Axial and Vector Correlator Mixing in Hot and Dense Hadronic Matter

We study the manifestations of chiral symmetry restoration which have a significance for the parity mixing. Restricting to pions and nucleons we establish a formalism for the expression of the vector correlator, which displays the mixing of the axial correlator into the vector one and unifies the cases of the heat bath and the dense medium. We give examples of mixing cross-sections. We also establish a link between the energy integrated mixing cross-sections and the pion scalar density which governs the quenching factors of coupling constants, such as the pion decay one, as well as the quark condensate evolution.Comment: 12 pages, Latex, 4 PostScript Figure

Isotope effect in total muon capture rates on nuclei and isotensor effective potential

Isotope effects are considered in the framework of the energy-weighted sum rule treatment of muon capture on nuclei. The possibility of exploiting total capture rates to convey information on nuclear structure is pointed out

Diferencias en el perfil reproductivo de mujeres autóctonas e inmigrantes residentes en Cataluña

ResumenObjetivoDescribir el perfil reproductivo en las mujeres autóctonas e inmigrantes residentes en Cataluña.MétodosLos abortos proceden del Registro de interrupción voluntaria del embarazo (IVE) del Departament de Salut, y los nacimientos y la población del Institut d’Estadística de Catalunya. Se han usado las variables «país de nacimiento» o «nacionalidad », según la fuente, para agrupar. Se analizan las tasas de fecundidad y aborto por edad, y las características sociodemográficas de las mujeres para el año 2005.ResultadosEl 20,8% de los 79.504 nacimientos y el 37,8% de las 16.798 IVE fueron de mujeres inmigrantes. El 14,2% de los embarazos de mujeres autóctonas y el 27,7% de los de mujeres inmigrantes terminan en aborto. Las tasa bruta de fecundidad y aborto es 1,4 y 3 veces superior, respectivamente, en las mujeres inmigrantes.ConclusionesHay importantes diferencias en las tasas y en las características sociodemográficas entre las mujeres autóctonas y las inmigrantes.AbstractObjectiveTo describe differences in reproductive patterns between autochthonous and immigrant women living in Catalonia (Spain).MethodsData on legal abortions were obtained from the abortions register in the Regional Ministry of Health, while data on births and the population were drawn from the Institute of Statistics of Catalonia. Depending on the source, the variables «country of birth» or «nationality» were used to compose the groups. Rates of fertility and abortion by age were computed for 2005 and the women's sociodemographic characteristics were analyzed.ResultsA total of 20.8% of the 79,504 births and 37.8% of the 16,798 abortions involved immigrant women, while 14.2% of pregnancies in autochthonous women and 27.7% of those in immigrant women terminated in abortion. Crude fertility and abortion rates were 1.4 and 3 times higher, respectively, in immigrant women.ConclusionsThere are important differences in abortion and fertility rates, as well as in social and demographic patterns, between autochthonous and immigrant women

Mesonic Contribution to the Compton Scattering Amplitude for Heavy Nuclei

The contribution of mesonic exchange currents to nuclear Compton scattering is investigated within the framework of a Fermi gas model of nuclear matter in the non-relativistic limit. The additional interaction between the nucleons is accounted for by including two- and three-body diagrams. As a test of this model, the enhancement constant $\kappa$ is calculated. The full correlators for the central and tensor part of the nucleon-nucleon interaction due to pion exchange are obtained and the energy dependence of the amplitude is investigated. The contribution of the $\Delta$-excitation to the mesonic part of the Compton amplitude is calculated explicitely using an effective Hamiltonian in the static limit.Comment: 21 pages, Latex, 12 figures available at http://www.physik2.gwdg.de/lokales/Forschungsberichte/Theorie/Meso

Meson-induced correlations of nucleons in nuclear Compton scattering

The non-resonant (seagull) contribution to the nuclear Compton amplitude at low energies is strongly influenced by nucleon correlations arising from meson exchange. We study this problem in a modified Fermi gas model, where nuclear correlation functions are obtained with the help of perturbation theory. The dependence of the mesonic seagull amplitude on the nuclear radius is investigated and the influence of a realistic nuclear density on this amplitude is dicussed. We found that different form factors appear for the static part (proportional to the enhancement constant $\kappa$) of the mesonic seagull amplitude and for the parts, which contain the contribution from electromagnetic polarizabilities.Comment: 15 pages, Latex, epsf.sty, 9 eps figures

Electromagnetic Polarizabilities of Nucleons bound in 40^{40}Ca, 16^{16}O and 4^4He

Differential cross sections for elastic scattering of photons have been measured for $^{40}$Ca at energies of 58 and 74 MeV and for $^{16}$O and $^4$He at 61 MeV, in the angular range from 45$^o$ to 150$^o$. Evidence is obtained that there are no significant in-medium modifications of the electromagnetic polarizabilities except for those originating from meson exchange currents.Comment: 20 pages including 5 Figure

The Spin-Dependent Structure Functions of Nuclei in the Meson-Nucleon Theory

A theoretical approach to the investigation of spin-dependent structure functions in deep inelastic scattering of polarized leptons off polarized nuclei, based on the effective meson-nucleon theory and operator product expansion method, is proposed and applied to deuteron and $^3He$. The explicit forms of the moments of the deuteron and $^3He$ spin-dependent structure functions are found and numerical estimates of the influence of nuclear structure effects are presented.Comment: 42 pages revtex, 7 postscript figures available from above e-mail upon request. Perugia preprint DFUPG 92/9

In-medium operator product expansion for heavy-light-quark pseudoscalar mesons

The operator product expansion (OPE) for heavy-light-quark pseudoscalar mesons (D-mesons and B-mesons) in medium is determined, both for a moving meson with respect to the surrounding medium as well as for a meson at rest. First of all, the OPE is given in terms of normal-ordered operators up to mass dimension 5, and the mass of the heavy-quark and the mass of the light-quark are kept finite. The Wilson coefficients of such an expansion are infrared (IR) divergent in the limit of a vanishing light-quark mass. A consistent separation of scales necessitates an OPE in terms of non-normal-ordered operators, which implies operator mixing, where the IR-divergences are absorbed into the operators. It is shown that the Wilson coefficients of such an expansion are IR-stable, and the limit of a vanishing light-quark mass is perfomed. Details of the major steps for the calculation of the Wilson coefficients are presented. By a comparison with previous results obtained by other theoretical groups we have found serious disagreements.Comment: 51 pages, 3 figure