Nuclear Theory·nucl-th

Tuesday·March 29, 2022

16 papers—9 primary·7 cross-listed

01
[Submitted on 25 Mar 2022]
Mapping out the thermodynamic stability of a QCD equation of state with a critical point using active learning
D. Mroczek🇺🇸 · M. Hjorth-Jensen🇺🇸 · J. Noronha-Hostler🇺🇸 · P. Parotto🇺🇸 · C. Ratti🇺🇸 · R. Vilalta🇺🇸
The Beam Energy Scan Theory (BEST) collaboration's equation of state (EoS) incorporates a 3D Ising model critical point into the Quantum Chromodynamics (QCD) equation of state from lattice simulations. However, it contains 4 free parameters related to the size and location of the critical region in the QCD phase diagram. Certain combinations of the free parameters lead to acausal or unstable realizations of the EoS that should not be considered. In this work, we use an active learning framework to rule out pathological EoS efficiently. We find that checking stability and causality for a small portion of the parameters' range is sufficient to construct algorithms that perform with $>$ 96% accuracy across the entire parameter space. Though in this work we focus on a specific case, our approach can be generalized to any EoS containing a parameter space-class correspondence.
Comments:
14 pages, 9 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2203.13876 [pdf]
PRC(2023)·26 citations
02
[Submitted on 26 Mar 2022]
Improved phenomenological nuclear charge radius formulae with kernel ridge regression
Jian-Qin Ma · Zhen-Hua Zhang
The kernel ridge regression (KRR) method with Gaussian kernel is used to improve the description of the nuclear charge radius by several phenomenological formulae. The widely used $A^{1/3}$ , $N^{1/3}$ and $Z^{1/3}$ formulae, and their improved versions by considering the isospin dependence are adopted as examples. The parameters in these six formulae are refitted using the Levenberg-Marquardt method, which give better results than the previous ones. The radius for each nucleus is predicted with the KRR network, which is trained with the deviations between experimental and calculated nuclear charge radii. For each formula, the resultant root-mean-square deviations of 884 nuclei with proton number $Z \geq 8$ and neutron number $N \geq 8$ can be reduced to about 0.017~fm after considering the modification of the KRR method. The extrapolation ability of the KRR method for the neutron-rich region is examined carefully and compared with the radial basis function method. It is found that the improved nuclear charge radius formulae by KRR method can avoid the risk of overfitting and have a good extrapolation ability. The influence of the ridge penalty term on the extrapolation ability of the KRR method is also discussed. At last, the nuclear charge radii of several recently observed K and Ca isotopes have been analyzed.
Comments:
9 pages, 5 figures, 2 tables
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2203.14027 [pdf]
CPC(2022)·39 citations
03
[Submitted on 27 Mar 2022]
Ab initio calculation of the $β$ -decay from $^{11}$ Be to a p $+^{10}$ Be resonance
M. C. Atkinson🇨🇦 · P. Navrátil🇨🇦 · G. Hupin🇫🇷 · K. Kravvaris🇺🇸 · S. Quaglioni🇺🇸
The exotic $β$ -delayed proton emission is calculated in $^{11}$ Be from first principles using chiral two- and three-nucleon forces. To investigate the unexpectedly-large branching ratio measured in [PRL 123, 082501 (2019)] we calculate the proposed $(1/ 2^{+}, 1/2)$ proton resonance in $^{11}$ B using the no-core shell model with continuum. This calculation helps to address whether this enhancement is caused by unknown dark decay modes or an unobserved proton resonance. We report a branching ratio of $b_{p} = (1.3 \pm 0.5) \times 1 0^{- 6}$ , suggesting that its unexpectedly-large value is caused by an unobserved proton resonance in $^{11}$ B.
Comments:
12 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2203.14176 [pdf]
PRC(2022)·9 citations
04
[Submitted on 27 Mar 2022]
Phase transitions and resilience of the MDCDW phase at finite temperature and density
William Gyory🇺🇸 · Vivian de la Incera🇺🇸
We study the phase transitions of the magnetic dual chiral density wave (MDCDW). This spatially inhomogeneous phase emerges in cold, dense QCD in the presence of a strong magnetic field. Starting from the generalized GL expansion of the free energy, we derive several analytical formulas that enable fast numerical computation of the expansion coefficients to arbitrary order, allowing high levels of precision in the determination of the physical dynamical parameters, as well as in the transition curves in the temperature vs. chemical potential plane at different magnetic fields. At magnetic fields and temperatures compatible with neutron star (NS) conditions, the MDCDW remains favored over the symmetric ground state at all densities. The phase's "resilience" manifests in (1) a region of small but nonzero remnant mass and significant modulation at intermediate densities, originating in part from the nontrivial topology of the lowest Landau level, and (2) a region of increasing condensate parameters at high densities. Our analysis suggests the MDCDW condensate remains energetically favored at densities and temperatures much higher than previously considered, opening the possibility for this phase to be a viable candidate for the matter structure of even young neutron stars produced by NS mergers.
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2203.14209 [pdf]
PRD(2022)·20 citations
05
[Submitted on 27 Mar 2022]
Astrophysical reaction rates with realistic nuclear level densities
Sangeeta · T. Ghosh · B. Maheshwari · G. Saxena · B. K. Agrawal
Realistic nuclear level densities (NLDs) obtained within the spectral distribution method (SDM) are employed to study nuclear processes of astrophysical interest. The merit of SDM lies in the fact that the NLDs corresponding to many body shell model Hamiltonian consisting of residual interaction can be obtained for the full configurational space without recourse to the exact diagnolization of huge matrices. We calculate NLDs and s-wave neutron resonance spacings which agree reasonably well with the available experimental data. By employing these NLDs, we compute reaction cross-sections and astrophysical reaction rates for radiative neutron capture in few Fe-group nuclei, and compare them with experimental data as well as with those obtained with NLDs from phenomenological and microscopic mean-field models. The results obtained for the NLDs from SDM are able to explain the experimental data quite well. These results are of particular importance since the configuration mixing through the residual interaction naturally accounts for the collective excitations. In the mean-field models, the collective effects are included through the vibrational and rotational enhancement factors and their NLDs are further normalized at low energies with neutron resonance data.
Comments:
Accepted in Physical Review C (2022)
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Experiment (nucl-ex)
arXiv:
2203.14220 [pdf]
PRC(2022)·12 citations
06
[Submitted on 28 Mar 2022]
New insights into four-boson renormalization group limit cycles
Bastian Kaspschak🇩🇪 · Ulf-G. Meißner🇩🇪
Using machine learning techniques, we verify that the emergence of renormalization group limit cycles beyond the unitary limit is transferred from the three-boson subsystems to the whole four-boson system. Focussing on four identical bosons, we first generate populations of synthetic singular potentials within the latent space of a boosted ensemble of variational autoencoders. After introducing the limit cycle loss for measuring the deviation of a given renormalization group flow from limit cycle behavior, we minimize it by applying an elitist genetic algorithm to the generated populations. The fittest potentials are observed to accumulate around the inverse-square potential, which we prove to generate limit cycles for four bosons and which is already known to produce limit cycles in the three-boson system. This also indicates that a four-body term does not enter low-energy observables at leading order, since we do not observe any additional scale to emerge.
Comments:
26 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); Machine Learning (cs.LG); High Energy Physics — Theory (hep-th); Computational Physics (physics.comp-ph); Quantum Physics (quant-ph)
arXiv:
2203.14597 [pdf]
0 citations
07
[Submitted on 28 Mar 2022]
Embedding short-range correlations in relativistic density functionals through quasi-deuterons
S. Burrello🇩🇪 · S. Typel🇩🇪
The formation of clusters at sub-saturation densities constitutes an essential feature for a reliable modelization of the nuclear matter equation of state (EoS). Phenomenological models that make use of energy density functionals (EDFs) offer a convenient approach to account for the presence of these bound states of nucleons when introduced as additional degrees of freedom. However, in these models clusters dissolve, by construction, when the nuclear saturation density is approached from below, revealing inconsistencies with recent findings that evidence the existence of short-range correlations (SRCs) even at larger densities. In this work, within the EDF framework, a novel approach is proposed to embed SRCs within a relativistic mean-field model with density dependent couplings. This is realized through the introduction of suitable in-medium modifications of the cluster binding energy shifts, which are responsible for describing the cluster dissolution. As a first exploratory step, the example of a quasi-deuteron within the generalized relativistic density functional approach is investigated. For the first time, suitable parameterizations of the cluster mass shift at zero temperature are derived for all baryon densities. They are constrained by experimental results for the effective deuteron fraction in nuclear matter near saturation and by microscopic many-body calculations in the low-density limit. The strength of the deuteron-meson couplings is assessed to be of crucial importance. The findings of the present study represent a first step to improve the description of nuclear matter and its EoS at supra-saturation densities in EDFs by considering correlations in an effective way. Novel effects on some thermodynamic quantities, such as the matter incompressibility, the symmetry energy and its slope, are finally discerned and discussed.
Comments:
28 pages, 12 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
arXiv:
2203.14635 [pdf]
EPJA(2022)·19 citations
08
[Submitted on 21 Feb 2022]
Constraining the parameterized neutron star equation of state with astronomical observations
Jaikhomba Singha · S. Mullai Vaneshwar · Ankit Kumar
We utilise the phenomenologically parameterized piecewise polytropic equations of state to study various neutron star properties. We investigate the compliance of these equations of state with several astronomical observations. We also demonstrate that the theoretical estimates of the fractional moment of inertia cannot explain all the pulsar glitches observed. We model the crust as a solid spheroidal shell to calculate the fractional moment of inertia of fast-spinning neutron stars. We also show that the braking index obtained in a simple magnetic dipole radiation model with a varying moment of inertia deviates significantly from the observed data. Future developments in both theory and observations may allow us to use the fractional moment of inertia and braking index as observational constraints for neutron star equation of state.
Comments:
Accepted for publication in Research in Astronomy nd Astrophysics (RAA) journal. 12 pgs, 6 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
arXiv:
2203.14722 [pdf]
Res.Astron.Astrophys.(2022)·5 citations
09
[Submitted on 22 Mar 2022]
$R$ -matrix analysis of $^{22}$ Ne( $α$ , n) $^{25}$ Mg and $^{22}$ Ne( $α$ , $γ$ ) $^{26}$ Mg reaction
Rajkumar Santra
The $^{22}$ Ne( $α$ , n) $^{25}$ Mg and its competing channel $^{22}$ Ne( $α$ , $γ$ ) $^{26}$ Mg has an major influence on neutron flux in weak s-process nucleosynthesis path in low mass AGB stars and massive stars of mass (M $\geq$ 10M $_{⊙}$ ). So the ratio rate of this two competing reaction control the neutron flux in weak s-process nucleosynthesis. Various experiment has been performed to study the properties of nuclear states of $^{26}$ Mg to evaluate rate of $^{22}$ Ne+ $α$ reaction rate and corresponding rate from these studies vary by up to a factor of 500 in the astrophysical relevant temperature. The recent evaluation by Philip et al. of $^{22}$ Ne( $α$ , n) $^{25}$ Mg reaction rate using most recent nuclear data of $^{26}$ Mg from number of sources shows similar result with previous estimation for $^{22}$ Ne( $α$ , $γ$ ) $^{26}$ Mg but got lower rate for $^{22}$ Ne( $α$ , n) $^{25}$ Mg reaction due to updated nuclear data. Also Philip et al. suggested that rate based on full $R$ -matrix modeling will required to take into accounted the interference effects between distant levels and sub-threshold resonance. In present work full $R$ -matrix calculation has been performed for $^{22}$ Ne( $α$ , n) $^{25}$ Mg and $^{22}$ Ne( $α$ , $γ$ ) $^{26}$ Mg reaction based on fitting the $^{22}$ Ne( $α$ , n) $^{25}$ Mg reaction data of Jaeger et al; in energy range 0.8 to 1.45 MeV and updated nuclear data of $^{26}$ Mg states. The $R$ -matrix fitting for the $^{22}$ Ne( $α$ , n) $^{25}$ Mg reaction nicely explain experimental data in 0.8 to 1.45 MeV energy range by changing spin, parity of E $_{x}$ = 11.784 and 11.63 MeV states from 1 $^{-}$ to 0 $^{+}$ .
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2203.14723 [pdf]
0 citations

Affiliations

first authorsco-authorsvia INSPIRE