共查询到20条相似文献,搜索用时 15 毫秒
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《Physics Reports》1997,278(1):1-77
We review quantum Monte Carlo methods for dealing with large shell model problems. These methods reduce the imaginary-time many-body evolution operator to a coherent superposition of one-body evolutions in fluctuating one-body fields; the resultant path integral is evaluated stochastically. We first discuss the motivation, formalism, and implementation of such Shell Model Monte Carlo (SMMC) methods. There then follows a sampler of results and insights obtained from a number of applications. These include the ground state and thermal properties of pf-shell nuclei, the thermal and rotational behavior of rare-earth and γ-soft nuclei, and the calculation of double beta-decay matrix elements. Finally, prospects for further progress in such calculations are discussed. 相似文献
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Alternative approaches to the calculation of two-neutrino double beta decay amplitudes are suggested which include neither the evaluation of the intermediate nucleus spectrum nor the closure approximation.Dedicated by the co-author to the memory of M. Gmitro.We wish to thank V. Belyaev, S. Bilenky, R. Eramzhyan, A. Ovchinnikova and E. Truhlik for interest and discussions. 相似文献
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《Nuclear Physics B》2001,596(3):587-610
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M. Hirsch O. Kadowaki H. V. Klapdor-Kleingrothaus K. Muto T. Oda 《Zeitschrift für Physik A Hadrons and Nuclei》1995,352(1):33-45
Reliable calculations of nuclear matrix elements are a prerequisite for the determination of the effective neutrino mass and other particle physics parameters from neutrinoless double beta decay. Here, the operator expansion method is improved by including Coulomb, tensor and central interactions simultaneously. Furthermore, the formalism of the OEM is extended to those matrix elements necessary to extract the right-handed parameters and from 0 decay. OEM includes the dependence of the nuclear matrix elements on the intermediate states implicitly and can therefore be understood as a step beyond the closure approximation. Numerical studies are carried out for the isotope76Ge combining the OEM expressions with ground-state wave functions calculated within a proton-neutron quasiparticle Random Phase Approximation (pn-QRPA) model. The influence and relative importance of central, tensor and Coulomb interactions is investigated. Within the OEM, contributions from the Coulomb force are found to be negligible in 0 decay, while the tensor force leads to a moderate change of the results, of the order of (10–30)%, giving a better agreement between sets of calculations which employ different NN-interactions. Generally, results of the OEM+QRPA calculation are similar to previous calculations of 0 decay matrix elements, indicating that 0 decay is not sensitive to model approximations and might therefore be more accurately calculated than the strongly suppressed 2 decay matrix elements. 相似文献
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The physics potential of neutrinoless double beta decay is discussed. Furthermore, experimental considerations as well as the current status of experiments are presented. Finally, an outlook towards the future, work on nuclear matrix elements and alternative processes is given. 相似文献
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Takaharu Otsuka 《Hyperfine Interactions》2001,132(1-4):405-412
The nuclear mass calculation is discussed in terms of large-scale shell model calculations. First, the development and limitations
of the conventional shell model calculations are mentioned. In order to overcome the limitations, the Quantum Monte Carlo
Diagonalization (QMCD) method has been proposed. The basic formulation and features of the QMCD method are presented as well
as its application to the nuclear shell model, referred to as Monte Carlo Shell Model (MCSM). The MCSM provides us with a
breakthrough in shell model calculations: the structure of low-lying states can be studied with realistic interactions for
a nearly unlimited variety of nuclei. Thus, the MCSM can contribute significantly to the study of nuclear masses. An application
to N∼20 unstable nuclei far from the β-stability line is mentioned.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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G. Pantis F. Šimkovic J. Schwieger Amand Faessler 《Czechoslovak Journal of Physics》1998,48(2):209-212
The standard quasiparticle random phase approximation(QRPA) is widely used to describe the neutrinoless double beta decay
process. Although it has been quite successful in many cases of interest, it has some shortcomings. The most important one
is that its solutions collapse for physical values of the particle-particle strength. We shall show that modifications can
be done which can extend the validity of this standard QRPA beyond the point of collapse. Such modifications are: The introduction
of proton-neutron pairing, the inclusion of the Pauli principle and the extension of the Hilbert space. If all these modifications
are introduced into the standard QRPA then the collapse does not occur for physical values of the particle-particle strengths.
Thus, one might be able to extract more accurate values on the effective neutrino mass by using the best available experimental
limits on the half life of neutrinoless double beta decay.
Presented by G. Pantis at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’97), Prague, May 27–31,
1997. 相似文献
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A class of discrete flavor-symmetry-based models predicts constrained neutrino mass matrix schemes that lead to specific neutrino mass sum-rules (MSR). We show how these theories may constrain the absolute scale of neutrino mass, leading in most of the cases to a lower bound on the neutrinoless double beta decay effective amplitude. 相似文献
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Oliviero Cremonesi 《Hyperfine Interactions》2018,239(1):54
The observation of neutrinoless double beta decay would unambiguosly demonstrate that neutrinos are Majorana particles and would provide unique information about the ordering and absolute scale of neutrino masses. This very rare decay is actively searched for in a number of candidate isotopes. It violates lepton-number and is predicted by many extensions of the standard model. The most recent experimental results are reviewed. The technological advances and the most compelling requirements for the new generation of experiments are discussed. 相似文献
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《Nuclear Physics A》1998,628(1):170-186
A derivation of the neutrinoless double beta decay rate, specially adapted for nuclear structure calculations, is presented. It is shown that the Fourier-Bessel expansion of the hadronic currents, jointly with angular momentum recoupling, leads to very simple final expressions for the nuclear form factors. This greatly facilitates the theoretical estimate of the half-life. Our approach does not require the closure approximation, which, however, can be implemented if desired. The method is exemplified for ββ decay 48Ca → 48Ti, both within the QRPA and a shell-model like model. 相似文献
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N. I. Rukhadze Ch. Briancon V. B. Brudanin V. G. Egorov A. A. Klimenko A. Kovalik V. V. Timkin P. Čhermák Yu. A. Shitov F. Šimkovic I. Štekl 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(7):879-882
A search for the β+β+, β+/EC, and EC/EC decays of 106Cd was performed at the Modane Underground Laboratory (France) located at a depth of 4800 m w.e. using a TGV-2 multidetector germanium spectrometer. A preliminary evaluation is performed of the experimental data accumulated during the measurements (12 900 h) of ~13.6 g of 106Cd (with an enrichment of 75%) and the spectrometer background without samples and with samples of natural Cd. New limits (at a 90% confidence level) of half-lives are obtained: T 1/2 ? 1.7 × 1020 yr and T 1/2 ? 1.6 × 1020 yr for the 0νEC/EC resonant decay of 106Cd to the 2741 keV and 2718 keV excited states of the daughter nucleus 106Pd and T 1/2 ? 4.2 × 1020 yr for the 2νEC/EC decay to the ground state of 106Pd (0+ → 0+, g.s.). The limits for other branches of the double beta decay of 106Cd with transitions to the ground and excited states of 106Pd are improved. 相似文献
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George A. Baker Jr. 《Journal of statistical physics》1993,72(3-4):621-641
In this paper we introduce a new Monte Carlo procedure based on the Markov property. This procedure is particularly well suited to massively parallel computation. We illustrate the method on the critical phenomena of the well known one-dimensional Ising model. In the course of this work we found that the autocorrelation time for the Metropolis Monte Carlo algorithm is closely given by the square of the correlation length. We find speedup factors of the order of 1 million for the method as implemented on the CM2 relative to a serial machine. Our procedure gives error estimates which are quite consistent with the observed deviations from the analytically known exact results. 相似文献
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《Nuclear Physics A》1997,626(3):735-750
We perform shell model Monte Carlo calculations of selected N = Z pf-shell nuclei with a schematic Hamiltonian containing isovector pairing and quadrupole-quadrupole interactions. Compared to realistic interactions, this Hamiltonian does not give rise to the SMMC “sign problem”, while at the same time resembles essential features of the realistic interactions. We study pairing correlations in the ground states of N = Z nuclei and investigate the thermal dependence of selected observables for the odd-odd nucleus 54Co and the even-even nuclei 60Zn and 60Ni. Comparison of the present results to those with the realistic KB3 interaction indicates a transition with increasing temperature from a phase of isovector pairing dominance to one where isoscalar pairing correlations dominate. In addition, our results confirm the qualitative reliability of the procedure used to cure the sign problem in the SMMC calculations with realistic forces. 相似文献
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