Photon-photon elastic scattering in the visible domain
We are investigating the direct detection of photon-photon elastic scattering at optical energies. In a first experiment using two high-intensity pulsed laser beams, we have explored the feasibility of the method, and in particular the rejection of back-ground noise. We obtained an upper limit of the photon-photon elastic scattering cross section at 95% confidence level of 10−39 cm2. This limit can be lowered by twenty orders of magnitude by stimulating the scattering by a third beam, and by using high repetition rate existing lasers.

title: Operation of the Cherenkov detector DIRC of BABAR at high luminosity
abstract: The DIRC (acronym for Detection of Internally Reflected Cherenkov (light)) is the ring imaging Cherenkov detector of the BABAR detector at the PEP-II ring of SLAC. It provides the identification of pions, kaons and protons for momenta up to 4 GeV/c with high efficiency. This is needed to reconstruct CP-violating B-decay final states and to provide B-meson flavour tagging for time dependent asymmetry measurements. The DIRC radiators consists of long rectangular bars made of synthetic fused silica and the photon detector is a water tank equipped with an array of 10.752 conventional photomultipliers. At the end of the year 2000 BABAR has recorded about 22 million B~B pairs reaching the design luminosity of L=3/spl middot/10/sup 33//cm/sup 2/s. The ability to keep the beam background level low at highest collision rates and the long term reliability of the DIRC components during continuous data taking are requirements of BABAR to accomplish its physics program.

title: Measurement of the CKM matrix element $|V_{ub}|$ with $B \to \rho e \nu$ decays

title: Measurements of branching fractions and CP-violating asymmetries in B-meson decays to the charmless two-body states K0 pi+, anti-K0 K+, and K0 anti-K0

title: Improved Measurement of CP Violation in Neutral B Decays to c cs

title: Branching fraction for $B^{+} \to \pi^0 \ell^{+} \nu$, measured in $\upsilon_{4S} \to B \bar{B}$ events tagged by $B^{-} \to D^0 \ell^{-}$ anti-v ($X$) decays

title: Edge states for topological insulators in two dimensions and their Luttinger-like liquids
abstract: Topological insulators in three spatial dimensions are known to possess a precise bulk-boundary correspondence, in that there is a one-to-one correspondence between the five classes characterized by bulk topological invariants and Dirac Hamiltonians on the boundary with symmetry protected zero modes. This holographic characterization of topological insulators is studied in two dimensions. Dirac Hamiltonians on the one-dimensional edge are classified according to the discrete symmetries of time reversal, particle hole, and chirality, extending a previous classification in two dimensions. We find 17 inequivalent classes, of which 11 have protected zero modes. Although bulk topological invariants are thus far known for only five of these classes, we conjecture that the additional six describe edge states of new classes of topological insulators. The effects of interactions in two dimensions are also studied. We show that all interactions that preserve the symmetry are exactly marginal, i.e., preserve the gaplessness. This leads to a description of the distinct variations of Luttinger liquids that can be realized on the edge.

title: String characters from kac-moody automorphisms
abstract: We construct modular invariant partition functions for strings which propagate on a group manifold. These string characters are built upon automorphisms of affine Kac-Moody algebras. Namely, to each element of the center of the group we associate infinite series of modular invariant string characters.

title: Strong–weak coupling duality in anisotropic current interactions
abstract: The recently proposed all orders β function for current interactions in two dimensions is further investigated. By using a strong–weak coupling duality of the β function, and some added topology of the space of couplings we are able to extend the flows to arbitrarily large or small scales. Using a nontrivial RG invariant we are able to identify sine-Gordon, sinh-Gordon and Kosterlitz–Thouless phases. We also find an additional phase with cyclic or roaming RG trajectories.

title: AFFINE SOLITONS: A RELATION BETWEEN TAU FUNCTIONS, DRESSING AND BÄCKLUND TRANSFORMATIONS
abstract: We reconsider the construction of solitons by dressing transformations in the sine-Gordon model. We show that the N-soliton solutions are in the orbit of the vacuum, and we identify the elements in the dressing group which allow us to build the N-soliton solutions from the vacuum solution. The dressed τ functions can be computed in two different ways: either using adjoint actions in the affine Lie algebra , and this gives the relation with the Backlund transformations, or using the level-one representations of the affine Lie algebra , and this directly gives the formulae for the τ functions in terms of vertex operators.

title: Non-local currents in 2D QFT: An alternative to the quantum inverse scattering method