Free Field Approach to 2-Dimensional Conformal Field Theories

title: Free field representation for SU(2)k WZNW models on Riemann surfaces
abstract: We give the extension of the free field representation of SU (2) k WZNW model conformal blocks to an arbitrary Riemann surface. In particular, we avoid the problems associated with the vertex corresponding to the dual of a given representation - namely that it does not transform as the appropriate highest weight field of the current algebra - in a way allowing the sewing procedure to be applied. After analysing the two-point function on the torus as an illustration of some of the subtleties in this free field representation, we go on to give the genus-two characters as an application.

title: Theoretical problems in nonsymmetric gravitational theory.
abstract: It has recenty been noted that the nonsymmetric metric model of gravity faces severe observational constraints. We show here that it is also subject to physically unacceptable formal difficulties even as an effective field theory: When expanded about a Riemannian background, the model exhibits curvature-coupled negative-energy (ghost) modes and unacceptable asymptotic behavior.

title: Nonsymmetric gravity theories: Inconsistencies and a cure.
abstract: Motivated by the apparent dependence of string σ models on the sum of spacetime metric and antisymmetric tensor fields, we reconsider gravity theories constructed from a nonsymmetric metric. We first show, by expanding in powers of the antisymmetric field, that all such ‘‘geometrical’’ theories homogeneous in second derivatives violate standard physical requirements: ghost freedom, absence of algebraic inconsistencies, or continuity of degree-of-freedom content. This no-go result applies in particular to the old unified theory of Einstein and its recent avatars. However, we find that the addition of nonderivative, ‘‘cosmological’’ terms formally restores consistency by giving a mass to the antisymmetric tensor field, thereby transmuting it into a fifth-force-like massive vector but with novel possible matter couplings. The resulting macroscopic models also exhibit ‘‘van der Waals’’–type gravitational effects, and may provide useful phenomenological foils to general relativity.

title: Observation of the decay $B_c \rightarrow J/\psi K^+ K^- \pi^+ $
abstract: The decay $B_c\rightarrow J/\psi K^+ K^- \pi^+$ is observed for the first time, using proton-proton collisions collected with the LHCb detector corresponding to an integrated luminosity of 3fb$^{-1}$. A signal yield of $78\pm14$ decays is reported with a significance of 6.2 standard deviations. The ratio of the branching fraction of $\B_c \rightarrow J/\psi K^+ K^- \pi^+$ decays to that of $B_c \rightarrow J/\psi \pi^+$ decays is measured to be $0.53\pm 0.10\pm0.05$, where the first uncertainty is statistical and the second is systematic.

title: G**p(E) / G**p(M) for bound protons: first results for O-16 with the recoil polarization technique
abstract: The first (e,e'p) polarization transfer measurements on a nucleus heavier than deuterium have been carried out at Jefferson Laboratory. Transverse and longitudinal components of the polarization of protons ejected in the reaction 16O(e,e'p) were measured in quasielastic perpendicular kinematics at a Q^2 of 0.8 (GeV/c)^2. The data are in good agreement with state of the art calculations, but do not exclude possible changes in the ratio of the electric to magnetic form factors of the nucleon in the nuclear medium at the level of recent theoretical predictions.

title: A solid polarized target for high-luminosity experiments
abstract: We have built a polarized proton and deuteron target for experiments using intense high-energy electron beams. This system exploits dynamical nuclear polarization of irradiated ammonia in a 5 T magnetic field at temperatures near 1 K. We describe the various features and the performance of the target.

title: Model calculation of nucleon structure functions
abstract: Deep inelastic polarized and unpolarized structure functions for a free nucleon are obtained in a modified center-of-mass bag model, which includes the symmetry-breaking effects from spin-dependent interactions. The quark distribution functions, calculated at [ital Q][sub 0][sup 2][congruent](0.9 GeV/[ital c])[sup 2], are evolved to a higher [ital Q][sup 2] region and compared with the data and other models. The model gives a reasonable description for the valence part of the structure functions at [ital x][gt]0.3. For the small-[ital x] region, the contributions from the sea are necessary. The spin-dependent effects are important in describing the existing data.

title: Measurement of the track reconstruction efficiency at LHCb
abstract: The determination of track reconstruction efficiencies at LHCb using J/psi -> mu(+)mu(-) decays is presented. Efficiencies above 95% are found for the data taking periods in 2010, 2011, and 2012. The ratio of the track reconstruction efficiency of muons in data and simulation is compatible with unity and measured with an uncertainty of 0.8% for data taking in 2010, and at a precision of 0.4% for data taking in 2011 and 2012. For hadrons an additional 1.4% uncertainty due to material interactions is assumed. This result is crucial for accurate cross section and branching fraction measurements in LHCb.