Comparing School Choice Mechanisms by Interim and Ex-Ante Welfare

The Boston mechanism and deferred acceptance (DA) are two competing mechanisms widely used in school choice problems across the United States. Recent work has highlighted welfare gains from the use of the Boston mechanism, in particular finding that when cardinal utility is taken into account, Boston interim Pareto dominates DA in certain incomplete information environments with no school priorities. We show that these previous interim results are not robust to the introduction of nontrivial (weak) priorities. However, we partially restore the earlier results by showing that from an ex-ante utility perspective, the Boston mechanism once again Pareto dominates any strategyproof mechanism (including DA), even allowing for arbitrary priority structures. Thus, we suggest ex-ante Pareto dominance as a criterion by which to compare school choice mechanisms. This criterion may be of interest to school district leaders, as they can be thought of as social planners whose goal is to maximize the overall ex-ante welfare of the students. From a policy perspective, school districts may have justification for the use the Boston mechanism over a strategyproof alternative, even with nontrivial priority structures.school choice, Boston mechanism, deferred acceptance, market design, weak priorities

Light-by-light scattering in Double-Logarithmic Approximation

In the present paper we consider the elastic 2 -> 2 -scattering of virtual photons at high energies in the forward kinematics at zero and non-zero values of t. Accounting for both gluon and quark double-logarithmic (DL) contributions to all orders in the QCD coupling, we obtain explicit expressions for amplitudes of this process in Double-Logarithmic Approximation (DLA). First we keep the QCD coupling fixed and then account for running coupling effects. Applying the saddle-point method to the obtained expressions for the scattering amplitude, we calculate the high-energy asymptotics of the amplitude, which proved to be of the Regge form. The Reggeon bears the vacuum quantum numbers and therefore it is a new, DL contribution to Pomeron. Comparison of the DL Pomeron to the BFKL Pomeron shows that contribution of the DL Pomeron to the high-energy asymptotics is of the same order as contribution of the BFKL Pomeron, so the DL Pomeron should be taken into account together with the BFKL Pomeron. We estimate the applicability region for the asymptotics of the light-by-light scattering amplitude, where the the DL Pomeron can reliably represent the parent amplitude.Comment: 16 pages, 4 figures. Multiple errors are corrected, 2 figs are added, comparizon to BFKL is done in more detai