Limitations of the heavy-baryon expansion as revealed by a pion-mass dispersion relation

Hall, Jonathan M. M.; Pascalutsa, Vladimir

doi:10.1140/epjc/s10052-012-2206-8

Cited by 7 publications

(11 citation statements)

References 50 publications

(56 reference statements)

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“…Through an examination of the flow of the low-energy coefficients constrained by the lattice QCD results as the regulator parameter, Λ is varied, and with an understanding of the dependence of this flow on the range of pion masses considered in the chiral expansion, one can identify a value of Λ which provides low-energy coefficients independent of the pion mass range considered, and are therefore consistent with the low-energy coefficients of χPT in the PCR [11,13,28,29,49]. A weighted average across studies of the leading-order chiral coefficients of the nucleon mass [28,50] (using PACS-CS results [19]), magnetic moment [11] and the electric charge radius [13] (using QCDSF results [21]) leads to a regulator parameter ofΛ scale ¼ 0.99ð27Þ GeV.…”

Section: Chiral Effective Field Theorymentioning

confidence: 89%

Finite-volume and partial quenching effects in the magnetic polarizability of the neutron

2014

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There has been much progress in the experimental measurement of the electric and magnetic polarizabilities of the nucleon. Similarly, lattice QCD simulations have recently produced dynamical QCD results for the magnetic polarizability of the neutron approaching the chiral regime. In order to compare the lattice simulations with experiment, calculation of partial quenching and finite-volume effects is required prior to an extrapolation in quark mass to the physical point. These dependencies are described using chiral effective field theory. Corrections to the partial quenching effects associated with the seaquark-loop electric charges are estimated by modeling corrections to the pion cloud. These are compared to the uncorrected lattice results. In addition, the behavior of the finite-volume corrections as a function of pion mass is explored. Box sizes of approximately 7 fm are required to achieve a result within 5% of the infinite-volume result at the physical pion mass. A variety of extrapolations are shown at different box sizes, providing a benchmark to guide future lattice QCD calculations of the magnetic polarizabilities. A relatively precise value for the physical magnetic polarizability of the neutron is presented, β n ¼ 1.93ð11Þ stat ð11Þ sys × 10 −4 fm 3 , which is in agreement with current experimental results.

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Section: Chiral Effective Field Theorymentioning

confidence: 89%

Finite-volume and partial quenching effects in the magnetic polarizability of the neutron

2014

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“…the order p 3 result for the magnetic polarizability of the nucleon [24,26]). The proton polarizability contribution to the Lamb shift is apparently such a case as well.…”

Section: "Effectiveness" Of Hbχ Pt Vs Bχ Ptmentioning

confidence: 97%

“…At least the LO results for nucleon polarizabilities are known to be very different in the two variants of the theory, e.g., the proton magnetic polarizability is (in units of 10 −4 fm 3 ): 1.2 in HBχ PT [20] vs. −1.8 in Bχ PT [21][22][23]. Thus, the LO effect of the pion cloud is paramagnetic in one case and diamagnetic in the other (see [24,25] for more on HBχ PT vs. Bχ PT). Due to these qualitative and quantitative differences it is interesting to examine the Bχ PT predictions for the 2γ contributions to the Lamb shift.…”

Section: Introductionmentioning

confidence: 99%

Chiral perturbation theory of muonic-hydrogen Lamb shift: polarizability contribution

2014

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The proton polarizability effect in the muonichydrogen Lamb shift comes out as a prediction of baryon chiral perturbation theory at leading order and our calculation yields E (pol) (2P − 2S) = 8 +3 −1 µeV. This result is consistent with most of evaluations based on dispersive sum rules, but it is about a factor of 2 smaller than the recent result obtained in heavy-baryon chiral perturbation theory. We also find that the effect of (1232)-resonance excitation on the Lamb shift is suppressed, as is the entire contribution of the magnetic polarizability; the electric polarizability dominates. Our results reaffirm the point of view that the proton structure effects, beyond the charge radius, are too small to resolve the 'proton radius puzzle'.

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“…As many recent calculations demonstrate (see, e.g., [22][23][24][25][26][27][28][29][30][31]), Bχ PT shows an improved convergence over the analogous HBχ PT calculations, and, as result, a more "natural" description of the nucleon polarizabilities and Compton scattering processes [32][33][34][35][36]. In this paper, we extend the previous Bχ PT calculations of Lensky et al [35][36][37], done for nucleon polarizabilities appearing in real and forward doubly virtual Compton scattering (RCS and VVCS, respectively), to the case of GPs and VCS.…”

Section: Introductionmentioning

confidence: 99%

Generalized polarizabilities of the nucleon in baryon chiral perturbation theory

2017

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The nucleon generalized polarizabilities (GPs), probed in virtual Compton scattering (VCS), describe the spatial distribution of the polarization density in a nucleon. They are accessed experimentally via the process of electronproton bremsstrahlung (ep → epγ ) at electron-beam facilities, such as MIT-Bates, CEBAF (Jefferson Lab), and MAMI (Mainz). We present the calculation of the nucleon GPs and VCS observables at next-to-leading order in baryon chiral perturbation theory (Bχ PT), and confront the results with the empirical information. At this order our results are predictions, in the sense that all the parameters are well known from elsewhere. Within the relatively large uncertainties of our calculation we find good agreement with the experimental observations of VCS and the empirical extractions of the GPs. We find large discrepancies with previous chiral calculations -all done in heavy-baryon χ PT (HBχ PT) -and discuss the differences between Bχ PT and HBχ PT responsible for these discrepancies.

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Limitations of the heavy-baryon expansion as revealed by a pion-mass dispersion relation

Cited by 7 publications

References 50 publications

Finite-volume and partial quenching effects in the magnetic polarizability of the neutron

Finite-volume and partial quenching effects in the magnetic polarizability of the neutron

Chiral perturbation theory of muonic-hydrogen Lamb shift: polarizability contribution

Generalized polarizabilities of the nucleon in baryon chiral perturbation theory

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