Elementary Modes Of Excitation Research Articles

Gamow–Teller transitions and neutron–proton-pair transfer reactions

We propose a schematic model of nucleons moving in spin–orbit partner levels, j=l±12, to explain Gamow–Teller and two-nucleon transfer data in N=Z nuclei above 40Ca. Use of the LS coupling scheme provides a more transparent approach to interpret the structure and reaction data. We apply the model to the analysis of charge-exchange, 42Ca(3He,t)42Sc, and np-transfer, 40Ca(3He,p)42Sc, reactions data to define the elementary modes of excitation in terms of both isovector and isoscalar pairs, whose properties can be determined by adjusting the parameters of the model (spin–orbit splitting, isovector pairing strength and quadrupole matrix element) to the available data. The overall agreement with experiment suggests that the approach captures the main physics ingredients and provides the basis for a boson approximation that can be extended to heavier nuclei. Our analysis also reveals that the SU(4)-symmetry limit is not realized in 42Sc.

Thermodynamic Hadron-Quark Phase Transition of Chiral Nuclear Matter at High Temperature

Based on the extended Nambu-Jona–Lasinio (NJL) model with the scalar-vector eightpoint interaction [15], we consider what ultimately happens to exact chiral nuclear matter as it is heated. In the realm of very high temperature the fundamental degrees of freedom of the strong interaction, quarks and gluons, come into play and a transition from nuclear matter consisting of confined baryons and mesons to a state with ‘liberated’ quarks and gluons is expected. In this paper, the hadron-quark phase transition occurs above a limited temperature and after the chiral phase transition in the nuclear matter. There is a so-called quarkyonic- like phase, in which the chiral symmetry is restored but the elementary excitation modes are nucleonic at high density, appears just before deconfinement.PACS: 21.65.-f, 21.65.Mn, 11.30.Rd, 12.39.Ba, 25.75.Nq, 68.35.Rh

Thermodynamic Hadron-Quark Phase Transition of Chiral Nuclear Matter to Quark-Gluon Plasma

After receiving very interesting results from investigations of chiral nuclear matter based on the extended Nambu-Jona--Lasinio model (ENJL) included the scalar-vector eight-point interaction, a fundamental question of nuclear physics is what happens to chiral nuclear matter as it is compressed or heated. At very high density and temperature, quarks and gluons come into play and a transition is expected to happen from a phase of nuclear matter consisting of confined hadrons and mesons to a state of `liberated' quarks and gluons. In this paper, we investigate the hadron-quark (HQ) phase transition occurs beyond the chiral phase transition in the nuclear matter. The results show that there exits a quarkyonic-like phase, appeared just before deconfinement, when the chiral symmetry is restored but the elementary excitation modes are still nucleonic.

Interweaving of elementary modes of excitation in superfluid nuclei through particle-vibration coupling: Quantitative account of the variety of nuclear structure observables

A complete characterization of the structure of nuclei can be obtained by combining information arising from inelastic scattering, Coulomb excitation and $\gamma-$decay, together with one- and two-particle transfer reactions. In this way it is possible to probe the single-particle and collective components of the nuclear many-body wavefunction resulting from their mutual coupling and diagonalising the low-energy Hamiltonian. We address the question of how accurately such a description can account for experimental observations. It is concluded that renormalizing empirically and on equal footing bare single-particle and collective motion in terms of self-energy (mass) and vertex corrections (screening), as well as particle-hole and pairing interactions through particle-vibration coupling allows theory to provide an overall, quantitative account of the data.

Quark–hadron phase transition in an extended Nambu–Jona-Lasinio model with scalar–vector interaction: Finite temperature and baryon chemical potential case

The quark-hadron phase transition at finite temperature and baryon chemical potential is investigated in an extended NJL model with scalar-vector eight-point interaction by comparing the pressure of symmetric nuclear matter with that of the quark matter. As a result, the extended NJL phase diagram is obtained in the temperature-baryon chemical potential plane and the effects of the scalar-vector coupling constant G_{sv}^q on the chiral phase transition are summarized. It is shown that a quarkyonic-like phase in which the chiral symmetry is restored but the elementary excitation modes are nucleonic appears just before deconfinement in this model.

Quasiparticle renormalization and pairing correlations in spherical superfluid nuclei

Within the framework of nuclear field theory (NFT), the spectrum of atomic nuclei is described in terms of collective and quasiparticle degrees of freedom, that is, of elementary modes of excitation that are directly related to experiment and of their coupling, whose strength and form factors are the basic ingredients entering in the calculations of absolute cross sections of inelastic and of one- and two-particle transfer reactions. We present a detailed discussion of the solution of the Dyson equation, also known as the Nambu-Gor'kov equations in the case of a superfluid system, which propagates medium polarization processes calculated making use of NFT to all orders of perturbation, resulting in the dressing of quasiparticles and in the induced pairing interaction. The formalism is applied to the superfluid nucleus ${}^{120}$Sn. Results concerning the low-energy spectrum, that is, the quasiparticle strength distribution of the neighboring odd-A nuclei ${}^{119}$Sn and ${}^{121}$Sn, are presented and compared with the experimental findings.

Elementary modes of excitation caused by the quadratic Zeeman term and the sensitivity of spin structures of small spin-2 condensates against the magnetic field

The response of spin-2 small condensates to an external magnetic field $B$ is studied. The parameters of the interaction are considered as variable. The emphasis is placed on clarifying the modes of excitation caused by the quadratic Zeeman term. The theoretical method used is beyond the mean field theory. A set of eigenstates with the $U(5)\supset SO(5)\supset SO(3)$ symmetry is introduced to facilitate the analysis. To obtain a quantitative evaluation on the response, the fidelity susceptibility and the $B$ -dependent average populations of spin-components have been calculated. Mostly the particle number N=30 is assumed. The effect with a larger or smaller $N$ is also considered. It was found that the sensitivity of the response depends strongly both on the interaction and on the inherent symmetry.

Elementary excitation modes in a granular glass above jamming

The dynamics of granular media in the jammed, glassy region is described in terms of "modes", by applying a Principal Component Analysis (PCA) to the covariance matrix of the position of individual grains. We first demonstrate that this description is justified and gives sensible results in a regime of time/densities such that a metastable state can be observed on long enough timescale to define the reference configuration. For small enough times/system sizes, or at high enough packing fractions, the spectral properties of the covariance matrix reveals large, collective fluctuation modes that cannot be explained by a Random Matrix benchmark where these correlations are discarded. We then present a first attempt to find a link between the softest modes of the covariance matrix during a certain "quiet" time interval and the spatial structure of the rearrangement event that ends this quiet period. The motion during these cracks is indeed well explained by the soft modes of the dynamics before the crack, but the number of cracks preceded by a "quiet" period strongly reduces when the system unjams, questioning the relevance of a description in terms of modes close to the jamming transition, at least for frictional grains.

Coherent State Combined with Mixed State for an Imperfect Boson System. II: -- Static Solution and Elementary Excitation --

The thermal equilibrium state and elementary modes of excitation are investigated for a spinless boson system with a contact interaction. In a homogeneous infinite system, the elementary mode associated with the bose condensation with 0 momentum is automatically damped. In a semi-infinite cubic system, there appear bound states in the semi-infinite direction for a free end condition on the finite side and then two-dimensional modes with a phonon-like spectrum.

Magnetic dipole and Gamow–Teller modes: quenching, fine structure and astrophysical implications

The magnetic dipole (M1) and Gamow–Teller (GT) response are prime examples to illustrate the importance of configuration mixing for an understanding of elementary excitation modes of the nucleus. Starting from the ’’classical’’ problem of quenching - whose proper description is still beyond the capabilities of microscopic models after all those years — I want to address some current developments of the field. Mandatory for the progress are high-resolution data from electron and hadron scattering and charge-exchange reactions.In medium-mass fp-shell nuclei, the detailed knowledge of the M1 and GT strength distribution provides a stringent test of state-of-the-art shell-model calculations, validating their applicability in astrophysical network calculations. As an example, it is demonstrated that high-precision M1 data on N = 28 isotones from electron scattering at Darmstadt permit the extraction of neutral-current neutrino-nucleus scattering cross sections important for supernova dynamics and nucleosynthesis.Fine structure of the GT mode is not only observed in light and medium-mass nuclei, but also in the GT resonance observed in a heavy nucleus like 90Nb studied in the 90Zr(3He, t) reaction at Osaka with a resolution ΔE ≃ 50 keV (FWHM). Novel methods, based on wavelet transforms, to extract scales characterizing the fine structure are presented. This in turn permits an interpretation of the physics underlying the phenomenon. These methods can also be used to extract spin- and parity-resolved level densities in a nearly model-independent way, again important to test models used in various astrophysical scenarios.As a final example, the influence of configuration mixing on the GT strength distribution at low energies is investigated for the heavy odd-odd nuclei 138La and 180Ta. The nucleosynthesis of these exotic nuclides, amongst the rarest in nature, is a long-standing problem. A likely source are charged-current neutrino-nucleus reactions which would be dominated by the GT response. However, the main GT resonance lies above the particle threshold and, therefore, does not contribute. Recent measurements of the GT strength distributions in 138La and 180Ta below the particle threshold and their astrophysical implications are discussed.

NN¯,Δ¯N,ΔN¯excitation for the pion propagator in nuclear matter

The particle-hole and $\ensuremath{\Delta}$-hole excitations are well-known elementary excitation modes for the pion propagator in nuclear matter. But, the excitation also involves antiparticles, namely, nucleon-antinucleon, anti-$\ensuremath{\Delta}$-nucleon and $\ensuremath{\Delta}$-antinucleon excitations. These are important for high-energy momentum as well, and have not been studied before, to our knowledge. In this paper, we give both the formulas and the numerical calculations for the real and the imaginary parts of these excitations.

THE TFD TREATMENT OF THE QUASIPARTICLE-PHONON INTERACTION AT FINITE TEMPERATURE

The coupling of elementary excitation modes in hot nuclei is studied. For this aim the quasiparticle-phonon nuclear model (QPM) is extended to a finite temperature by using the formalism of the thermofield dynamics. First the energies and structures of one-phonon states are calculated in the thermal random phase approximation and then the thermal QPM Hamiltonian HQPM is expressed in terms of thermal quasiparticles and thermal RPA-phonons. The equation for the energies taking into account mixing of one-and two-thermal phonon states is derived. The expression of the coupling matrix element between thermal phonons is given.

Auger decay of excited atoms near metal surfaces

Excited atomic particles couple to the elementary excitation modes of a surface as, for instance, surface plasmons or electron-hole pair excitations. Such coupling may result in a nonradiative Auger-type deexcitation of the atom. Particle-hole pair and surface plasmon assisted Auger decay (AD) of atomic p to s levels have been studied for atoms in front of a metal surface. Based on the self-energy formalism and making use of recent results of the dielectric linear response theory AD rates are estimated as a function of the particle surface distance and the particle velocity parallel to the surface plane. It turns out that the AD process can be rather efficient depending, however, on the electronic properties of the collision system under consideration.

Elementary excitations and quasi-two-dimensional behavior in a GaAs field-effect transistor

The elementary excitation modes in a narrow channel of conducting electrons in a special GaAs field-effect transistor are evaluated within the random-phase approximation. The system is found to be quasi-two-dimensional (2D) when the width of the channel is small, i.e., there are collective excitations with a dispersion very close to the strictly 2D form. In addition to the low-lying quasi-2D mode there are higher collective modes associated with the subband structure of the device.

Cluster of nucleons as elementary modes of excitation in nuclei

Conditions which must be fulfilled by clusters of nucleons to qualify as elementary modes of excitation are analysed in terms of simple criteria involving experimental binding energies. It is found that the most complex possible mode is the α-like cluster.

Chapter 3. A New Microscopic Method for Describing the Elementary Modes of Excitation in the Intrinsic Subspace

Chapter 3. A New Microscopic Method for Describing the Elementary Modes of Excitation in the Intrinsic Subspace

Angular Momentum Transfer in Deep-Inelastic Reactions as Inferred from Angular Distributions of Sequential-Fission Fragments

Theoretical results of a model of heavy-ion collisions in terms of elementary modes of excitation are presented for the reaction Kr+Pb at 610 MeV with special emphasis on the transfer of angular momentum. The angular distributions of the fragments resulting from the sequential fission of the heavy reaction partner are calculated in a semiclassical model. Conflicting experimental results reported for similar reactions are discussed and the still rather open range of possibilities in the analysis of the data is stressed.

Quasiparticle-Shell-Model Calculations of So-Called Two-Phonon States in Cd and Sn Isotopes

The anharmonicity effect due to the couplings between pamng vibrational modes and quadrupole correlation modes is investigated in the cases of Cd and Sn isotopes by carrying out the quasiparticle-shell-model calculations. It is clarified that the effect is so large in the first excited o+ state in Sn isotopes that its energy drops down dramatically in 114• 116• 11 '• 120Sn. In Cd isotopes, the coupling effect is indispensable for formation of roughly degenerate two­ phonon triplet. The static quadrupole moments and B(E2) values in Cd isotopes are also calculated and the results do not contradict with experiment. §I. Introduction The mechanism of the spherical-cleformecl transition in medium and heavy nuclei 1s considered to be governed by mutual interweaving of two different types of cor­ relation, i.e., the pairing correlation and the quadrupole correlation. Therefore, it is natural to consider that the elementary modes of excitation in these nuclei are pairing vibrational mode and quadrupole phonon mode under the random-phase ap­ proximation (RPA) and that the anharmonicity effects which manifest themselves as couplings between these elementary modes of excitation play an essential role in structure of low-lying states of transitional nuclei. The existence of hidden regu­ larities in the anharmonicity effects has been suggested by the quasi-band structure 1) and there have been a number of theoretical attempts to elucidate the microscopic structure of the anharmonicity effects in transitional nuclei. It has been pointed out in our previous papers 2>.a> that the anharmonicity effects clue to the couplings between pairing vibrational mode and quadrupole phonon mode play so important a role that the so-called two-phonon o+ state and the pairing vibra­ tional state couple with each other and the energy of the first excited o+ state drops do·wn in the transitional nuclei, for example, in Se and Mo isotopes. A similar situation may be expected in Cd and Te isotopes, because the neutron-single­ particle-level structure fairly resembles that in Se region. On the other hand, Cd isotopes have so far been referred to as typical examples of appearance of two­ phonon-triplet states. Standing on the viewpoint of usual phonon (boson) picture, we find no structural difference between the members of the two-phonon triplet. However, if the excited o+ state is strongly affected by the pairing vibrational mode,

Treatment of the spurious states in nuclear field theory

It is shown, in the framework of a schematic model, that the nuclear field theory (based on the particle-vibration coupling), is a systematic method to eliminate the spurious states occurring in the descriptions of a many-body system which are based on the concept of elementary modes of excitation.

Elementary Modes of Excitation in the Nucleus

In the field of nuclear dynamics a central theme has been the struggle to find the proper place for the complementary concepts referring to the independent motion of the individual nucleons and the collective behaviour of the nuccleus as a whole. This development has been a continuing process involving the interplay of ideas and discoveries relating to all different aspects of nuclear phenomena. The multi-dimensionality of this development makes it tempting to go directly to a description of our present understanding and to the problems and perspectives as they appear today. However, an attempt to follow the evolution of some of the principal ideas may be instructive in illustrating the struggle for understanding of many-body systems, which have continued to inspire the development of fundamental new concepts, even in cases where the basic equations of motion are well established. Concepts appropriate for describing the wealth of nuclear phenomena have been derived from a combination of many different approaches, including the exploration of general relations following from considerations of symmetry, the study of model systems, sometimes of a grossly oversimplified nature, and, of course, the clues provided by the experimental discoveries which have again and again given the development entirely new directions.