Wed·Dec 1, 2021Wednesday·December 1, 2021

1. 01*

   Statistical Hauser-Feshbach model description of $(n,\alpha )$ reaction cross sections for the weak s-process

   Sema Küçüksucu · Mustafa Yiğit · Nils Paar🇭🇷

   The $(n,\alpha )$ reaction contributes in many processes of energy generation and nucleosynthesis in stellar environment. Since experimental data are available for a limited number of nuclei and in restricted energy ranges, at present only theoretical studies can provide predictions for all astrophysically relevant $(n,\alpha )$ reaction cross sections. The purpose of this work is to study $(n,\alpha )$ reaction cross sections for a set of nuclei contributing in the weak s-process nucleosynthesis. Theory framework is based on the statistical Hauser-Feshbach model implemented in TALYS code with nuclear masses and level densities based on Skyrme energy density functional. In addition to the analysis of the properties of calculated $(n,\alpha )$ cross sections, the Maxwellian averaged cross sections are described and analyzed for the range of temperatures in stellar environment. Model calculations determined astrophysically relevant energy windows in which $(n,\alpha )$ reactions occur in stars. In order to reduce the uncertainties in modeling $(n,\alpha )$ reaction cross sections for the s-process, novel experimental studies are called for. Presented results on the effective energy windows for $(n,\alpha )$ reaction in weak s-process provide a guidance for the priority energy ranges in the future experimental studies.

   ↳ nucl-thastro-ph.SRnucl-exUniverse(2022)·3 citations
2. 02*

   Microscopic analysis of induced nuclear fission dynamics

   Z. X. Ren🇨🇳 · J. Zhao · D. Vretenar🇭🇷 · T. Niksic🇭🇷 · P. W. Zhao🇨🇳 · J. Meng🇨🇳

   The dynamics of low-energy induced fission is explored using a consistent microscopic framework that combines the time-dependent generator coordinate method (TDGCM) and time-dependent nuclear density functional theory (TDDFT). While the former presents a fully quantum mechanical approach that describes the entire fission process as an adiabatic evolution of collective degrees of freedom, the latter models the dissipative dynamics of the final stage of fission by propagating the nucleons independently toward scission and beyond. By combining the two methods, based on the same nuclear energy density functional and pairing interaction, we perform an illustrative calculation of the charge distribution of yields and total kinetic energy for induced fission of ${}^{240}$Pu. For the saddle-to-scission phase a set of initial points for the TDDFT evolution is selected along an iso-energy curve beyond the outer fission barrier on the deformation energy surface, and the TDGCM is used to calculate the probability that the collective wave function reaches these points at different times. Fission observables are computed with both methods and compared with available data. The relative merits of including quantum fluctuations (TDGCM) and the one-body dissipation mechanism (TDDFT) are discussed.

   ↳ nucl-thnucl-exPRC(2022)·37 citations
3. 03*

   A new ${}^{12}$C + ${}^{12}$C nuclear reaction rate: impact on stellar evolution

   E. Monpribat🇫🇷 · S. Martinet🇨🇭 · S. Courtin🇫🇷 · M. Heine🇫🇷 · S. Ekström🇨🇭 · D. G. Jenkins🇬🇧 · A. Choplin🇧🇪 · P. Adsley🇺🇸 · D. Curien🇫🇷 · M. Moukaddam🇫🇷 · J. Nippert🇫🇷 · S. Tsiatsiou🇨🇭 · G. Meynet🇨🇭

   This work presents new ${}^{12}$C + ${}^{12}$C reaction rates in the form of numerical tables with associated uncertainty estimation, as well as analytical formulae that can be directly implemented into stellar evolution codes. This article further describes the impact of these new rates on C-burning in stars. We determine reaction rates for two cross-section extrapolation models: one based on the fusion-hindrance phenomenon, and the other on fusion-hindrance plus a resonance, and compare our results to previous data. Using the GENEC stellar evolution code, we study how these new rates impact the C-burning phases in two sets of stellar models for stars with 12 M${}_{\odot }$ and 25 M${}_{\odot }$ initial masses chosen to be highly representative of the diversity of massive stars. The effective temperatures of C-burning in both sets of stellar models are entirely covered by the sensitivity of the present experimental data, and no extrapolation of the rates is required. Although, the rates may differ by more than an order of magnitude for temperatures typical of C-burning, the impacts on the stellar structures during that phase remain modest. This is a consequence of the readjustment of the stellar structure to a change of nuclear reaction rate for reactions important for energy production. For the hindrance case, the C-burning phase is found to occur at central temperatures 10\% higher than with the hindrance plus resonance rate. Its C-burning lifetime is reduced by a factor of two. This model, nevertheless, loses more entropy than the other one thus enters earlier into the degeneracy regime which will impact the last stages of the evolution at the pre-core collapse time. The hindrance model produces up to 60% more neon. The impact of the different rates on the s-process occurring during the C-burning phase is modest, changing final abundances of s-processed elements by at most 20% (cobalt).

   ↳ astro-ph.SRnucl-exAstron.Astrophys.(2022)·20 citations
4. 04*

   Nonequilibrium evolution of quarkonium in medium

   Yukinao Akamatsu🇯🇵 · Takahiro Miura🇯🇵

   We review recent progress in open quantum system approach to the description of quarkonium in the quark-gluon plasma. A particular emphasis is put on the Lindblad equations for quarkonium and its numerical simulations.

   ↳ hep-phcond-mat.quant-gasnucl-exnucl-th+1EPJ Web Conf.(2022)·8 citations
5. 05*

   Quadrupole-octupole coupling and the evolution of collectivity in neutron-deficient Xe, Ba, Ce, and Nd isotopes

   K. Nomura🇭🇷 · R. Rodríguez-Guzmán🇰🇼 · L.M. Robledo🇪🇸

   The evolution of quadrupole and octupole collectivity in neutron-deficient Xe, Ba, Ce, and Nd nuclei near the "octupole magic" neutron number $N=56$ is investigated within the mapped $sdf$-IBM framework. Microscopic input is obtained via quadrupole and octupole constrained Hartree-Fock-Bogoliubov calculations, based on the parametrization D1M of the Gogny energy density functional. Octupole-deformed mean-field ground states are predicted for Ba and Ce isotopes near $N=56$. Excitation energies of positive- and negative-parity states as well as electric transition rates are computed with wave functions resulting from the diagonalization of the mapped IBM Hamiltonian. The parameters of the Hamiltonian are determined via the mapping of the mean-field potential energy surfaces onto the expectation value of the Hamiltonian in the condensate state of the $s$, $d$, and $f$ bosons. Enhanced octupolarity is predicted for Xe, Ba, and Ce isotopes near $N=56$. The shape/phase transition from octupole-deformed to strongly quadrupole-deformed near $N=60$ is analyzed in detail.

   ↳ nucl-thnucl-exPRC(2021)·16 citations
6. 06*

   Beyond-mean-field approaches for nuclear neutrinoless double beta decay in the standard mechanism

   J. M. Yao🇨🇳 · J. Meng🇨🇳 · Y. F. Niu🇨🇳 · P. Ring🇩🇪

   Nuclear weak decays provide important probes to fundamental symmetries in nature. A precise description of these processes in atomic nuclei requires comprehensive knowledge on both the strong and weak interactions in the nuclear medium and on the dynamics of quantum many-body systems. In particular, an observation of the hypothetical double beta decay without emission of neutrinos ($0\nu \beta \beta$) would unambiguously demonstrate the Majorana nature of neutrinos and the existence of the lepton-number-violation process. It would also provide unique information on the ordering and absolute scale of neutrino masses. The next-generation tonne-scale experiments with sensitivity up to $10^{28}$ years after a few years of running will probably provide a definite answer to these fundamental questions based on our current knowledge on the nuclear matrix element (NME), the precise determination of which is a challenge to nuclear theory. Beyond-mean-field approaches have been frequently adapted for the study of nuclear structure and decay throughout the nuclear chart for several decades. In this review, we summarize the status of beyond-mean-field calculations of the NMEs of $0\nu \beta \beta$ decay assuming the standard mechanism of an exchange of light Majorana neutrinos. The challenges and prospects in the extension and application of beyond-mean-field approaches for $0\nu \beta \beta$ decay are discussed.

   ↳ nucl-thhep-exhep-phnucl-exPPNP(2022)·66 citations
7. 07*

   Scaling approach to nuclear structure in high-energy heavy-ion collisions

   Jiangyong Jia🇺🇸 · Chun-Jian Zhang🇺🇸

   In high-energy heavy-ion collisions, the initial condition of the produced quark-gluon plasma (QGP) and its evolution are sensitive to collective nuclear structure parameters describing the shape and radial profiles of the nuclei. We find a general scaling relation between these parameters and many experimental observables such as elliptic flow, triangular flow, and particle multiplicity distribution. In particular, the ratios of observables between two isobar systems depend only on the differences of these parameters, but not on the details of the final state interactions, hence offering a new way to constrain the QGP initial condition. Using this scaling relation, we show how the structure parameters of ${}_{44}^{96}$Ru and ${}_{40}^{96}$Zr conspire to produce the rich centrality dependences of these ratios, as measured by the STAR Collaboration. Our scaling approach demonstrates that isobar collisions are a precision tool to probe the initial condition of heavy-ion collisions, as well as the collective nuclear structures, including the neutron skin, of the atomic nuclei across energy scales.

   ↳ nucl-thhep-exhep-phnucl-exPRC(2023)·61 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.