Nucleon generalized polarizabilities within a relativistic Constituent Quark Model

Nucleon generalized polarizabilities are investigated within a relativistic framework, defining such quantities through a Lorentz covariant multipole expansion of the amplitude for virtual Compton scattering. The key physical ingredients in the calculation of the nucleon polarizabilities are the Lorentz invariant reduced matrix elements of the electromagnetic transition current, which can be evaluated from off-energy-shell helicity amplitudes. The evolution of the proton paramagnetic polarizability, $\beta_{para}(q)$, as a function of the virtual-photon three-momentum transfer $q,$ is explicitly evaluated within a relativistic constituent quark model by adopting transition form factors obtained in the light-front formalism. The discussion is focussed on the role played by the effects due to the relativistic approach and to the transition form factors, derived within different models.Comment: 14 pages and three figures (included), to appear in Phys. Rev. C (May 1998

Real and Virtual Compton Scattering: the nucleon polarisabilities

We give an overview of low-energy Compton scattering (gamma^(*) p --> gamma p) with a real or virtual incoming photon. These processes allow the investigation of one of the fundamental properties of the nucleon, i.e. how its internal structure deforms under an applied static electromagnetic field. Our knowledge of nucleon polarisabilities and their generalization to non-zero four-momentum transfer will be reviewed, including the presently ongoing experiments and future perspectives.Comment: 20 pages, 12 figures. Minireview/Proceedings of "Many-Body Structure of Strongly Interacting Systems", Mainz, Germany, Feb. 23-25 2011 . V2: typos corrected. version to appear in EPJ Special Topic

Generalized Polarizabilities of the Nucleon in Chiral Effective Theories

Using the techniques of chiral effective field theories we evaluate the so called generalized polarizabilities of the nucleon, which characterize the structure dependent components in virtual Compton scattering (VCS) as probed in the electron scattering reaction e N \to e' N gamma. Results are given for both spin-dependent and spin-independent structure effects to O(p^3) in SU(2) Heavy Baryon Chiral Perturbation Theory and to O(epsilon^3) in the SU(2) Small Scale Expansion. Finally we compare our calculations with results from the pioneering VCS experiment on the proton from Mainz.Comment: 39 pages, 12 figures, revte

Real and Virtual Compton Scattering off the Nucleon

A review is given of the very recent developments in the fields of real and virtual Compton scattering off the nucleon. Both real and virtual Compton scattering reactions are discussed at low outgoing photon energy where one accesses polarizabilities of the nucleon. The real Compton scattering at large momentum transfer is discussed which is asymptotically a tool to obtain information on the valence quark wave function of the nucleon. The rapid developments in deeply virtual Compton scattering and associated meson electroproduction reactions at high energy, high photon virtuality and small momentum transfer to the nucleon are discussed. A unified theoretical description of those processes has emerged over the last few years, which gives access to new, generalized parton distributions. The experimental status and perspectives in these fields are also discussed.Comment: 25 pages, 17 figure

Hadron Polarizabilities and Form Factors

This is the summary of the working group on Hadron Polarizabilities and Form Factors of the Chiral Dynamics Workshop in Mainz, September 1-5, 1997.Comment: 21 pages LaTeX2e, uses epsf, 9 fig

Frequências do fornecimento da dieta sobre as características da carcaça bovina em confinamento

Objetivou-se avaliar a influência de diferentes freqüências do fornecimento do volumoso e con- centrado sobre as características da carcaça nas categorias vaca e novilha, terminadas em confinamento. Foram utilizadas 16 novilhas e 16 vacas, com idade média de 20 e 66 meses e peso médio inicial de 338 e 432 kg, respectivamente, provenientes de gerações avançadas do cruzamento rotativo contínuo entre as raças Charolês e Nelore. Os tratamentos representados pelas freqüências do fornecimento do volumoso (V) e do concentrado (C), foram: 2 V/C (V e C duas vezes ao dia); 1 V/C (V e C uma vez ao dia); 1 V/ 2 C (V uma vez e o C duas vezes ao dia); 1 V/3 C (V uma vez e o C três vezes ao dia). Cada fornecimento alimentar foi ofertado às categorias vaca e novilha. A dieta fornecida foi composta de 60 % de silagem de milho e 40 % de concentrado com base na matéria seca. O abate foi realizado em frigorífico comercial, seguindo as normas do estabelecimento. O delineamento experimental utilizado foi inteiramente casualizado em arranjo fatorial 4 x 2 (fornecimento x categoria). Os dados foram submetidos à análise de variância e as médias comparadas pelo teste t. Não houve interação significativa entre freqüência de fornecimento e categoria animal. A freqüência de fornecimento não promoveu alterações nas ca- racterísticas da carcaça avaliadas (p>0,05). As vacas apresentaram maior peso de abate e de carcaça quente e fria em relação às novilhas (525,5; 291,0; 281,7 kg vs. 424,7; 236,1; 227,5 kg, respectivamente). Entretanto, as carcaças das novilhas apresentaram maior porcentagem de traseiro do que as vacas.The influence of different frequencies of supply of roughage and supplement on carcass characteristics of feedlot cows and heifers was studied. Sixteen heifers and sixteen cows, with average age of 20 and 66 months and initial weight of 338 and 432 kg, respectively, from advanced generations of Charolais and Nellore continuous rotational crossbreeding were used. The treatments, representing the frequencies of the supply of roughage (V) and concentrate (C), were: 2 V/C (V and C twice a day); 1 V/C (V and C once a day); 1 V/2 C (V once a day and C twice a day); 1 V/3 C (V once a day and C three times a day). Each treatment was offered to cows and heifers. The supplied diet was composed by 60 % of corn silage and 40 % of concentrate, on dry matter basis. The slaughter was carried out in commercial refrigerated slaugher house, following the rules of the establishment. The complete randomized experimental design was used, with a factorial arrangement of 4 x 2 (frequency of supply x category). Data were submitted to a variance analysis and the means were compared by t test. No significant interaction was observed between frequency of supply and animal category. The frequency of supply did not change the eva- luated carcass characteristics (p>0.05). The cows presented higher slaughter weight and hot and cold carcass weights when compared to heifers (525.5, 291.0, 281.7 kg vs. 424.7, 236.1, 227.5 kg, respectively). However, the carcasses of heifers showeda higher percentage of rear cows