Nuclear Theory·nucl-th

Tuesday·January 19, 2021

13 papers—9 primary·4 cross-listed

01
Generalizing the calculable $R$ -matrix theory and eigenvector continuation to the incoming wave boundary condition
Dong Bai🇨🇳 · Zhongzhou Ren🇨🇳
The calculable $R$ -matrix theory has been formulated successfully for regular boundary conditions with vanishing radial wave functions at the coordinate origins [P. Descouvemont and D. Baye, Rept. Prog. Phys. 73, 036301 (2010)]. We generalize the calculable $R$ -matrix theory to the incoming wave boundary condition (IWBC), which is widely used in theoretical studies of low-energy heavy-ion fusion reactions to simulate the strong absorption of incoming flux inside the Coulomb barriers. The generalized calculable $R$ -matrix theory also provides a natural starting point to extend eigenvector continuation (EC) [D. Frame et al., Phys. Rev. Lett. 121, 032501 (2018)] to fusion observables. The $^{14} N +^{12} C$ fusion reaction is taken as an example to validate these new theoretical tools. Both local and nonlocal potentials are considered in numerical calculations. Our generalizations of the calculable $R$ -matrix theory and EC are found to work well for IWBC.
nucl-thPRC(2021)·43 citations
02
g-mode Oscillations in Hybrid Stars: A Tale of Two Sounds
Prashanth Jaikumar🇺🇸 · Alexandra Semposki🇺🇸 · Madappa Prakash🇺🇸 · Constantinos Constantinou🇮🇹
We study the principal core g-mode oscillation in hybrid stars containing quark matter and find that they have an unusually large frequency range ( $\approx$ 200 - 600 Hz) compared to ordinary neutron stars or self-bound quark stars of the same mass. Theoretical arguments and numerical calculations that trace this effect to the difference in the behaviour of the equilibrium and adiabatic sound speeds in the mixed phase of quarks and nucleons are provided. We propose that the sensitivity of core g-mode oscillations to non-nucleonic matter in neutron stars could be due to the presence of a mixed quark-nucleon phase. Based on our analysis, we conclude that for binary mergers where one or both components may be a hybrid star, the fraction of tidal energy pumped into resonant g-modes in hybrid stars can exceed that of a normal neutron star by a factor of 2-3, although resonance occurs during the last stages of inspiral. A self-bound star, on the other hand, has a much weaker tidal overlap with the g-mode. The cumulative tidal phase error in hybrid stars, $Δ ϕ ≅$ 0.5 rad, is comparable to that from tides in ordinary neutron stars, presenting a challenge in distinguishing between the two cases. However, should the principal g-mode be excited to sufficient amplitude for detection in a post-merger remnant with quark matter in its interior, its frequency would be a possible indication for the existence of non-nucleonic matter in neutron stars.
nucl-thastro-ph.SRgr-qcPRD(2021)·71 citations
03
r-mode instability of neutron stars in low-mass X-ray binaries: effects of Fermi surface depletion and superfluidity of dense matter
J. M. Dong
The nucleon-nucleon correlation between nucleons leads to the Fermi surface depletion measured by a $Z$ -factor in momentum distribution of dense nuclear matter. The roles of the Fermi surface depletion effect ( $Z$ -factor effect) and its quenched neutron triplet superfluidity of nuclear matter in viscosity and hence in the gravitational-wave-driven $r$ -mode instability of neutron stars (NSs) are investigated. The bulk viscosity is reduced by both the two effects, especially the superfluid effect at low temperatures which is also able to reduce the inferred core temperature of NSs. Intriguingly, due to the neutron superfluidity, the core temperature of the NSs in known low-mass X-ray binaries (LMXBs) are found to be clearly divided into two groups: high and low temperatures which correspond to NSs with short and long recurrence times for nuclear-powered bursts respectively. Yet, a large number of NSs in these LMXBs are still located in the $r$ -mode instability region. If the density-dependent symmetry energy is stiff enough, the occurence of direct Urca process reduces the inferred core temperature by about one order of magnitude. Accordingly, the contradiction between the predictions and observations is alleviated to some extent, but some NSs are still located inside the unstable region.
nucl-thastro-ph.HEMNRAS(2021)·11 citations
04
The relevance of pion-exchange contributions versus contact terms in the chiral effective field theory description of nucleon-nucleon scattering
H. Alanazi🇺🇸 · R. Machleidt (University of Idaho)🇺🇸
The standard way to demonstrate the relevance of chiral symmetry for the NN interaction is to consider higher partial waves of NN scattering which are controlled entirely by chiral pion-exchanges (since contacts vanish). However, in applications of NN-potentials to nuclear structure and reactions, the lower partial waves are the important ones, making the largest contributions. Lower partial waves are sensitive to the short-range potential, and so, when the short-range contacts were to dominate over the chiral pion-contributions in lower partial waves, then the predictions from "chiral potentials" would have little to do with chiral symmetry. To address this issue, we investigate systematically the role of the (chiral) one- and two-pion exchanges, on the one hand, and the effect of the contacts, on the other hand, in the lower partial waves of NN scattering. We are able to clearly identify the signature of chiral symmetry in lower partial waves. Our study has also a pedagogical spin-off as it demonstrates in detail how the reproduction of the lower partial-wave phase shifts comes about from the various ingredients of the theory.
nucl-thnucl-exFew Body Syst.(2021)·26 citations
05
Exchange effects in nucleus-nucleus reactions
J. Dohet-Eraly🇧🇪 · P. Descouvemont🇧🇪
We present a scattering model for nuclei with similar masses. In this three-body model, the projectile has a core+valence structure, whereas the target is identical to the core nucleus. The three-body wave functions must be symmetrized for the exchange of the cores. This property gives rise to non-local potentials, which are computed without approximation. The present model is an extension of the Continuum Discretized Coupled Channel (CDCC) formalism, with an additional treatment of core exchange. We solve the coupled-channel system, including non-local terms, by the $R$ -matrix method using Lagrange functions. This model is applied to the $^{13} C +^{12}$ C, $^{13} N +^{12}$ C and $^{16} O +^{12}$ C systems. Experimental scattering cross sections are fairly well reproduced without any parameter fitting. The backward-angle enhancement of the elastic cross sections is due to the non-local potential. We discuss in more detail the various non-local contributions and present effective local potentials.
nucl-thPRC(2021)·3 citations
06
Diffuseness parameter as a bottleneck for accurate half-life calculations
Aladdin Abdul-latif · Omar Nagib
An investigation of the calculated $α$ decay half-lives of super heavy nuclei (SHN) reveals that the diffuseness parameter is a great bottleneck for achieving accurate results and predictions. In particular, when universal proximity function is adopted for nuclear potential, half-life is found to vary significantly and nonlinearly as a function of diffuseness parameter. To overcome this limiting hurdle, a new semiempirical formula for diffuseness that is dependent on charge and neutron numbers is proposed in this work. With the model at hand, half-lives of 218 SHN are computed, for 68 of which there exists available experimental data and 150 of which are predicted. The calculations of half-lives for 68 SHN are compared against experimental data and the calculated data obtained by using deformed Woods-Saxon, deformed Coulomb potentials model, and six semiempirical formulas. The predictions of 150 SHN are compared against the predictions of seven of the current best semiempirical formulas. Calculations of the present study are in good agreement with the experimental half-lives outperforming all but ImSahu semiempirical formula. Moreover, the predictions of our model are consistent with predictions of the semiempirical formulas. We strongly conclude that more attention should be directed toward obtaining accurate diffuseness parameter values for using it in nuclear calculations.
nucl-thPRC(2019)·20 citations
07
Manifestation of Hidden Symmetries in Baryonic Matter: From Finite Nuclei to Neutron Stars
Mannque Rho🇫🇷 · Yong-Liang Ma🇨🇳
The hadron-quark/gluon duality formulated in terms of a topology change at a density $n \gsim 2 n_{0}$ $n_{0} ≃ 0.16$ fm $^{- 3}$ is found to describe the core of massive compact stars in terms of quasiparticles of fractional baryon charges, behaving neither like pure baryons nor like deconfined quarks. This can be considered as the Cheshire-Cat mechanism~\cite{CC} for the hadron-quark continuity arrived at bottom-up from skyrmions that is equivalent to the "MIT-bag"-to-skyrmion continuity arrived at top-down from quarks/gluons. Hidden symmetries, both local gauge and pseudo-conformal (or broken scale), emerge and give rise both to the long-standing "effective $g_{A}^{*} \approx 1$ " in nuclear Gamow-Teller transitions at $\lsim n_{0}$ and to the pseudo-conformal sound velocity $v_{p cs}^{2} / c^{2} \approx 1/3$ at $\gsim 3 n_{0}$ . It is suggested that what has been referred to, since a long time, as "quenched $g_{A}$ " in light nuclei reflects what leads to the dilaton-limit $g_{A}^{DL} = 1$ at near the (putative) infrared fixed point of scale invariance. These properties are confronted with the recent observations in Gamow-Teller transitions and in astrophysical observations.
nucl-thastro-ph.HEhep-phMod.Phys.Lett.A(2021)·28 citations
08
$α$ -decay half-lives of superheavy nuclei with $Z = 122 - 125$
Omar Nagib
For $α$ decay half-life calculations in this work, the Coulomb and proximity potential model with a new semiempirical formula for diffuseness parameter developed in previous work [Phys. Rev. C 100, 024601 (2019)] is used. The present model in this work is compared with the generalized liquid-drop model (GLDM), universal decay law (UDL), and experimental half-lives in the region $Z = 104 - 118$ . Next, the predicted half-lives of 51 superheavy nuclei (SHN) with $Z = 122 - 125$ by the present model are compared with those of GLDM, and UDL. The present model is revealed to be more accurate in reproducing experimental half-lives compared to GLDM and UDL. Moreover, it is found that the predictions of the present model and UDL are highly consistent while GLDM largely deviates from the other two. A study of the competition between $α$ decay and spontaneous fission (SF) shows that $α$ decay is the dominant mode. Among the studied SHN with $Z = 122 - 125$ , $^{295 - 307} 122$ and $^{314 - 320} 125$ are identified as potential candidates whose half-lives are relatively long enough to be experimentally detected in the future through their $α$ -decay chains. The identified candidates are in good agreement with other recent work.
nucl-thPRC(2020)·16 citations
09
Comment on " $Λ_{c} N$ interaction in leading order covariant chiral effective field theory"
J. Haidenbauer🇩🇪 · G. Krein🇧🇷
Song et al. [Phys. Rev. C 102, 065208 (2020)] presented results for the $Λ_{c} N$ interaction based on an extrapolation of lattice simulations by the HAL QCD Collaboration at unphysical quark masses to the physical point via covariant chiral effective field theory. We point out that their predictions for the $^{3} D_{1}$ partial wave disagree with available lattice results. We discuss the origin of that disagreement and present a comparison with predictions from conventional (non-relativistic) chiral effective field theory.
nucl-thhep-ph4 citations
10
Hyper-order baryon number fluctuations at finite temperature and density
Wei-jie Fu🇨🇳 · Xiaofeng Luo🇨🇳 · Jan M. Pawlowski🇩🇪 · Fabian Rennecke🇺🇸 · Rui Wen🇨🇳 · Shi Yin🇨🇳
Fluctuations of conserved charges are sensitive to the QCD phase transition and a possible critical endpoint in the phase diagram at finite density. In this work, we compute the baryon number fluctuations up to tenth order at finite temperature and density. This is done in a QCD-assisted effective theory that accurately captures the quantum- and in-medium effects of QCD at low energies. A direct computation at finite density allows us to assess the applicability of expansions around vanishing density. By using different freeze-out scenarios in heavy-ion collisions, we translate these results into baryon number fluctuations as a function of collision energy. We show that a non-monotonic energy dependence of baryon number fluctuations can arise in the non-critical crossover region of the phase diagram. Our results compare well with recent experimental measurements of the kurtosis and the sixth-order cumulant of the net-proton distribution from the STAR collaboration. They indicate that the experimentally observed non-monotonic energy dependence of fourth-order net-proton fluctuations is highly non-trivial. It could be an experimental signature of an increasingly sharp chiral crossover and may indicate a QCD critical point. The physics implications and necessary upgrades of our analysis are discussed in detail.
↳ hep-phnucl-exnucl-thPRD(2021)·130 citations
11
Unruh effect and information entropy approach
M.V. Teslyk🇺🇦 · O.M. Teslyk🇺🇦 · L.V. Zadorozhna🇺🇦 · L. Bravina🇳🇴 · E. Zabrodin🇳🇴
Total entropy generated by the Unruh effect is calculated within the framework of information theory. In contrast to previous studies, here the calculations are done for the finite time of existence of the non-inertial reference frame. In this case only the finite number of particles is produced. Dependence on mass of the emitted particles is taken into account. Analytic expression for the entropy of radiated boson and fermion spectra is derived. We study also its asymptotics corresponding to limiting cases of low and high acceleration. The obtained results can be further generalized to other intrinsic degrees of freedom of the emitted particles, such as spin and electric charge.
↳ hep-thgr-qcnucl-thParticles(2022)·6 citations
12
Journey to the Bound States
Paul Hoyer🇫🇮
Guided by the observed properties of hadrons I formulate a perturbative bound state method for QED and QCD. The expansion starts with valence Fock states ( $e^{+} e^{-}, q q ˉ, q q q, g g$ ) bound by the instantaneous interaction of temporal gauge ( $A^{0} = 0$ ). The method is tested on Positronium atoms at rest and in motion, including hyperfine splitting at $O (α^{4})$ , electromagnetic form factors and deep inelastic scattering. Relativistic binding is studied for QED in $D = 1 + 1$ dimensions, demonstrating the frame independence of the DIS electron distribution and its sea for $x_{bj} \to 0$ . In QCD a homogeneous solution of Gauss' constraint in $D = 3 + 1$ implies $O (α_{s}^{0})$ confining potentials for $q q ˉ, q q ˉ g, q q q$ and $g g$ states, whereas $q q ˉ q q ˉ$ is unconfined. Meson states lie on linear Regge trajectories and have the required frame dependence. A scalar bound state with vanishing four-momentum causes spontaneous chiral symmetry breaking when mixed with the vacuum. These lecture notes assume knowledge of field theory methods, but not of bound states. Brief reviews of existing bound state methods and Dirac electron states are included. Solutions to the exercises are given in the Appendix.
↳ hep-phnucl-thSpringerBriefs in Physics (Springer, 2021)·12 citations
13
Heavy-hadron molecular spectrum from light-meson exchange saturation
Fang-Zheng Peng🇨🇳 · Mario Sánchez Sánchez🇫🇷 · Mao-Jun Yan🇨🇳 · Manuel Pavon Valderrama🇨🇳
If known, the spectrum of heavy-hadron molecules will be a key tool to disentangle the nature of the exotic states that are being discovered in experiments. Here we argue that the general features of the molecular spectrum can be deduced from the idea that the short-range interaction between the heavy hadrons is effectively described by scalar and vector meson exchange, i.e. the $σ$ , $ω$ and $ρ$ mesons. By means of a contact-range theory where the couplings are saturated by the aforementioned light mesons we are indeed able to postdict the $X (3872)$ (as a $D^{*} D ˉ$ molecule) from the three $P_{c} (4312)$ , $P_{c} (4440)$ and $P_{c} (4457)$ pentaquarks (as $D ˉ Σ_{c}$ and $D ˉ^{*} Σ_{c}$ molecules). We predict a $J^{P C} = 1^{--}$ $D D ˉ_{1}$ molecule at $4240 - 4260 MeV$ which might support the hypothesis that the $Y (4260)$ is at least partly molecular. The extension of these ideas to the light baryons requires minor modifications, after which we recover approximate SU(4)-Wigner symmetry in the two-nucleon system and approximately reproduce the masses of the deuteron and the virtual state.
↳ hep-phhep-exhep-latnucl-thPRD(2022)·33 citations

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