219 research outputs found

### Mixing of Pseudoscalar Mesons

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

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

We describe the construction of light-cone sum rules (LCSRs) for exclusive
$B$-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 $B \to \pi$ 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

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

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

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

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

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

- â€¦