Paul Hoyer

University of Helsinki

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Stanley J. Brodsky

Stanford University

Stéphane Peigné

Laboratoire de Physique Subatomique et des Technologies Associées

M. Vänttinen

Technical University of Munich

F. Halzen

University of Wisconsin–Madison

Matti Järvinen

Asia Pacific Center for Theoretical Physics

Nils Marchal

Laboratoire d'Annecy-le-Vieux de Physique Théorique

D.P. Roy

Tata Institute of Fundamental Research

R. Vogt

University of California, Davis

W.-K. Tang

SLAC National Accelerator Laboratory

Dennis D. Dietrich

Ludwig-Maximilians-Universität München

Cooperative Institutions

European Organization for Nuclear Research

Centre National de la Recherche Scientifique

Office of Chief Medical Examiner

University of Helsinki

Helsinki Institute of Physics

Brookhaven National Laboratory

Istituto Nazionale di Fisica Nucleare

Argonne National Laboratory

Institut National de Physique Nucléaire et de Physique des Particules

King County Medical Examiner's Office

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't Hooft model in the temporal gauge

arXiv (Cornell University) (2025)

Paul Hoyer

I consider QCD$_2$ in the $N_c \to \infty$ limit at fixed $g^2N_c$. The derivation starts from equal-time $q\bar q$ bound states in coordinate space and temporal ($A^0=0$) gauge, avoiding the use of quark and gluon propagators. The wave function is given analytically by a $_1F_1$ function with an explicit frame dependence. In the Infinite Momentum Frame the Fourier transformed wave function satisfies the 't Hooft equation, however with contributions also from quarks with negative kinetic energy. This difference with previous analyses of the model may be related to boundary conditions.

10.48550/arxiv.2501.18352

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Semi-exclusive production of photons at HERA

The European Physical Journal C (2000)

Paul Hoyer M. Maul Andreas Metz

Recoil

Fragmentation

10.1007/s100520000467

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Polarization as a Probe to the Production Mechanisms of Charmonium in $πN$ Collisions

arXiv (Cornell University) (1994)

W.-K. Tang Stanley J. Brodsky M. Vänttinen Paul Hoyer

Measurements of the polarization of $\jp$ produced in pion-nucleus collisions are in disagreement with leading twist QCD prediction where $\jp$ is observed to have negligible polarization whereas theory predicts substantial polarization. We argue that this discrepancy cannot be due to poorly known structure functions nor the relative production rates of $\jp$ and $χ_J$. The disagreement between theory and experiment suggests important higher twist corrections, as has earlier been surmised from the anomalous non-factorized nuclear $A$-dependence of the $\jp$ cross section.

10.48550/arxiv.hep-ph/9408371

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New QCD effects at large x

Lectures given at (1992)

Paul Hoyer

In heavy quark production at large Feynman x there are two hardness scales, one given by the heavy quark pair mass M 2 and the other by Λ QCD 2 /(1 − x). When these two scales are comparable, the twist expansion of Perturbative QCD breaks down. We discuss the dynamics in this new QCD limit, where μ 2 = M 2 (1 - x) is held fixed as M 2 →∞. New diagrams are found to contribute, which can enhance the cross section above that expected for leading twist. The heavy quarks are produced by a peripheral scattering on the target of hardness μ 2 . This leads, in particular, to a nuclear target dependence of A 2/3 at small μ. Qualitatively, the dynamics in the new limit agrees with earlier phenomenological models of «intrinsic» heavy quark production

Perturbative QCD

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Hadroproduction and polarization of charmonium

Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields (1995)

M. Vänttinen Paul Hoyer Stanley J. Brodsky W.-K. Tang

In the limit of heavy-quark mass, the production cross section and polarization of quarkonia can be calculated in perturbative QCD. We study the ${\mathit{p}}_{\mathrm{\ensuremath{\perp}}}$-averaged production of charmonium states in \ensuremath{\pi}N collisions at fixed target energies. The data on the relative production rates of J/\ensuremath{\psi} and ${\mathrm{\ensuremath{\chi}}}_{\mathit{J}}$ are found to disagree with leading twist QCD. The polarization of the J/\ensuremath{\psi} indicates that the discrepancy is not due to poorly known parton distributions nor to the size of higher order effects (K factors). Rather, the disagreement suggests important higher twist corrections, as has been surmised earlier from the nuclear target A dependence of the production cross section.

Perturbative QCD

10.1103/physrevd.51.3332

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Citations (41)

The tetrahadron

Nuclear Physics B (1977)

Paul Hoyer

10.1016/0550-3213(77)90452-7

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Hadrons as QCD Bound States

arXiv (Cornell University) (2021)

Paul Hoyer

Bound state perturbation theory is well established for QED atoms. Today the hyperfine splitting of Positronium is known to $O(\alpha^7\log\alpha)$. Whereas standard expansions of scattering amplitudes start from free states, bound states are expanded around eigenstates of the Hamiltonian including a binding potential. The eigenstate wave functions have all powers of $\alpha$, requiring a choice in the ordering of the perturbative expansion. Temporal $(A^0=0)$ gauge permits an expansion starting from valence Fock states, bound by their instantaneous gauge field. This formulation is applicable in any frame and seems promising even for hadrons in QCD. The $O(\alpha_s^0)$ confining potential is determined (up to a universal scale) by a homogeneous solution of Gauss' law.

Positronium

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Rescattering in DIS and other QCD processes

The European Physical Journal A (2005)

Paul Hoyer

Pomeron

Unitarity

Gluon field

Virtual particle

QCD vacuum

10.1140/epjad/s2005-05-024-8

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Filling Perturbative Ground States

arXiv (Cornell University) (2003)

Paul Hoyer

I discuss a degree of freedom in formulating perturbation theory that is often neglected: the in- and out-states need not be empty. The inclusion of (free) particles in the asymptotic states modifies the on-shell prescription of the free propagator. This affects loop contributions -- but the modified expansion is {\it a priori} as justified as the standard one with Feynman prescription. It is possible to dress the quark propagator to all orders with zero-momentum gluons from the perturbative ground state. The dressed quark has no pole and thus cannot appear as an external particle in the S-matrix. Chiral symmetry may be spontaneously broken, but Lorentz and gauge symmetry is exact. Adding loop corrections to this ``dressed tree approximation'' gives a formally exact PQCD expansion.

Non-perturbative

10.48550/arxiv.hep-ph/0304022

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QCD factorization at fixed Q^2(1-x)

arXiv (Cornell University) (2009)

Paul Hoyer

Amplitudes of hard {\it exclusive} processes such as γ^*(Q^2) N \to γY, where Y=N (DVCS) or any other state with a limited mass (M_Y^2 << Q^2), factorize into a hard subprocess amplitude and a target (transition) GPD. The corresponding {\it inclusive} cross section, summed over all states Y of a given (limited) mass, is then given by the discontinuity of a forward multiparton distribution. An application to the Drell-Yan process π^+ N \to γ^*(x_F,Q^2)+Y allows to explain the observed longitudinal polarization of the virtual photon at high x_F.

Virtual particle

10.48550/arxiv.0903.4962

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Citations (1)