118611979
Training the Next Generation of Astronomers
While both society and astronomy have evolved greatly over the past fifty years, the academic institutions and incentives that shape our field have remained largely stagnant. As a result, the astronomical community is faced with several major challenges, including: (1) the training that we provide does not align with the skills that future astronomers will need, (2) the postdoctoral phase is becoming increasingly demanding and demoralizing, and (3) our jobs are increasingly unfriendly to families with children. Solving these problems will require conscious engineering of our profession. Fortunately, this Decadal Review offers the opportunity to revise outmoded practices to be more effective and equitable. The highest priority of the Subcommittee on the State of the Profession should be to recommend specific, funded activities that will ensure the field meets the challenges we describe.
15041406
Spitzer Space Telescope Observations of the Magnetic Cataclysmic Variable AE Aquarii
The magnetic cataclysmic variable AE Aquarii hosts a rapidly rotating white dwarf that is thought to expel most of the material streaming onto it. Observations of AE Aqr have been obtained in the wavelength range 5-70 μm with the IRS, IRAC, and MIPS instruments on board the Spitzer Space Telescope. The spectral energy distribution reveals a significant excess above the K4 V spectrum of the donor star, with the flux increasing with wavelength above 12.5 μm. Superposed on the energy distribution are several hydrogen emission lines, identified as Pfα and Huα, Huβ, and Huγ. The infrared spectrum above 12.5 μm can be interpreted as synchrotron emission from electrons accelerated to a power-law distribution dN ∝ E-2.4 dE in expanding clouds, with an initial evolutionary timescale of seconds. However, too many components must then be superposed to explain satisfactorily both the mid-infrared continuum and the observed radio variability. Thermal emission from cold circumbinary material could contribute, but it requires a disk temperature profile intermediate between that produced by local viscous dissipation in the disk and that characteristic of a passively irradiated disk. Future high time resolution observations spanning the optical-to-radio regime could shed light on the acceleration process and the subsequent particle evolution.
15773266
Generalised T-duality and non-geometric backgrounds
We undertake a systematic analysis of non-geometric backgrounds in string theory by seeking stringy liftings of a class of gauged supergravity theories. In addition to conventional flux compactifications and non-geometric T-folds with T-duality transition functions, we find a new class of non-geometric backgrounds with non-trivial dependence on the dual coordinates that are conjugate to the string winding number. We argue that T-duality acts in our class of theories, including those cases without isometries in which the conventional Buscher rules cannot be applied, and that these generalised T-dualities can take T-folds or flux compactifications on twisted tori to examples of the new non-geometric backgrounds. We show that the new class of non-geometric backgrounds and the generalised T-dualities arise naturally in string field theory, and are readily formulated in terms of a doubled geometry, related to generalised geometry. At special points in moduli space, some of the non-geometric constructions become equivalent to asymmetric orbifolds which are known to provide consistent string backgrounds. We construct the bosonic sector of the corresponding gauged supergravity theories and show that they have a universal form in any dimension, and in particular construct the scalar potential. We apply this to the supersymmetric WZW model, giving the complete non-linear structure for a class of WZW-model deformations.
13889163
Unity of superstring dualities
Abstract The effective action for type II string theory compactified on a six-torus is N = 8 supergravity, which is known to have an E7 duality symmetry. We show that this is broken by quantum effects to a discrete subgroup, E 7 ( Z ) , which contains both the T-duality group O(6, 6; Z ) and the S-duality group SL(2; Z ). We present evidence for the conjecture that E 7 ( Z ) is an exact ‘U-duality’ symmetry of type II string theory. This conjecture requires certain extreme black hole states to be identified with massive modes of the fundamental string. The gauge bosons from the Ramond-Ramond sector couple not to string excitations but to solitons. We discuss similar issues in the context of toroidal string compactifications to other dimensions, compactifications of the type II string on K3 × T2 and compactifications of 11-dimensional supermembrane theory.
121730347
N=2 current algebra and coset models
Abstract The N = 2 supersymmetric extension of the Kac-Moody algebra and the corresponding Sugawara construction of the N = 2 superconformal algebra are discussed both in components and in N = 1 superspace. A formulation of the Kac-Moody algebra and Sugawara construction is given in N = 2 superspace in terms of supercurrents satisfying a non-linear chiral constraint. The operator product of two supercurrents includes terms that are non-linear in the supercurrents. The N = 2 generalization of the GKO coset construction is then given and the conditions found by Kazama and Suzuki are seen to arise from the non-linearity of the algebra.