19013941
String dynamics at strong coupling
The dynamics of superstring, supergravity and M-theories and their compactifications are probed by studying the various perturbation theories that emerge in the strong and weak-coupling limits for various directions in coupling constant space. The results support the picture of an underlying non-perturbative theory that, when expanded perturbatively in different coupling constants, gives different perturbation theories, which can be perturbative superstring theories or superparticle theories. The p-brane spectrum is considered in detail and a criterion found to establish which p-branes govern the strong-coupling dynamics. In many cases there are competing conjectures in the literature, and this analysis decides between them. In other cases, new results are found. The chiral 6-dimensional theory resulting from compactifying the type IIB string on K3 is studied in detail and it is found that certain strong-coupling limits appear to give new theories, some of which hint at the possibility of a 12-dimensional origin.
16699525
Duality and Strings, Space and Time
Duality symmetries in M--theory and string theory are reviewed, with particular emphasis on the way in which string winding modes and brane wrapping modes can lead to new spatial dimensions. Brane world-volumes wrapping around Lorentzian tori can give rise to extra time dimensions and in this way dualities can change the number of time dimensions as well as the number of space dimensions. This suggests that brane wrapping modes and spacetime momenta should be on an equal footing and M--theory should not be formulated in a spacetime of definite dimension or signature.
53609381
Generalized metric formulation of double field theory
The generalized metric is a T-duality covariant symmetric matrix constructed from the metric and two-form gauge field and arises in generalized geometry. We view it here as a metric on the doubled spacetime and use it to give a simple formulation with manifest T-duality of the double field theory that describes the massless sector of closed strings. The gauge transformations are written in terms of a generalized Lie derivative whose commutator algebra is defined by a double field theory extension of the Courant bracket.
16768456
String-string duality in ten dimensions
Abstract The heterotic string occurs as a soliton of the type I superstring in ten dimensions, supporting the conjecture that these two theories are equivalent. The conjecture that the type IIB string is self-dual, with the strong coupling dynamics described by a dual type IIB theory, is supported by the occurrence of the dual string as a Ramond-Ramond soliton of the weakly coupled theory.
12805037
BPS supermultiplets in five dimensions
BPS representations of 5-dimensional supersymmetry algebras are classified. For BPS states preserving 1/2 the supersymmetry, there are two distinct classes of multiplets for N = 4 supersymmetry and three classes for N = 8 supersymmetry. For N = 4 matter theories, the two 1/2 supersymmetric BPS multiplets are the massive vector multiplet and the massive self-dual 2-form multiplet. Some applications to super-Yang-Mills, supergravity and little string theories are considered.
122185797
World Sheet Supergravity Anomaly Cancellation for the Heterotic String in a Ten-dimensional Supergravity Background
Abstract The world-sheet (1,0) superspace-supergravity action for the heterotic string in an arbitrary (bosonic) ten-dimensional supergravity background is presented. By means of a (1,0) supergraph computation it is shown that the world-sheet supergravitational and superconformal anomalies arising from the nontrivial background cancel if the conformal anomaly cancels, at least to leading nontrivial order in α′.
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.
195323488
Spitzer IRS Observations of Class I/II Objects in Taurus: Composition, Temperature and Thermal History of the Circumstellar Ices
We present observations of Taurus-Auriga Class I/II protostars obtained with the Spitzer InfraRed Spectrograph. Detailed spectral fits to the 6 and 15 micron features are made, using publicly-available laboratory data, to constrain the molecular composition, abundances, and levels of thermal processing along the lines of sight. We provide an inventory of the molecular environments observed, which have an average composition dominated by water ice with ∼12% CO2 (abundance relative to H2O), &2-9% CH3OH, .14% NH3, ∼4% CH4, ∼2% H2CO, ∼0.6% HCOOH, and ∼0.5% SO2. We find CO2/H2O ratios nearly equivalent to those observed in cold clouds and lines of sight toward the galactic center. The unidentified 6.8 micron profile shapes vary from source to source, and it is shown to be likely that even combinations of the most common candidates (NH4 and CH3OH) are inadequate to explain the feature fully. We discuss correlations among SED spectral indices, abundance ratios, and thermallyprocessed ice fractions and their implications for CO2 formation and evolution. Comparison of our spectral fits to cold molecular cloud sight-lines indicate abundant prestellar ice environments made even richer by the radiative effects of protostars. Our results add additional constraints and a finer level of detail to current full-scale models of protostellar and protoplanetary systems. Subject headings: stars: pre-main sequence — ISM: abundances — ISM: molecules — infrared: ISM — astrochemistry
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.
49776726
THE ALLEN TELESCOPE ARRAY Pi GHz SKY SURVEY. I. SURVEY DESCRIPTION AND STATIC CATALOG RESULTS FOR THE BOOeTES FIELD
The Pi GHz Sky Survey (PiGSS) is a key project of the Allen Telescope Array. PiGSS is a 3.1 GHz survey of radio continuum emission in the extragalactic sky with an emphasis on synoptic observations that measure the static and time-variable properties of the sky. During the 2.5 year campaign, PiGSS will twice observe similar to 250,000 radio sources in the 10,000 deg(2) region of the sky with b > 30 degrees to an rms sensitivity of similar to 1 mJy. Additionally, sub-regions of the sky will be observed multiple times to characterize variability on timescales of days to years. We present here observations of a 10 deg(2) region in the Bootes constellation overlapping the NOAO Deep Wide Field Survey field. The PiGSS image was constructed from 75 daily observations distributed over a 4 month period and has an rms flux density between 200 and 250 mu Jy. This represents a deeper image by a factor of 4-8 than we will achieve over the entire 10,000 deg(2). We provide flux densities, source sizes, and spectral indices for the 425 sources detected in the image. We identify similar to 100 new flat-spectrum radio sources; we project that when completed PiGSS will identify 10(4) flat-spectrum sources. We identify one source that is a possible transient radio source. This survey provides new limits on faint radio transients and variables with characteristic durations of months.