Pion and Rho Structure Functions from Lattice QCD

We calculate the lower moments of the deep-inelastic structure functions of the pion and the rho meson on the lattice. Of particular interest to us are the spin-dependent structure functions of the rho. The calculations are done with Wilson fermions and for three values of the quark mass, so that we can perform an extrapolation to the chiral limit.Comment: 30pp, LaTeX2e with 15 eps figures using epsfig. Postscript file also available from ftp://ftp.th.physik.uni-frankfurt.de/pub/cbest/pionrho.ps or http://www.th.physik.uni-frankfurt.de/~cbest/pionrho.p

Formalism for dilepton production via virtual photon bremsstrahlung in hadronic reactions

We derive a set of new formulas for various distributions in dilepton production via virtual photon bremsstrahlung from pseudoscalar mesons and unpolarized spin-one-half fermions. These formulas correspond to the leading and sub-leading terms in the Low-Burnett-Kroll expansion for real photon bremsstrahlung. The relation of our leading-term formulas to previous works is also shown. Existing formulas are examined in the light of Lorentz covariance and gauge invariance. Numerical comparison is made in a simple example, where an "exact" formula and real photon data exist. The results reveal large discrepancies among different bremsstrahlung formulas. Of all the leading-term bremsstrahlung formulas, the one derived in this work agrees best with the exact formula. The issues of M_T-scaling and event generators are also addressed.Comment: 37 pages, RevTeX, epsf.sty, 10 embedded figure

Worldline Approach to Forward and Fixed Angle fermion-fermion Scattering in Yang-Mills Theories at High Energies

Worldline techniques are employed to study the general behaviour of the fermion-fermion collision amplitude at very high energies in a non-abelian gauge field theory for the forward and fixed angle scattering cases. A central objective of this work is to demonstrate the simplicity by which the worldline methodology isolates that sector of the full theory which carries the soft physics, relevant to each process. Anomalous dimensions pertaining to a given soft sector are identified and subseuently used to facilitate the renormalization group running of the respective four point functions. Gluon reggeization is achieved for forward, while Sudakov suppression is established for fixed angle scattering.Comment: 28 pages, 10 figures in three file

Weak gauge principle and electric charge quantization

Starting from a weak gauge principle we give a new and critical revision of the argument leading to charge quantization on arbitrary spacetimes. The main differences of our approach with respect to previous works appear on spacetimes with non trivial torsion elements on its second integral cohomology group. We show that in these spacetimes there can be topologically non-trivial configurations of charged fields which do not imply charge quantization. However, the existence of a non-exact electromagnetic field always implies the quantization of charges. Another consequence of the theory for spacetimes with torsion is the fact that it gives rise to two natural quantization units that could be identified with the electric quantization unit (realized inside the quarks) and with the electron charge. In this framework the color charge can have a topological origin, with the number of colors being related to the order of the torsion subgroup. Finally, we discuss the possibility that the quantization of charge may be due to a weak non-exact component of the electromagnetic field extended over cosmological scales.Comment: Latex2e, 24 pages, no figure

Parton distribution functions from nonlocal light-cone operators with definite twist

We introduce the chiral-even and chiral-odd quark distributions as forward matrix elements of related bilocal quark operators with well-defined (geometric) twist. Thereby, we achieve a Lorentz invariant classification of these distributions which differ from the conventional ones by explicitly taking into account the necessary trace terms. The relations between both kinds of distribution functions are given and the mismatch between their different definition of twist is discussed. Wandzura-Wilczek--like relations between the conventional distributions (based on dynamical twist) are derived by means of geometric twist distribution functions.Comment: 17 pages, REVTEX, Extended version, The Introduction has been rewritten, Setion V "Wandzura-Wilczek--like relations" and App. B are added; Sign errors are correcte

A Dependence of Hadron Production in Inelastic Muon Scattering and Dimuon Production by Protons

The A dependence of the production of hadrons in inelastic muon scattering and of the production of dimuons in high $Q^2$ proton interactions are simply related. Feynman x distributions and z scaling distributions in nuclei are compared with energy loss models. Suggestions for new data analyses are presented.Comment: 14pp +13 figures, UPR report 607T (available from ftp://dept.physics.upenn.edu/muhad

Proton--induced deuteron breakup at GeV energies with forward emission of a fast proton pair

A study of the deuteron breakup reaction $pd \to (pp)n$ with forward emission of a fast proton pair with small excitation energy $E_{pp}<$ 3 MeV has been performed at the ANKE spectrometer at COSY--J\"ulich. An exclusive measurement was carried out at six proton--beam energies $T_p=$~0.6,~0.7,~0.8,~0.95,~1.35, and 1.9 GeV by reconstructing the momenta of the two protons. The differential cross section of the breakup reaction, averaged up to $8^{\circ}$ over the cm polar angle of the total momentum of the $pp$ pairs, has been obtained. Since the kinematics of this process is quite similar to that of backward elastic $pd \to dp$ scattering, the results are compared to calculations based on a theoretical model previously applied to the $pd \to dp$ process.Comment: 17 pages including 6 figures and 1 table v2: minor changes; v3: minor change of author list; v4: changes in accordance with referee remark

Strong coupling of excited heavy mesons

We compute the strong coupling constant $G_{B^{**} B \pi} \; (G_{D^{**} D \pi})$, where $B^{**}$ ($D^{**}$) is the $0^+$ $P-$wave $b \bar q \; (c \bar q)$ state, by QCD sum rules and by light-cone sum rules. The two methods give compatible results in the limit $m_Q \to \infty$, with a rather large value of the coupling constant. We apply the results to the calculation of the hadronic widths of the positive parity $B$ and $D$ states and to the chiral loop contribution to the ratio $f_{D_s}/f_D$.Comment: 31 pages, RevTeX, 4 figures appended as uuencoded fil

Four Dimensional CFT Models with Rational Correlation Functions

Recently established rationality of correlation functions in a globally conformal invariant quantum field theory satisfying Wightman axioms is used to construct a family of soluble models in 4-dimensional Minkowski space-time. We consider in detail a model of a neutral scalar field $\phi$ of dimension 2. It depends on a positive real parameter c, an analogue of the Virasoro central charge, and admits for all (finite) c an infinite number of conserved symmetric tensor currents. The operator product algebra of $\phi$ is shown to coincide with a simpler one, generated by a bilocal scalar field $V(x_1,x_2)$ of dimension (1,1). The modes of V together with the unit operator span an infinite dimensional Lie algebra $L_V$ whose vacuum (i.e. zero energy lowest weight) representations only depend on the central charge c. Wightman positivity (i.e. unitarity of the representations of $L_V$) is proven to be equivalent to $c \in N$.Comment: 28 pages, LATEX, amsfonts, latexsym. Proposition 2.3, and Conjecture in Sec. 6 are revised. Minor errors are correcte