M. A. Caprio

Excited state quantum phase transitions in many-body systems

Phenomena analogous to ground state quantum phase transitions have recently been noted to occur among states throughout the excitation spectra of certain many-body models. These excited state phase transitions are manifested as simultaneous singularities in the eigenvalue spectrum (including the gap or level density), order parameters, and wave function properties. In this article, the characteristics of excited state quantum phase transitions are investigated. The finite-size scaling behavior is determined at the mean-field level. It is found that excited state quantum phase transitions are universal to two-level bosonic and fermionic models with pairing interactions.

LevelScheme: A level scheme drawing and scientific figure preparation system for Mathematica ☆

LevelScheme is a scientific figure preparation system for Mathematica. The main emphasis is upon the construction of level schemes, or level energy diagrams, as used in nuclear, atomic, molecular, and hadronic physics. LevelScheme also provides a general infrastructure for the preparation of publication-quality figures, including support for multipanel and inset plotting, customizable tick mark generation, and various drawing and labeling tasks. Coupled with Mathematicas plotting functions and powerful programming language, LevelScheme provides a flexible system for the creation of figures combining diagrams, mathematical plots, and data plots.

Effects of β − γ coupling in transitional nuclei and the validity of the approximate separation of variables

Exact numerical diagonalization is carried out for the Bohr Hamiltonian with a {beta}-soft, axially stabilized potential. Wave function and observable properties are found to be dominated by strong {beta}-{gamma} coupling effects. The validity of the approximate separation of variables introduced with the X(5) model, extensively applied in recent analyses of axially stabilized transitional nuclei, is examined, and the reasons for its breakdown are analyzed.

Phase structure of a two-fluid bosonic system

Abstract The phase diagram of a two-fluid bosonic system is investigated. The proton–neutron interacting boson model (IBM-2) possesses a rich phase structure involving three control parameters and multiple order parameters. The surfaces of quantum phase transition between spherical, axially symmetric deformed, and SU π ν ∗ ( 3 ) triaxial phases are determined, and the evolution of classical equilibrium properties across these transitions is investigated. Spectroscopic observables are considered in relation to the phase diagram.

Analytic descriptions for transitional nuclei near the critical point

Abstract Exact solutions of the Bohr Hamiltonian with a five-dimensional square well potential, in isolation or coupled to a fermion by the five-dimensional spin–orbit interaction, are considered as examples of a new class of dynamical symmetry or Bose–Fermi dynamical symmetry. The solutions provide baselines for experimental studies of even–even [ E ( 5 ) ] and odd-mass [ E ( 5 | 4 ) ] nuclei near the critical point of the spherical to deformed γ -unstable phase transition.

Phase structure of the two-fluid proton-neutron system.

The phase structure of a two-fluid bosonic system is investigated. The proton-neutron interacting boson model possesses a rich phase structure involving three control parameters and multiple order parameters. The surfaces of quantum phase transition between spherical, axially symmetric deformed, and SU(*)(pinu)(3) triaxial phases are determined.

The YRAST Ball array

The Yale Rochester Array for SpecTroscopy, YRAST Ball, is described. Containing up to 30 Compton suppressed Ge detectors YRAST Ball is a powerful new array for c-ray spectroscopy. Several of its auxiliary detectors, including a multi-element solar cell array for heavy charged fragment detection and a new state of the art plunger system for recoil distance measurements are also described. ( 2000 Elsevier Science B.V. All rights reserved.

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.

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.

Large-scale ab initio configuration interaction calculations for light nuclei

In ab-initio Configuration Interaction calculations, the nuclear wavefunction is expanded in Slater determinants of single-nucleon wavefunctions and the many-body Schrodinger equation becomes a large sparse matrix problem. The challenge is to reach numerical convergence to within quantified numerical uncertainties for physical observables using finite truncations of the infinite-dimensional basis space. We discuss strategies for constructing and solving the resulting large sparse matrix eigenvalue problems on current multicore computer architectures. Several of these strategies have been implemented in the code MFDn, a hybrid MPI/OpenMP Fortran code for ab-initio nuclear structure calculations that can scale to 100,000 cores and more. Finally, we will conclude with some recent results for 12C including emerging collective phenomena such as rotational band structures using SRG evolved chiral N3LO interactions.