3,530 research outputs found
The axial anomaly in lattice QED. A universal point of view
We give a perturbative proof that U(1) lattice gauge theories generate the
axial anomaly in the continuum limit under very general conditions on the
lattice Dirac operator. These conditions are locality, gauge covariance and the
absense of species doubling. They hold for Wilson fermions as well as for
realizations of the Dirac operator that satisfy the Ginsparg-Wilson relation.
The proof is based on the lattice power counting theorem.Comment: 7 pages, Latex2e, some misprints removed, reference inserte
Removing the Veil of Ignorance in Assessing the Distributional Impacts of Social Policies
This paper summarizes our recent research on evaluating the distributional consequences of social programs. This research advances the economic policy evaluation literature beyond estimating assorted mean impacts to estimate distributions of outcomes generated by different policies and determine how those policies shift persons across the distributions of potential outcomes produced by them. Our approach enables analysts to evaluate the distributional effects of social programs without invoking the 'Veil of Ignorance' assumption often used in the literature in applied welfare economics. Our methods determine which persons are affected by a given policy, where they come from in the ex-ante outcome distribution and what their gains are. We apply our methods to analyze two proposed policy reforms in American education. These reforms benefit the middle class and not the poor.
Estimating Distributions of Treatment Effects with an Application to the Returns to Schooling and Measurement of the Effects of Uncertainty on College
This paper uses factor models to identify and estimate distributions of counterfactuals. We extend LISREL frameworks to a dynamic treatment effect setting, extending matching to account for unobserved conditioning variables. Using these models, we can identify all pairwise and joint treatment effects. We apply these methods to a model of schooling and determine the intrinsic uncertainty facing agents at the time they make their decisions about enrollment in school. Reducing uncertainty in returns raises college enrollment. We go beyond the Veil of Ignorance' in evaluating educational policies and determine who benefits and who loses from commonly proposed educational reforms.
The effect of schooling and ability on achievement test scores
This paper develops two methods for estimating the effect of schooling on achievement test scores that control for endogeneity of schooling by postulating that both schooling and test scores are generated by a common unobserved latent ability. These methods are applied to data on schooling and test scores. Estimates from the two methods are in close agreement. We find that the effects of schooling on test scores are roughly linear across schooling levels. The effects of schooling on measured test scores are slightly larger for lower latent ability levels. We find that schooling increases the AFQT score on average between 2 and 4 percentage points, roughly twice as large as the effect claimed by Herrnstein and Murray (1994) but in agreement with estimates produced by Neal and Johnson (1996) and Winship and Korenman (1997). We extend the previous literature by estimating the impact of schooling on measured test scores at various quantiles of the latent ability distribution.Education; ability; latent variables; selection; MCMC
Lattice QED and Universality of the Axial Anomaly
We give a perturbative proof that U(1) lattice gauge theories generate the
axial anomaly in the continuum limit under very general conditions on the
lattice Dirac operator. These conditions are locality, gauge covariance and the
absense of species doubling. They hold for Wilson fermions as well as for
realizations of the Dirac operator that satisfy the Ginsparg-Wilson relation.
The proof is based on the lattice power counting theorem. The results
generalize to non-abelian gauge theories.Comment: LATTICE99(theoretical developments) 3 page
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High performance computing on smartphones
Nowadays there is a strong demand to simulate even real-world engineering problems on small computing devices with very limited capacity, such as a smartphone. We explain, using a concrete example, how we can obtain a reduction in complexity – to enable such computations – using mathematical methods
CO oxidation at Pd(100): A first-principles constrained thermodynamics study
The possible formation of oxides or thin oxide films (surface oxides) on late
transition metal surfaces is recently being recognized as an essential
ingredient when aiming to understand catalytic oxidation reactions under
technologically relevant gas phase conditions. Using the CO oxidation at
Pd(100) as example, we investigate the composition and structure of this model
catalyst surface over a wide range of (T,p)-conditions within a multiscale
modeling approach where density-functional theory is linked to thermodynamics.
The results show that under the catalytically most relevant gas phase
conditions a thin surface oxide is the most stable "phase" and that the system
is actually very close to a transition between this oxidic state and a reduced
state in form of a CO covered Pd(100) surface.Comment: 13 pages including 7 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
Strong Non-Ultralocality of Ginsparg-Wilson Fermionic Actions
It is shown that it is impossible to construct a free theory of fermions on
infinite hypercubic Euclidean lattice in even number of dimensions that: (a) is
ultralocal, (b) respects the symmetries of hypercubic lattice, (c) chirally
nonsymmetric part of its propagator is local, and (d) describes single species
of massless Dirac fermions in the continuum limit. This establishes
non-ultralocality for arbitrary doubler-free Ginsparg-Wilson fermionic action
with hypercubic symmetries ("strong non-ultralocality"), and complements the
earlier general result on non-ultralocality of infinitesimal
Ginsparg-Wilson-Luscher symmetry transformations ("weak non-ultralocality").Comment: 21 pages, 1 figure, LATEX. Few typos corrected; few sentences
reformulated; figure centere
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