219 research outputs found

    Mixing of Pseudoscalar Mesons

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    Eta-eta' mixing is discussed in the quark-flavor basis with the hypothesis that the decay constants follow the pattern of particle state mixing. On exploiting the divergences of the axial vector currents - which embody the axial vector anomaly - all mixing parameters are fixed to first order of flavor symmetry breaking. An alternative set of parameters is obtained from a phenomenological analysis. We also discuss mixing in the octet-singlet basis and show how the relevant mixing parameters are related to those in the quark-flavor basis. The dependence of the mixing parameters on the strength of the anomaly and the amount of flavor symmetry breaking is investigated. Finally, we present a few applications of the quark-flavor mixing scheme, such as radiative decays of vector mesons, the photon-pseudoscalar meson transition form factors, the coupling constants of eta and eta' to nucleons, and the isospin-singlet admixtures to the pi^0 meson.Comment: 21 pages, 6 figures, Proc. WORKSHOP ON ETA PHYSICS, Uppsala, October 22-27, 200

    Spectator interactions and factorization in B -> pi ell nu decay

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    We investigate the factorization of different momentum modes that appear in matrix elements for exclusive B meson decays into light energetic particles for the specific case of B -> pi form factors at large pion recoil. We first integrate out hard modes with virtualities of order m_b^2 (m_b being the heavy quark mass), and then hard-collinear modes with virtualities m_b Lambda (Lambda being the strong interaction scale). The resulting effective theory contains soft and collinear fields with virtualities Lambda^2. We prove a previously conjectured factorization formula for B -> pi form factors in the heavy quark limit to all orders in alpha_s, paying particular attention to `endpoint singularities' that might have appeared in hard spectator interactions.Comment: Contribution to International Europhysics Conference on High Energy Physics, EPS 2003, Aachen (Germany), 3 pages + 1 figur

    Light-cone sum rules: A SCET-based formulation

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    We describe the construction of light-cone sum rules (LCSRs) for exclusive BB-meson decays into light energetic hadrons from correlation functions within soft-collinear effective theory (SCET). As an example, we consider the SCET sum rule for the B→πB \to \pi transition form factor at large recoil, including radiative corrections from hard-collinear loop diagrams at first order in the strong coupling constant.Comment: LaTex, 4 pages, 2 eps figures. Talk given at QCD05, 12th International QCD Conference, 4-9th July 2005, Montpellier, Franc

    The Overlap Representation of Skewed Quark and Gluon Distributions

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    Within the framework of light-cone quantisation we derive the complete and exact overlap representation of skewed parton distributions for unpolarised and polarised quarks and gluons. Symmetry properties and phenomenological applications are discussed.Comment: LaTex, 36 pages. v2: incorrect paper attached originally. v3: erratum adde

    Soft-collinear effective theory and heavy-to-light currents beyond leading power

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    An important unresolved question in strong interaction physics concerns the parameterization of power-suppressed long-distance effects to hard processes that do not admit an operator product expansion (OPE). Recently Bauer et al.\ have developed an effective field theory framework that allows one to formulate the problem of soft-collinear factorization in terms of fields and operators. We extend the formulation of soft-collinear effective theory, previously worked out to leading order, to second order in a power series in the inverse of the hard scale. We give the effective Lagrangian and the expansion of ``currents'' that produce collinear particles in heavy quark decay. This is the first step towards a theory of power corrections to hard processes where the OPE cannot be used. We apply this framework to heavy-to-light meson transition form factors at large recoil energy.Comment: 46 pages, LaTeX; v2: two references added, eq. (52) correcte

    Multipole-expanded soft-collinear effective theory with non-abelian gauge symmetry

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    In position space the interaction terms of soft-collinear effective theory must be multipole-expanded to obtain interaction terms with homogeneous scaling behaviour. In this note we provide a manifestly gauge-invariant formulation of the theory after this expansion in the presence of non-abelian gauge fields, extending our previous result. We give the effective Lagrangian (including the Yang-Mills Lagrangian for collinear and ultrasoft gluons) and heavy-to-light transition currents to second order in the power expansion, paying particular attention to the field redefinitions that lead to the gauge symmetries of the effective Lagrangian.Comment: 11 pages, LaTe

    Proton mass effects in wide-angle Compton scattering

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    We investigate proton mass effects in the handbag approach to wide-angle Compton scattering. We find that theoretical uncertainties due to the proton mass are significant for photon energies presently studied at Jefferson Lab. With the proposed energy upgrade such uncertainties will be clearly reduced.Comment: 4 pages, uses revtex, 3 figure

    Systematic approach to exclusive B ->V l^+l^-, V gamma decays

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    We show -- by explicit computation of first-order corrections -- that the QCD factorization approach previously applied to hadronic two-body decays and to form factor ratios also allows us to compute non-factorizable corrections to exclusive, radiative B meson decays in the heavy quark mass limit. This removes a major part of the theoretical uncertainty in the region of small invariant mass of the photon. We discuss in particular the decays B\to K^* \gamma and B\to K^* l^+l^- and complete the calculation of corrections to the forward-backward asymmetry zero. The new correction shifts the asymmetry zero by 30%, but the result confirms our previous conclusion that the asymmetry zero provides a clean phenomenological determination of the Wilson coefficient C_9.Comment: 34 pages, LaTeX; (v2): reference added, typo in Eq. (93) corrected, Eq. (47) + conventions in Table 1 correcte
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