Atomic Energy Levels with QED and Contribution of the Screened Self-Energy

We present an introduction to the principles behind atomic energy level calculations with Quantum Electrodynamics (QED) and the two-time Green's function method; this method allows one to calculate an effective Hamiltonian that contains all QED effects and that can be used to predict QED Lamb shifts of degenerate, quasidegenerate and isolated atomic levels.Comment: 4 pages, 6 figures, summary of a talk given at the QED2000 Conference held in Trieste, Italy in Oct. 200

Numerical investigation of the Rayleigh hypothesis for electromagnetic scattering by a particle

The validity of the Rayleigh hypothesis has been a long-standing issue in the applicability of the T-matrix method to near-field calculations, and despite numerous theoretical works, the practical consequences for numerical simulations have remained unclear. Such calculations are increasingly important in the field of nanooptics, for which accurate and efficient modeling tools are in high demand. We here tackle this challenge by investigating numerically the convergence behavior of series expansions of the electric field around spheroidal particles, which provides us with unambiguous examples to clarify the conditions of convergence. This study is made possible by the combination of alternative methods to compute near-fields accurately, and crucially, the recent improvements in the calculation of T-matrix elements free from numerical instabilities, as such errors would otherwise obfuscate the intrinsic convergence properties of the field series. The resulting numerical confirmation for the range of validity of the Rayleigh hypothesis, complemented by a better understanding of the convergence behavior of the field expansions, is a crucial step toward future developments

Candidate Entry, Screening, and the Political Budget Cycle

We investigate whether relevant private information about citizens’ competence in political office can be credibly revealed by their entry and campaign expenditure decisions, as opposed to choice of policy once in office. We find that this depends on whether voters and candidates have common or conflicting interests ; only in the former case can entry be revealing in equilibrium. We apply these results to Rogoff’s (1990) model of the political budget cycle, allowing for candidate entry, as well as elections : as interests are common, low-ability candidates are screened out at the entry stage, and so there is no signaling via fiscal policy (i.e. no “political budget cycle”). In a variant of the Rogoff model where citizens differ in honesty, rather than ability, interests are conflicting, and so the political budget cycle can persist in equilibrium.Asymmetric Information ; Citizen-Candidate ; Representative Democracy ; Signaling Games ; Political Budget Cycles

ML vs GMM Estimates of Hybrid Macroeconomic Models (With an Application to the "New Phillips Curve")

Many macroeconomic models (including the NKPC - "New Keynesian" Phillips Curve) involve hybrid equations, in which some variables depend on both their lags and leads. Hybrid models have produced conflicting empirical results: GMM (respectively ML) estimation find the forward- looking component to be large (small). A rationalization for this conflict is provided, allowing for two kinds of misspecifications (omitted dynamics and measurement error): we show analytically in a simple DGP that the GMM (ML) estimator overstates (understates) the size of the forward- looking component. Monte-Carlo experiments indicate this result has some generality. We use these findings to rationalize discrepancies observed in NKPC estimates.Rational-expectation model, GMM estimator, ML estimator, Inflation, New Phillips curve.

Testing for a Forward-Looking Phillips Curve. Additional Evidence from European and US data

The "New Keynesian" Phillips Curve (NKPC) states that inflation has a purely forward-looking dynamics. In this paper, we test whether European and US inflation dynamics can be described by this model. For this purpose, we estimate hybrid Phillips curves, which include both backward and forward-looking components, for major European countries, the euro area, and the US. Estimation is performed using the GMM technique as well as the ML approach. We examine the sensitivity of the results to the choice of output gap or marginal cost as the driving variable, and test the stability of the obtained specifications. Our findings can be summarized as follows. First, in all countries, the NKPC has to be augmented by additional lags and leads of inflation, in contrast to the prediction of the core model. Second, the fraction of backward-looking price setters is large (in most cases, more than 50 percent), suggesting only limited differences between the US and the euro area. Finally, our preferred specification includes marginal cost in the case of the US and the UK, and output gap in the euro area.Forward-looking Phillips curve, euro area, GMM estimator, ML estimator.

DO ELECTIONS ALWAYS NOTIVATE INCUMBENTS? LEARNING VS CAREER CONCERNS

This paper studies a principal-agent model of the relationship between officeholder and the electorate, where everyone is initially uninformed about the officeholder’s ability. If office-holder effort and ability interact in the determination of performance in office, then an office-holder has an incentive to learn i.e. raise effort so that performance becomes a more accurate signal of her ability. Elections reduce the learning effect, and the reduction in this effect may more than offset the positive “career concerns” effect of elections on effort. Moreover, when this occurs, appointment of officials may welfare-dominate elections.Career Concerns ; Elections ; Citizen-Candidate ; Learning ; Effort ; Incomplete Information