Explosion phenomena in stochastic coagulation-fragmentation models

First we establish explosion criteria for jump processes with an arbitrary locally compact separable metric state space. Then these results are applied to two stochastic coagulation-fragmentation models--the direct simulation model and the mass flow model. In the pure coagulation case, there is almost sure explosion in the mass flow model for arbitrary homogeneous coagulation kernels with exponent bigger than 1. In the case of pure multiple fragmentation with a continuous size space, explosion occurs in both models provided the total fragmentation rate grows sufficiently fast at zero. However, an example shows that the explosion properties of both models are not equivalent.Comment: Published at http://dx.doi.org/10.1214/105051605000000386 in the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

Out of Office Reply

Poetry by Tyler Wagner. Runner up in the 2018 Manuscripts Poetry Contest

Aggregate liquidity shortages, idiosyncracic liquidity smoothing and banking regulation

This paper develops a model of banking fragility driven by aggregate liquidity shortages. Inefficiencies arise because liquidity smoothing across banks breaks down when there is such a shortage, causing unnecessary and value-reducing transfer of assets between banks. We find that a Lender of Last Resort policy is ineffective in restoring efficiency as it leads to offsetting changes in the banks’ supply of liquidity. In contrast, subsidizing the purchase of assets from troubled banks increases welfare by improving the banks’ liquidity holdings. The first best, however, is achieved by redistributing liquidity from healthy to troubled banks in a crisis

Physics Insights from Recent MAGIC AGN Observations

The total set of the 14 active galactic nuclei detected by MAGIC so far includes well-studied bright blazars like Mkn 501, the giant radio galaxy M 87, but also the distant flat-spectrum radio quasar 3C 279, and an intriguing gamma-ray source in the 3C 66A/B region, whose energy spectrum is not compatible with the expectations from 3C 66A. Besides scheduled observations, so far MAGIC succeeded in discovering TeV gamma rays from three blazars following triggers from high optical states. I report selected highlights from recent MAGIC observations of extragalactic TeV gamma-ray sources, emphasizing and discussing the new physics insights the MAGIC observations were able to contribute.Comment: 4 pages, no figures, invited talk at the 2nd Heidelberg workshop: "High-Energy Gamma-rays and Neutrinos from Extra-Galactic Sources", 2009 January, to be published in Int. J. Mod. Phys.