Congruences for L-functions of additive exponential sums

We give a congruence for L-functions coming from affine additive exponential sums over a finite field. Precisely, we give a congruence for certain operators coming from Dwork's theory. This congruence is very similar to the congruence of Manin for the characteristic polynomial of the action of Frobenius on the Jacobian of a curve defined over a finite field.Comment: This paper generalizes and extends the results in the previous paper arXiv:0912.205

The effect of colored noise on heteroclinic orbits

The dynamics of a weakly dissipative Hamiltonian system submitted to stochastic perturbations has been investigated by means of asymptotic methods. The probability of noise-induced separatrix crossing, which drastically changes the fate of the system, is derived analytically in the case where noise is an additive Kubo-Anderson process. This theory shows how the geometry of the separatrix, as well as the noise intensity and correlation time, affect the statistics of crossing. Results can be applied to a wide variety of systems, and are valid in the limit where the noise correlation time scale is much smaller than the time scale of the undisturbed Hamiltonian dynamics

The Shimer Puzzle and the Correct Identification of Productivity Shocks

Shimer (2005a) claims that the Mortensen-Pissarides search model of unemployment lacks an ampiflication mechanism because it cannot generate the observed business cycle fluctuations in unemployment given labor productivity shocks of plausible magnitude. This paper argues that part of the problem lies with the correct identification of productivity shocks. Because of the endogeneity of measured labor productivity, filtering out the trend component as in Shimer (2005a) may not correctly identify the shocks driving unemployment. Using a New- Keynesian framework with search unemployment, this paper estimates that close to 50% of the Shimer puzzle is due to the misidentification of productivity shocks. In addition, I show that extending the search model with an aggregate demand side remarkably improves the ability of the standard search model to match the moments of key labor market variables.unemployment fluctuations, labor productivity, search and matching model, New-Keynesian model