18,891 research outputs found
The estimation of three-dimensional fixed effects panel data models
The paper introduces for the most frequently used three-dimensional fixed effects panel data models the appropriate Within estimators. It analyzes the behaviour of these estimators in the case of no-self-flow data, unbalanced data and dynamic autoregressive models.panel data, unbalanced panel, dynamic panel data model, multidimensional panel data, fixed effects, trade models, gravity models, FDI
Unification mechanism for gauge and spacetime symmetries
A group theoretical mechanism for unification of local gauge and spacetime
symmetries is introduced. No-go theorems prohibiting such unification are
circumvented by slightly relaxing the usual requirement on the gauge group:
only the so called Levi factor of the gauge group needs to be compact
semisimple, not the entire gauge group. This allows a non-conventional
supersymmetry-like extension of the gauge group, glueing together the gauge and
spacetime symmetries, but not needing any new exotic gauge particles. It is
shown that this new relaxed requirement on the gauge group is nothing but the
minimal condition for energy positivity. The mechanism is demonstrated to be
mathematically possible and physically plausible on a U(1) based gauge theory
setting. The unified group, being an extension of the group of spacetime
symmetries, is shown to be different than that of the conventional
supersymmetry group, thus overcoming the McGlinn and Coleman-Mandula no-go
theorems in a non-supersymmetric way.Comment: 20 pages, 4 figure
Recent developments in quantum mechanics with magnetic fields
We present a review on the recent developments concerning rigorous
mathematical results on Schr\"odinger operators with magnetic fields. This
paper is dedicated to the sixtieth birthday of Barry Simon.Comment: Update of the previous versions; some more references added and typos
and some minor errors correcte
Linearization of group stack actions and the Picard group of the moduli of \SL_r/\mu_s-bundles on a curve
We first study the descent theory of line bundles under a morphism which is
tors or under a group stack and then use this technical result to determine the
exact structure of \Pic(\M_G) where G=\SL_r/\mu_s (we include a minor
modification to explain the genus 0 case).Comment: 13 pages, PlainTe
Random matrices, log-gases and Holder regularity
The Wigner-Dyson-Gaudin-Mehta conjecture asserts that the local eigenvalue
statistics of large real and complex Hermitian matrices with independent,
identically distributed entries are universal in a sense that they depend only
on the symmetry class of the matrix and otherwise are independent of the
details of the distribution. We present the recent solution to this
half-century old conjecture. We explain how stochastic tools, such as the Dyson
Brownian motion, and PDE ideas, such as De Giorgi-Nash-Moser regularity theory,
were combined in the solution.
We also show related results for log-gases that represent a universal model
for strongly correlated systems. Finally, in the spirit of Wigner's original
vision, we discuss the extensions of these universality results to more
realistic physical systems such as random band matrices.Comment: Proceedings of ICM 201
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