Isospin mixing and Fermi transitions: Selfconsistent deformed mean field calculations and beyond

We study Fermi transitions and isospin mixing in an isotopic chain 70-78 Kr considering various approximations that use the same Skyrme-Hartree-Fock single particle basis. We study Coulomb effects as well as the effect of BCS and quasiparticle random phase approximation (QRPA) correlations. A measure of isospin mixing in the approximate ground state is defined by means of the expectation value of the isospin operator squared in N=Z nuclei (which is generalized to N different from Z nuclei). Starting from strict Hartree-Fock approach without Coulomb, it is shown that the isospin breaking is negligible, on the order of a few per thousand for (N-Z)=6, increasing to a few percent with Coulomb. Pairing correlations induce rather large isospin mixing and Fermi transitions of the forbidden type (beta- for NZ). The enhancement produced by BCS correlations is compensated to a large extent by QRPA correlations induced by isospin conserving residual interactions that tend to restore isospin symmetry.Comment: 14 pages, 5 figures, to be published in Phys. Rev.

Gamow-Teller strength distributions in Fe and Ni stable isotopes

We study Gamow-Teller strength distributions in some selected nuclei of particular Astrophysical interest within the iron mass region. The theoretical framework is based on a proton-neutron Quasiparticle Random Phase Approximation built on a deformed selfconsistent mean field basis obtained from two-body density-dependent Skyrme forces. We compare our results to available experimental information obtained from (n,p) and (p,n) charge exchange reactions.Comment: 11 pages, 3 figure

Few-body decay and recombination in nuclear astrophysics

Three-body continuum problems are investigated for light nuclei of astrophysical relevance. We focus on three-body decays of resonances or recombination via resonances or the continuum background. The concepts of widths, decay mechanisms and dynamic evolution are discussed. We also discuss results for the triple $\alpha$ decay in connection with $2^+$ resonances and density and temperature dependence rates of recombination into light nuclei from $\alpha$-particles and neutrons.Comment: 9 pages, 8 figures. Proceedings of the 21st European Few Body Conference held in Salamanca (Spain) in August-September 201

Rotational symmetry and degeneracy: a cotangent-perturbed rigid rotator of unperturbed level multiplicity

We predict level degeneracy of the rotational type in diatomic molecules described by means of a cotangent-hindered rigid rotator. The problem is shown to be exactly solvable in terms of non-classical Romanovski polynomials. The energies of such a system are linear combinations of t(t+1) and 1/[t(t+1)+1/4] terms with the non-negative integer principal quantum number t=n+|/bar{m}| being the sum of the degree n of the polynomials and the absolute value, |/bar{m}|, of the square root of the separation constant between the polar and azimuthal motions. The latter obeys, with respect to t, the same branching rule, |/bar{m}|=0,1,..., t, as does the magnetic quantum number with respect to the angular momentum, l, and, in this fashion, the t quantum number presents itself indistinguishable from l. In effect, the spectrum of the hindered rotator has the same (2t+1)-fold level multiplicity as the unperturbed one. For small t values, the wave functions and excitation energies of the perturbed rotator differ from the ordinary spherical harmonics, and the l(l+1) law, respectively, while approaching them asymptotically with increasing t. In this fashion the breaking of the rotational symmetry at the level of the representation functions is opaqued by the level degeneracy. The model provides a tool for the description of rotational bands with anomalously large gaps between the ground state and its first excitation.Comment: 10 pages, 6 figures; Molecular Physics 201

Degradação ambiental da Bacia do São Francisco na região Semiárida por ações antrópicas.

O Rio São Francisco possui quatro regiões fisiográficas: alto (da nascente até a região de Pirapora, em Minas Gerais, médio (de Pirapora até Remanso, na Bahia), submédio (de Remanso até Paulo Afonso, na Bahia) e baixo São Francisco (de Paulo Afonso até a foz em Alagoas e Sergipe). O submédio São Francisco (Figura 2), área de abrangência desta abordagem, abrange áreas dos estados da Bahia, Pernambuco, Alagoas e Sergipe, estendendo-se da Barragem de Sobradinho, Bahia, até Belo Monte, em Alagoas, com 117.351 km2 , ou 18,4% da área da bacia, tendo 568 km de extensão do rio principal e com uma população de cerca de 2,48 milhões de habitantes. Inclui as sub-bacias dos rios Pontal, Garças, Brígida, Terra Nova, Pajeú e Moxotó (margem esquerda) e Salitre, Poço, Curaçá, Vargem Grande e Macururé (margem direita) (BRASIL, 2006). A vasta área do Submédio São Francisco dificulta a administração para o desenvolvimento regional. Para facilitar as articulações das ações a serem realizadas regionalmente, foi criada a Rede de Desenvolvimento Integrado do Polo Petrolina, PE e Juazeiro, BA (RIDE Petrolina/Juazeiro)

Heat Kernel for Spin-3/2 Rarita-Schwinger Field in General Covariant Gauge

The heat kernel for the spin-3/2 Rarita-Schwinger gauge field on an arbitrary Ricci flat space-time ($d>2$) is investigated in a family of covariant gauges with one gauge parameter $\alpha$. The $\alpha$-dependent term of the kernel is expressed by the spin-1/2 heat kernel. It is shown that the axial anomaly and the one-loop divegence of the action are $\alpha$-independent, and that the conformal anomaly has an $\alpha$-dependent total derivative term in $d=2m\geq6$ dimensions.Comment: 11 pages, latex, ITP-SB-94-3

Direct and sequential radiative three-body reaction rates at low temperatures

We investigate the low-temperature reaction rates for radiative capture processes of three particles. We compare direct and sequential capture mechanisms and rates using realistic phenomenological parametrizations of the corresponding photodissociation cross sections.Energy conservation prohibits sequential capture for energies smaller than that of the intermediate two-body structure. A finite width or a finite temperature allows this capture mechanism. We study generic effects of positions and widths of two- and three-body resonances for very low temperatures. We focus on nuclear reactions relevant for astrophysics, and we illustrate with realistic estimates for the $\alpha$-$\alpha$-$\alpha$ and $\alpha$-$\alpha$-$n$ radiative capture processes. The direct capture mechanism leads to reaction rates which for temperatures smaller than 0.1 GK can be several orders of magnitude larger than those of the NACRE compilation.Comment: To be published in European Physical Journal