82 research outputs found
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 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 -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 ) 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 Ca, O and He
Differential cross sections for elastic scattering of photons have been
measured for Ca at energies of 58 and 74 MeV and for O and He
at 61 MeV, in the angular range from 45 to 150. 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 . The explicit
forms of the moments of the deuteron and 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
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