A numerical formulation of resummation in effective field theory

In this article we show how the resummation of infrared and collinear logarithms within Soft-Collinear Effective Theory (SCET) can be formulated in a way that makes it suitable for a Monte-Carlo implementation. This is done by applying the techniques developed for automated resummation using the branching formalism, which have resulted in the general resummation approach CAESAR/ARES. This work builds a connection between the two resummation approaches, and paves the way to automated resummation in SCET. As a case study we consider the resummation of the thrust distribution in electron-positron collisions at next-to-leading logarithm (NLL). However, the results presented here are easily generalizable to more complicated observables and processes as well as to higher orders in the logarithmic accuracy.Comment: 47 page

A Scholar in Action in Interwar America. John H. Williams’ contributions to trade theory and international monetary reform

In this paper we analyse the scientific contributions of Harvard economist John H. Williams as international trade theorist and monetary reformer, together with his activities as a Vice President of the Federal Reserve Bank of New York. In the first two Sections we present a succinct overview of Williams’ main contributions to international trade theory and to the interwar debate on the reform of the international monetary system. Particular attention will be devoted to his early academic writings which contained different critical arguments against the two main tenets of classical international economics: the Ricardian theory of comparative advantages and the gold standard. These criticisms formed the theoretical rationale and the analytical background of Williams’ key currency approach to the reform of the international monetary system. The key currency plan was first formulated when Williams advised Roosevelt and Morghenthau to sign a Tripartite agreement with Britain and France, and was later refined during the negotiations which concluded with the approval of the Bretton Woods agreements. In this respect, Section 4 is devoted to the analysis of the contents of Williams’ proposal and to the reconstruction of his main criticisms of the two official plans presented by John Maynard Keynes and Harry Dexter White. Section 5 is devoted to examining Keynes’ and White’s reactions and to elucidating what aspects of Williams’ ideas managed to influence the shaping of the Bretton Woods Agreements. Finally, Section 6 presents some general conclusions. Sections 4 and 5 have greatly benefited from the use of archival sources which have been quoted at length, mostly in the footnotesJohn H. Williams; John Maynard Keynes; Harry D. White; Bretton Woods Agreements; Key currency; gold standard; economists in Government

Acetylene on Si(100) from first principles: adsorption geometries, equilibrium coverages and thermal decomposition

Adsorption of acetylene on Si(100) is studied from first principles. We find that, among a number of possible adsorption configurations, the lowest-energy structure is a ``bridge'' configuration, where the C$_2$H$_2$ molecule is bonded to two Si atoms. Instead, ``pedestal'' configurations, recently proposed as the lowest-energy structures, are found to be much higher in energy and, therefore, can represent only metastable adsorption sites. We have calculated the surface formation energies for two different saturation coverages, namely 0.5 and 1 monolayer, both observed in experiments. We find that although, in general, the full monolayer coverage is favored, a narrow range of temperatures exists in which the 0.5 monolayer coverage is the most stable one, where the acetylene molecules are adsorbed in a $2\times 2$ structure. This result disagrees with the conclusions of a recent study and represents a possible explanation of apparently controversial experimental findings. The crucial role played by the use of a gradient-corrected density functional is discussed. Finally, we study thermal decomposition of acetylene adsorbed on Si(100) by means of finite-temperature Molecular Dynamics, and we observe an unexpected behavior of dehydrogenated acetylene molecules.Comment: 8 pages, 3 figures (submitted to J. Chem. Phy

Giustizia sociale e misconoscimento

Negli Stati costituzionali del secondo ‘900, il sistema dei “diritti fondamentali” – all’indomani delle positivizzazioni internazionali e costituzionali fiorite dopo la sconfitta dei totalitarismi – posto al vertice della gerarchia delle fonti, ha assunto il ruolo di inviolabile presupposto del riconoscimento della dignità individuale e sociale degli esseri umani. Ma proprio per il loro forte ruolo simbolico di mediazione delle relazioni di riconoscimento sociale e intersoggetivo e di orientamento della prassi comune, la loro implementazione interpretativa nel sistema di ogni società ‘aperta’ dipende da concrete aspettative di giustizia derivate da pratiche sociali di misconoscimento dei gruppi minoritari e quindi dalla risposta ‘integratrice’ del sistema in sede legislativa o (più spesso) giurisdizionale, con le tecniche di bilanciamento dei principi ad opera delle Corti Costituzionali. Nel saggio si intende quindi evidenziare come a) nella cornice costituzionale di ogni società democratica, la ‘lotta per il diritti’ non deve essere strategia conservativa di status ma lotta per l’eguaglianza e la parità di trattamento di soggetti discriminati; b) affinché i diritti fondamentali costituiscano il fondamento morale della democrazia bisogna prepararsi a fornire argomentazioni sulla loro validità in base a ragioni giustificabili dal punto di vista di tutti gli esseri umani (Habermas, Benhabib)