Searcharxiv⌕ Search

arXiv subjects

M. A. Caprio

Publications and source records attributed to M. A. Caprio.

At least 37 records · Page 2Linked to original sources
arXiv2014

Tidal Waves in $^{102}$Pd: A Phenomenological Analysis

Rotational and electromagnetic properties of the yrast band in $^{102}$Pd are analyzed in terms of a phenomenological phonon model that includes anharmonic terms. Both the moment of inertia and $B(E2)$'s are well reproduced by the model, providing an independent confirmation of the multi-phonon picture recently proposed. The (empirical) dependence of the phonon-phonon interaction on the phonon frequency, in Ru, Pd, and Ru isotopes, follows the expectations from particle-vibration coupling.

nucl-ex↗
arXiv2014

Halo nuclei 6He and 8He with the Coulomb-Sturmian basis

The rapid Gaussian falloff of the oscillator functions at large radius makes them poorly suited for the description of the asymptotic properties of the nuclear wave function, a problem which becomes particularly acute for halo nuclei. We consider an alternative basis for ab initio no-core configuration interaction (NCCI) calculations, built from Coulomb-Sturmian radial functions, allowing for realistic exponential falloff. NCCI calculations are carried out for the neutron halo nuclei 6,8He, as well as the baseline case 4He, with the JISP16 nucleon-nucleon interaction. Estimates are made for the root-mean-square radii of the proton and matter distributions.

nucl-th↗
arXiv2014

Halo nuclei with the Coulomb-Sturmian basis

The rapid falloff of the oscillator functions at large radius (Gaussian asymptotics) makes them poorly suited for the description of the asymptotic properties of the nuclear wave function, a problem which becomes particularly acute for halo nuclei. We consider an alternative basis for ab initio no-core configuration interaction (NCCI) calculations, built from Coulomb-Sturmian radial functions, allowing for realistic (exponential) radial falloff. NCCI calculations are carried out for the neutron-rich He isotopes, and estimates are made for the RMS radii of the proton and neutron distributions.

nucl-th↗
arXiv2014

Generalized seniority with realistic interactions in open-shell nuclei

Generalized seniority provides a truncation scheme for the nuclear shell model, based on pairing correlations, which offers the possibility of dramatically reducing the dimensionality of the nuclear shell-model problem. Systematic comparisons against results obtained in the full shell-model space are required to assess the viability of this scheme. Here, we extend recent generalized seniority calculations for semimagic nuclei, the Ca isotopes, to open-shell nuclei, with both valence protons and valence neutrons. The even-mass Ti and Cr isotopes are treated in a full major shell and with realistic interactions, in the generalized seniority scheme with one broken proton pair and one broken neutron pair. Results for level energies, orbital occupations, and electromagnetic observables are compared with those obtained in the full shell-model space. We demonstrate that, even for the Ti isotopes, significant benefit would be obtained in going beyond the approximation of one broken pair of each type, while the Cr isotopes require further broken pairs to provide even qualitative accuracy.

nucl-th↗
arXiv2013

Collective Modes in Light Nuclei from First Principles

Results for ab initio no-core shell model calculations in a symmetry-adapted SU(3)-based coupling scheme demonstrate that collective modes in light nuclei emerge from first principles. The low-lying states of 6Li, 8Be, and 6He are shown to exhibit orderly patterns that favor spatial configurations with strong quadrupole deformation and complementary low intrinsic spin values, a picture that is consistent with the nuclear symplectic model. The results also suggest a pragmatic path forward to accommodate deformation-driven collective features in ab initio analyses when they dominate the nuclear landscape.

nucl-th↗
arXiv2013

Tidal Waves in $^{102}$Pd: A Rotating Condensate of Multiple $d$ bosons

Low-lying collective excitations in even-even vibrational and transitional nuclei may be described semi-classically as quadrupole running waves on the surface of the nucleus ("tidal waves"), and the observed vibrational-rotational behavior can be thought of as resulting from a rotating condensate of interacting $d$ bosons. These concepts have been investigated by measuring lifetimes of the levels in the yrast band of the $^{102}$Pd nucleus with the Doppler Shift Attenuation Method. The extracted $B(E2)$ reduced transition probabilities for the yrast band display a monotonic increase with spin, in agreement with the interpretation based on rotation-induced condensation of aligned $d$ bosons.

nucl-ex↗
arXiv2013

Emergence of rotational bands in ab initio no-core configuration interaction calculations of light nuclei

The emergence of rotational bands is observed in no-core configuration interaction (NCCI) calculations for the odd-mass Be isotopes (7<=A<=13) with the JISP16 nucleon-nucleon interaction, as evidenced by rotational patterns for excitation energies, quadrupole moments, and E2 transitions. Yrast and low-lying excited bands are found. The results demonstrate the possibility of well-developed rotational structure in NCCI calculations using a realistic nucleon-nucleon interaction.

nucl-th↗
arXiv2013

Coulomb-Sturmian basis for the nuclear many-body problem

Calculations in ab initio no-core configuration interaction (NCCI) approaches, such as the no-core shell model or no-core full configuration methods, have conventionally been carried out using the harmonic-oscillator many-body basis. However, the rapid falloff (Gaussian asymptotics) of the oscillator functions at large radius makes them poorly suited for the description of the asymptotic properties of the nuclear wave function. We establish the foundations for carrying out NCCI calculations with an alternative many-body basis built from Coulomb-Sturmian functions. These provide a complete, discrete set of functions with a realistic exponential falloff. We present illustrative NCCI calculations for 6Li with a Coulomb-Sturmian basis and investigate the center-of-mass separation and spurious excitations.

nucl-th↗
arXiv2012

Construction of the center-of-mass free space for the SU(3) no-core shell model

We address the removal of states with center-of-mass excitation from the SU(3) no-core shell model [SU(3)-NCSM] space, i.e., construction of the nonspurious subspace. A procedure is formulated based on solution of the null-space problem for the center-of-mass harmonic oscillator lowering operator Bcm, operating at the level of SU(3) irreducible representations. Isolation of the center-of-mass free subspace for the SU(3)-NCSM provides the foundation for exact removal of center-of-mass dynamics in the proposed Sp(3,R) symplectic no-core shell model. We outline the construction process for the matrix representation of Bcm, present the algorithm for obtaining the nonspurious space, and examine the dimensions obtained for center-of-mass free SU(3) subspaces in representative light nuclei.

nucl-th↗
arXiv2012

The no-core shell model with general radial bases

Calculations in the ab initio no-core shell model (NCSM) have conventionally been carried out using the harmonic-oscillator many-body basis. However, the rapid falloff (Gaussian asymptotics) of the oscillator functions at large radius makes them poorly suited for the description of the asymptotic properties of the nuclear wavefunction. We establish the foundations for carrying out no-core configuration interaction (NCCI) calculations using a basis built from general radial functions and discuss some of the considerations which enter into using such a basis. In particular, we consider the Coulomb-Sturmian basis, which provides a complete set of functions with a realistic (exponential) radial falloff.

nucl-th↗
arXiv2012

Generalized seniority for the shell model with realistic interactions

The generalized seniority scheme has long been proposed as a means of dramatically reducing the dimensionality of nuclear shell model calculations, when strong pairing correlations are present. However, systematic benchmark calculations, comparing results obtained in a model space truncated according to generalized seniority with those obtained in the full shell model space, are required to assess the viability of this scheme. Here, a detailed comparison is carried out, for semimagic nuclei taken in a full major shell and with realistic interactions. The even-mass and odd-mass Ca isotopes are treated in the generalized seniority scheme, for generalized seniority v<=3. Results for level energies, orbital occupations, and electromagnetic observables are compared with those obtained in the full shell model space.

nucl-th↗
arXiv2012

Tidal wave in 102Pd: Rotating condensate of up to seven d-bosons

The yrast states of even even vibrational and transitional nuclei are inter- preted as a rotating condensate of interacting d-bosons and the corresponding semi-classical tidal wave concept. A simple experimental manifestation of the anharmonicity caused by the boson interaction is found. The interpretation is substantiated by calculations based on the Collective Model and the Cranking Model.

nucl-th↗
arXiv2011

Exact diagonalization of the Bohr Hamiltonian for rotational nuclei: Dynamical gamma softness and triaxiality

Detailed quantitative predictions are obtained for phonon and multiphonon excitations in well-deformed rotor nuclei within the geometric framework, by exact numerical diagonalization of the Bohr Hamiltonian in an SO(5) basis. Dynamical gamma deformation is found to significantly influence the predictions through its coupling to the rotational motion. Basic signatures for the onset of rigid triaxial deformation are also obtained.

nucl-th↗
arXiv2011

Dual algebraic structures for the two-level pairing model

Duality relations are explicitly established relating the Hamiltonians and basis classification schemes associated with the number-conserving unitary and number-nonconserving quasispin algebras for the two-level system with pairing interactions. These relations are obtained in a unified formulation for both bosonic and fermionic systems, with arbitrary and, in general, unequal degeneracies for the two levels. Illustrative calculations are carried out comparing the bosonic and fermionic quantum phase transitions.

quant-ph↗
arXiv2010

Racah's method for general subalgebra chains: Coupling coefficients of SO(5) in canonical and physical bases

It is shown that the method of infinitesimal generators ("Racah's method") can be broadly and systematically formulated as a method applicable to the calculation of reduced coupling coefficients for a generic subalgebra chain G>H, provided the reduced matrix elements of the generators of G and the recoupling coefficients of H are known. The calculation of SO(5)>SO(4) reduced coupling coefficients is considered as an example, and a procedure for transformation of reduced coupling coefficients between canonical and physical subalegebra chains is presented. The problem of calculating coupling coefficients for generic irreps of SO(5), reduced with respect to any of its subalgebra chains, is completely resolved by this approach.

math-ph↗
arXiv2009

Construction of SO(5)>SO(3) spherical harmonics and Clebsch-Gordan coefficients

The SO(5)>SO(3) spherical harmonics form a natural basis for expansion of nuclear collective model angular wave functions. They underlie the recently-proposed algebraic method for diagonalization of the nuclear collective model Hamiltonian in an SU(1,1)xSO(5) basis. We present a computer code for explicit construction of the SO(5)>SO(3) spherical harmonics and use them to compute the Clebsch-Gordan coefficients needed for collective model calculations in an SO(3)-coupled basis. With these Clebsch-Gordan coefficients it becomes possible to compute the matrix elements of collective model observables by purely algebraic methods.

physics.comp-ph↗
arXiv2009

Phonon and multi-phonon excitations in rotational nuclei by exact diagonalization of the Bohr Hamiltonian

Exact numerical diagonalization of the Bohr Hamiltonian by SU(1,1)xSO(5) methods is used to obtain detailed quantitative predictions for single-phonon and multi-phonon excitations in well-deformed rotor nuclei. Dynamical gamma deformation is found to significantly influence the predictions through its coupling to the rotational motion. Basic signatures for the onset of rigid triaxial deformation are obtained.

nucl-th↗