513 research outputs found

    Narrow Resonances in Effective Field Theory

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    We discuss the power counting for effective field theories with narrow resonances near a two-body threshold. Close to threshold, the effective field theory is perturbative and only one combination of coupling constants is fine-tuned. In the vicinity of the resonance, a second, ``kinematic'' fine-tuning requires a nonperturbative resummation. We illustrate our results in the case of nucleon-alpha scattering.Comment: 11 pages, revtex4, 3 ps figure

    The Nucleon Anapole Form Factor in Chiral Perturbation Theory to Sub-leading Order

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    The anapole form factor of the nucleon is calculated in chiral perturbation theory to sub-leading order. This is the lowest order in which the isovector anapole form factor does not vanish. The anapole moment depends on counterterms that reflect short-range dynamics, but the momentum dependence or the form factor is determined by pion loops in terms of parameters that could in principle be fixed from other processes. If these parameters are assumed to have natural size, the sub-leading corrections do not exceed ~ 30% at momentum Q ~ 300 MeV.Comment: 11 pages, 6 figures, epsf.sty, submitted to Phys. Lett

    Effective Field Theory and Time-Reversal Violation in Light Nuclei

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    Thanks to the unnaturally small value of the QCD vacuum angle ξˉ<10−10\bar\theta < 10^{-10}, time-reversal (TT) violation offers a window into physics beyond the Standard Model (SM) of particle physics. We review the effective-field-theory framework that establishes a clean connection between TT-violating mechanisms, which can be represented by higher-dimensional operators involving SM fields and symmetries, and hadronic interactions, which allow for controlled calculations of low-energy observables involving strong interactions. The chiral properties of TT-violating mechanisms leads to a pattern that should be identifiable in measurements of the electric dipole moments of the nucleon and light nuclei.Comment: 35 pages. Accepted for publication in Ann. Rev. Nucl. Part. Sci. 65 (2015

    Effective Field Theory of Nucleon-Nucleon Scattering on Large Discrete Lattices

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    Nuclear effective field theory is applied to the effective range expansion of S-wave nucleon-nucleon scattering on a discrete lattice. Lattice regularization is demonstrated to yield the effective range expansion in the same way as in the usual continuous open space. The relation between the effective range parameters and the potential parameters is presented in the limit of a large lattice.Comment: 24pages, 1 figur

    πN\pi N Scattering in the Δ(1232)\Delta(1232) Region in an Effective Field Theory

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    We develop a generalized version of heavy-baryon chiral perturbation theory to describe pion-nucleon scattering in a kinematic domain that extends continuously from threshold to the delta-isobar peak. The PP-wave phase shifts are used to illustrate this framework. We also compare our approach with those in the literature that concern the delta resonance.Comment: 46 pages, 17 figures, version to appear in Nucl. Phys.

    Compton Scattering on the Deuteron in Baryon Chiral Perturbation Theory

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    Compton scattering on the deuteron is studied in the framework of baryon chiral perturbation theory to third order in small momenta, for photon energies of order the pion mass. The scattering amplitude is a sum of one- and two-nucleon mechanisms with no undetermined parameters. Our results are in good agreement with existing experimental data, and a prediction is made for higher-energy data being analyzed at SAL.Comment: 39 pages LaTeX, 19 figures (uses epsf

    The anapole form factor of the nucleon

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    The anapole form factor of the nucleon is calculated in chiral perturbation theory in leading order. To this order, the form factor originates from the pion cloud, and is proportional to the non-derivative parity-violating pion-nucleon coupling. The momentum dependence of the form factor - and in particular, its radius - is completely determined by the pion mass.Comment: 9 pages, 2 eps figures included by epsf.sty, minor changes in note adde