## Abstract

We investigate the influence of negative-energy states in proton-proton bremsstrahlung in a fully relativistic framework using the T matrix of Fleischer and Tjon. The contribution from negative-energy states in the single-scattering diagrams is shown to be large, indicating that relativistic effects are important. The rescattering contribution compensates some of the effect, which is shown to be a consequence of a low-energy theorem. The net effect of negative-energy states nevertheless is of the order of 20% at higher energies. We investigate retardation effects in the nucleon-nucleon (NN) interaction by means of a one-pion exchange model, which gives effects of the order of 15% at the pion-production threshold. We furthermore modify the NN T matrix tb incorporate some of these effects, and find that on the level of single-scattering contributions they are of the order of 10%. We show predictions at incoming proton energy T-lab=190 MeV, where high accuracy measurements are being done at KVI, and conclude that even at these relatively low energies off-shell effects in the NN interaction and contributions from negative-energy states clearly show up.

Original language | English |
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Pages (from-to) | 2945-2962 |

Number of pages | 18 |

Journal | Physical Review C |

Volume | 56 |

Issue number | 6 |

Publication status | Published - Dec-1997 |

## Keywords

- NUCLEON-NUCLEON-SCATTERING
- COMPOSITE SPIN-1/2 SYSTEM
- BETHE-SALPETER-EQUATION
- PARTIAL-WAVE ANALYSIS
- ONE-BOSON-EXCHANGE
- VECTOR INTERACTIONS
- PP-BREMSSTRAHLUNG
- DEUTERON
- SCALAR
- PION