Hydrogen Atom in Relativistic Motion

The Lorentz contraction of bound states in field theory is often appealed to in qualitative descriptions of high energy particle collisions. Surprisingly, the contraction has not been demonstrated explicitly even in simple cases such as the hydrogen atom. It requires a calculation of wave functions evaluated at equal (ordinary) time for bound states in motion. Such wave functions are not obtained by kinematic boosts from the rest frame. Starting from the exact Bethe-Salpeter equation we derive the equal-time wave function of a fermion-antifermion bound state in QED, i.e., positronium or the hydrogen atom, in any frame to leading order in alpha. We show explicitly that the bound state energy transforms as the fourth component of a vector and that the wave function of the fermion-antifermion Fock state contracts as expected. Transverse photon exchange contributes at leading order to the binding energy of the bound state in motion. We study the general features of the corresponding fermion-antifermion-photon Fock states, and show that they do not transform by simply contracting. We verify that the wave function reduces to the light-front one in the infinite momentum frame.Comment: 20 pages, 10 figures; v2: some changes in discussion, accepted for publication in Phys.Rev.

Systematics of Heavy Quark Production at HERA

We discuss heavy quark and quarkonium production in various kinematic regions at the HERA ep collider. In contrast to fixed target experiments, collider kinematics allows the possibility of detailed measurements of particle production in the proton fragmentation region. One thus can study parton correlations in the proton Fock states materialized by the virtual photon probe. We discuss various configurations of inelastic electron-proton scattering, including peripheral, diffractive, and deep inelastic processes. In particular, we show that intrinsic heavy quark Fock states can be identified by the observation of quarkonium production at large $x_F$ and a low mean transverse momentum which is insensitive to the virtuality $Q^2$ of the photon.Comment: 17 pages, postscript. To obtain a copy of this paper send e-mail to [email protected]

Light-Cone Quantization and Hadron Structure

In this talk, I review the use of the light-cone Fock expansion as a tractable and consistent description of relativistic many-body systems and bound states in quantum field theory and as a frame-independent representation of the physics of the QCD parton model. Nonperturbative methods for computing the spectrum and LC wavefunctions are briefly discussed. The light-cone Fock state representation of hadrons also describes quantum fluctuations containing intrinsic gluons, strangeness, and charm, and, in the case of nuclei, "hidden color". Fock state components of hadrons with small transverse size, such as those which dominate hard exclusive reactions, have small color dipole moments and thus diminished hadronic interactions; i.e., "color transparency". The use of light-cone Fock methods to compute loop amplitudes is illustrated by the example of the electron anomalous moment in QED. In other applications, such as the computation of the axial, magnetic, and quadrupole moments of light nuclei, the QCD relativistic Fock state description provides new insights which go well beyond the usual assumptions of traditional hadronic and nuclear physics.Comment: LaTex 36 pages, 3 figures. To obtain a copy, send e-mail to [email protected]

The Two Roads to "Intrinsic Charm" in B Decays

We describe two complementary ways to show the presence of higher order effects in the 1/m_Q expansion for inclusive B decays that have been dubbed "Intrinsic Charm". Apart from the lessons they can teach us about QCD's nonperturbative dynamics their consideration is relevant for precise extractions of |V_{cb}|: for they complement the estimate of the potential impact of 1/m_Q^4 contributions. We draw semiquantitative conclusions for the expected scale of Weak Annihilation in semileptonic B decays, both for its valence and non-valence components.Comment: 17 pages, 3 figure

Partonic calculation of the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer

We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer through the scattering off a parton in the proton. We relate the process on the nucleon to the generalized parton distributions which also enter in other wide angle scattering processes. We find that when taking the polarization transfer determinations of the form factors as input, adding in the 2 photon correction, does reproduce the Rosenbluth data.Comment: 4 pages, 4 figure

Optimal Renormalization Scale and Scheme for Exclusive Processes

We use the BLM method to fix the renormalization scale of the QCD coupling in exclusive hadronic amplitudes such as the pion form factor and the photon-to-pion transition form factor at large momentum transfer. Renormalization-scheme-independent commensurate scale relations are established which connect the hard scattering subprocess amplitudes that control exclusive processes to other QCD observables such as the heavy quark potential and the electron-positron annihilation cross section. The commensurate scale relation connecting the heavy quark potential, as determined from lattice gauge theory, to the photon-to-pion transition form factor is in excellent agreement with $\gamma e \to \pi^0 e$ data assuming that the pion distribution amplitude is close to its asymptotic form $\sqrt{3}f_\pi x(1-x)$. We also reproduce the scaling and normalization of the $\gamma \gamma \to \pi^+ \pi^-$ data at large momentum transfer. Because the renormalization scale is small, we argue that the effective coupling is nearly constant, thus accounting for the nominal scaling behavior of the data. However, the normalization of the space-like pion form factor $F_\pi(Q^2)$ obtained from electroproduction experiments is somewhat higher than that predicted by the corresponding commensurate scale relation. This discrepancy may be due to systematic errors introduced by the extrapolation of the $\gamma^* p \to \pi^+ n$ electroproduction data to the pion pole.Comment: 22 pages, Latex, 7 Latex figures. Several references added, discussion of scale fixing revised for clarity. Final version to appear in Phys. Rev.

Light-cone QCD predictions for elastic ed-scattering in the intermediate energy region

The contributions of helicity-flip matrix elements to the deuteron form factors are discussed in the light-cone frame. Normalized $A(Q^2)$, $B(Q^2)$, $G_Q(Q^2)$ and $T_{20}$ are obtained in a simple QCD-inspired model. We find that $G_{+-}^+$ plays an important role in $G_Q(Q^2)$. Our numerical results are consistent with the data in the intermediate energy region.Comment: 9 pages, REVTeX file, 5 figure

On the dependence of the wave function of a bound nucleon on its momentum and the EMC effect

It is widely discussed in the literature that the wave function of the nucleon bound in a nucleus is modified due to the interaction with the surrounding medium. We argue that the modification should strongly depend on the momentum of the nucleon. We study such an effect in the case of the point-like configuration component of the wave function of a nucleon bound in a nucleus A, considering the case of arbitrary final state of the spectator A-1 system. We show that for non relativistic values of the nucleon momentum, the momentum dependence of the nucleon deformation appears to follow from rather general considerations and discuss the implications of our theoretical observation for two different phenomena: i) the search for medium induced modifications of the nucleon radius of a bound nucleon through the measurement of the electromagnetic nucleon form factors via the A(e,e'p)X process, and ii) the A-dependence of the EMC effect; in this latter case we also present a new method of estimating the fraction of the nucleus light-cone momentum carried by the photons and find that in a heavy nuclei protons loose about 2% of their momentum.Comment: 38 pages, 1 figure; changed references and text in Section I (Introduction

Bringing Legacy to Life: How Video Storytelling Inspires Multigenerational Involvement in Family Philanthropy

Most family foundations go through some sort of process to define donor intent and formalize their values, whether at the beginning of their life span or after their founders’ passing. Video is a powerful tool in that process, vividly bringing stories to life for family members, older and younger alike. So how can video help foundations capture the important story of their donor intent and legacy, and use it to inspire future involvement in their mission? With the experience of the Marion I. & Henry J. Knott Foundation serving as the backdrop, this article examines how a donor legacy video can not only help inspire multigenerational participation in the governance of a family foundation, but also extend multiple direct benefits to grant applicants and grantees. Grounded in research and reflective practice, this article details the power of video in preserving family stories, the goals and outcomes of the Knott Foundation’s successful video project, and some practical suggestions for other family foundations. Key findings show that video storytelling can inspire new board member participation, enhance everyone’s understanding of the founders’ legacy, and benefit a foundation’s wider grantee community

The second moment of the pion's distribution amplitude

We present preliminary results for the second moment of the pion's distribution amplitude. The lattice formulation and the phenomenological implications are briefly reviewed, with special emphasis on some subtleties that arise when the Lorentz group is replaced by the hypercubic group. Having analysed more than half of the available configurations, the result obtained is \xi^2_L = 0.06 \pm 0.02.Comment: Lattice 99 (matrix elements), 3 page