SOME EVIDENCE ON PECUNIARY ECONOMIES OF SIZE FOR FARM FIRMS

Agricultural Finance,

Nucleon electroweak form factors in a meson-cloud model

The meson-cloud model of the nucleon consisting of a system of three valence quarks surrounded by a meson cloud is applied to study the electroweak structure of the proton and neutron. The electroweak nucleon form factors are calculated within a light-front approach, by obtaining an overall good description of the experimental data. Charge densities as a function of the transverse distance with respect to the direction of the three-momentum transfer are also discussed.Comment: Prepared for Proceedings of NSTAR2007, Workshop on the physics of excited nucleons, Bonn (Germany), 5-8 September 200

Complete next-to-leading order calculation for pion production in nucleon-nucleon collisions at threshold

Based on a counting scheme that explicitly takes into account the large momentum sqrt(M m_pi) characteristic for pion production in nucleon-nucleon collisions we calculate all diagrams for the reaction NN --> NN pi at threshold up to next-to-leading order. At this order there are no free parameters and the size of the next-to-leading order contributions is in line with the expectation from power counting. The sum of loop corrections at that order vanishes for the process pp --> pp pi^0 at threshold. The total contribution at next-to-leading order from loop diagrams that include the delta degree of freedom vanishes at threshold in both reaction channels pp --> pp pi^0, pn pi^+.Comment: 9 pages, 4 figure

Towards a field theoretic understanding of NN->NNpi

We study the production amplitude for the reaction NN->NNpi up to next--to--leading order in chiral perturbation theory using a counting scheme that takes into account the large scale introduced by the initial momentum. In particular we investigate a subtlety that arises once the leading loop contributions are convoluted with the NN wavefunctions as demanded by the non--perturbative nature of the NN interaction. We show how to properly identify the irreducible contribution of loop diagrams in such type of reaction. The net effect of the inclusion of all next-to-leading order loops is to enhance the leading rescattering amplitude by a factor of 4/3, bringing its contribution to the cross section for pp->dpi+ close to the experimental value.Comment: 15 Pages, 5 Figure

Isospin breaking in the vector current of the nucleon

Extraction of the nucleon's strange form factors from experimental data requires a quantitative understanding of the unavoidable contamination from isospin violation. A number of authors have addressed this issue during the past decade, and their work is reviewed here. The predictions from early models are largely consistent with recent results that rely as much as possible on input from QCD symmetries and related experimental data. The resulting bounds on isospin violation are sufficiently precise to be of value to on-going experimental and theoretical studies of the nucleon's strange form factors.Comment: 5 pages, 3 figures. Presented at the International Workshop "From Parity Violation to Hadronic Structure and more...", Milos, Greece, 16-20 May 2006. Version 2 is only to update Refs. [21] and [25

Toy Model for Pion Production in Nucleon-Nucleon Collisions

We develop a toy model of pion production in nucleon-nucleon collisions that reproduces some of the features of the chiral Lagrangian calculations. We calculate the production amplitude and examine some common approximations.Comment: 9 pages, 3 figure

Isospin violation and the proton's neutral weak magnetic form factor

The effects of isospin violation on the neutral weak magnetic form factor of the proton are studied using two-flavour chiral perturbation theory. The first nonzero contributions appear at O(p^4) in the small-momentum expansion, and the O(p^5) corrections are also calculated. The leading contributions from an explicit Delta(1232) isomultiplet are included as well. At such a high order in the chiral expansion, one might have expected a large number of unknown parameters to contribute. However, it is found that no unknown parameters can appear within loop diagrams, and a single tree-level counterterm at O(p^4) is sufficient to absorb all divergences. The momentum dependence of the neutral weak magnetic form factor is not affected by this counterterm.Comment: 26 pages including 9 figure

Fathers' experiences of supporting breastfeeding: challenges for breastfeeding promotion and education

Increasing breastfeeding rates is a strategic priority in the UK and understanding the factors that promote and encourage breastfeeding is critical to achieving this. It is established that women who have strong social support from their partner are more likely to initiate and continue breastfeeding. However, little research has explored the fathers' role in breastfeeding support and more importantly, the information and guidance he may need. In the current study, 117 men whose partner had given birth in the previous 2 years and initiated breastfeeding at birth completed an open-ended questionnaire exploring their experiences of breastfeeding, the information and support they received and their ideas for future breastfeeding education and promotion aimed at fathers and families. Overall, the findings showed that fathers were encouraging of breastfeeding and wanted to be able to support their partner. However, they often felt left out of the breastfeeding relationships and helpless to support their partner at this time. Many reported being excluded from antenatal breastfeeding education or being considered unimportant in post-natal support. Men wanted more information about breastfeeding to be directed towards them alongside ideas about how they could practically support their partner. The importance of support mechanisms for themselves during this time was also raised. The results highlight the need for health professionals to direct support and information towards fathers as well as the mother–infant dyad and to recognise their importance in promoting and enabling breastfeeding

Quasi-free Compton Scattering from the Deuteron and Nucleon Polarizabilities

Cross sections for quasi-free Compton scattering from the deuteron were measured for incident energies of 236--260 MeV at the laboratory angle -135 degrees. The recoil nucleons were detected in a liquid-scintillator array situated at 20 degrees. The measured differential cross sections were used, with the calculations of Levchuk et al., to determine the polarizabilities of the bound nucleons. For the bound proton, the extracted values were consistent with the accepted value for the free proton. Combining our results for the bound neutron with those from Rose et al., we obtain one-sigma constraints of alpha_n = 7.6-14.0 and beta_n = 1.2-7.6.Comment: 4 pages, 3 figures, accepted in PR

Chiral Perturbation Approach to the pp -> pp pi0 Reaction Near Threshold

The usual theoretical treatments of the near-threshold $pp \rightarrow pp\pi^0$ reaction are based on various phenomenological Lagrangians. In this work we examine the relationship between these approaches and a systematic chiral perturbation method. Our chiral perturbation calculation indicates that the pion rescattering term should be significantly enhanced as compared with the traditional phenomenological treatment, and that this term should have substantial energy and momentum dependence. An important consequence of this energy-momentum dependence is that, for a representative threshold kinematics and within the framework of our semiquantitative calculation, the rescattering term interferes destructively with the Born-term in sharp contrast to the constructive interference obtained in the conventional treatment. This destructive interference makes theoretical cross sections for $pp \rightarrow pp\pi^0$ much smaller than the experimental values, a feature that suggests the importance of the heavy-meson exchange contributions to explain the experimental data.Comment: 35 pages (REVTeX), 5 figures as 1 PostScript file acknowledgement changed, reference added, Phys.Rev.C (in print