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K. Kubodera

Publications and source records attributed to K. Kubodera.

At least 37 records · Page 2Linked to original sources
arXiv2007

Two-pion-exchange contributions to the pp\to ppπ^0 reaction

Our previous study of the near-threshold pp\to ppπ^0 reaction based on a hybrid nuclear effective field theory is further elaborated by examining the momentum dependence of the relevant transition operators. We show that the two-pion exchange diagrams give much larger contributions than the one-pion exchange diagram, even though the former is of higher order in the Weinberg counting scheme. The relation between our results and an alternative counting scheme, the momentum counting scheme, is also discussed.

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arXiv2005

Use of V_{low-k} in a chiral-perturbation-theory description of the $pp\to ppπ^0$ reaction

Previously, the near-threhold $pp\to ppπ^0$ reaction was studied with the use of transition operators derived from chiral perturbation theory ($χ$PT) and the nuclear wave functions generated by high-precision phenomenological potentials. A conceptual problem in that approach was that the transition amplitude receives contributions from very high momentum components (above the cutoff scale of $χ$PT) in the nuclear wave functions. In the present work, we avoid this problem by replacing the "bare" phenomenological potentials with V_{low-k}, which is an effective potential derived from a bare potential by integrating out momentum components higher than a specified cutoff scale. The use of V_{low-k} is found to give an enhancement of the $pp\to ppπ^0$ cross sections over the values obtained with bare potentials. Although this enhancement brings the calculated cross sections closer to the experimental values, the incident-energy dependence of the cross section is not well reproduced, a problem that seems to indicate the necessity of including higher chiral order terms than considered in the present work.

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arXiv2005

Comparison of the extended linear sigma model and chiral perturbation theory

The pion-nucleon scattering amplitudes are calculated in tree approximation with the use of the extended linear sigma model (ELSM) as well as heavy baryon chiral perturbation theory (HB$χ$PT), and the non-relativistic forms of the ELSM results are compared with those of HB$χ$PT. We find that the amplitudes obtained in ELSM do not agree with those derived from the more fundamental effective approach, HB$χ$PT.

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arXiv2005

Ratio of the proton electromagnetic form factors from meson dressing

The Dressed K-matrix Model, developed previously for low- and intermediate-energy Compton scattering, is generalized to calculate the photon-nucleon vertex with a virtual photon and an off-shell nucleon. Using this model, the ratio of the proton electromagnetic form factors is computed. The calculated ratio is in excellent agreement with the ratio measured in polarized electron-proton scattering.

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arXiv2004

Neutron beta decay in effective field theory

Radiative corrections to the lifetime and angular correlation coefficients of neutron beta-decay are evaluated in effecitive field theory. We also evaluate the lowest order nucleon recoil corrections, including weak-magnetism. Our results agree with those of the long-range and model-independent part of previous calculations. In an effective theory the model-dependent radiative corrections are replaced by well-defined low-energy constants. The effective field theory allows a systematic evaluation of higher order corrections to our results to the extent that the relevant low-energy constants are known.

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arXiv2004

Astrophysical weak-interaction processes and nuclear effective field theory

Low-energy nuclear weak-interaction processes play important roles in many astrophysical contexts, and effective field theory is believed to be a highly useful framework for describing these processes in a model-independent manner. I present a brief account of the basic features of the nuclear effective theory approach, and some examples of actual calculations carried out in this method.

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arXiv2004

The Adler-Weisberger and Goldberger-Miyazawa-Oehme sum rules as probes of constraints from analyticity and chiral symmetry in dynamical models for pion-nucleon scattering

The Adler-Weisberger and Goldberger-Miyazawa-Oehme sum rules are calculated within a relativistic, unitary and crossing symmetric dynamical model for pion-nucleon scattering using two different methods: 1) by evaluating the scattering amplitude at the corresponding low-energy kinematics and 2) by evaluating the sum-rule integrals with the calculated total cross section. The discrepancy between the results of the two methods provides a measure of the breaking of analyticity and chiral symmetry in the model. The contribution of the $Δ$ resonance, including its dressing with meson loops, is discussed in some detail and found to be small.

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arXiv2003

Neutrino-nucleus reactions and effective field theory

Effetive field theory is believed to provide a useful framework for describing low-energy nuclear phenomena in a model-independent fashion. I give here a brief account of the basic features of this approach, some of its latest developments, and examples of actual calculations carried out in this framework.

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arXiv2003

In-medium meson properties and field transformations

Since the existing calculations of the effective meson mass in nuclear medium involve approximations, it is important to examine whether they satisfy the general requirement of the equivalence theorem that the physical observables should be independent of the choice of field variables. We study here consequences of nucleon field transformations. As an illustrative case we consider the in-medium effective pion mass calculated for the s-wave pion-nucleon interaction in the linear density approximation. We demonstrate that it is necessary to include the Born term explicitly in order that the effective pion mass should obey the equivalence theorem.

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arXiv2003

Solar-neutrino reactions on deuteron in effective field theory

The cross sections for low-energy neutrino-deuteron reactions are calculated within heavy-baryon chiral perturbation theory employing cut-off regularization scheme. The transition operators are derived up to next-to-next-to-next-to-leading order in the Weinberg counting rules, while the nuclear matrix elements are evaluated using the wave functions generated by a high-quality phenomenological NN potential. With the adoption of the axial-current-four-nucleon coupling constant fixed from the tritium beta decay data, our calculation is free from unknown low-energy constants. Our results exhibit a high degree of stability against different choices of the cutoff parameter, a feature which indicates that, apart from radiative corrections, the uncertainties in the calculated cross sections are less than 1 %.

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arXiv2002

Neutrino-deuteron reactions at solar neutrino energies

In interpreting the SNO experiments, accurate estimates of the νd reaction cross sections are of great importance. In our recent work, we have improved our previous calculation by updating some of its inputs and by incorporating the results of a recent effective-field-theoretical calculation. The new cross sections are slightly (\sim 1%) larger than the previously reported values. It is reasonable to assign 1% uncertainty to the νd cross sections reported here; this error estimate does not include radiative corrections.

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arXiv2002

Parameter-free effective field theory calculation for the solar proton-fusion and hep processes

Spurred by the recent complete determination of the weak currents in two-nucleon systems up to ${\cal O}(Q^3)$ in heavy-baryon chiral perturbation theory, we carry out a parameter-free calculation of the threshold $S$-factors for the solar $pp$ (proton-fusion) and $hep$ processes in an effective field theory that {\it combines} the merits of the standard nuclear physics method and systematic chiral expansion. The power of the EFT adopted here is that one can correlate in a unified formalism the weak-current matrix elements of two-, three- and four-nucleon systems. Using the tritium $β$-decay rate as an input to fix the only unknown parameter in the theory, we can evaluate the threshold $S$ factors with drastically improved precision; the results are $S_{pp}(0) = 3.94\times(1 \pm 0.004) \times 10^{-25} {MeV-b}$ and $S_{hep}(0) = (8.6\pm 1.3)\times 10^{-20} {keV-b}$. The dependence of the calculated $S$-factors on the momentum cutoff parameter $Λ$ has been examined for a physically reasonable range of $Λ$. This dependence is found to be extremely small for the $pp$ process, and to be within acceptable levels for the $hep$ process, substantiating the consistency of our calculational scheme.

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arXiv2002

Quark-quark correlations and baryon electroweak observables

The simple independent quark models have difficulties explaining simultaneously the totality of the known hyperon magnetic moments and hyperon semi-leptonic decay rates. We show that both the Goldstone boson loop contributions and the two-quark effective exchange currents are essential in explaining these observables.

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arXiv2002

Neutrino-deuteron reactions at solar neutrino energies

In interpreting the SNO experiments, very accurate estimates of the νd reaction cross sections are of great importance. We improve the previous estimates of our group by updating some of its inputs and by taking into account the results of a recent effective-field-theoretical calculation. The new cross sections are slightly (\sim 1%) larger than the previously reported values. We present arguments that lead to the conclusion that it is reasonable to assign 1% uncertainty to the νd cross sections reported here.

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arXiv2001

Muon capture in hydrogen

Theoretical difficulties in reconciling the measured rates for ordinary and radiative muon capture are discussed, based on heavy-baryon chiral perturbation theory. We also examine ambiguity in our analysis due to the formation of p$μ$p molecules in the liquid hydrogen target.

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