Nuclear Theory·nucl-th

Thursday·March 23, 2017

8 papers—2 primary·6 cross-listed

01
Influence of complex configurations on properties of pygmy dipole resonance in neutron-rich Ca isotopes
N. N. Arsenyev🇷🇺 · A. P. Severyukhin🇷🇺 · V. V. Voronov🇷🇺 · Nguyen Van Giai🇫🇷
Starting from the quasiparticle random phase approximation based on the Skyrme interaction SLy5, we study the effects of phonon-phonon coupling~(PPC) on the low-energy electric dipole response in $^{40 - 58}$ Ca. Using the same set of parameters we describe available experimental data for $^{40, 44, 48}$ Ca and give prediction for $^{50 - 58}$ Ca. The inclusion of the PPC results in the formation of low-energy $1^{-}$ states. There is an impact of the PPC effect on low-energy $E 1$ ~strength of $^{40, 44, 48}$ Ca. The PPC effect on the electric dipole polarizability is discussed. We predict a strong increase of the summed $E 1$ ~strength below 10MeV, with increasing neutron number from $^{48}$ Ca till $^{58}$ Ca.
nucl-thPRC(2017)·18 citations
02
Third-order particle-hole ring diagrams with contact-interactions and one-pion exchange
N. Kaiser
The third-order particle-hole ring diagrams are evaluated for a NN-contact interaction of the Skyrme type. The pertinent four-loop coefficients in the energy per particle $E ˉ (k_{f}) \sim k_{f}^{5 + 2 n}$ are reduced to double-integrals over cubic expressions in euclidean polarization functions. Dimensional regularization of divergent integrals is performed by subtracting power-divergences and the validity of this method is checked against the known analytical results at second-order. The complete $O (p^{2})$ NN-contact interaction is obtained by adding two tensor terms and their third-order ring contributions are also calculated in detail. The third-order ring energy arising from long-range $1 π$ -exchange is computed and it is found that direct and exchange contributions are all attractive. The very large size of the pion-ring energy, $E ˉ (k_{f 0}) ≃ - 92$ MeV at saturation density, is however in no way representative for that of realistic chiral NN-potentials. Moreover, the third-order (particle-particle and hole-hole) ladder diagrams are evaluated with the full $O (p^{2})$ contact interaction and the simplest three-ring contributions to the isospin-asymmetry energy $A (k_{f}) \sim k_{f}^{5}$ are studied.
nucl-thEPJA(2017)·10 citations
03
Uncertainties in s-process nucleosynthesis in massive stars determined by Monte Carlo variations
Nobuya Nishimura · Raphael Hirschi · Thomas Rauscher · Alexander St. J. Murphy · Gabriele Cescutti
The $s$ -process in massive stars produces the weak component of the $s$ -process (nuclei up to $A \sim 90$ ), in amounts that match solar abundances. For heavier isotopes, such as barium, production through neutron capture is significantly enhanced in very metal-poor stars with fast rotation. However, detailed theoretical predictions for the resulting final $s$ -process abundances have important uncertainties caused both by the underlying uncertainties in the nuclear physics (principally neutron capture reaction and $β$ -decay rates) as well as by the stellar evolution modeling. In this work, we investigated the impact of nuclear-physics uncertainties relevant to the $s$ -process in massive stars. Using a Monte-Carlo based approach, we performed extensive nuclear reaction network calculations that include newly evaluated upper and lower limits for the individual temperature dependent reaction rates. We found that most of the uncertainty in the final abundances is caused by uncertainties in the neutron capture rates, while $β$ -decay rate uncertainties affect only a few nuclei near $s$ -process branchings. The $s$ -process in rotating metal-poor stars shows quantitatively different uncertainties and key reactions, although the qualitative characteristics are similar. We confirmed that our results do not significantly change at different metallicities for fast rotating massive stars in the very low metallicity regime. We highlight which of the identified key reactions are realistic candidates for improved measurement by future experiments.
↳ astro-ph.SRnucl-exnucl-thMNRAS(2017)·42 citations
04
Pentaquark photoproduction
C. Fernandez-Ramirez🇲🇽 · A.N. Hiller Blin🇪🇸 · A. Pilloni🇺🇸
We present results and suggestions on how to confirm the existence and resonant nature of the $P c (4450)$ detected at LHCb through photoproduction experiments. We find that this narrow structure might have escaped detection in past experiments and use those to give a constraint for the upper limit of the branching ratio/coupling to the $J / ψ p$ channel.
↳ hep-phnucl-thJ.Phys.Conf.Ser.(2017)·4 citations
05
Two-fermion Bethe-Salpeter Equation in Minkowski Space: the Nakanishi Way
Giovanni Salme' (INFN-Rome)🇮🇹 · Wayne de Paula (ITA-S. Jose' dos Campos)🇧🇷 · Tobias Frederico (ITA-S. Jose' dos Campos)🇧🇷 · Michele Viviani (INFN-Pisa)🇮🇹
The possibility of solving the Bethe-Salpeter Equation in Minkowski space, even for fermionic systems, is becoming actual, through the applications of well-known tools: i) the Nakanishi integral representation of the Bethe-Salpeter amplitude and ii) the light-front projection onto the null-plane. The theoretical background and some preliminary calculations are illustrated, in order to show the potentiality and the wide range of application of the method.
↳ hep-phcond-mat.str-elnucl-thFew Body Syst.(2017)·8 citations
06
Producing the Deuteron in Stars: Anthropic Limits on Fundamental Constants
Luke A. Barnes · Geraint F. Lewis
Stellar nucleosynthesis proceeds via the deuteron (D), but only a small change in the fundamental constants of nature is required to unbind it. Here, we investigate the effect of altering the binding energy of the deuteron on proton burning in stars. We find that the most definitive boundary in parameter space that divides probably life-permitting universes from probably life-prohibiting ones is between a bound and unbound deuteron. Due to neutrino losses, a ball of gas will undergo rapid cooling or stabilization by electron degeneracy pressure before it can form a stable, nuclear reaction-sustaining star. We also consider a less-bound deuteron, which changes the energetics of the $pp$ and $p e p$ reactions. The transition to endothermic $pp$ and $p e p$ reactions, and the resulting beta-decay instability of the deuteron, do not seem to present catastrophic problems for life.
↳ astro-ph.COnucl-thJCAP(2017)·9 citations
07
Two-body Wave Functions, Compositeness, And The Internal Structure Of Dynamically Generated Resonances
Takayasu Sekihara (JAEA, Ibaraki)🇯🇵 · Tetsuo Hyodo (Kyoto U., Yukawa Inst., Kyoto)🇯🇵 · Daisuke Jido (Tokyo Metropolitan U.)🇯🇵 · Junko Yamagata-Sekihara (Kyoto Sangyo U.)🇯🇵 · Shigehiro Yasui (Tokyo Inst. Tech.)🇯🇵
Recently, the compositeness, defined as the norm of a two-body wave function for bound and resonance states, has been investigated to discuss the internal structure of hadrons in terms of hadronic molecular components. From the studies of the compositeness, it has been clarified that the two-body wave function of a bound state can be extracted from the residue of the scattering amplitude at the bound state pole. Of special interest is that the two-body wave function from the scattering amplitude is automatically normalized. In particular, while the compositeness is unity for energy-independent interactions, it deviates from unity for energy-dependent interactions, which can be interpreted as a missing-channel contribution. In this manuscript, we show the formulation of the two-body wave function from the scattering amplitude, evaluate the compositeness for several dynamically generated resonances such as $f_{0} (980)$ , $Λ (1405)$ , and $Ξ (1690)$ , and investigate their internal structure in terms of the hadronic molecular components.
↳ hep-phhep-exnucl-exnucl-th+1PoS(2017)·0 citations
08
Are two nucleons bound in lattice QCD for heavy quark masses? -- Consistency check with Lüscher's finite volume formula --
Takumi Iritani🇯🇵 · Sinya Aoki🇯🇵 · Takumi Doi🇯🇵 · Tetsuo Hatsuda🇯🇵 · Yoichi Ikeda🇯🇵 · Takashi Inoue🇯🇵 · Noriyoshi Ishii🇯🇵 · Hidekatsu Nemura🇯🇵 · Kenji Sasaki🇯🇵
On the basis of the Lüscher's finite volume formula, a simple test (consistency check or sanity check) is introduced and applied to inspect the recent claims of the existence of the nucleon-nucleon ( $N N$ ) bound state(s) for heavy quark masses in lattice QCD. We show that the consistency between the scattering phase shifts at $k^{2} > 0$ and/or $k^{2} < 0$ obtained from the lattice data and the behavior of phase shifts from the effective range expansion (ERE) around $k^{2} = 0$ exposes the validity of the original lattice data, otherwise such information is hidden in the energy shift $Δ E$ of the two nucleons on the lattice. We carry out this sanity check for all the lattice results in the literature claiming the existence of the $N N$ bound state(s) for heavy quark masses, and find that (i) some of the $N N$ data show clear inconsistency between the behavior of ERE at $k^{2} > 0$ and that at $k^{2} < 0$ , (ii) some of the $N N$ data exhibit singular behavior of the low energy parameter (such as the divergent effective range) at $k^{2} < 0$ , (iii) some of the $N N$ data have the unphysical residue for the bound state pole in S-matrix, and (iv) the rest of the $N N$ data are inconsistent among themselves. Furthermore, we raise a caution of using the ERE in the case of the multiple bound states. Our finding, together with the fake plateau problem previously pointed out by the present authors, brings a serious doubt on the existence of the $N N$ bound states for pion masses heavier than 300 MeV in the previous studies.
↳ hep-lathep-phnucl-thPRD(2017)·85 citations

Affiliations

first authorsco-authorsvia INSPIRE