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Barry R. Holstein

Publications and source records attributed to Barry R. Holstein.

At least 73 records · Page 4Linked to original sources
arXiv1998

SU(3) Baryon Chiral Perturbation Theory and Long Distance Regularization

The use of SU(3) chiral perturbation theory in the analysis of low energy meson-baryon interactions is discussed. It is emphasized that short distance effects, arising from propagation of Goldstone bosons over distances smaller than a typical hadronic size, are model-dependent and can lead to a lack of convergence in the SU(3) chiral expansion if they are included in loop diagrams. In this paper we demonstrate how to remove such effects in a chirally consistent fashion by use of a cutoff and demonstrate that such removal ameliorates problems which have arisen in previous calculations due to large loop effects.

hep-ph↗
arXiv1998

Low Energy Compton Scattering and Nucleon Structure

The low energy virtual Compton scattering process $eN\to e'Nγ$ offers a new and potentially high resolution window on nucleon sturcture via measurement of so-called generalized polarizabilities (GPs). We present calculations of GPs within heavy baryon chiral perturbation theory and discuss present experimental efforts.

nucl-th↗
arXiv1998

Nucleon Axial Matrix Elements

Current issues associated with nucleon axial matrix elements are studied, including the Goldberger-Treiman discrepancy, the induced pseudoscalar, and SU(3) chiral perturbation theory.

nucl-th↗
arXiv1998

Improving the convergence of SU(3) baryon chiral perturbation theory

Baryon chiral perturbation theory as conventionally applied using dimensional regularization has a well-known problem with the convergence of the SU(3) chiral expansion. One can reformulate the theory equally rigorously using a momentum-space cutoff and we show that the convergence is thereby greatly improved for reasonable values of the cutoff. In effect, this is accomplished because the cutoff formalism removes the spurious physics of propagation at distance scales much smaller than the baryon size.

hep-ph↗
arXiv1998

Compton Scattering and the Spin Structure of the Nucleon at Low Energies

We analyze polarized Compton scattering which provides information on the spin-structure of the nucleon. For scattering processes with photon energies up to 100 MeV the spin-structure dependence can be encoded into four independent parameters-the so-called spin-polarizabilities $γ_i, i=1...4$ of the nucleon, which we calculate within the framework of the "small scale expansion" in SU(2) baryon chiral perturbation theory. Specific application is made to "forward" and "backward" spin- polarizabilities.

nucl-th↗
arXiv1997

Chiral Anomaly and Eta-Eta' Mixing

We determine the $η-η'$ mixing angle via a procedure relatively independent of theoretical assumptions by simultaneously fitting $η- eta'$ reactions involving the anomaly--$η,η'\toγγ, π^+π^-γ$. We extract reasonably precise renormalized values of the octet and singlet pseudoscalar decay constants $F_8,F_0$ as well as the mixing angle $θ$.

hep-ph↗
arXiv1997

Chiral Perturbation Theory and Nucleon Polarizabilities

Compton scattering offers in principle an intriguing new window on nucleon structure. Existing experiments and future programs are discussed and the state of theoretical understanding of such measurements is explored.

hep-ph↗
arXiv1997

Generalized Polarizabilities and the Chiral Structure of the Nucleon

We are studying the electron scattering process e p to e' p' gamma in order to obtain information on the genuine virtual Compton scattering (VCS) process gamma^* N to gamma N. In addition to the two kinematical variables of real Compton scattering, e.g. the scattering angle theta and the energy omega' of the outgoing photon, the invariant amplitude for VCS depends on a third kinematical variable, which we choose as the absolute value of the three-momentum transfer to the nucleon. The structure-dependent coefficients in the VCS amplitude therefore acquire a momentum dependence and are termed ``generalized polarizabilities'' of the nucleon in analogy to real Compton scattering. Utilizing the heavy baryon formalism of chiral perturbation theory we present predictions for the momentum dependence of the ``generalized polarizabilities'' and discuss the VCS response functions to be measured in the scheduled electron scattering experiments.

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arXiv1997

Isospin Mixing and Model Dependence

We show that recent calculations of ΔI=3/2 effects in nonleptonic hyperon decay induced by m_d-m_u\neq 0 are subject to significant model dependence.

hep-ph↗
arXiv1996

Delta(1232) and the Polarizabilities of the Nucleon

Previous calculations of the polarizabilities of the nucleon within the framework of heavy baryon chiral perturbation theory have included the contribution of the $Δ$(1232) only its effect on various contact terms or have been performed in chiral SU(3) where systematic errors are difficult to control. Herein we perfrom a corresponding calculation in chiral SU(2) wherein $Δ$(1232) is treated as an explicit degree of freedom and the expansion is taken to third order in soft momenta, the pion mass and the quantity $M_Δ-M_N$, collectively denoted by $ε$. We present the results of a systematic $O(ε^3)$ calculation of forward Compton scattering off the nucleon, extract the electric polarizability $\barα_E$, the magnetic polarizability $\barβ_M$ and the spin polarizability $γ$ and compare with available information from experiments and from previous calculations. Concluding with a critical discussion of our results, we point out the necessity of a future $O(ε^4)$ calculation.

hep-ph↗
arXiv1996

Systematic 1/M Expansion for Spin 3/2 Particles

Starting from a relativistic formulation of the pion-nucleon-delta system, the most general structure of 1/M corrections for a heavy baryon chiral lagrangian including spin 3/2 resonances is given. The heavy components of relativistic nucleons and delta fields are integrated out and their contributions to the next-to-leaing order lagrangians are constructed explicitly. The effective theory obtained admits a systematic expansion in terms of soft momenta, the pion mass $m_π$ and the delta-nucleon mass difference $Δ$. As an application, we consider neutral pion photoproduction at threshold to third order in this small scale expansion.

hep-ph↗
arXiv1996

Virtual Compton Scattering off the Nucleon in Chiral Perturbation Theory

We investigate the spin-independent part of the virtual Compton scattering (VCS) amplitude off the nucleon within the framework of chiral perturbation theory. We perform a consistent calculation to third order in external momenta according to Weinberg's power counting. With this calculation we can determine the second- and fourth-order structure-dependent coefficients of the general low-energy expansion of the spin-averaged VCS amplitude based on gauge invariance, crossing symmetry and the discrete symmetries. We discuss the kinematical regime to which our calculation can be applied and compare our expansion with the multipole expansion by Guichon, Liu and Thomas. We establish the connection of our calculation with the generalized polarizabilities of the nucleon where it is possible.

nucl-th↗
arXiv1996

Low Energy Tests of Chiral Symmetry

The present status of low energy test of chiral invariance via chiral perturbation theory is reviewed, both in the meson and baryon sectors, and future prospects are discussed.

hep-ph↗
arXiv1996

Theory of Weak Hypernuclear Decay

The weak nonmesonic decay of Lambda-hypernuclei is studied in the context of a one-meson-exchange model. Predictions are made for the decay rate, p/n stimulation ratio and the asymmetry in polarized hypernuclear decay.

nucl-th↗
arXiv1995

Chiral Anomaly and $γ3π$

Measurement of the $γ3π$ process has revealed a possible conflict with what should be a solid prediction generated by the chiral anomaly. We show that inclusion of appropirate energy-momentum dependence in the matrix element reduces the discrepancy.

hep-ph↗
arXiv1995

Parity Violation and the Nucleon-Nucleon System

The status of the field of nuclear parity violation---both experimental and theoretical---is reviewed, with special emphasis on those results which have been obtained since the 1985 review article by Adelberger and Haxton.

nucl-th↗
arXiv1995

Weak Hypernuclear Decay

Because of Pauli suppression effects the $Nπ$ decay of the free $Λ$ is not of importance in hypernuclei with $A\geq 10$. Rather the decay of such hypernuclei proceeds via the nucleon-stimulated mode $ΛN\rightarrow NN$, analysis of which presents a considerable theoretical challenge and about which there exists only a limited amount of experimental information. Herein we confront existing data wih various theoretical analyses which have been developed.

nucl-th↗