34,485 research outputs found
D-brane Bound States and the Generalised ADHM Construction
We discuss the sigma model description of a D-string bound to k D-fivebranes
in type I string theory. The effective theory is an (0,4) supersymmetric
hyper-Kahler with torsion sigma model on the moduli space of Sp(k) instantons
on R^4. Upon toroidal compactification to five dimensions the model is related
to the type II picture where the target space is a symmetric product of K3's.Comment: 17 pages Phyzzx. Minor corrections, to appear in Nucl. Phys.
Partial inner product spaces: Some categorical aspects
We make explicit in terms of categories a number of statements from the
theory of partial inner product spaces (PIP spaces) and operators on them.
In particular, we construct sheaves and cosheaves of operators on certain PIP
spaces of practical interest.Comment: 21 page
Ancient solutions in Lagrangian mean curvature flow
Ancient solutions of Lagrangian mean curvature flow in C^n naturally arise as
Type II blow-ups. In this extended note we give structural and classification
results for such ancient solutions in terms of their blow-down and, motivated
by the Thomas-Yau Conjecture, focus on the almost calibrated case. In
particular, we classify Type II blow-ups of almost calibrated Lagrangian mean
curvature flow when the blow-down is a pair of transverse planes or, when n=2,
a multiplicity two plane. We also show that the Harvey-Lawson Clifford torus
cone in C^3 cannot arise as the blow-down of an almost calibrated Type II
blow-up.Comment: 30 pages, v2: minor typos corrected, accepted in Ann. Sc. Norm.
Super. Pisa Cl. Sc
Copernicus observations of Betelgeuse and Antares
Copernicus observations of the M-supergiants, alpha Ori and alpha Sco, are presented. The MgII h and k resonance lines are strongly in emission in both stars. The k line is highly asymmetric in both stars but the h line is symmetric. Upper limits for several other resonance lines are given for alpha Ori. The possibility is explored that the k line asymmetry is caused by overlying resonance lines of MnI and FeI formed in the cool circumstellar gas shells around these stars. Observations of the MnI 4030-4033 A lines are used to show that circumstellar shell absorption is too weak to explain the asymmetry. It is suggested that the absorption occurs in a cool turbulent region between the base of the circumstellar shell and the top of the chromosphere
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