Nuclear Theory·nucl-th

Tuesday·June 13, 2023

12 papers—9 primary·3 cross-listed

01
Isospin Equilibration in Neutron Star Mergers
Mark G. Alford🇺🇸 · Alexander Haber🇺🇸 · Ziyuan Zhang🇺🇸
We analyze the isospin equilibration properties of neutrinoless nuclear ( $n p e$ ) matter in the temperature and density range that is relevant to neutron star mergers. Our analysis incorporates neutrino-transparency corrections to the isospin (``beta'') equilibrium condition which become noticeable at $T ≳ 1$ MeV. We find that the isospin relaxation rate rises rapidly as temperature rises, and at $T \approx 5$ MeV it is comparable to the timescale of the density oscillations that occur immediately after the merger. This produces a resonant peak in the bulk viscosity at $T \approx 5$ MeV, which causes density oscillations to be damped on the timescale of the merger. Our calculations suggest that isospin relaxation dynamics may also be relevant when neutrinos are treated more accurately via neutrino transport schemes.
nucl-thastro-ph.HEgr-qchep-phPRC(2024)·40 citations
02
Evidence against a strong first-order phase transition in neutron star cores: impact of new data
Len Brandes🇩🇪 · Wolfram Weise🇩🇪 · Norbert Kaiser🇩🇪
With the aim of exploring the evidence for or against phase transitions in cold and dense baryonic matter, the inference of the sound speed and equation-of-state for dense matter in neutron stars is extended in view of recent new observational data. The impact of the heavy (2.35 $M_{⊙}$ ) black widow pulsar PSR J0952-0607 and of the unusually light supernova remnant HESS J1731-347 is inspected. In addition a detailed re-analysis is performed of the low-density constraint based on chiral effective field theory and of the perturbative QCD constraint at asymptotically high densities, in order to clarify the influence of these constraints on the inference procedure. The trace anomaly measure, $Δ = 1/3 - P / ε$ , is also computed and discussed. A systematic Bayes factor assessment quantifies the evidence (or non-evidence) of low averaged sound speeds $(c_{s}^{2} \leq 0.1)$ , a prerequisite for a phase transition, within the range of densities realized in the core of neutron stars. One of the consequences of including PSR J0952-0607 in the data base is a further stiffening of the equation-of-state, resulting for a 2.1 solar-mass neutron star in a reduced central density of less than five times the equilibrium density of normal nuclear matter at the 68\% level. The evidence against small sound speeds in neutron star cores is further strengthened. Within the inferred 68\% posterior credible bands, only a weak first-order phase transition with a coexistence density interval $Δ n / n ≲ 0.2$ would be compatible with the observed data.
nucl-thastro-ph.HEgr-qchep-ph+1PRD(2023)·92 citations
03
Prediction of the neutron drip line in oxygen isotopes using quantum computation
Chandan Sarma🇮🇳 · Olivia Di Matteo🇨🇦 · Abhishek Abhishek🇨🇦 · Praveen C. Srivastava🇮🇳
In the noisy intermediate-scale quantum era, variational algorithms have become a standard approach to solving quantum many-body problems. Here, we present variational quantum eigensolver (VQE) results of selected oxygen isotopes within the shell model description. The aim of the present work is to locate the neutron drip line of the oxygen chain using unitary coupled cluster (UCC) type ansatze with different microscopic interactions (DJ16, JISP16, and N3LO), in addition to a phenomenological USDB interaction. While initially infeasible to execute on contemporary quantum hardware, the size of the problem is reduced significantly using qubit tapering techniques in conjunction with custom circuit design and optimization. The optimal values of ansatz parameters from classical simulation are taken for the DJ16 interaction, and the tapered circuits are run on IonQ's Aria, a trapped-ion quantum computer. After applying gate error mitigation for three isotopes, we reproduced exact ground state energies within a few percent error. The post-processed results from hardware also clearly show $^{24}$ O as the drip line nucleus of the oxygen chain. Future improvements in quantum hardware could make it possible to locate drip lines of heavier nuclei.
nucl-thnucl-exquant-phPRC(2023)·39 citations
04
Continuum-discretized coupled-channel calculations for $^{6}$ Li fusion reactions with closed channels
Wendi Chen · D.Y. Pang · Hairui Guo · Ye Tao · Weili Sun · Yangjun Ying
Fusion reactions induced by the weakly bound nucleus $^{6}$ Li with targets $^{28}$ Si, $^{64}$ Ni, $^{144}$ Sm and $^{209}$ Bi at energies around the Coulomb barrier are investigated within a three-body model where $^{6}$ Li is described with an $α + d$ cluster model. The total fusion (TF) cross sections are calculated with the continuum-discretized coupled-channel (CDCC) method and the complete fusion (CF) cross sections are extracted through the sum-rule model. The calculations demonstrate that (i) for the TF cross section calculations, the continuum states up to 40 MeV are found to be necessary, which corresponds to the inclusion of closed channels for light and medium mass targets, such as $^{28}$ Si, $^{59}$ Co and $^{144}$ Sm, (ii) the converged CDCC results for TF cross section at energies above the Coulomb barrier are almost the same as single channel results in which the continuum coupling effect is neglected, and (iii) the continuum coupling strongly influences partial wave fusion cross sections and the closed channels play a significant role in the improvement of the description of the CF cross sections at energies below the Coulomb barrier for the $^{6}$ Li+ $^{28}$ Si, $^{59}$ Co and $^{144}$ Sm systems.
nucl-thPRC(2023)·5 citations
05
Complex valence-space effective operators for observables: the Gamow-Teller transition
Z. C. Xu · S. Zhang · J. G. Li · S. L. Jin · Q. Yuan · Z. H. Cheng · N. Michel · F. R. Xu
Nuclei in the vicinity of driplines have been receiving a lot of attention in nuclear structure studies. In the nuclei, the continuum coupling is crucial in reproducing weakly-bound and unbound phenomena. To calculate observables of the nuclei as open quantum systems, we have developed valence-space effective operators in the complex-energy Berggren basis using many-body perturbation theory. We focus on the Gamow-Teller $β$ decay in the {\it sd} shell. The two- plus three-nucleon force from the chiral effective field theory (EFT), named EM1.8/2.0, has been used. The Gamow shell model which takes the continuum coupling into account can properly reproduce experimental observations of weakly-bound and unbound states. The $β$ -decay isospin asymmetry between the dripline nucleus $^{22} Si$ and its mirror partner $^{22} O$ is reproduced, in which the $s_{1/2}$ continuum plays a key role. Significant Thomas-Ehrman shift is seen through mirror energy differences between the mirror daughters $^{22} Al$ and $^{22} F$ , in which the continuum effect plays an important role.
nucl-thPRC(2023)·16 citations
06
Correlation of density fluctuation in a magnetized QCD matter near the critical end point
Mahfuzur Rahaman🇮🇳 · Md Hasanujjaman🇮🇳 · Golam Sarwar🇮🇳 · Abhijit Bhattacharyya🇮🇳 · Jan-e Alam🇮🇳
The dynamical correlation of density fluctuation in quark gluon plasma with a critical end point has been investigated within the scope of the Müller-Israel-Stewart theory in the presence of static ultra-high external magnetic field. The dynamic structure factor of the density fluctuation exhibits three Lorentzian peaks in absence of external magnetic field- a central Rayleigh peak and two Brillouin peaks situated symmetrically on the opposite sides of the Rayleigh peak. The spectral structure displays five peaks in presence of the magnetic field due to the coupling of the magnetic field with the hydrodynamic fields in second-order hydrodynamics. The emergence of the extra peaks is due to the asymmetry in the pressure gradient caused by the external magnetic field in the system. Interestingly, it is observed that near the critical end point, all the Brillouin peaks disappear irrespective of the presence or absence of the external magnetic field.
nucl-thEPJC(2024)·2 citations
07
Decoding Neutron Star Observations: Revealing Composition through Bayesian Neural Networks
Valéria Carvalho🇵🇹 · Márcio Ferreira🇵🇹 · Tuhin Malik🇵🇹 · Constança Providência🇵🇹
We exploit the great potential offered by Bayesian Neural Networks (BNNs) to directly decipher the internal composition of neutron stars (NSs) based on their macroscopic properties. By analyzing a set of simulated observations, namely NS radius and tidal deformability, we leverage BNNs as effective tools for inferring the proton fraction and sound speed within NS interiors. To achieve this, several BNNs models were developed upon a dataset of $\sim$ 25K nuclear EoS within a relativistic mean-field framework, obtained through Bayesian inference that adheres to minimal low-density constraints. Unlike conventional neural networks, BNNs possess an exceptional quality: they provide a prediction uncertainty measure. To simulate the inherent imperfections present in real-world observations, we have generated four distinct training and testing datasets that replicate specific observational uncertainties. Our initial results demonstrate that BNNs successfully recover the composition with reasonable levels of uncertainty. Furthermore, using mock data prepared with the DD2, a different class of relativistic mean-field model utilized during training, the BNN model effectively retrieves the proton fraction and speed of sound for neutron star matter.
nucl-thastro-ph.HEhep-phPRD(2023)·28 citations
08
$Λ$ hypernuclear potentials beyond linear density dependence
E. Friedman🇮🇱 · A. Gal🇮🇱
In a recent paper [PLB 837 (2023) 137669] we showed that all measured ( $1 s_{Λ}$ , $1 p_{Λ}$ ) pairs of $Λ$ binding energies in $Λ$ -hypernuclei across the periodic table, $12 \leq A \leq 208$ , can be obtained from a $Λ$ -nucleus optical potential with only two adjustable $Λ N$ and $Λ N N$ parameters, associated with leading linear and quadratic terms in the nuclear density, derived by fitting $_{Λ}^{16}$ N binding energies. Here we extend the previous analysis by performing least-squares fits to the full set of data points. Consequences of suppressing $Λ N N$ interactions between `core' nucleons and `excess' neutrons are studied and related predictions are made for ( $1 s_{Λ}$ , $1 p_{Λ}$ ) binding energies in $_{Λ}^{40, 48}$ K, obtainable from upcoming $^{40, 48}$ Ca( $e, e^{'} K^{+}$ ) JLab experiments. We find $Λ$ -nucleus partial potential depths of $D_{Λ}^{(2)} = - 38.6 \pm 0.8$ ~MeV ( $Λ N$ ) and $D_{Λ}^{(3)} = 11.3 \pm 1.4$ ~MeV ( $Λ N N$ ), with a total depth $D_{Λ} = - 27.3 \pm 0.6$ ~MeV at nuclear-matter density $ρ_{0}$ =0.17~fm $^{- 3}$ , consistently with our previous results. Extrapolation to higher nuclear densities and possible relevance to the `hyperon puzzle' in neutron-star matter are discussed.
nucl-thhep-phnucl-exNPA(2023)·26 citations
09
Derivation of transition density from the observed 4He(e,e')4He(0^+_2) form factor raising the alpha-particle monopole puzzle
Masayasu Kamimura
Recently, the monopole transition form factor of the electron-scattering excitation of the 0^+_2 state (E_x=20.21 MeV) of the 4He nucleus was observed over a broad momentum transfer range (0.5 < q^2 < 5.0 fm^-2) with dramatically improved preision compared with older sets of data; modern nuclear forces, including those derived from the chiral effective field theory, failed to reproduce the form factor, which is called the alpha-particle monopole puzzle. To resolve this puzzle by improving the study of spatial structure of the 0^+_2 state, we derive in this letter a possible 0^+_1 --> 0^+_2 transition density \rho_tr(r) for r > 1 fm from the observed form factor. The shape of the transition density is significantly different from that obtained theoretically in the literature
nucl-thnucl-exPTEP(2023)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE