Nuclear Theory·nucl-th

Thursday·June 21, 2018

8 papers—4 primary·4 cross-listed

01
[Submitted on 19 Jun 2018]
Shell-model coupled-cluster method for open-shell nuclei
Z. H. Sun · T. D. Morris · G. Hagen · G. R. Jansen · T. Papenbrock
We present an approach to derive effective shell-model interactions from microscopic nuclear forces. The similarity-transformed coupled-cluster Hamiltonian decouples the single-reference state of a closed-shell nucleus and provides us with a core for the shell model. We use a second similarity transformation to decouple a shell-model space from the excluded space. We show that the three-body terms induced by both similarity transformations are crucial for an accurate computation of ground and excited states. As a proof of principle we use a nucleon-nucleon interaction from chiral effective field theory, employ a $^{4}$ He core, and compute low-lying states of $^{6 - 8}$ He and $^{6 - 8}$ Li in $p$ -shell model spaces. Our results agree with benchmarks from full configuration interaction.
Comments:
12 pages, 16 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1806.07405 [pdf]
PRC(2018)·50 citations
02
[Submitted on 20 Jun 2018]
Analytical description of the excited state phase transition to octupole deformed shape in alternating parity bands
E.V. Mardyban · T.M. Shneidman · E.A. Kolganova · R.V. Jolos · S.-G. Zhou
Angular momentum dependences of the parity splitting and electric dipole transitions in the alternating parity bands of heavy nuclei have been analyzed. It is shown that these dependences can be treated in a universal way with a single parameter of critical angular momentum, which characterizes phase transition from octupole vibrations to the stable octupole deformation. Using the simple but useful model of axially-symmetric reflection-asymmetric mode, the analytical expression for the parity splitting and electric dipole transitional moment have been obtained. The results obtained are in a good agreement with the experimental data for various isotopes of Ra, Th, U, and Pu.
Comments:
11 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1806.07548 [pdf]
CPC(2018)·7 citations
03
[Submitted on 20 Jun 2018]
Effects of $ΛΛ - Ξ N$ mixing in the decay of $S = - 2$ hypernuclei
Jordi Maneu Victoria🇪🇸 · Assumpta Parreño🇪🇸 · Àngels Ramos🇪🇸
We study the non-mesonic weak decay of the doubly-strange hypernucleus $_{6}^{ΛΛ}$ He within a model which considers the exchange of pseudoscalar and vector mesons. Special attention is paid into quantifying the strong interaction effects, focussing on the interaction among the two {\Lambda} hyperons which induces novel weak transitions, whereby {\Lambda}{\Lambda}, {\Xi}N and {\Sigma}{\Sigma} states decay into a hyperon-nucleon pair. The initial strangeness -2 wave function is obtained from the solution of a G-matrix equation with the input of realistic strong baryon-baryon potentials, while the final hyperon-nucleon wave functions are derived analogously from a microscopic T-matrix calculation. The new {\Lambda}{\Lambda} $\to$ Y N decay rate studied in this work, $Γ_{Λ n} + Γ_{Σ^{0} n} + Γ_{Σ^{-} p}$ , represents 3-4% of the total one-baryon induced non-mesonic decay and is remarkably affected by strong interaction effects. In particular, the relative importance of the partial decay rates, encoded in the ratio $Γ_{Λ n} / (Γ_{Σ^{0} n} + Γ_{Σ^{-} p})$ , gets inverted when the mixing to {\Xi}N states is incorporated in the initial correlated {\Lambda}{\Lambda} wave function. This sensitivity can be used experimentally to learn about the strong interaction in the strangeness -2 sector.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1806.07666 [pdf]
PRC(2018)·1 citation
04
[Submitted on 20 Jun 2018]
A systematic study of giant quadrupole resonances with the subtracted second random--phase approximation: beyond--mean--field centroids and fragmentation
Olivier Vasseur🇫🇷 · Danilo Gambacurta🇷🇴 · Marcella Grasso🇫🇷
A systematic analysis of giant quadrupole resonances is performed for several nuclei, from $^{30}$ Si to $^{208}$ Pb, within the subtracted second random--phase--approximation (SSRPA) model in the framework of the energy--density--functional theory. Centroid energies and widths of the isoscalar giant quadrupole resonances are compared with the corresponding random--phase--approximation (RPA) values. We find lower SSRPA centroid energies compared to the RPA values leading, in general, to a better agreement with the experimental data. As far as the widths are concerned, we observe for both SSRPA and RPA cases a global attenuation of the single--particle Landau damping going from lighter to heavier nuclei and we obtain, systematically, larger widths in the SSRPA model compared to the RPA case. For some selected nuclei for which high--resolution ( $p, p^{'}$ ) experimental data are available, namely $^{40}$ Ca, $^{90}$ Zr, $^{120}$ Sn, and $^{208}$ Pb, the theoretical strength distributions are directly compared with the experimental spectra. We observe a significant improvement, with respect to RPA results, in the description of the spreading widths and of the fragmentation of the obtained spectra, due to the coupling between 1 particle-1 hole and 2 particle-2 hole configurations.
Comments:
7 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1806.07807 [pdf]
PRC(2018)·12 citations
05
[Submitted on 19 Jun 2018] (cross-list from hep-ph)
Manifestly Soft Gauge Invariant Formulation of vNRQCD
Ira Z. Rothstein🇺🇸 · Prashant Shrivastava🇺🇸 · Iain W. Stewart🇺🇸
Homogeneous power counting in Non-Relativistic QCD (NRQCD) implies the simultaneous existence of both soft and ultrasoft gluons. In the velocity renormalization group (vNRQCD) formalism we show that operators involving soft fields interacting with heavy potential quarks can be put in a manifestly gauge invariant form by utilizing gluon and quark building blocks which contain Wilson lines, and are analogous to those used in the soft collinear effective theory. This leads to several simplifications, in particular significantly reducing the size of the operator basis, which stream-lines matching and anomalous dimension calculations at subleading order in the velocity expansion. Also, soft ghosts no longer couple via potential like interactions to the heavy quark fields, and hence do not appear until two loops. Furthermore the the color structures that appear at each order in $α_{s}$ in the static potential are only those which should arise according to non-Abelian exponentiation. We also discuss how zero-bin subtractions clarify the role of $i ε$ terms in the heavy quark propagator poles carrying soft momenta. Even though the choice of the direction of the soft Wilson lines in our building blocks does not matter, there is still a limited set of consistent choices, and the predicted form of the eikonal poles does influence results at two-loops and beyond.
Comments:
29 pages, 7 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1806.07398 [pdf]
NPB(2019)·13 citations
06
[Submitted on 20 Jun 2018] (cross-list from hep-ph)
Parton distributions from nonlocal chiral SU(3) effective theory. I. Splitting functions
Y. Salamu🇨🇳 · Chueng-Ryong Ji🇺🇸 · W. Melnitchouk🇺🇸 · A. W. Thomas🇦🇺 · P. Wang🇨🇳
We present a new formulation of pseudoscalar meson loop corrections to nucleon parton distributions within a nonlocal covariant chiral effective field theory, including contributions from SU(3) octet and decuplet baryons. The nonlocal Lagrangian, constrained by requirements of local gauge invariance and Lorentz-invariant ultraviolet regularization, generates additional interactions associated with gauge links. We use these to compute the full set of proton $\to$ meson + baryon splitting functions, which in general contain on-shell and off-shell contributions, in addition to $δ$ -function terms at zero momentum, along with nonlocal contributions associated with the finite size of the proton. We illustrate the shapes of the various local and nonlocal functions numerically using a simple example of a dipole regulator.
Comments:
43 pages, 6 figures, version to appear in Phys. Rev. D
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1806.07551 [pdf]
PRD(2019)·30 citations
07
[Submitted on 20 Jun 2018] (cross-list from hep-ph)
Shear viscosity of ultrarelativistic Boson systems in the presence of a Bose-Einstein condensate
Zhengyu Chen🇨🇳 · Carsten Greiner🇩🇪 · Zhe Xu🇨🇳 · Pengfei Zhuang🇨🇳
We calculate for the first time the shear viscosity of ultrarelativistic Boson systems in the presence of a Bose-Einstein condensate (BEC). Two different methods are used. One is the Grad's method of moments and another is the Green-Kubo relation within a kinetic transport approach. In this work we consider a Boson system with isotropic elastic collisions and a gluon system with elastic scatterings described by perturbation QCD (pQCD). The results show that the presence of a BEC lowers the shear viscosity. This effect becomes stronger for the increasing proportion of the BEC in the Boson system and is insensitive to the detail of interactions.
Comments:
11 pages, 3 figures, matches published version
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1806.07594 [pdf]
PRC(2019)·6 citations
08
[Submitted on 20 Jun 2018] (cross-list from hep-ph)
Proton shape fluctuations and its relation to DIS
Heikki Mäntysaari🇫🇮
We review the recent progress in extracting the proton fluctuating substructure by studying exclusive processes at HERA, and the applications of these developments in the interpretation of the LHC heavy ion data. The possibilities to extract the proton geometry directly from the LHC high-multiplicity proton-nucleus and proton-proton collision data is also discussed.
Comments:
10 pages, 8 figures. Invited talk at the XXVI International Workshop on Deep-Inelastic Scattering and Related Subjects, April 2018
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1806.07612 [pdf]
PoS(2018)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE