Time-reversal noninvariance in nucleon-nucleon scattering. I. General formalism and zero-range parameterization

doi:10.1016/0003-4916(81)90255-4

Annals of Physics

Volume 133, Issue 2, May 1981, Pages 355-389

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Abstract

The observation that, in a time-irreversible one-boson-exchange nucleon-nucleon potential model due to Bryan and Gersten, T-violation occurs mostly in the lowest-permitted angular momentum states, leads us to construct a phase-shift parameterization of the 50 to 450 MeV NN data where T-violation takes place only in the lowest possible angular momentum states. The five ordinary (T-symmetric) Wolfenstein amplitudes are taken from phase shift analysis, and the sixth, T-asymmetric amplitude, t(θ), is parameterized by a single infinitesimal phase parameter λ₁(λ₂) in the case of np(pp) scattering. This leads to unique predictions for the relative angular distributions of time-reversal-asymmetric observables P − $a$ and P_A − P_B, even though the absolute magnitudes remain undetermined. The model corresponds to an ordinary interaction that yields the usual experimental data, plus a superimposed very short-range T-noninvariant force. As such, it directs experimentalists to those angular regions of pp and np P − $a$ and P_A − P_B measurements where T-violation due to short-range forces will be most strongly manifest. As the model incorporates isospin invariance, known to hold only at the few-percent level in np scattering, the predictions are likely to have greater significance in the case of pp scattering.

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ΔI = 1 axial-vector mixing and charge symmetry breaking
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Phenomenological Lagrangians that exhibit (broken) chiral symmetry as well as isospin violation suggest short-range charge symmetry breaking (CSB) nucleon-nucleon potentials with a σ₁ · σ₂ structure. This structure could be realized by the mixing of axial-vector (1⁺) mesons in a single-meson exchange picture. The Coleman-Glashow scheme for ΔI_z = 1 charge symmetry breaking applied to meson and baryon SU(2) mass splittings suggests a universal scale. This scale can be extended to ΔI = 1 nonstrange CSB transitions 〈a₁^o|H_em|f₁〉 of size −0.005 GeV². The resulting nucleon-nucleon axial-vector meson exchange CSB potential then predicts ΔI = 1 effects which are small.
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The contribution of A₁ exchange to the nucleon-nucleon potential is studied in a broken chiral symmetric model. The A₁ is treated as a finite-width resonance in the πρ s-wave. Connections between pseudoscalar and pseudovector pion-nucleon coupling in the underlying model lagrangian are studied in detail. It is found that large terms in the NN interaction arising from πρ exchange with pseudoscalar coupling are suppressed by interference with a₁ exchange. With pseudovector coupling there is a suppression of the A₁ exchange by the so-called “seagull” terms in πρ exchange which arise from gauge invariance. The suppression becomes an exact cancellation in the limit of infinite ρ and a₁ masses and exact chiral symmetry. We found that inclusion of the a₁ decay into the πρ state strongly modifies the a₁] exchange potential, suppressing the tensor part but leaving the spin-spin part almost unchanged.
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^∗: Supported in part by the U. S. Department of Energy, Contract EY-76-S-05-5223.

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Annals of Physics

Time-reversal noninvariance in nucleon-nucleon scattering. I. General formalism and zero-range parameterization

Abstract

Phys. Rev.

Phys. Rev.

Suppl. Progr. Theoret. Phys.

Phys. Rev. Lett.

Phys. Rev.

Phys. Rev.

Phys. Rev.

Phys. Rev. Lett.

Phys. Rev. Lett.

Phys. Rev. D

Phys. Rev. C

Phys. Lett. B

ΔI = 1 axial-vector mixing and charge symmetry breaking

Chiral symmetry and the A<inf>1</inf> contribution to the nucleon-nucleon interaction

Symmetries and the N-N interaction

Parametrization of the elastic sector of the nucleon-nucleon scattering matrix. II