The labour market after age 50: some elements of a Franco-American comparison

This paper examines various supply and demand side aspects of the French labour market for older workers and puts them in perspective by comparing them to the US case. We first consider the supply side incentives (or disincentives) of basic pension schemes for the two countries : for France, we discuss how these incentives have been changed by the 1993 and 2003 pension reforms and we present some projections of the impact of these reforms on labour force participation rates, based on the DESTINIE dynamic microsimulation model. We then discuss, on the demand side, the hypothesis of a wage-productivity gap for older workers which could explain their lower employment rates. Evidence in favor of this hypothesis is not overwhelming. Nevertheless, workers who lose their jobs at older ages probably suffer a large loss of firm-specific and sector-specific human capital. In the US, this does not preclude re-employment, but at the cost of significant drops of wage levels. In France, the collective choice has been made since the 1970s to allow older workers who lose their jobs to completely withdraw from the labour market : these workers have access to preretirement schemes or specific dispositions of unemployment insurance (including an exemption from seeking employment). This system proved difficult to regulate. Due to these difficulties, France has not been able to do more than stabilize the employment rate in the 55-64 age bracket during the 1990s, after 20 years of continuous decline. The key unanswered question is whether it will be possible to increase the employment rate of this age group in the next two decades.Pensions, preretirement, senior workers

BF Theories and Group-Level Duality

It is known that the partition function and correlators of the two-dimensional topological field theory $G_K(N)/ G_K(N)$ on the Riemann surface $\Sigma_{g,s}$ is given by Verlinde numbers, dim($V_{g,s,K}$) and that the large $K$ limit of dim($V_{g,s,K}$) gives Vol(${\cal M}_s$), the volume of the moduli space of flat connections of gauge group $G(N)$ on $\Sigma_{g,s}$, up to a power of $K$. Given this relationship, we complete the computation of Vol(${\cal M}_s$) using only algebraic results from conformal field theory. The group-level duality of $G(N)_K$ is used to show that if $G(N)$ is a classical group, then $\displaystyle \lim_{N\rightarrow \infty} G_K(N) / G_K(N)$ is a BF theory with gauge group $G(K)$. Therefore this limit computes Vol(${\cal M}^\prime_s$), the volume of the moduli space of flat connections of gauge group $G(K)$

Penrose Limits and Spacetime Singularities

We give a covariant characterisation of the Penrose plane wave limit: the plane wave profile matrix $A(u)$ is the restriction of the null geodesic deviation matrix (curvature tensor) of the original spacetime metric to the null geodesic, evaluated in a comoving frame. We also consider the Penrose limits of spacetime singularities and show that for a large class of black hole, cosmological and null singularities (of Szekeres-Iyer ``power-law type''), including those of the FRW and Schwarzschild metrics, the result is a singular homogeneous plane wave with profile $A(u)\sim u^{-2}$, the scale invariance of the latter reflecting the power-law behaviour of the singularities.Comment: 9 pages, LaTeX2e; v2: additional references and cosmetic correction

Lorentzian homogeneous spaces admitting a homogeneous structure of type T1+T3

We show that a Lorentzian homogeneous space admitting a homogeneous structure of type T1 + T3 is either a (locally) symmetric space or a singular homogeneous plane wave.Comment: 7 pages, Latex2e, a small note and a reference adde

PP-wave and Non-supersymmetric Gauge Theory

We extend the pp-wave correspondence to a non supersymmetric example. The model is the type 0B string theory on the pp-wave R-R background. We explicitly solve the model and give the spectrum of physical states. The field theory counterpart is given by a sector of the large N SU(N) x SU(N) CFT living on a stack of N electric and N magnetic D3-branes. The relevant effective coupling constant is g_{eff}=g_sN/J^2. The string theory has a tachyon in the spectrum, whose light-cone energy can be exactly computed as a function of g_{eff}. We argue that the perturbative analysis in g_{eff} in the dual gauge theory is reliable, with corrections of non perturbative type. We find a precise state/operator map, showing that the first perturbative corrections to the anomalous dimensions of the operators have the behavior expected from the string analysis.Comment: 19 pages. Revised versio

Boundary fermion currents and subleading order chiral anomaly in the AdS/CFT correspondence

We construct a wave-functional whose argument couples to boundary fermion currents in the AdS/CFT correspondence. Using this we calculate the contributions from bulk fermions to the chiral anomaly that give the subleading order term in the exact $N$-dependence of the chiral anomaly of ${\cal N}=4$ SYM. The result agrees with the calculation of Bilal & Chu.Comment: 6 page

Matrix string states in pure 2d Yang Mills theories

We quantize pure 2d Yang-Mills theory on a torus in the gauge where the field strength is diagonal. Because of the topological obstructions to a global smooth diagonalization, we find string-like states in the spectrum similar to the ones introduced by various authors in Matrix string theory. We write explicitly the partition function, which generalizes the one already known in the literature, and we discuss the role of these states in preserving modular invariance. Some speculations are presented about the interpretation of 2d Yang-Mills theory as a Matrix string theory.Comment: Latex file of 38 pages plus 6 eps figures. A note and few references added, figures improve

Self-replaceable thermocouple for molten steel bath - A concept

Thermocouple wires, consisting of tungsten-rhenium alloy protected by ablative ceramic coating, are wound on a reel and fed continuously into bath. Tests indicate accuracy and reliability are comparable to conventional devices

Generalized two-dimensional Yang-Mills theory is a matrix string theory

We consider two-dimensional Yang-Mills theories on arbitrary Riemann surfaces. We introduce a generalized Yang-Mills action, which coincides with the ordinary one on flat surfaces but differs from it in its coupling to two-dimensional gravity. The quantization of this theory in the unitary gauge can be consistently performed taking into account all the topological sectors arising from the gauge-fixing procedure. The resulting theory is naturally interpreted as a Matrix String Theory, that is as a theory of covering maps from a two-dimensional world-sheet to the target Riemann surface.Comment: LaTeX, 10 pages, uses espcrc2.sty. Presented by A. D'adda at the Third Meeting on Constrained Dynamics and Quantum Gravity, Villasimius (Sardinia, Italy) September 13-17, 1999; to appear in the proceeding