Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Exotic modes of excitation in atomic nuclei far from stability  [PDF]
N. Paar,D. Vretenar,E. Khan,G. Colo
Physics , 2007, DOI: 10.1088/0034-4885/70/5/R02
Abstract: We review recent studies of the evolution of collective excitations in atomic nuclei far from the valley of $\beta$-stability. Collective degrees of freedom govern essential aspects of nuclear structure, and for several decades the study of collective modes such as rotations and vibrations has played a vital role in our understanding of complex properties of nuclei. The multipole response of unstable nuclei and the possible occurrence of new exotic modes of excitation in weakly-bound nuclear systems, present a rapidly growing field of research, but only few experimental studies of these phenomena have been reported so far. Valuable data on the evolution of the low-energy dipole response in unstable neutron-rich nuclei have been gathered in recent experiments, but the available information is not sufficient to determine the nature of observed excitations. Even in stable nuclei various modes of giant collective oscillations had been predicted by theory years before they were observed, and for that reason it is very important to perform detailed theoretical studies of the evolution of collective modes of excitation in nuclei far from stability. We therefore discuss the modern theoretical tools that have been developed in recent years for the description of collective excitations in weakly-bound nuclei. The review focuses on the applications of these models to studies of the evolution of low-energy dipole modes from stable nuclei to systems near the particle emission threshold, to analyses of various isoscalar modes, those for which data are already available, as well as those that could be observed in future experiments, to a description of charge-exchange modes and their evolution in neutron-rich nuclei, and to studies of the role of exotic low-energy modes in astrophysical processes.
Exotic nuclei far from the stability line  [PDF]
K. Hagino,I. Tanihata,H. Sagawa
Physics , 2012,
Abstract: The recent availability of radioactive beams has opened up a new era in nuclear physics. The interactions and structure of exotic nuclei close to the drip lines have been studied extensively world wide, and it has been revealed that unstable nuclei, having weakly bound nucleons, exhibit characteristic features such as a halo structure and a soft dipole excitation. We here review the developments of the physics of unstable nuclei in the past few decades. The topics discussed in this Chapter include the halo and skin structures, the Coulomb breakup, the dineutron correlation, the pair transfer reactions, the two-nucleon radioactivity, the appearance of new magic numbers, and the pygmy dipole resonances.
Effective lagrangian approach to structure of selected nuclei far from sta bility  [PDF]
Marco A. Huertas
Physics , 2002, DOI: 10.1103/PhysRevC.67.019901
Abstract: The convergence of the effective field theory (EFT) approach of Furnstahl, Serot and Tang to the nuclear many-body problem is studied by applying it to selected doubly-magic nuclei far from stability. An independently developed code, which can incorporate various levels of approximation of the chiral effective lagrangi an, is used to solve the self-consistent relativistic Hartree equations. Results are obtained for ground-state properties such as binding energies, single-parti cle level structure, and densities of the selected spherical, doubly-magic nucle i 132-Sn, 100-Sn and 48-Ni, 78-Ni. Calculated spectra of neigh boring nuclei differing by one particle or one hole show agreement with the most recent experimental data. Predictions for nucleon densities are presented.
Effective field theory approach to electroweak transitions of nuclei far from stability  [PDF]
M. A. Huertas
Physics , 2003,
Abstract: In a previous paper, the convergence of the effective field theory approach of Furnstahl, Serot and Tang to the nuclear many-body problem was studied by applying it to selected doubly-magic, and neighboring single-particle and single-hole, nuclei far from stability. The success of that approach, interpreted through density functional theory, would imply reliable densities. In this paper, the single-particle (Kohn-Sham) wave functions are probed using weak transitions near the Fermi surface. The weak currents are the Noether currents derived from the effective Lagrangian. The general single-particle transition matrix elements, from which any semi-leptonic weak rate can be calculated, are obtained in terms of upper and lower components of the Dirac wave functions. Here beta-decays in nuclei neighboring 132-Sn are studied and compared with available experimental data. Calibration of the theoretical results for such decays may also have useful application in element formation.
E2 properties of nuclei far from stability and the proton-halo problem of 8B  [PDF]
Hitoshi Nakada,Takaharu Otsuka
Physics , 1993, DOI: 10.1103/PhysRevC.49.886
Abstract: E2 properties of A=6--10 nuclei, including those of nuclei far from stability, are studied by a $(0+2)\hbar\omega$ shell-model calculation which includes E2 core-polarization effects explicitly. The quadrupole moments and the E2 transition strengths in A=6--10 nuclei are described quite well by the present calculation. This result indicates that the relatively large value of the quadrupole moment of $^8$B can be understood without introducing the proton-halo in $^8$B. An interesting effect of the $2\hbar\omega$ core-polarization is found for effective charges used in the $0\hbar\omega$ shell model; although isoscalar effective-charges are almost constant as a function of nucleus, appreciable variations are needed for isovector effective-charges which play important roles in nuclei with high isospin-values.
Skyrme mean-field studies of nuclei far from the stability line  [PDF]
P. -H. Heenen,P. Bonche,S. 'Cwiok,W. Nazarewicz,A. Valor
Physics , 1999,
Abstract: Two applications of mean-field calculations based on 3D coordinate-space techniques are presented. The first concerns the structure of odd-N superheavy elements that have been recently observed experimentally and shows the ability of the method to describe, in a self-consistent way, very heavy odd-mass nuclei. Our results are consistent with the experimental data. The second application concerns the introduction of correlations beyond a mean-field approach by means of projection techniques and configuration mixing. Results for Mg isotopes demonstrate that the restoration of rotational symmetry plays a crucial role in the description of 32Mg.
Transition from phase slips to the Josephson effect in a superfluid 4He weak link  [PDF]
E. Hoskinson,Y. Sato,I. Hahn,R. E. Packard
Physics , 2005, DOI: 10.1038/nphys190
Abstract: The rich dynamics of flow between two weakly coupled macroscopic quantum reservoirs has led to a range of important technologies. Practical development has so far been limited to superconducting systems, for which the basic building block is the so-called superconducting Josephson weak link. With the recent observation of quantum oscillations in superfluid 4He near 2K, we can now envision analogous practical superfluid helium devices. The characteristic function which determines the dynamics of such systems is the current-phase relation Is(phi), which gives the relationship between the superfluid current Is flowing through a weak link and the quantum phase difference phi across it. Here we report the measurement of the current-phase relation of a superfluid 4He weak link formed by an array of nano-apertures separating two reservoirs of superfluid 4He. As we vary the coupling strength between the two reservoirs, we observe a transition from a strongly coupled regime in which Is(phi) is linear and flow is limited by 2pi phase slips, to a weak coupling regime where Is(phi) becomes the sinusoidal signature of a Josephson weak link.
Phase sensitive two mode squeezing and photon correlations from exciton superfluid  [PDF]
T. Shi,Longhua Jiang,Jinwu Ye
Physics , 2009, DOI: 10.1103/PhysRevB.81.235402
Abstract: There have been experimental and theoretical studies on Photoluminescence (PL) from possible exciton superfluid in semiconductor electron-hole bilayer systems. However, the PL contains no phase information and no photon correlations, so it can only lead to suggestive evidences. It is important to identify smoking gun experiments which can lead to convincing evidences. Here we study two mode phase sensitive squeezing spectrum and also two photon correlation functions. We find the emitted photons along all tilted directions are always in a two mode squeezed state between $ \vec{k} $ and $ - \vec{k} $. There are always two photon bunching, the photon statistics is super-Poissonian. Observing these unique features by possible future phase sensitive homodyne experiment and HanburyBrown-Twiss type of experiment could lead to conclusive evidences of exciton superfluid in these systems.
Quantum quench in a p + i p superfluid: Winding numbers and topological states far from equilibrium  [PDF]
Matthew S. Foster,Maxim Dzero,Victor Gurarie,Emil A. Yuzbashyan
Physics , 2013, DOI: 10.1103/PhysRevB.88.104511
Abstract: We study the non-adiabatic dynamics of a 2D p+ip superfluid following a quantum quench of the BCS coupling constant. The model describes a topological superconductor with a non-trivial BCS (trivial BEC) phase appearing at weak (strong) coupling strengths. We extract the exact long-time asymptotics of the order parameter \Delta(t) by exploiting the integrability of the classical p-wave Hamiltonian, which we establish via a Lax construction. Three different types of behavior can occur depending upon the strength and direction of the quench. In phase I, the order parameter asymptotes to zero. In phase II, \Delta(t) goes to a non-zero constant. Phase III is characterized by persistent oscillations of \Delta(t). For quenches within I and II, we determine the topological character of the asymptotic states. We show that two different formulations of the bulk topological winding number, although equivalent in the ground state, must be regarded as independent out of equilibrium. The first number Q characterizes the Anderson pseudospin texture of the initial state; we show that it is conserved. For non-zero Q, this leads to the prediction of a "gapless topological" state when \Delta(t) goes to zero. The presence or absence of Majorana edge modes in a sample with a boundary is encoded in the second winding number W, formulated in terms of the retarded Green's function. We show that W can change following a quench across the quantum critical point. We discuss the implications for the (dis)appearance of Majorana edge modes. Finally, we show that the parity of zeros in the bulk out-of-equilibrium Cooper pair distribution function constitutes a Z2-valued quantum number, which is non-zero whenever W differs from Q. The pair distribution can in principle be measured using RF spectroscopy in an ultracold atom realization, allowing direct experimental detection of the bulk Z2 number.
Sweeping from the superfluid to Mott phase in the Bose-Hubbard model  [PDF]
Ralf Schützhold,Michael Uhlmann,Yan Xu,Uwe R. Fischer
Physics , 2006, DOI: 10.1103/PhysRevLett.97.200601
Abstract: We study the sweep through the quantum phase transition from the superfluid to the Mott state for the Bose-Hubbard model with a time-dependent tunneling rate $J(t)$. In the experimentally relevant case of exponential decay, $J(t)\propto e^{-\gamma t}$, an adapted mean-field expansion for large fillings $n$ yields a scaling solution for the fluctuations. This enables us to analytically calculate the evolution of the number and phase variations (on-site) and correlations (off-site) for slow ($\gamma\ll\mu$), intermediate, and fast (non-adiabatic $\gamma\gg\mu$) sweeps, where $\mu$ is the chemical potential. Finally, we derive the dynamical decay of the off-diagonal long-range order as well as the temporal shrinkage of the superfluid fraction in a persistent ring-current setup.
Page 1 /100
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.