A substructure inside spiral arms, and a mirror image across the Galactic Meridian

While the galactic density wave theory is over 50 years old and well known in science, whether it fits our own Milky Way disk has been difficult to say. Here we show a substructure inside the spiral arms. This substructure is reversing with respect to the Galactic Meridian (longitude zero), and crosscuts of the arms at negative longitudes appear as mirror images of crosscuts of the arms at positive longitudes. Four lanes are delineated: mid-arm (extended 12CO gas at mid arm, HI atoms), in-between offset by about 100 pc (synchrotron, radio recombination lines), in between offset by about 200 pc (masers, colder dust), and inner edge (hotter dust seen in Mid-IR and Near-IR).Comment: 25 pages, 2 figures, 10 tables, 1 appendix, accepted 13 February 2016 by Astrophysical Journal (in press

Different studies of the global pitch angle of the Milky Way's spiral arms

There are many published values for the pitch angle of individual spiral arms, and their wide distribution (from -3 to -28 degrees) begs for various attempts for a single value. Each of the four statistical methods used here yields a mean pitch angle in a small range, between -12 and -14 degrees (table 7, figure 2). The final result of our meta-analysis yields a mean global pitch angle in the Milky Way's spiral arms of -13.1 degrees, plus or minus 0.6 degree.Comment: 18 pages; 2 figures, 7 tables, 1 appendix; accepted on 2015 April 14, by Monthly Notices of the Royal Astronomical Society (in press

Evading the sign problem in random matrix simulations

We show how the sign problem occurring in dynamical simulations of random matrices at nonzero chemical potential can be avoided by judiciously combining matrices into subsets. For each subset the sum of fermionic determinants is real and positive such that importance sampling can be used in Monte Carlo simulations. The number of matrices per subset is proportional to the matrix dimension. We measure the chiral condensate and observe that the statistical error is independent of the chemical potential and grows linearly with the matrix dimension, which contrasts strongly with its exponential growth in reweighting methods.Comment: 4 pages, 3 figures, minor corrections, as published in Phys. Rev. Let

Cooperation under incomplete contracting

We examine the notion of the core when cooperation takes place in a setting with time and uncertainty. We do so in a two-period general equilibrium setting with incomplete markets. Market incompleteness implies that players cannot make all possible binding commitments regarding their actions at different date-events. We unify various treatments of dynamic core concepts existing in the literature. This results in definitions of the Classical Core, the Segregated Core, the Two-stage Core, the Strong Sequential Core, and the Weak Sequential Core. Except for the Classical Core, all these concepts can be defined by requiring absence of blocking in period 0 and at any date-event in period 1. The concepts only differ with respect to the notion of blocking in period 0. To evaluate these concepts, we study three market structures in detail: strongly complete markets, incomplete markets in finance economies, and incomplete markets in settings with multiple commodities

A Note on The Weak Sequential Core of Dynamic TU Games

This paper addresses a problem with an argument in Kranich, Perea, and Peters (2005) supporting their definition of the Weak Sequential Core and their characterization result. We also provide the remedy, a modification of the definition, to rescue the characterization