safety requirements. The system on which we instantiate our approach is a specific Required Navigation Performance system from a Thalès Avionics named Localizer Performance with Vertical guidance Approach (LPV). In this article, we describe how to define such a system architecture and how to verify safety objectives