Leonard Gamberg

Improved experimental limits on the production of magnetic monopoles

We present new limits on low mass accelerator-produced pointlike Dirac magnetic monopoles trapped and bound in matter surrounding the D0 collision region of the Tevatron at Fermilab (experiment E-882). In the context of a Drell-Yan mechanism, we obtain cross section limits for the production of monopoles with magnetic charge values of 1, 2, 3, and 6 times the minimum Dirac charge of the order of picobarns, some 100 times smaller than found in similar previous Fermilab searches. Mass limits inferred from these cross section limits are presented.

Hadron structure functions in a chiral quark model: Regularization, scaling and sum rules☆

Abstract We provide a consistent regularization procedure for calculating hadron structure functions in a chiral quark model. The structure functions are extracted from the absorptive part of the forward Compton amplitude in the Bjorken limit. Since this amplitude is obtained as a time-ordered correlation function its regularization is consistently determined from the regularization of the bosonized action. We find that the Pauli-Villars regularization scheme is most suitable because it preserves both the anomaly structure of QCD and the leading scaling behavior of hadron structure functions in the Bjorken limit. We show that this procedure yields the correct pion structure function. In order to render the sum rules of the regularized polarized nucleon structure functions consistent with their corresponding axial charges we find it mandatory to further specify the regularization procedure. This specification goes beyond the double subtraction scheme commonly employed when studying static hadron properties in this model. In particular the present approach serves to determine the regularization prescription for structure functions whose leading moments are not given by matrix elements of local operators. In this regard we conclude somewhat surprisingly that in this model the Gottfried sum rule does not undergo regularization.

Nucleon structure functions from a chiral soliton

Abstract Nucleon structure functions are studied within the chiral soliton approach to the bosonized Nambu-Jona-Lasinio model. The valence quark approximation is employed which is justified for moderate constituent quark masses (∼ 400 MeV) as the contribution of the valence quark level dominates the predictions of nucleon properties. As examples the unpolarized structure functions for the vp and ν p scattering and the structure functions entering the Gottfried sum rule are discussed. For the latter the model prediction is found to reasonably well agree with a corresponding low-scale parametrization of the empirical data.

Chiral odd structure functions from a chiral soliton

We calculate the chiral odd quark distributions and the corresponding structure functions h{sub T}(x,Q{sup 2}) and h{sub L}(x,Q{sup 2}) within the Nambu{endash}Jona-Lasinio chiral soliton model for the nucleon. The Q{sup 2} evolution of the twist-2 contributions is performed according to the standard GLAP formalism while the twist-3 piece {bar h}{sub L}(x) is evolved according to the large N{sub C} scheme. We carry out a comparison between the chiral odd structure functions of the proton and the neutron. At the low model scale (Q{sub 0}{sup 2}) we find that the leading twist effective quark distributions f{sub 1}{sup (q)}(x,Q{sub 0}{sup 2}), g{sub 1}{sup (q)}(x,Q{sub 0}{sup 2}) and h{sub T}{sup (q)}(x,Q{sub 0}{sup 2}) satisfy Soffer{close_quote}s inequality for both quark flavors q=u,d. {copyright} {ital 1998} {ital The American Physical Society}

Dual quantum electrodynamics: Dyon-dyon and charge-monopole scattering in a high-energy approximation

We develop the quantum field theory of electron-point magnetic monopole interactions and, more generally, dyon-dyon interactions, based on the original string-dependent nonlocal action of Dirac and Schwinger. We demonstrate that a viable nonperturbative quantum field theoretic formulation can be constructed that results in a string independent cross section for monopole-electron and dyon-dyon scattering. Such calculations can be done only by using nonperturbative approximations such as the eikonal approximation and not by some mutilation of lowest-order perturbation theory. (c) 2000 The American Physical Society.

Direct and indirect searches for low mass magnetic monopoles

Recently, there has been renewed interest in the search for low-mass magnetic monopoles. At the University of Oklahoma we are performing an experiment (Fermilab E882) using material from the old D0 and CDF detectors to set limits on the existence of Dirac monopoles of masses of the order of 500 GeV. To set such limits, estimates must be made of the production rate of such monopoles at the Tevatron collider, and of the binding strength of any such produced monopoles to matter. Here we sketch the still primitive theory of such interactions, and indicate why we believe a credible limit may still be obtained. On the other hand, there have been proposals that the classic Euler–Heisenberg Lagrangian together with duality could be employed to set limits on magnetic monopoles having masses less than 1 TeV, based on virtual, rather than real processes. The D0 collaboration at Fermilab has used such a proposal to set mass limits based on the nonobservation of pairs of photons each with high transverse momentum. We critique the underlying theory, by showing that the cross section violates unitarity at the quoted limits and is unstable with respect to radiative corrections. We therefore believe that no significant limit can be obtained from the current experiments, based on virtual monopole processes.

THEORETICAL AND EXPERIMENTAL STATUS OF MAGNETIC MONOPOLES

The Tevatron has inspired new interest in the subject of magnetic monopoles. First there was the 1998 D0 limit on the virtual production of monopoles, based on the theory of Ginzburg and collaborators. In 2000 the first results from an experiment (Fermilab E882) searching for real magnetically charged particles bound to elements from the CDF and D0 detectors were reported. This also required new developments in theory. The status of the experimental limits on monopole masses will be discussed, as well as the limitation of the theory of magnetic charge at present.

Hadron structure functions within a chiral quark model

Department of Physics and AstronomyUniversity of Oklahoma, 440 West Brooks, Norman, Ok 73019, USAWe outline a consistent regularization procedure to compute hadron structure functionswithin bosonized chiral quark models. We impose the Pauli–Villars scheme, which repro-duces the chiral anomaly, to regularize the bosonized action. We derive the Comptonamplitude from this action and utilize the Bjorken limit to extract structure functionsthat are consistent with the scaling laws and sum rules of deep inelastic scattering.1. THE CHIRAL MODELThe bosonized action of chiral quark models can be cast in the formA[S,P] = −iN

NUCLEON STRUCTURE FUNCTIONS FROM A CHIRAL SOLITON IN THE INFINITE MOMENTUM FRAME

We study the frame dependence of nucleon structure functions obtained within a chiral soliton model for the nucleon. Employing light cone coordinates and introducing collective coordinates together with their conjugate momenta, translational invariance of the solitonic quark fields (which describe the nucleon as a localized object) is restored. This formulation allows us to perform a Lorentz boost to the infinite momentum frame of the nucleon. The major result is that the Lorentz contraction associated with this boost causes the leading twist contribution to the structure functions to properly vanish when the Bjorken variable x exceeds unity. Furthermore we demonstrate that for structure functions calculated in the valence quark approximation to the Nambu–Jona-Lasinio chiral soliton model the Lorentz contraction also has significant effects on the structure functions for moderate values of the Bjorken variable x.

Hadron structure functions in the bosonized nambu-jona-lasinio model

We outline a consistent regularization procedure to compute hadron structure functions within bosonized chiral quark models. We impose the Pauli-Villars scheme, which reproduces the chiral anomaly, to regularize the bosonized action. Applying the Bjorken limit to the Compton amplitude to extract structure functions that are consistent with the scaling laws and sum rules of deep inelastic scattering.