Attractors and Black Rings

The attractor mechanism is usually thought of as the fixing of the near horizon moduli of a BPS black hole in terms of conserved charges measured at infinity. Recent progress in understanding BPS solutions in five dimensions indicates that this is an incomplete story. Moduli can instead be fixed in terms of dipole charges, and their corresponding values can be found by extremizing a certain attractor function built out of these charges. BPS black rings provide an example of this phenomenon. We give a general derivation of the attractor mechanism in five dimensions based on the recently developed classification of BPS solutions. This analysis shows when it is the dipole charges versus the conserved charges that fix the moduli. It also yields explicit expressions for the fixed moduli.Comment: 18 pages, Harvma

Fundamental Strings, Holography, and Nonlinear Superconformal Algebras

We discuss aspects of holography in the AdS_3 \times S^p near string geometry of a collection of straight fundamental heterotic strings. We use anomalies and symmetries to determine general features of the dual CFT. The symmetries suggest the appearance of nonlinear superconformal algebras, and we show how these arise in the framework of holographic renormalization methods. The nonlinear algebras imply intricate formulas for the central charge, and we show that in the bulk these correspond to an infinite series of quantum gravity corrections. We also makes some comments on the worldsheet sigma-model for strings on AdS_3\times S^2, which is the holographic dual geometry of parallel heterotic strings in five dimensions.Comment: 25 page

Kinematics of the Outer Stellar Halo

We have tested whether the simple model for the kinematics of the Galactic stellar halo (in particular the outer halo) proposed by Sommer-Larsen, Flynn and Christensen (SLFC) is physically realizable, by directly integrating particles in a 3-D model of the Galactic potential. We are able to show that the SLFC solution can be realized in terms of a distribution of particles with stationary statistical properties in phase-space. Hence, the SLFC model, which shows a notable change in the anisotropy from markedly radial at the sun to markedly tangential beyond about Galactocentric radius r=20 kpc, seems a tenable description of outer halo kinematics.Comment: 13 pages, 6 figures, accepted for publication in MNRAS. also available at http://astro.utu.fi/~cflynn/papers/fslc4/fslc4.htm

D-branes and Strings as Non-commutative Solitons

The non-commutative geometry of a large auxiliary $B$-field simplifies the construction of D-branes as solitons in open string field theory. Similarly, fundamental strings are constructed as localized flux tubes in the string field theory. Tensions are determined exactly using general properties of non-BPS branes, and the non-Abelian structure of gauge fields on coincident D-branes is recovered.Comment: 31 pages, 2 figures, harvmac; v2: crucial sign error in vortex solution corrected, additional comments on electric flux tube, references adde

Kulturpolitikk og sosiologi

Sosiologi i dag 44, 1/2014, 5-11 http://ojs.novus.no/index.php/SI