Extended N=2 Superconformal Structure of Gravity and W-Gravity Coupled to Matter

We show that almost all string theories, including the bosonic string, the superstring and $W$-string theories, possess a twisted N=2 superconformal symmetry. This enables us to establish a connection between topological gravity and the field theoretical description of matter coupled to gravity. We also show how the \brs operators of the $W_n$-string can be obtained by hamiltonian reduction of $SL(n|n-1)$. The tachyonic and ground ring states of $W$-strings are described in the light of the N=2 superconformal structure, and the ground ring generators for the non-critical $W_3$-string are explicitly constructed. The relationship to $G/G$ models and quantum integrable systems is also briefly described.Comment: 48 page

Diffusive electron acceleration at SNR shock fronts and the observed SNR radio spectral indices

The radio synchrotron emission from relativistic electrons in shell supernova remnants (SNRs) provides a unique opportunity to probe the energy distribution of energetic electrons at their acceleration site (SNR shock fronts). This information provides insight into the acceleration mechanism(s). The implications of these observations for the diffusive (first-order Fermi) acceleration of electrons at the SNR shock fronts are discussed

Calculations for Mirror Symmetry with D-branes

We study normal functions capturing D-brane superpotentials on several one- and two-parameter Calabi-Yau hypersurfaces and complete intersections in weighted projective space. We calculate in the B-model and interpret the results using mirror symmetry in the large volume regime, albeit without identifying the precise A-model geometry in all cases. We identify new classes of extensions of Picard-Fuchs equations, as well as a novel type of topology changing phase transition involving quantum D-branes. A 4-d domain wall which is obtained in one region of closed string moduli space from wrapping a four-chain interpolating between two Lagrangian submanifolds is, for other values of the parameters, represented by a disk ending on a single Lagrangian.Comment: 42 page

On Heterotic/Type I Duality in d=8

We discuss heterotic corrections to quartic internal U(1) gauge couplings and check duality by calculating one-loop open string diagrams and identifying the D-instanton sum in the dual type I picture. We also compute SO(8)^4 threshold corrections and finally R^2 corrections in type I theory.Comment: 9 pages, Latex, To appear in the proceedings of "Quantum Aspects of Gauge Theories, Supersymmetries and Unification", Corfu, September 199

Bright Flash Neutron Radiography at the McClellan Nuclear Research Reactor

AbstractThe University of California, Davis McClellan Nuclear Research Center (MNRC) operates a 2 MW TRIGATM reactor, which is currently the highest power TRIGATM reactor in the United States. The Center was originally build by the US Air Force to detect hidden defects in aircraft structures using neutron radiography; the Center can accommodate samples as large as 10.00 m long, 3.65 m high, and weighing up to 2,270kg.The MNRC reactor can be pulsed to 350 MW for about 30ms (FWHM). The combination of a short neutron pulse with a fast microchannel plate based neutron detector enables high-resolution flash neutron radiography to complement conventional neutron radiograph

Hints for Off-Shell Mirror Symmetry in type II/F-theory Compactifications

We perform a Hodge theoretic study of parameter dependent families of D-branes on compact Calabi-Yau manifolds in type II and F-theory compactifcations. Starting from a geometric Gauss-Manin connection for B type branes we study the integrability and flatness conditions. The B model geometry defines an interesting ring structure of operators. For the mirror A model this indicates the existence of an open-string extension of the so-called A model connection, whereas the discovered ring structure should be part of the open-string A model quantum cohomology. We obtain predictions for genuine Ooguri-Vafa invariants for Lagrangian branes on the quintic in P4 that pass some non-trivial consistency checks. We discuss the lift of the brane compactifications to F-theory on Calabi-Yau 4-folds and the effective couplings in the effective supergravity action as determined by the N = 1 special geometry of the open-closed deformation space.Comment: 49 pages, 1 table; v2: Appendix and references added, minor corrections; v3: discussion in sect. 2 extended, version published in Nucl.Phys.

Aspects of quark mass generation on a torus

In this talk we report on recent results for the quark propagator on a compact manifold. The corresponding Dyson-Schwinger equations on a torus are solved on volumes similar to the ones used in lattice calculations. The quark-gluon interaction is fixed such that the lattice results are reproduced. We discuss both the effects in the infinite volume/continuum limit as well as effects when the volume is small.Comment: 3 pages, 3 figures; talk given by CF at QNP06, Madrid, June 200

New Symmetries of Supersymmetric Effective Lagrangians

We consider the structure of effective lagrangians describing the low-energy dynamics of supersymmetric theories in which a global symmetry $G$ is spontaneously broken to a subgroup $H$ while supersymmetry is unbroken. In accordance with the supersymmetric Goldstone theorem, these lagrangians contain Nambu--Goldstone superfields associated with a coset space $G^c / \hat{H}$, where $G^c$ is the complexification of $G$ and $\hat{H}$ is the largest subgroup of $G^c$ that leaves the order parameter invariant. The lagrangian may also contain additional light matter fields. To analyze the effective lagrangian for the matter fields, we first consider the case where the effective lagrangian is obtained by integrating out heavy modes at weak coupling (but including non-perturbative effects such as instantons). We show that the superpotential of the matter fields is $\hat{H}$ invariant, which can give rise to non-trivial relations among independent $H$-invariants in the superpotential. We also show that the Kahler potential of the matter fields can be restricted by a remnant of $\hat{H}$ symmetry. These results are non-perturbative and have a simple group-theoretic interpretation. When we relax the weak-coupling constraint, there appear to be additional possibilities for the action of $\hat{H}$ on the matter fields, hinting that the constraints imposed by $\hat{H}$ may be even richer in strongly coupled theories.Comment: 23 pages, plain Te

Heterotic/type I duality, D-instantons and an N=2 AdS/CFT correspondence

D-instanton effects are studied for the IIB orientifold T^2/I\Omega(-1)^{F_L} of Sen using type I/heterotic duality. An exact one loop threshold calculation of t_8 \tr F^4 and t_8(\tr F^2)^2 terms for the heterotic string on T^2 with Wilson lines breaking SO(32) to SO(8)^4 is related to D-instanton induced terms in the worldvolume of D7 branes in the orientifold. Introducing D3 branes and using the AdS/CFT correspondence in this case, these terms are used to calculate Yang-Mills instanton contributions to four point functions of the large N_c limit of N=2 USp(2N_c) SYM with four fundamental and one antisymmetric tensor hypermultiplets.Comment: 25 pages, harvmac(b), one figure, v2: minor changes, version to appear in PR

Channeled blast wave behavior based on longitudinal instabilities

To address the important issue of how kinetic energy of collimated blast waves is converted into radiation, Pohl & Schlickeiser (2000) have recently investigated the relativistic two-stream instability of electromagnetic turbulence. They have shown that swept-up matter is quickly isotropized in the blast wave, which provides relativistic particles and, as a result, radiation. Here we present new calculations for the electrostatic instability in such systems. It is shown that the electrostatic instability is faster than the electromagnetic instability for highly relativistic beams. However, even after relaxation of the beam via the faster electrostatic turbulence, the beam is still unstable with respect to the electromagnetic waves, thus providing the isotropization required for efficient production of radiation. While the emission spectra in the model of Pohl and Schlickeiser have to be modified, the basic characteristics persist.Comment: Astronomy & Astrophysics, in pres