The status of |Vub|

I survey the theoretical and experimental information available for determination of |Vub| with inclusive and exclusive techniques. Using recent experimental and theoretical advances, I outline a procedure in which the inclusive information can be combined to obtain an inclusive |Vub| that includes experimentally--derived uncertainty estimates for outstanding theoretical corrections.Comment: 9 pages, 5 figures, uses aipproc.cls, submitted to Proceedings of Beauty 200

Layoffs and Lemons

In this paper we provide theoretical and empirical analyses of an asymmetric-information model of layoffs in which the current employer is better informed about its workers' abilities than prospective employers are. The key feature of the model is that when firms have discretion with respect to whom to lay off, the market infers that laid-off workers are of low ability. Since no such negative inference should be attached o workers displaced in a plant closing, our model predicts that the postdisplacement wages of otherwise observationally equivalent workers will be higher for those displaced by plant closings than for those displaced by layoffs. An extension of our model predicts that the average postdisplacement unemployment spell of otherwise observationally equivalent workers will be shorter for those displaced by plant closings than for those displaced by layoffs. In our empirical work, we use data from the Displaced Workers Supplements in the January 1984 and 1986 Current Population Surveys. We find that the evidence (with respect to both re-employment wages and postdisplacement unemployment duration) is consistent with the idea that laid off workers are viewed less favorably by the market than are those losing jobs in plant closings. Our findings are much stronger for workers laid off from jobs where employers have discretion over whom to lay off.

Comparative Advantage, Learning, and Sectoral Wage Determination

We develop a model in which a worker's skills determine the worker's current wage and sector. Both the market and the worker are initially uncertain about some of the worker's skills. Endogenous wage changes and sector mobility occur as labor-market participants learn about these unobserved skills. We show how the model can be estimated using non-linear instrumental-variables techniques. We then apply our methodology to study the wages and allocation of workers across occupations and across industries. For both occupations and industries, we find that high-wage sectors employ high-skill workers and offer high returns to workers' skills. Estimates of these sectoral wage differences that do not account for sector-specific returns are therefore misleading. We also suggest further applications of our theory and methodology.

Comparative Advantage, Learning, and Sectoral Wage Determination

We develop a model in which a worker's skills determine the worker's current wage and sector. Both the market and the worker are initially uncertain about some of the worker's skills. Endogenous wage changes and sector mobility occur as labor-market participants learn about these unobserved skills. We show how the model can be estimated using non-linear instrumental-variables techniques. We then apply our methodology to study the wages and allocation of workers across occupations and across industries. For both occupations and industries, we find that high-wage sectors employ high-skill workers and offer high returns to workers' skills. Estimates of these sectoral wage differences that do not account for sector-specific returns are therefore misleading. We also suggest further applications of our theory and methodology. Dans cet article, nous cherchons à développer un modèle par lequel le salaire d'un travailleur est fonction de ses qualifications. Le marché ainsi que le travailleur sont au préalable dans l'incertitude quant à certaines de ces qualifications. L'endogénéité à la fois des changements de salaire et des décisions de changements du secteur d'affiliation résulte du processus d'apprentissage relié aux qualifications du travailleur. Nous montrons ensuite comment le modèle peut être estimé par les méthodes des variables instrumentales non-linéaires. Nous appliquons notre méthodologie à l'étude des salaires et de l'allocation des travailleurs aux différentes occupations et industries. Nous trouvons que les secteurs à salaires élevés emploient des travailleurs ayant davantage de qualifications et que ces secteurs rémunèrent ces qualifications à un taux supérieur relativement aux secteurs à faibles salaires. Les estimés des rendements associés aux qualifications qui ne tiennent pas compte du fait que les rendements diffèrent d'un secteur à un autre sont par conséquent erronés. Nous proposons enfin d'autres applications possibles de notre méthodologie.comparative advantage, learning, non-linear instrumental variables, avantages comparés, apprentissage, variables instrumentales

Layoffs and Lemons

We provide theoretical and empirical analyses of an asymmetric-information model of layoffs. When firms have discretion with respect to whom to lay off, the market infers that laid-off workers are of low ability. Assuming that no such negative inference is warranted if workers are displaced in a plant closing, postdisplacement wages should be lower and postdisplacement unemployment spells should be longer for those displaced by layoffs than for those displaced by plant closings, but predisplacement wages should not differ by cause of displacement. Evidence on displaced workers from Current Population Surveys supports all three of our model's predictions.Economic

Does Unmeasured Ability Explain Inter-Industry Wage Differentials?

This paper provides empirical assessments of the two leading explanations of measured inter-industry wage differentials: (1) true wage differentials exist across industries, and (2) the measured differentials simply reflect unmeasured differences in workers' productive abilities. First, we summarize the existing evidence on the unmeasured-ability explanation, which is based on first-differenced regressions using patched Current Population Survey (CPS) data. We argue that these existing approaches implicitly hypothesize that unmeasured productive ability is equally rewarded in all industries. Second, we construct a simple model in which unmeasured ability in not equally valued in all industries; instead, there is matching. This model illustrates two endogeneity problems inherent in the first-differenced regressions using CPS data: whether a worker changes jobs in endogenous, as is the industry of the new job the worker finds. Third, we propose two new empirical approaches designed to minimize these endogeneity problems. We implement these procedures on a sample that allows us to approximate the experiment of exogenous job loss: a sample of workers displaced by plant closings. We conclude from our findings using this sample that neither of the contending explanations fits the evidence without recourse to awkward modifications, but that a modified version of the true-industry-effects explanation fits more easily than does any existing version of the unmeasured-ability explanation.

On the instability of 3d null singularities

String propagation on a three-dimensional Lorentzian string orbifold with a null singularity has been studied by Horowitz and Steif, and more recently by Liu, Moore and Seiberg. We analyze the target space as a classical gravitational background. The singularity becomes spacelike when an arbitrarily small amount of matter is thrown at the singularity. This can be seen directly by studying the null singularity as a limit of the M=0, J=0 BTZ black hole metric.Comment: 9 pages, uses harvmac.tex. v2: minor wording changes in introduction, fixed reference typo, new reference

Ultra-high energy cosmic rays threshold in Randers-Finsler space

Kinematics in Finsler space is used to study the propagation of ultra high energy cosmic rays particles through the cosmic microwave background radiation. We find that the GZK threshold is lifted dramatically in Randers-Finsler space. A tiny deformation of spacetime from Minkowskian to Finslerian allows more ultra-high energy cosmic rays particles arrive at the earth. It is suggested that the lower bound of particle mass is related with the negative second invariant speed in Randers-Finsler space