17056116
A two-loop test of M(atrix) theory
Abstract We consider the scattering of two Dirichlet zero-branes in M(atrix) theory. Using the formulation of M(atrix) theory in terms of ten-dimensional super Yang-Mills theory dimensionally reduced to (0+1) dimensions, we obtain the effective (velocity-dependent) potential describing these particles. At one loop we obtain the well-known result for the leading order of the effective potential V eff ∼ v 4 / r 7 , where v and r are the relative velocity and distance between the two zero-branes, respectively. A calculation of the effective potential at two loops shows that no renormalizations of the v 4 term of the effective potential occur at this order.
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.
41684471
Testing M(atrix) theory at two loops
Abstract I discuss the relation between M-theory and M(atrix)-theory in flat space by considering the effective potential for the scattering of two groups of D0-branes in both theories. An explicit calculation of this potential up to two loop order in M(atrix)-theory reveals a fascinating agreement.
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.
14726887
Compactifying M-theory to four dimensions
We consider compactifications of M-theory to four-dimensional Minkowski space on seven-dimensional non-compact manifolds. These compactifications include a warp factor which is non constant due to the presence of sources coming from five-branes wrapping two-dimensional submanifolds of the internal seven-dimensional space. We derive the expression for the field strengths and consider an explicit example of this general class of solutions.
40898720
A fast embedded system for radio detection of cosmic rays
For the detection of radio signals from ultra high energy (> 1017 eV) cosmic rays in the frequency range up to 80 MHz an embedded system was designed, built, and tested. A steep band-pass filter in the range of 30 to 80 MHz suppresses the main source of radio frequency interferences. To fulfill the data acquisition (DAQ) task, four 180 MHz twelve bit ADCs have to be read-out by a FPGA into a two gigabyte buffer memory. Furthermore the FPGA contains the trigger and a Altera NIOS II soft-core processor for data management. A GPS receiver controls the timing of the system. For the read-out an Ethernet-link and a CAN interface to a WLAN communication board is foreseen. The architecture of the system and the measured performance of the DAQ-board are described.
125135710
THE FREJUS NUCLEON DECAY EXPERIMENT
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.
109075983
Development of a new first level trigger for the surface array in the Pierre Auger Observatory based on the CycloneTM Altera® FPGA
Abstract The development of a new first level trigger for the surface array in the Pierre Auger Observatory is described. It utilizes the new Altera ® family Cyclone TM which is available since March 2003. Different from previous and the currently used design based on the APEX TM and ACEX ® families, respectively, it offers much higher capacity of logic registers and memories, a simplified board design, lower power consumption, and lower cost. The paper describes the board design, internal structures of the programming routines, various trigger implementations and test results obtained in the laboratory.
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.