Nuclear Theory·nucl-th

Wednesday·September 29, 2021

11 papers—6 primary·5 cross-listed

01
The importance of few-nucleon forces in chiral effective field theory
C.-J. Yang🇸🇪 · A. Ekström🇸🇪 · C. Forssén🇸🇪 · G. Hagen🇺🇸 · G. Rupak🇺🇸 · U. van Kolck🇫🇷
We study the importance of few-nucleon forces in chiral effective field theory for describing many-nucleon systems. A combinatorial argument suggests that three-nucleon forces -- which are conventionally regarded as next-to-next-to-leading order -- should accompany the two-nucleon force already at leading order (LO) starting with mass number $A \approx 10 - 20$ . We find that this promotion enables the first realistic description of the $^{16}$ O ground state based on a renormalization-group-invariant LO interaction. We also performed coupled-cluster calculations of the equation of state for symmetric nuclear matter and our results indicate that LO four-nucleon forces could play a crucial role for describing heavy-mass nuclei. The enhancement mechanism we found is very general and could be important also in other many-body problems.
nucl-thEPJA(2023)·37 citations
02
Beta Decay in Medium-Mass Nuclei with the In-Medium Similarity Renormalization Group
S. R. Stroberg🇺🇸
We review the status of ab initio calculations of allowed beta decays (both Fermi and Gamow-Teller), within the framework of the valence-space in-medium similarity renormalization group approach.
nucl-thParticles(2021)·21 citations
03
Multinucleon excitations in neutrino-nucleus scattering: connecting different microscopic models for the correlations
G. Chanfray🇫🇷 · M. Ericson🇫🇷 · M. Martini🇫🇷
The problem of nucleon-nucleon correlations and meson exchange currents has been vividly debated in connection with the neutrino-nucleus cross sections. In this work we focus on nucleon-nucleon correlations by discussing a formal correspondence between the approaches based on independent particles and the ab initio approaches involving correlated wave functions. We use a general technique based on unitary transformation mapping the Fermion operators relative to bare nucleons into quasi-particle operators relative to dressed nucleons. We derive formulas for spectral functions, response functions, momentum distribution, separation energy, general enough to be applied with any kind of effective nucleon-nucleon interaction. We establish the relation between the non-energy-weighted sum rule and the Fermi sea depopulation. With our tools we evaluate whether approaches based on effective interactions are compatible with the expected amount of correlations coming from ab initio calculations. For this purpose we use as a test the Fermi sea depopulation and the value of the kinetic energy per nucleon.
nucl-thEur.Phys.J.ST(2021)·5 citations
04
Uncertainties in the pasta-phase properties of catalysed neutron stars
H. Dinh Thi🇫🇷 · T. Carreau🇫🇷 · A. F. Fantina🇫🇷 · F. Gulminelli🇫🇷
The interior of a neutron star is expected to exhibit different states of matter. In particular, complex non-spherical configurations known as `pasta' phases may exist at the highest densities in the inner crust, potentially having an impact on different neutron-star phenomena. We study the properties of the pasta phase and the uncertainties in the pasta observables which are due to our incomplete knowledge of the nuclear energy functional. To this aim, we employed a compressible liquid-drop model approach with surface parameters optimised either on experimental nuclear masses or theoretical calculations. To assess the model uncertainties, we performed a Bayesian analysis by largely varying the model parameters using uniform priors, and generating posterior distributions with filters accounting for both our present low-density nuclear physics knowledge and high-density neutron-star physics constraints. Our results show that the nuclear physics constraints, such as the neutron-matter equation of state at very low density and the experimental mass measurements, are crucial in determining the crustal and pasta observables. Accounting for all constraints, we demonstrate that the presence of pasta phases is robustly predicted in an important fraction of the inner crust. We estimate the relative crustal thickness associated with pasta phases as $R_{pasta} / R_{crust} = 0.128 \pm 0.047$ and the relative moment of inertia as $I_{pasta} / I_{crust} = 0.480 \pm 0.137$ . Our findings indicate that the surface and curvature parameters are more influential than the bulk parameters for the description of pasta observables. We also show that using a surface tension that is inconsistent with the bulk functional leads to an underestimation of both the average values and the uncertainties in the pasta properties, thus highlighting the importance of a consistent calculation of the nuclear functional.
nucl-thastro-ph.HEAstron.Astrophys.(2021)·63 citations
05
Theoretical study on favored alpha-decay half-lives of deformed nuclei
M. Hassanzad · O. N. Ghodsi
A systematic study on $α$ -decay half-lives for the nuclei in the range $93 \leq Z \leq 118$ is done by employing various versions of proximity potentials. To obtain the more reliable results, the deformation terms are included up to hexadecapole ( $β_{4}$ ) in the spherical-deformed nuclear and Coulomb interaction potentials. The favored $α$ -decays process in this region are categorized as the even-even, odd A, and odd-odd nuclei, first, and second they are grouped into two parts as a ground state to ground state and ground state to isomeric states transition. Due to their root-mean-square deviations (RMSD's) comparison, $B a ss 77$ and $N g o 80$ have the least values and better compromise in reproducing experimental data. Besides, by considering preformation probability within the cluster formation model, the results validate that the significant reduction in root-mean-square deviations has been obtained for different versions of proximity; Hence detract the deviation between calculated and experimental data.
nucl-thCPC(2021)·3 citations
06
Optical potential parameters of light nuclear fusion based on precise Coulomb wave functions
Binbing Wu · Hao Duan · Jie Liu
Based on precise Coulomb wave functions (CWFs), we attempt to calculate the fusion cross sections of light nuclei in a complex spherical square-well nuclear potential (i.e., optical potential model). Comparing with experimental benchmark cross section data, we can calibrate optical potential parameters associated with D+D, D+T, D+3He, p+D, p+6Li and p+7Li fusion reactions. Surprisingly, we find that our calculated optical potential parameters are quite different from those of many previous results (e.g., Phys. Rev. C. 61 (2000) 024610, Nucl. Phys. A 986 (2019) 98, etc.), in which approximate Coulomb wave functions (ACWFs) with only retaining the leading terms are exploited for the continuity conditions at the radius of nuclear potential. Furthermore, with the obtained optical potential parameters, we compare the fusion cross sections and astrophysical S-factors with that formulated from ACWFs approach, and also find apparent deviations especially for the fusion reactions with resonance peaks such as D+T and D+3He fusion reactions. We then calculate the phase diagrams of the fusion cross sections with respect to the optical potential parameters and demonstrate several narrow shape resonance belts. It implies that a small deviation of ACWFs from the exact CWFs at nuclear radius might lead to fall off the resonance regimes and therefore causes the big difference on the optical parameters as well as the cross sections.
nucl-thNPA(2022)·8 citations
07
Meson-Baryon Couplings Revisited
N. F. Nasrallah🇱🇧
The theoretical evaluation of the coupling constants gpiNN , gKNLambda and gKNSigma is undertaken using QCD sum rules. These quantities were previously calculated with exponential (Borel) kernels used to suppress the unknown contributions of the hadronic continua. This method however introduces arbitrariness and instability in the calculation. In order to avoid these I redo the calculation using polynomial kernels tailored to vanish at the baryonic resonance masses. The results are gpiNN = 12.5 +- 1.0, gKNSigma = 5.45 +- .4, gKNSigma= -(12.7 - 15.0) which are close to experiment and to the predictions of SU(3) and which , with the corresponding Goldberger-Treiman Discrepancy satisfy quite well the Dashen-Weinstein relation.
↳ hep-phnucl-th0 citations
08
Rotation and deformation of strangeon stars in the Lennard-Jones model
Yong Gao🇨🇳 · Xiao-Yu Lai🇨🇳 · Lijing Shao🇨🇳 · Ren-Xin Xu🇨🇳
The strong interactions at low energy scales determine the state of the supranuclear matter in the pulsar-like compact objects. It is proposed that the bulk strong matter could be composed of strangeons, which are quark clusters with a nearly equal number of three light-flavor quarks. In this work, to characterize the strong-repulsive interactions at short distances and the non-relativistic nature of the strangeons, the Lennard-Jones model is used to describe the equation of state (EoS) of strangeon stars (SSs). We investigate the static, the slowly rotating, and the tidally deformed SSs in detail. The corrections resulted from the finite surface densities are considered crucially in the perturbative approaches. We also study the universal relations between the moments of inertia, the tidal deformabilities, and the quadrupole moments. Those results are ready to be used for various purposes in astrophysics, and possible constraints from contemporary observations on the parameter space of the Lennard-Jones model are discussed. Future observations of the pulsars' radio signals, the X-ray emissions from the hot spots on the surface of the stars, and the gravitational waves (GWs) from binary mergers can give tighter constraints or even verify or falsify the existence of SSs.
↳ gr-qcastro-ph.HEhep-phnucl-thMNRAS(2021)·38 citations
09
Consistent approach to study gluon quasi-particles
Chowdhury Aminul Islam🇨🇳 · Munshi G. Mustafa🇮🇳 · Rajarshi Ray🇮🇳 · Pracheta Singha🇮🇳
We discuss a novel approach to estimate the partition function in effective model frameworks when the effective potentials have multiple extrema, so that ascertaining a mean field becomes difficult. Using this approach we present a consistent model to study the thermodynamic properties of gluon quasi-particles as a function of temperature, both in the color confined and the color deconfined phases.
↳ hep-phhep-latnucl-thPRD(2022)·7 citations
10
Critical Coupling for Two-dimensional $ϕ^{4}$ Theory in Discretized Light-Cone Quantization
James P. Vary🇺🇸 · Mengyao Huang🇺🇸 · Shreeram Jawadekar🇺🇸 · Mamoon Sharaf🇺🇸 · Avaroth Harindranath🇮🇳 · Dipankar Chakrabarti🇮🇳
We solve for the critical coupling in the symmetric phase of two-dimensional $ϕ^{4}$ field theory using Discretized Light-Cone Quantization. We adopt periodic boundary conditions, neglect the zero mode, and obtain a critical coupling consistent with the critical coupling reported using conformal truncation in light-front quantization. We find a 17% dfference from the critical coupling reported with light-front quantization in a symmetric polynomial basis.
↳ hep-thnucl-thPRD(2022)·12 citations
11
Nuclear-Level Effective Theory of $μ \to e$ Conversion
Evan Rule · W. C. Haxton · Ken McElvain
The Mu2e and COMET $μ \to e$ conversion experiments are expected to significantly advance limits on new sources of charged lepton flavor violation (CLFV). Almost all theoretical work in the field has focused on just two operators. However, general symmetry arguments lead to a $μ \to e$ conversion rate with six response functions, each of which, in principle, is observable by varying nuclear properties of targets. We construct a nucleon-level nonrelativistic effective theory (NRET) to clarify the microscopic origin of these response functions and to relate rate measurements in different targets. This exercise identifies three operators and their small parameters that control the NRET operator expansion. We note inconsistencies in past treatments of these parameters. The NRET is technically challenging, involving 16 operators, several distorted electron partial waves, bound muon upper and lower components, and an exclusive nuclear matrix element. We introduce a trick for treating the electron Coulomb effects accurately, which enables us to include all of these effects while producing transition densities whose one-body matrix elements can be evaluated analytically, greatly simplifying the nuclear physics. We derive bounds on operator coefficients from existing and anticipated $μ \to e$ conversion experiments. We discuss how similar NRET formulations have impacted dark matter phenomenology, noting that the tools this community has developed could be adapted for CLFV studies.
↳ hep-phnucl-thPRL(2023)·23 citations

Affiliations

first authorsco-authorsvia INSPIRE