118470926
Disc amplitudes, picture changing and space-time actions
A bstractWe study in detail the procedure for obtaining couplings of D-branes to closed string fields by evaluating string theory disc amplitudes. We perform a careful construction of the relevant vertex operators and discuss the effects of inserting the boundary state which encodes the presence of the D-brane. We confront the issue of non-decoupling of BRSTexact states and prove that the problem is evaded for the computations we need, thus demonstrating that our amplitudes are automatically gauge-invariant and independent of the distribution of picture charge. Finally, we compute explicitly the two-point amplitudes of two NS-NS fields or one NS-NS and one R-R field on the disc, and we carefully compare all the lowest order terms with predictions from supergravity.
2844671
Graviton scattering amplitudes in M theory
We compute graviton scattering amplitudes in M theory using Feynman rules for a scalar particle coupled to gravity in eleven dimensions. The processes that we consider describe the single graviton exchange and the double graviton exchange, that in M(atrix) theory correspond to the v^4/r^7 and v^6/r^14 term, respectively. We argue that the v^6/r^14 term appearing in M(atrix) theory at two loops can be obtained from the covariant eleven-dimensional four-graviton amplitude. Finally, we calculate the v^8/r^18 term appearing at two loops in M(atrix) theory. It has been previously conjectured that this term is related to a four graviton scattering amplitude involving the R^4 vertex of M theory.
16083194
Supersymmetry breaking, heterotic strings and fluxes
In this paper we consider compactifications of heterotic strings in the presence of background flux. The background metric is a T2 fibration over a K3 base times four-dimensional Minkowski space. Depending on the choice of three-form flux different amounts of supersymmetry are preserved (N=2,1,0). For supersymmetric solutions unbroken space–time supersymmetry determines all background fields except one scalar function which is related to the dilaton. The heterotic Bianchi identity gives rise to a differential equation for the dilaton which we discuss in detail for solutions preserving an N=2 supersymmetry. In this case the differential equation is of Laplace type and as a result the solvability is guaranteed.
7411732
A note on fluxes in six-dimensional string theory backgrounds
Abstract We study the structure of warped compactifications of type IIB string theory to six space–time dimensions. We find that the most general four-manifold describing the internal dimensions is conformal to a Kahler manifold, in contrast with the heterotic case where the four-manifold must be conformally Calabi–Yau.
118439643
Higher derivative brane couplings from T-duality
The Wess-Zumino coupling on D-branes in string theory is known to receive higher derivative corrections which couple the Ramond-Ramond potential to terms involving the square of the spacetime curvature tensor. Consistency with T-duality implies that the branes should also have four-derivative couplings that involve the NS-NS B-field. We use T-duality to predict some of these couplings. We then confirm these results with string worldsheet computations by evaluating disc amplitudes with insertions of one R-R and two NS-NS vertex operators.
14043557
Fivebranes, membranes and non-perturbative string theory
Abstract Non-perturbative instanton corrections to the moduli space geometry of type IIA string theory compactified on a Calabi-Yau space are derived and found to contain order e −1/ g s contributions, where g s is the string coupling. The computation reduces to a weighted sum of supersymmetric extremal maps of strings, membranes and fivebranes into the Calabi-Yau space, all three of which enter on equal footing. It is shown that a supersymmetric 3-cycle is one for which the pullback of the Kahler form vanishes and the pullback of the holomorphic three-form is a constant multiple of the volume element. Quantum mirror symmetry relates the sum in the IIA theory over supersymmetric, odd-dimensional cycles in the Calabi-Yau space to a sum in the IIB theory over supersymmetric, even-dimensional cycles in the mirror.
12509407
An international intercomparison of environmental dosimeters.
2219103
AMANDA - first running experiment to use GRID in production
The Grid technologies are in ongoing development. Using current Grid toolkits like the Globus toolkit gives one the possibility to build up virtual organizations. Although these tookits are in still under development and do not feature all functionality, they can already now be used to set up an efficient computing environment for physics collaborations with only moderate work. We discuss in this paper the use of such a computing structure in two running experiments - the AMANDA (AMANDA = Antarctic muon and neutrino detector array) neutrino telescope and the D0 experiment at Tevatron, Fermilab. One of the main features of our approach is to avoid reprogramming of the existing software which is based on several programming languages (FORTRAN, C/C++, JAVA). This was realized with software layers around the collaboration software taking care about in- and output, user notification, tracking of running jobs, etc. A further important aspect is the resolution of library dependencies, which occur when a user runs self-compiled jobs on machines, where these libraries are not installed. These dependencies are also resolved with this layers.
6918482
Faint Scattering Around Pulsars: Probing the Interstellar Medium on Solar System Size Scales
We have made high-resolution, high-sensitivity dynamic spectra of a sample of strong pulsars at 430 MHz with the Arecibo radio telescope. For four pulsars we find faint but sharply delineated features in the secondary spectra. These are examples of the previously observed "crisscross" or "multiple drift slope" phenomenon presumed to be due to multiple imaging of the pulsar by the interstellar medium (ISM). The unprecedented resolution and dynamic range of our observations allow a deeper level of analysis. Distances to the dominant scattering screen along the line of sight are determined and are shown to agree well with those inferred from other scintillation phenomena. Multiple imaging of the pulsar by the ISM is required. A compact central image surrounded by a faint scattering halo, roughly circularly symmetric, is consistent with the data. Scattering from filaments may also be consistent. The angular extent of the scattering material parallel to the direction of the pulsar velocity is ~5 mas, corresponding to a linear extent of ~2 AU. Further observations of these features should allow better discrimination between models and an identification of the scattering structures.
124471126
The 3rd generation Front-End cards of the Pierre Auger surface detectors: Test results and performance in the field
The surface detector array of the Pierre Auger Observatory comprises 1600 water Cherenkov detectors distributed over an area of 3000 km 2 . The Cherenkov light is detected by three 9-in. photo-multiplier tubes from which the signals of the anode and last dynode are digitized by 10 bit 40 MHz FADCs. An Altera Cyclone FPGA is employed to generate different local triggers and to handle the data transfer to a communication board. After briefly discussing the design of the cards we present an autonomous test-bench, which has been set up in order to test the large number of boards prior to installation in the field. The qualification procedure and the results obtained in the laboratory are presented. Up to three years of operation in the field demonstrate a very good performance and reliability of the Front-End cards.
4411256
Discovery of radio emission from the brown dwarf LP944-20
Brown dwarfs are not massive enough to sustain thermonuclear fusion of hydrogen at their centres, but are distinguished from gas-giant planets by their ability to burn deuterium. Brown dwarfs older than ∼10 Myr are expected to possess short-lived magnetic fields and to emit radio and X-rays only very weakly from their coronae. An X-ray flare was recently detected on the brown dwarf LP944-20, whereas previous searches for optical activity (and one X-ray search) yielded negative results. Here we report the discovery of quiescent and flaring radio emission from LP944-20, with luminosities several orders of magnitude larger than predicted by the empirical relation between the X-ray and radio luminosities that has been found for many types of stars. Interpreting the radio data within the context of synchrotron emission, we show that LP944-20 has an unusually weak magnetic field in comparison to active M-dwarf stars, which might explain the previous null optical and X-ray results, as well as the strength of the radio emissions compared to those at X-ray wavelengths.