Structure of the doublet bands in doubly odd nuclei: The case of 128Cs^{128}Cs

The structure of the $\Delta J = 1$ doublet bands in $^{128}Cs$ is investigated within the framework of the Interacting Vector Boson Fermion Model (IVBFM). A new, purely collective interpretation of these bands is given on the basis of the used boson-fermion dynamical symmetry of the model. The energy levels of the doublet bands as well as the absolute $B(E2)$ and $B(M1)$ transition probabilities between the states of both yrast and yrare bands are described quite well. The observed odd-even staggering of both $B(M1)$ and $B(E2)$ values is reproduced by the introduction of an appropriate interaction term of quadrupole type, which produces such a staggering effect in the transition strengths. The calculations show that the appearance of doublet bands in certain odd-odd nuclei could be a consequence of the realization of a larger dynamical symmetry based on the non-compact supersymmetry group $OSp(2\Omega /12, R)$.Comment: 12 pages, 8 figure

Bursts in the Chaotic Trajectory Lifetimes Preceding the Controlled Periodic Motion

The average lifetime ($\tau(H)$) it takes for a randomly started trajectory to land in a small region ($H$) on a chaotic attractor is studied. $\tau(H)$ is an important issue for controlling chaos. We point out that if the region $H$ is visited by a short periodic orbit, the lifetime $\tau(H)$ strongly deviates from the inverse of the naturally invariant measure contained within that region ($\mu_N(H)^{-1}$). We introduce the formula that relates $\tau(H)/\mu_N(H)^{-1}$ to the expanding eigenvalue of the short periodic orbit visiting $H$.Comment: Accepted for publication in Phys. Rev. E, 3 PS figure

Measuring gravitational lensing of the cosmic microwave background using cross correlation with large scale structure

We cross correlate the gravitational lensing map extracted from cosmic microwave background measurements by the Wilkinson Microwave Anisotropy Probe (WMAP) with the radio galaxy distribution from the NRAO VLA Sky Survey (NVSS) by using a quadratic estimator technique. We use the full covariance matrix to filter the data, and calculate the cross-power spectra for the lensing-galaxy correlation. We explore the impact of changing the values of cosmological parameters on the lensing reconstruction, and obtain statistical detection significances at $>3\sigma$. The results of all cross correlations pass the curl null test as well as a complementary diagnostic test using the NVSS data in equatorial coordinates. We forecast the potential for Planck and NVSS to constrain the lensing-galaxy cross correlation as well as the galaxy bias. The lensing-galaxy cross-power spectra are found to be Gaussian distributed.Comment: 16 pages, 10 figure

Collective excitations in the Unitary Correlation Operator Method and relativistic QRPA studies of exotic nuclei

The collective excitation phenomena in atomic nuclei are studied in two different formulations of the Random Phase Approximation (RPA): (i) RPA based on correlated realistic nucleon-nucleon interactions constructed within the Unitary Correlation Operator Method (UCOM), and (ii) relativistic RPA (RRPA) derived from effective Lagrangians with density-dependent meson-exchange interactions. The former includes the dominant interaction-induced short-range central and tensor correlations by means of an unitary transformation. It is shown that UCOM-RPA correlations induced by collective nuclear vibrations recover a part of the residual long-range correlations that are not explicitly included in the UCOM Hartree-Fock ground state. Both RPA models are employed in studies of the isoscalar monopole resonance (ISGMR) in closed-shell nuclei across the nuclide chart, with an emphasis on the sensitivity of its properties on the constraints for the range of the UCOM correlation functions. Within the Relativistic Quasiparticle RPA (RQRPA) based on Relativistic Hartree-Bogoliubov model, the occurrence of pronounced low-lying dipole excitations is predicted in nuclei towards the proton drip-line. From the analysis of the transition densities and the structure of the RQRPA amplitudes, it is shown that these states correspond to the proton pygmy dipole resonance.Comment: 15 pages, 4 figures, submitted to Physics of Atomic Nuclei, conference proceedings, "Frontiers in the Physics of Nucleus", St. Petersburg, 28. June-1. July, 200

Deformed Gaussian Orthogonal Ensemble Analysis of the Interacting Boson Model

A Deformed Gaussian Orthogonal Ensemble (DGOE) which interpolates between the Gaussian Orthogonal Ensemble and a Poissonian Ensemble is constructed. This new ensemble is then applied to the analysis of the chaotic properties of the low lying collective states of nuclei described by the Interacting Boson Model (IBM). This model undergoes a transition order-chaos-order from the $SU(3)$ limit to the $O(6)$ limit. Our analysis shows that the quantum fluctuations of the IBM Hamiltonian, both of the spectrum and the eigenvectors, follow the expected behaviour predicted by the DGOE when one goes from one limit to the other.Comment: 10 pages, 4 figures (avaiable upon request), IFUSP/P-1086 Replaced version: in the previous version the name of one of the authors was omitte

Transport, magnetic and superconducting properties of RuSr2RCu2O8 (R= Eu, Gd) doped with Sn

Ru{1-x}Sn{x}Sr2EuCu2O8 and Ru{1-x}Sn{x}Sr2GdCu2O8 have been comprehensively studied by microwave and dc resistivity and magnetoresistivity and by the dc Hall measurements. The magnetic ordering temperature T_m is considerably reduced with increasing Sn content. However, doping with Sn leads to only slight reduction of the superconducting critical temperature T_c accompanied with the increase of the upper critical field B_c2, indicating an increased disorder in the system and a reduced scattering length of the conducting holes in CuO2 layers. In spite of the increased scattering rate, the normal state resistivity and the Hall resistivity are reduced with respect to the pure compound, due to the increased number of itinerant holes in CuO2 layers, which represent the main conductivity channel. Most of the electrons in RuO2 layers are presumably localized, but the observed negative magnetoresistance and the extraordinary Hall effect lead to the conclusion that there exists a small number of itinerant electrons in RuO$_2$ layers that exhibit colossal magnetoresistance.Comment: 10 pages, 9 figure

Nuclear Mass Dependence of Chaotic Dynamics in Ginocchio Model

The chaotic dynamics in nuclear collective motion is studied in the framework of a schematic shell model which has only monopole and quadrupole degrees of freedom. The model is shown to reproduce the experimentally observed global trend toward less chaotic motion in heavier nuclei. The relation between current approach and the earlier studies with bosonic models is discussed.Comment: 11 Page REVTeX file, 2 postscript figures, uuencode

Low-lying dipole response in the Relativistic Quasiparticle Time Blocking Approximation and its influence on neutron capture cross sections

We have computed dipole strength distributions for nickel and tin isotopes within the Relativistic Quasiparticle Time Blocking approximation (RQTBA). These calculations provide a good description of data, including the neutron-rich tin isotopes $^{130,132}$Sn. The resulting dipole strengths have been implemented in Hauser-Feshbach calculations of astrophysical neutron capture rates relevant for r-process nucleosynthesis studies. The RQTBA calculations show the presence of enhanced dipole strength at energies around the neutron threshold for neutron rich nuclei. The computed neutron capture rates are sensitive to the fine structure of the low lying dipole strength, which emphasizes the importance of a reliable knowledge of this excitation mode.Comment: 15 pages, 4 figures, Accepted in Nucl. Phys.

Excitation of Pygmy Dipole Resonance in neutron-rich nuclei via Coulomb and nuclear fields

We study the nature of the low-lying dipole strength in neutron-rich nuclei, often associated to the Pygmy Dipole Resonance. The states are described within the Hartree-Fock plus RPA formalism, using different parametrizations of the Skyrme interaction. We show how the information from combined reactions processes involving the Coulomb and different mixtures of isoscalar and isovector nuclear interactions can provide a clue to reveal the characteristic features of these states.Comment: 9 Pages, 8 figures, contribution to International Symposium On Nuclear Physics, December 8-12, 2009,Bhabha Atomic Research Centre, Mumbai, Indi

Misleading signatures of quantum chaos

The main signature of chaos in a quantum system is provided by spectral statistical analysis of the nearest neighbor spacing distribution and the spectral rigidity given by $\Delta_3(L)$. It is shown that some standard unfolding procedures, like local unfolding and Gaussian broadening, lead to a spurious increase of the spectral rigidity that spoils the $\Delta_3(L)$ relationship with the regular or chaotic motion of the system. This effect can also be misinterpreted as Berry's saturation.Comment: 4 pages, 5 figures, submitted to Physical Review