9,623 research outputs found
Central Compact Objects in Supernova Remnants
Central Compact Objects (CCOs) are a handful of sources located close to the
geometrical center of young supernova remnants. They only show thermal-like,
soft X-ray emission and have no counterparts at any other wavelength. While the
first observed CCO turned out to be a very peculiar magnetar, discovery that
three members of the family are weakly magnetised Isolated Neutron Stars (INSs)
set the basis for an interpretation of the class. However, the phenomeology of
CCOs and their relationship with other classes of INSs, possibly ruled by
supernova fall-back accretion, are still far from being well understood.Comment: 7 pages, to appear in the proceedings of "Physics of Neutron Stars -
2017" Conference (July 10-14, Saint Petersburg), JPCS, eds. G.G. Pavlov, J.A.
Pons, P.S. Shternin & D.G. Yakovle
Non-Equilibrium Steady State generated by a moving defect: the supersonic threshold
We consider the dynamics of a system of free fermions on a 1D lattice in the
presence of a defect moving at constant velocity. The defect has the form of a
localized time-dependent variation of the chemical potential and induces at
long times a Non-Equilibrium Steady State (NESS), which spreads around the
defect. We present a general formulation which allows recasting the
time-dependent protocol in a scattering problem on a static potential. We
obtain a complete characterization of the NESS. In particular, we show a strong
dependence on the defect velocity and the existence of a sharp threshold when
such velocity exceeds the speed of sound. Beyond this value, the NESS is not
produced and remarkably the defect travels without significantly perturbing the
system. We present an exact solution for a like defect traveling with
an arbitrary velocity and we develop a semiclassical approximation which
provides accurate results for smooth defects.Comment: 18 pages, 13 figure
The Decomposition Theorem and the topology of algebraic maps
We give a motivated introduction to the theory of perverse sheaves,
culminating in the Decomposition Theorem of Beilinson, Bernstein, Deligne and
Gabber. A goal of this survey is to show how the theory develops naturally from
classical constructions used in the study of topological properties of
algebraic varieties. While most proofs are omitted, we discuss several
approaches to the Decomposition Theorem, indicate some important applications
and examples.Comment: 117 pages. New title. Major structure changes. Final version of a
survey to appear in the Bulletin of the AM
What is a perverse sheaf?
Three-page article on the notion of perverse sheaf to appear in the "What
is?" series in the Notices of the AMS.Comment: to appear in the May 2010 issue of the Notices of the AMS
http://www.ams.org/notice
The perverse filtration and the Lefschetz Hyperplane Theorem
We describe the perverse filtration in cohomology using the Lefschetz
Hyperplane Theorem.Comment: Revised version with minor changes. To appear in Annals of
Mathematic
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