Nuclear Theory·nucl-th

Friday·July 14, 2017

11 papers—3 primary·8 cross-listed

01
Neutrinoless double-beta decay matrix elements in large shell-model spaces with the generator-coordinate method
C.F. Jiao🇺🇸 · J. Engel🇺🇸 · J.D. Holt🇨🇦
We use the generator-coordinate method with realistic shell-model interactions to closely approximate full shell-model calculations of the matrix elements for the neutrinoless double-beta decay of $^{48}$ Ca, $^{76}$ Ge, and $^{82}$ Se. We work in one major shell for the first isotope, in the $f_{5/2} p g_{9/2}$ space for the second and third, and finally in two major shells for all three. Our coordinates include not only the usual axial deformation parameter $β$ , but also the triaxiality angle $γ$ and neutron-proton pairing amplitudes. In the smaller model spaces our matrix elements agree well with those of full shell-model diagonalization, suggesting that our Hamiltonian-based GCM captures most of the important valence-space correlations. In two major shells, where exact diagonalization is not currently possible, our matrix elements are only slightly different from those in a single shell.
nucl-thPRC(2017)·64 citations
02
Pairing and short-range correlations in nuclear systems
A. Rios · A. Polls · W. H. Dickhoff
The structure and density dependence of the pairing gap in infinite matter is relevant for astrophysical phenomena and provides a starting point for the discussion of pairing properties in nuclear structure. Short-range correlations can significantly deplete the available single-particle strength around the Fermi surface and thus provide a reduction mechanism of the pairing gap. Here, we study this effect in the singlet and triplet channels of both neutron matter and symmetric nuclear matter. Our calculations use phase-shift equivalent interactions and chiral two-body and three-body interactions as a starting point. We find an unambiguous reduction of the gap in all channels with very small dependence on the NN force in the singlet neutron matter and the triplet nuclear matter channel. In the latter channel, short range correlations alone provide a 50% reduction of the pairing gap.
nucl-thJ.Low Temp.Phys.(2017)·31 citations
03
Effects of cluster-shell competition and BCS-like pairing in $^{12}$ C
H. Matsuno · N. Itagaki
The antisymmetrized quasi-cluster model (AQCM) was proposed to describe {\alpha}-cluster and $j j$ -coupling shell models on the same footing. In this model, the cluster-shell transition is characterized by two parameters; $R$ representing the distance between {\alpha} clusters and {\alpha} describing the breaking of {\alpha} clusters, and the contribution of the spin-orbit interaction, very important in the $j j$ -coupling shell model, can be taken into account starting with the {\alpha} cluster model wave function. Not only the closure configurations of the major shells, but also the subclosure configurations of the $j j$ -coupling shell model can be described starting with the {\alpha}-cluster model wave functions; however, the particle hole excitations of single particles have not been fully established yet. In this study we show that the framework of AQCM can be extended even to the states with the character of single particle excitations. For $^{12}$ C, two particle two hole (2p2h) excitations from the subclosure configuration of $0 p_{3/2}$ corresponding to BCS-like pairing are described, and these shell model states are coupled with the three {\alpha} cluster model wave functions. The correlation energy from the optimal configuration can be estimated not only in the cluster part but also in the shell model part. We try to pave the way to establish a generalized description of the nuclear structure.
nucl-thPTEP(2017)·14 citations
04
Hard processes in small systems
Dennis V. Perepelitsa🇺🇸
These proceedings from the Quark Matter 2017 conference give an overview of the latest experimental results on hard processes in small collision systems at RHIC and the LHC, discuss their implications, and consider several prospects for future measurements.
↳ nucl-exnucl-thNPA(2017)·1 citation
05
Big Bang Nucleosynthesis with Stable $^{8}$ Be and the Primordial Lithium Problem
Richard T. Scherrer🇺🇸 · Robert J. Scherrer🇺🇸
A change in the fundamental constants of nature or plasma effects in the early universe could stabilize $^{8}$ Be against decay into two $^{4}$ He nuclei. Coc et al. examined this effect on big bang nucleosynthesis as a function of $B_{8}$ , the mass difference between two $^{4}$ He nuclei and a single $^{8}$ Be nucleus, and found no effects for $B_{8} \leq 100$ keV. Here we examine stable $^{8}$ Be with larger $B_{8}$ and also allow for a variation in the rate for $^{4}$ He + $^{4}$ He $⟶$ $^{8}$ Be to determine the threshold for interesting effects. We find no change to standard big bang nucleosynthesis for $B_{8} < 1$ MeV. For $B_{8} ≳ 1$ MeV and a sufficiently large reaction rate, a significant fraction of $^{4}$ He is burned into $^{8}$ Be, which fissions back into $^{4}$ He when $B_{8}$ assumes its present-day value, leaving the primordial $^{4}$ He abundance unchanged. However, this sequestration of $^{4}$ He results in a decrease in the primordial $^{7}$ Li abundance. Primordial abundances of $^{7}$ Li consistent with observationally-inferred values can be obtained for reaction rates similar to those calculated for the present-day (unbound $^{8}$ Be) case. Even for the largest binding energies and largest reaction rates examined here, only a small fraction of $^{8}$ Be is burned into heavier elements, consistent with earlier studies. There is no change in the predicted deuterium abundance for any model we examined.
↳ astro-ph.COhep-phnucl-thPRD(2017)·2 citations
06
Generalizing spin and pseudospin symmetries for relativistic spin 1/2 fermions
P. Alberto · M. Malheiro · T. Frederico · A. de Castro
We propose a generalization of pseudospin and spin symmetries, the SU(2) symmetries of Dirac equation with scalar and vector mean-field potentials originally found independently in the 70's by Smith and Tassie, and Bell and Ruegg. As relativistic symmetries, they have been extensively researched and applied to several physical systems for the last 18 years. The main feature of these symmetries is the suppression of the spin-orbit coupling either in the upper or lower components of the Dirac spinor, thereby turning the respective second-order equations into Schrödinger-like equations, i.e, without a matrix structure. In this paper we use the original formalism of Bell and Ruegg to derive general requirements for the Lorentz structures of potentials in order to have these SU(2) symmetries in the Dirac equation, again allowing for the suppression of the matrix structure of the second-order equation of either the upper or lower components of the Dirac spinor. Furthermore, we derive equivalent conditions for spin and pseudospin symmetries with 2- and 1-dimensional potentials and list some possible candidates for 3, 2, and 1 dimensions. We suggest applications for physical systems in three and two dimensions, namely electrons in graphene.
↳ quant-phnucl-thJ.Phys.Conf.Ser.(2016)·2 citations
07
Lightly Bound Skyrmions, Tetrahedra and Magic Numbers
Nicholas S. Manton🇬🇧
In the lightly bound Skyrme model, several Skyrmions having particularly strong binding are clusters of unit baryon number Skyrmions arranged as truncated tetrahedra. Their baryon numbers form the sequence B = 4, 16, 40, 80, 140, 224. This is the standard sequence of tetrahedral numbers multiplied by four, and therefore agrees with the sequence of magic proton and neutron numbers 2, 8, 20, 40, 70, 112 that occurs in the nuclear shell model in the absence of strong spin-orbit coupling. This sequence includes several of the magic numbers that are predicted for tetrahedrally deformed nuclei, and also appears in the context of the FCC lattice geometry investigated long ago by Wigner and revived more recently.
↳ hep-thnucl-th9 citations
08
Sensitivity of jet substructure to jet-induced medium response
José Guilherme Milhano🇵🇹 · Urs Achim Wiedemann🇨🇭 · Korinna Christine Zapp🇵🇹
Jet quenching in heavy ion collisions is expected to be accompanied by recoil effects, but unambiguous signals for the induced medium response have been difficult to identify so far. Here, we argue that modern jet substructure measurements can improve this situation qualitatively since they are sensitive to the momentum distribution inside the jet. We show that the groomed subjet shared momentum fraction $z_{g}$ , and the girth of leading and subleading subjets signal recoil effects with dependencies that are absent in a recoilless baseline. We find that recoil effects can explain most of the medium modifications to the $z_{g}$ distribution observed in data. Furthermore, for jets passing the Soft Drop Condition, recoil effects induce in the differential distribution of subjet separation $Δ R_{12}$ a characteristic increase with $Δ R_{12}$ , and they introduce a characteristic enhancement of the girth of the subleading subjet with decreasing $z_{g}$ . We explain why these qualitatively novel features, that we establish in \textsc{Jewel+Pythia} simulations, reflect generic physical properties of recoil effects that should therefore be searched for as telltale signatures of jet-induced medium response.
↳ hep-phnucl-exnucl-thPLB(2018)·111 citations
09
Deep-inelastic multinucleon transfer processes in the $^{16}$ O+ $^{27}$ Al reaction
B. J. Roy · Y. Sawant · P. Patwari · S. Santra · A. Pal · A. Kundu · D. Chattopadhyay · V. Jha · S. K. Pandit · V. V. Parkar · K. Ramachandran · K. Mahata and 7 other authors
The reaction mechanism of deep-inelastic multinucleon transfer processes in the $^{16}$ O+ $^{27}$ Al reaction at an incident $^{16}$ O energy ( $E_{lab} = 134$ MeV) substantially above the Coulomb barrier has been studied both experimentally and theoretically. Elastic-scattering angular distribution, total kinetic energy loss spectra and angular distributions for various transfer channels have been measured. The $Q$ -value- and angle-integrated isotope production cross sections have been deduced. To obtain deeper insight into the underlying reaction mechanism, we have carried out a detailed analysis based on the time-dependent Hartree-Fock (TDHF) theory. A recently developed method, TDHF+GEMINI, has been applied to evaluate production cross sections for secondary products. From a comparison between the experimental and theoretical cross sections, we find that the theory qualitatively reproduces the experimental data. Significant effects of secondary light-particle emissions are demonstrated. Possible interplay between fusion-fission, deep-inelastic, multinucleon transfer and particle evaporation processes are discussed.
↳ nucl-exnucl-thPRC(2018)·12 citations
10
Generalised global symmetries in holography: magnetohydrodynamic waves in a strongly interacting plasma
Sašo Grozdanov🇳🇱 · Napat Poovuttikul🇳🇱
We begin the exploration of holographic duals to theories with generalised global (higher-form) symmetries. In particular, we focus on the case of magnetohydrodynamics (MHD) in strongly coupled plasmas by constructing and analysing a holographic dual to a recent, generalised global symmetry-based formulation of dissipative MHD. The simplest holographic dual to the effective theory of MHD that was proposed as a description of plasmas with any equation of state and transport coefficients contains dynamical graviton and two-form gauge field fluctuations in a magnetised black brane background. The dual field theory, which is closely related to the large- $N_{c}$ , $N = 4$ supersymmetric Yang-Mills theory at (infinitely) strong coupling, is, as we argue, in our setup coupled to a dynamical $U (1)$ gauge field with a renormalisation condition-dependent electromagnetic coupling. After constructing the holographic dictionary for gauge-gravity duals of field theories with higher-form symmetries, we compute the dual equation of state and transport coefficients, and for the first time analyse phenomenology of MHD waves in a strongly interacting, dense plasma with a (holographic) microscopic description. From weak to extremely strong magnetic fields, several predictions for the behaviour of Alfvén and magnetosonic waves are discussed.
↳ hep-thcond-mat.str-elnucl-thphysics.plasm-phJHEP(2019)·85 citations
11
Radioactive Decay Seen as Temporal Canonical Ensemble
Slobodan Prvanovic
The operator of time formalism is applied to radioactive decay. It appears that the proposed approach offers better insight and understanding of the phenomena in a way that the decay exponential-law becomes the Boltzmann distribution in Gibbs treatment of canonical ensemble. The radioactive decay is seen as temporal canonical ensemble where the radioactive constant appears as the analog of the absolute temperature multiplied by Boltzmann constant. The stochastic character of decay process becomes plausible in the proposed approach and the explanation why decay is characterized by constant, and not by some parameter, is offered.
↳ quant-phnucl-thIndian J.Phys.(2019)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE