118125996
Moduli Stabilization and String Geometry
I describe recent progress in using conformal field theory techniques to describe the stabilization of moduli fields arising in compactifications of type IIB string theory to four dimensions.
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.
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.
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.
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.
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.
12509407
An international intercomparison of environmental dosimeters.
59354134
Qualification tests of the 11 000 photomultipliers for the Pierre Auger Observatory fluorescence detectors
We describe the test system built to perform the acceptance tests of more than 11 000 photomultiplier (PMT) tubes employed in the fluorescence detector of the Pierre Auger Observatory. The results obtained on the properties of the PMT are presented and discussed.
122266663
Methods to determine the angular resolution of the HEGRA extended air shower scintillator array
A precise knowledge of the angular resolution of scintillator arrays used to observe extended air showers (EAS) is of key importance in the search for VHE/UHE γ point sources. Four independent methods have been used to determine the mean resolution for which a value of 〈ΔΘ63〉 of 0.8°(1.0°) at a proton threshold of 50 (40) TeV has been found for the HEGRA EAS-array.
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.
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.