5,051 research outputs found
Mean Field Approach to the Giant Wormhole Problem
We introduce a gaussian probability density for the space-time distribution
of wormholes, thus taking effectively into account wormhole interaction. Using
a mean-field approximation for the free energy, we show that giant wormholes
are probabilistically suppressed in a homogenous isotropic ``large'' universe.Comment: 10 pages, Late
Moduli Spaces of Curves with Homology Chains and c=1 Matrix Models
We show that introducing a periodic time coordinate in the models of
Penner-Kontsevich type generalizes the corresponding constructions to the case
of the moduli space of curves with homology chains
\gamma\in H_1(C,\zet_k). We make a minimal extension of the resulting models
by adding a kinetic term, and we get a new matrix model which realizes a simple
dynamics of \zet_k-chains on surfaces. This gives a representation of
matter coupled to two-dimensional quantum gravity with the target space being a
circle of finite radius, as studied by Gross and Klebanov.Comment: IFUM 459/FT (LaTeX, 9 pages; a few misprints have been corrected and
the introduction has been slightly modified
Non-linear WKB Analysis of the String Equation
We apply non-linear WKB analysis to the study of the string equation. Even
though the solutions obtained with this method are not exact, they approximate
extremely well the true solutions, as we explicitly show using numerical
simulations. ``Physical'' solutions are seen to be separatrices corresponding
to degenerate Riemann surfaces. We obtain an analytic approximation in
excellent agreement with the numerical solution found by Parisi et al. for the
case.Comment: 21 pages. To appear in the proceedings of the Research Conference on
Advanced Quantum Field Theory and Critical Phenomena, held in Como (Italy),
June 17-21, 1991 -- World Scientifi
Capital Regulation, Liquidity Requirements and Taxation in a Dynamic Model of Banking
This paper formulates a dynamic model of a bank exposed to both credit and liquidity risk, which can resolve financial distress in three costly forms: fire sales, bond issuance and equity issuance. We use the model to analyze the impact of capital regulation, liquidity requirements and taxation on banks' optimal policies and metrics of efficiency of intermediation and social value. We obtain three main results. First, mild capital requirements increase bank lending, bank efficiency and social value relative to an unregulated bank, but these benefits turn into costs if capital requirements are too stringent. Second, liquidity requirements reduce bank lending, efficiency and social value significantly, they nullify the benifits of mild capital requirements, and their private and social costs increase monotonically with their stringency. Third, increases in corporate income and bank liabilities taxes reduce bank lending, bank effciency and social value, with tax receipts increasing with the former but decreasing with the latter. Moreover, the effects of an increase in both forms of taxation are dampened if they are jointly implemented with increases in capital and liquidity requirements.Capital requirements;liquidity requirements;taxation of liabilities. JEL Classifications
Moment inequalities and high-energy tails for the Boltzmann equations with inelastic interactions
We study the high-energy asymptotics of the steady velocity distributions for
model systems of granular media in various regimes. The main results obtained
are integral estimates of solutions of the hard-sphere Boltzmann equations,
which imply that the velocity distribution functions behave in a certain
sense as for large. The values of , which we call
{\em the orders of tails}, range from to , depending on the model of
external forcing. The method we use is based on the moment inequalities and
careful estimating of constants in the integral form of the Povzner-type
inequalities.Comment: 22 page
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