Optimal Unemployment Insurance in a Matching Equilibrium

This paper considers the optimal design of unemployment insurance (UI) within an equilibrium matching framework when wages are determined by strategic bargaining. Unlike the Nash bargaining approach, reducing UI payments with duration is welfare increasing. A co-ordinated policy approach, however, one that chooses job creation subsidies and UI optimally, implies a much greater welfare gain than one which considers optimal UI alone. Once job creation subsidies are chosen optimally, the welfare value of making UI payments duration dependent is small.

Duration Dependent Unemployment Insurance and Stabilisation Policy

In the context of a standard equilibrium matching framework, this paper shows how a duration dependent unemployment insurance (UI) system stabilises unemployment levels over the business cycle. It establishes that re-entitlement effects induced by a finite duration UI program generate intertemporal tranfers from firms that hire in future booms to firms that hire in current recessions. These transfers imply a net hiring subsidy in recessions which stabilises unemployment levels over the cycle.

Re-entitlement Effects with Duration Dependent Unemployment Insurance in a Stochastic Matching Equilibrium

In the context of a standard equilibrium matching framework, this paper considers how a duration dependent unemployment insurance (UI) system affects the dynamics of unemployment and wages in an economy subject to stochastic job-destruction shocks. It establishes that re-entitlement effects induced by a finite duration UI program generate intertemporal transfers from firms that hire in future booms to firms that hire in current recessions. These transfers imply a net hiring subsidy in recessions which stabilizes unemployment levels over the cycleMatching frictions, Unemployment, Duration Dependent UI.

The Bull's-Eye Effect as a Probe of Ω\Omega

We compare the statistical properties of structures normal and transverse to the line of sight which appear in theoretical N-body simulations of structure formation, and seem also to be present in observational data from redshift surveys. We present a statistic which can quantify this effect in a conceptually different way from standard analyses of distortions of the power-spectrum or correlation function. From tests with $N$--body experiments, we argue that this statistic represents a new and potentially powerful diagnostic of the cosmological density parameter, $\Omega_0$.Comment: Minor revisions; final version accepted for publication in ApJ Letters. Latex, 16 pages, including 3 figures. Higher resolution versions of figures, including supplementary figures not included in the manuscript, are available at: ftp://kusmos.phsx.ukans.edu/preprints/melott/omeg

A Test of the Particle Paradigm in N-Body Simulations

We present results of tests of the evolution of small ``fluid elements'' in cosmological N--body simulations, to examine the validity of their treatment as particles. We find that even very small elements typically collapse along one axis while expanding along another, often to twice or more their initial comoving diameter. This represents a possible problem for high--resolution uses of such simulations.Comment: Uses aasms4.sty; accepted for publication in ApJ Letters. Files available also at ftp://kusmos.phsx.ukans.edu/preprints/ates

Bias and Hierarchical Clustering

It is now well established that galaxies are biased tracers of the distribution of matter, although it is still not known what form this bias takes. In local bias models the propensity for a galaxy to form at a point depends only on the overall density of matter at that point. Hierarchical scaling arguments allow one to build a fully-specified model of the underlying distribution of matter and to explore the effects of local bias in the regime of strong clustering. Using a generating-function method developed by Bernardeau & Schaeffer (1992), we show that hierarchical models lead one directly to the conclusion that a local bias does not alter the shape of the galaxy correlation function relative to the matter correlation function on large scales. This provides an elegant extension of a result first obtained by Coles (1993) for Gaussian underlying fields and confirms the conclusions of Scherrer & Weinberg (1998) obtained using a different approach. We also argue that particularly dense regions in a hierarchical density field display a form of bias that is different from that obtained by selecting such peaks in Gaussian fields: they are themselves hierarchically distributed with scaling parameters $S_p=p^{(p-2)}$. This kind of bias is also factorizable, thus in principle furnishing a simple test of this class of models.Comment: Latex, accepted for publication in ApJL; moderate revision