Nuclear Theory·nucl-th

Friday·September 1, 2023

17 papers—6 primary·11 cross-listed

01
Distilling the essential elements of nuclear binding via neural-network quantum states
A. Gnech · B. Fore · A. Lovato
In pursuing the essential elements of nuclear binding, we compute ground-state properties of atomic nuclei with up to $A = 20$ nucleons, using as input a leading order pionless effective field theory Hamiltonian. A variational Monte Carlo method based on a new, highly-expressive, neural-network quantum state ansatz is employed to solve the many-body Schrödinger equation in a systematically improvable fashion. In addition to binding energies and charge radii, we accurately evaluate the magnetic moments of these nuclei, as they reveal the self-emergence of the shell structure, which is not a priori encoded in the neural-network ansatz. To this aim, we introduce a novel computational protocol based on adding an external magnetic field to the nuclear Hamiltonian, which allows the neural network to learn the preferred polarization of the nucleus within the given magnetic field.
nucl-thPRL(2024)·44 citations
02
Solid-State $^{229} Th$ Nuclear Laser with Two-Photon Pumping
Haowei Xu · Hao Tang · Guoqing Wang · Changhao Li · Boning Li · Paola Cappellaro · Ju Li
The radiative excitation of the 8.3 eV isomeric state of thorium-229 is an outstanding challenge due to the lack of tunable far-ultraviolet (F-UV) sources. In this work, we propose an efficient two-photon pumping scheme for thorium-229 using the optonuclear quadrupolar effect, which only requires a 300 nm UV-B pumping laser. We further demonstrate that population inversion between the nuclear isomeric and ground states can be achieved at room temperature using a two-step pumping process. The nuclear laser, which has been pursued for decades, may be realized using a Watt-level UV-B pumping laser and ultrawide bandgap thorium compounds (e.g., $Th F_{4}$ , $N a_{2} Th F_{6}$ , or $K_{2} Th F_{6}$ ) as the gain medium.
nucl-thcond-mat.mtrl-sciphysics.opticsPRA(2023)·9 citations
03
Topological transition in a parallel electromagnetic field
Gaoqing Cao🇨🇳
In this work, we attack the problem of "chiral phase instability" ( $χ$ PI) in a quantum chromodynamics (QCD) system under a parallel and constant electromagnetic field. The $χ$ PI refers to that: When $I_{2} \equiv E \cdot B$ is larger than the threshold $I_{2}^{c}$ , no homogeneous solution can be found for $σ$ or $π^{0}$ condensate, and the chiral phase (or angle) $θ$ becomes unstable. Within the two-flavor chiral perturbation theory, we obtain an effective Lagrangian density for $θ (x)$ where the chiral anomalous Wess-Zumino-Witten term is found to play a role of "source" to the "potential field" $θ (x)$ . The Euler-Lagrangian equation is applied to derive the equation of motion for $θ (x)$ , and physical solutions are worked out for several shapes of system. In the case $I_{2} > I_{2}^{c}$ , it is found that the $χ$ PI actually implies an inhomogeneous QCD phase with $θ (x)$ spatially dependent. By its very nature, the homogeneous-inhomogeneous phase transition is of pure topological and second order at $I_{2}^{c}$ . Finally, the work is extended to the three-flavor case, where an inhomogeneous $η$ condensation is also found to be developed for $I_{2} > I_{2}^{c}$ . Correspondingly, there is a second critical point, $I_{2}^{c^{'}} = 24.3 I_{2}^{c}$ , across which the transition is also of topological and second order by its very nature.
nucl-thcond-mat.mtrl-scihep-thPRD(2024)·3 citations
04
Influence of the symmetry energy on the nuclear binding energies and the neutron drip line position
Ante Ravlić · Esra Yüksel · Tamara Nikšić · Nils Paar
A clear connection can be established between properties of nuclear matter and finite-nuclei observables, such as the correlation between the slope of the symmetry energy and dipole polarizability, or between compressibility and the isoscalar monopole giant resonance excitation energy. Establishing a connection between realistic atomic nuclei and an idealized infinite nuclear matter leads to a better understanding of underlying physical mechanisms that govern nuclear dynamics. In this work, we aim to study the dependence of the binding energies and related quantities (e.g. location of drip lines, the total number of bound even-even nuclei) on the symmetry energy $S_{2} (ρ)$ . The properties of finite nuclei are calculated by employing the relativistic Hartree-Bogoliubov (RHB) model, assuming even-even axial and reflection symmetric nuclei. Calculations are performed by employing two families of relativistic energy density functionals (EDFs), based on different effective Lagrangians, constrained to a specific symmetry energy at saturation density $J$ within the interval of $30$ -- $36$ MeV. Nuclear binding energies and related quantities of bound nuclei are calculated between $8 \leq Z \leq 104$ from the two-proton to the two-neutron drip line. As the neutron drip line is approached, the interactions with stiffer $J$ tend to predict more bound nuclei, resulting in a systematic shift of the two-neutron drip line towards more neutron-rich nuclei. Consequentially, a correlation between the number of bound nuclei $N_{n u c l}$ and $S_{2} (ρ)$ is established for a set of functionals constrained using the similar optimization procedures. The direction of the relationship between the number of bound nuclei and symmetry energy highly depends on the density under consideration.
nucl-thnucl-exPRC(2023)·9 citations
05
The nuclear liquid-gas transition in QCD
Kenji Fukushima🇯🇵 · Jan Horak🇩🇪 · Jan M. Pawlowski🇩🇪 · Nicolas Wink🇩🇪 · Carl Philipp Zelle🇩🇪
We estimate the nuclear saturation density and the binding energy in a nuclear liquid from precision data on the coupling of the four-quark scattering vertex in the vector channel, computed within functional QCD. We show that this coupling is directly related to the density-density potential and the latter is used for the estimates. In a first qualitative computation we find a saturation density of 0.2 fm $^{- 3}$ and an upper bound for the binding energy of 21.5 MeV, in agreement with the empirical values of 0.16 fm $^{- 3}$ and 16 MeV, respectively. We also use the scattering vertex for constructing an emergent low-energy effective theory for the liquid gas transition from QCD correlation function, whose coupling parameters can be determined within QCD. As a first consistency check of this construction we estimate the in-medium reduction of the nucleon pole mass.
nucl-thhep-phPRD(2024)·12 citations
06
Effect of initial-state geometric configurations on the nuclear liquid-gas phase transition
Y. T. Cao · X. G. Deng · Y. G. Ma
Within the framework of an extended quantum molecular dynamics model, we simulated $^{40}$ Ca + $^{16}$ O collisions at beam energies ranging from 60 to 150 MeV/nucleon for $^{16}$ O with different $α$ -cluster configurations. Results imply that different $α$ -cluster configurations lead to different yields of deuteron, triton, $^{3}$ He and $^{4}$ He, but not for proton and neutron. We discuss the effect of geometric fluctuations which are presented by double ratios of light nuclei, namely $O_{p-d-t}$ and $O_{p-d-He}$ . It is found that magnitude hierarchy of geometric fluctuations is chain, kite, square and tetrahedron structure of $^{16}$ O. $O_{p-d-t}$ has maximum value around 80 -- 100 MeV/nucleon which could be related to liquid-gas phase transition, that is consistent with results from the charge distribution of the heaviest fragments in the collisions.
nucl-thnucl-exPRC(2023)·14 citations
07
Eigenstate Thermalization in 2+1 dimensional SU(2) Lattice Gauge Theory
Lukas Ebner🇩🇪 · Berndt Müller🇺🇸 · Andreas Schäfer🇩🇪 · Clemens Seidl🇩🇪 · Xiaojun Yao🇺🇸
We present preliminary numerical evidence for the hypothesis that the Hamiltonian SU(2) gauge theory discretized on a lattice obeys the Eigenstate Thermalization Hypothesis (ETH). To do so we study three approximations: (a) a linear plaquette chain in a reduced Hilbert space limiting the electric field basis to $j = 0, \frac{1}{2}$ , (b) a two-dimensional honeycomb lattice with periodic or closed boundary condition and the same Hilbert space constraint, and (c) a chain of only three plaquettes but such a sufficiently large electric field Hilbert space ( $j \leq \frac{7}{2})$ that convergence of all energy eigenvalues in the analyzed energy window is observed. While an unconstrained Hilbert space is required to reach the continuum limit of SU(2) gauge theory, numerical resource constraints do not permit us to realize this requirement for all values of the coupling constant and large lattices. In each of the three studied cases we check first for random matrix theory (RMT) behavior in the eigenenergy spectrum and then analyze the diagonal as well as the off-diagonal matrix elements between energy eigenstates for a few operators. Within current uncertainties all results for (a), (b) and (c) agree with ETH predictions. Furthermore, we find the off-diagonal matrix elements of the electric energy operator exhibit RMT behavior in frequency windows that are small enough in (b) and (c). To unambiguously establish ETH behavior and determine for which class of operators it applies, an extension of our investigations is necessary.
↳ hep-latcond-mat.stat-mechcond-mat.str-elhep-ph+2PRD(2024)·44 citations
08
One-loop matching of the $C P$ -odd three-gluon operator to the gradient flow
Òscar L. Crosas🇨🇭 · Christopher J. Monahan🇺🇸 · Matthew D. Rizik🇺🇸 · Andrea Shindler🇩🇪 · Peter Stoffer🇨🇭
The calculation of the neutron electric dipole moment within effective field theories for physics beyond the Standard Model requires non-perturbative hadronic matrix elements of effective operators composed of quark and gluon fields. In order to use input from lattice computations, these matrix elements must be translated from a scheme suitable for lattice QCD to the minimal-subtraction scheme used in the effective-field-theory framework. The accuracy goal in the context of the neutron electric dipole moment necessitates at least a one-loop matching calculation. Here, we provide the one-loop matching coefficients for the $C P$ -odd three-gluon operator between two different minimally subtracted 't Hooft-Veltman schemes and the gradient flow. This completes our program to obtain the one-loop gradient-flow matching coefficients for all $C P$ -violating and flavor-conserving operators in the low-energy effective field theory up to dimension six.
↳ hep-lathep-exhep-phnucl-thPLB(2023)·13 citations
09
Secular Outflows from 3D-MHD Hypermassive Neutron Star Accretion Disk Systems
Steven Fahlman · Rodrigo Fernández · Sharon Morsink
Magnetized hypermassive neutron stars (HMNSs) have been proposed as a way for neutron star (NS) mergers to produce high electron fraction, high velocity ejecta, as required by kilonova models to explain the observed light curve of GW170817. The HMNS drives outflows through neutrino energy deposition and mechanical oscillations, and raises the electron fraction of outflows through neutrino interactions before collapsing to a black hole (BH). Here we perform 3D numerical simulations of HMNS-torus systems in ideal magnetohydrodynamics, using a leakage/absorption scheme for neutrino transport, the nuclear APR equation of state, and Newtonian self-gravity, with a pseudo-Newtonian potential added after BH formation. Due to the uncertainty in the HMNS collapse time, we choose two different parameterized times to induce collapse. We also explore two initial magnetic field geometries in the torus, and evolve the systems until the outflows diminish significantly ( $\sim 1 - 2$ $s$ ). We find bluer, faster outflows as compared to equivalent BH-torus systems, producing $M \sim 1 0^{- 3} M_{⊙}$ of ejecta with $Y_{e} \geq 0.25$ and $v \geq 0.25 c$ by the simulation end. Approximately half the outflows are launched in disk winds at times $t ≲ 500$ $ms$ , with a broad distribution of electron fractions and velocities, depending on the initial condition. The remaining outflows are thermally-driven, characterized by lower velocities and electron fractions. Nucleosynthesis with tracer particles shows patterns resembling solar abundances in all models. Although outflows from our simulations do not match those inferred from two-component modelling of the GW170817 kilonova, self-consistent multidimensional detailed kilonova models are required to determine if our outflows can power the blue kilonova.
↳ astro-ph.HEgr-qcnucl-thMNRAS(2023)·7 citations
10
Medium induced mixing, spatial modulations and critical modes in QCD
Maximilian Haensch🇩🇪 · Fabian Rennecke🇩🇪 · Lorenz von Smekal🇩🇪
The mixing between the chiral condensate and the density in hot and dense QCD matter is familiar. We show that the mixing relevant for the ground state is considerably more extensive, and in particular also involves gluonic degrees of freedom. As a result, the Hessian of the QCD effective action is non-Hermitian, but retains a symmetry under combined charge- and complex conjugation. This can lead to complex-conjugate pairs of eigenvalues of this Hessian, signaling regimes with spatially modulated correlations. Furthermore, based on the analytic structure of the quark determinant at a chiral critical point, we demonstrate that the corresponding massless critical mode is composed of the chiral condensate, the density and the Polyakov loops. Due to an avoided crossing, the critical mode turns out to be disconnected from the chiral condensate in vacuum. We present general arguments for all these features and illustrate them through explicit model calculations.
↳ hep-phhep-thnucl-thPRD(2024)·30 citations
11
Schwinger displacement of the quark-gluon vertex
A. C. Aguilar🇧🇷 · M .N. Ferreira🇪🇸 · D. Ibañez🇪🇸 · J. Papavassiliou🇪🇸
The action of the Schwinger mechanism in pure Yang-Mills theories endows gluons with an effective mass, and, at the same time, induces a measurable displacement to the Ward identity satisfied by the three-gluon vertex. In the present work we turn to Quantum Chromodynamics with two light quark flavors, and explore the appearance of this characteristic displacement at the level of the quark-gluon vertex. When the Schwinger mechanism is activated, this vertex acquires massless poles, whose momentum-dependent residues are determined by a set of coupled integral equations. The main effect of these residues is to displace the Ward identity obeyed by the pole-free part of the vertex, causing modifications to its form factors, and especially the one associated with the tree-level tensor. The comparison between the available lattice data for this form factor and the Ward identity prediction reveals a marked deviation, which is completely compatible with the theoretical expectation for the attendant residue. This analysis corroborates further the self-consistency of this mass-generating scenario in the general context of real-world strong interactions.
↳ hep-phhep-lathep-thnucl-thEPJC(2023)·15 citations
12
Un-screened forces in Quark-Gluon Plasma?
Alexei Bazavov🇺🇸 · Daniel Hoying🇨🇭 · Rasmus N. Larsen🇳🇴 · Swagato Mukherjee🇺🇸 · Peter Petreczky🇺🇸 · Alexander Rothkopf🇳🇴 · Johannes Heinrich Weber🇩🇪
We study the correlator of temporal Wilson lines at non-zero temperature in 2+1 flavor lattice QCD with the aim to define the heavy quark-antiquark potential at non-zero temperature. For temperatures $153 MeV \leq T \leq 352 MeV$ the spectral representation of this correlator is consistent with a broadened peak in the spectral function, position or width of which then defines the real or imaginary parts of the heavy quark-antiquark potential at non-zero temperature, respectively. We find that the potential's real part is not screened contrary to the widely-held expectations. We comment on how this fact may modify the picture of quarkonium melting in the quark-gluon plasma.
↳ hep-lathep-phnucl-thPRD(2024)·53 citations
13
Revisit spin effects induced by thermal vorticity
Jian-Hua Gao🇨🇳 · Shi-Zheng Yang🇨🇳
We revisit the spin effects induced by thermal vorticity by calculating them directly from the spin-dependent distribution functions. For the spin-1/2 particles, we give the polarization up to the first order of thermal vorticity and compare it with the usual result calculated from the spin vector. For the spin-1 particles, we find that all the non-diagonal elements vanish and there is no spin alignment up the first order of thermal vortcity. We present the spin alignment at second-order contribution from thermal vorticity. We also find that the spin effects for both Dirac and vector particles will receive extra contribution when the spin direction is associated with the particle's momentum.
↳ hep-phhep-thnucl-thCPC(2024)·5 citations
14
Effects of the $α$ -cluster structure and the intrinsic momentum component of nuclei on the longitudinal asymmetry in relativistic heavy-ion collisions
Ru-XIn Cao🇨🇳 · Song Zhang🇨🇳 · Yu-Gang Ma🇨🇳
The longitudinal asymmetry in relativistic heavy ion collisions arises from the fluctuation in the number of nucleons involved. This asymmetry causes a rapidity shift in the center of mass of the participating zone. Both the rapidity shift and the longitudinal asymmetry have been found to be significant at the top CERN Large Hadron Collider (LHC) energy for collisions of identical nuclei, and the longitudinal asymmetry is important for reconstructing the colliding vertex and correcting the rapidity shift. However, much discussion of the longitudinal asymmetry has treated the initial condition as a nonzero momentum contributed only by the number of participants, i.e., the asymmetry depends only on the number of participating nucleons. So we naturally raise a physical problem, can other initial conditions, such as two typical initial conditions for nuclei, geometric configuration, and momentum distribution, provide effects on the longitudinal asymmetry? Therefore, in this work we consider other effects on the longitudinal asymmetry other than the fluctuation in the number of participants, e.g., the {\alpha} clustering structure as well as the intrinsic momentum distribution in the target and projectile nuclei for the collisions in the framework of a multiphase transport (AMPT) model. By introducing systems with different {\alpha}-clustering structure and intrinsic momentum distribution, we calculated the ratio of the rapidity distributions of different systems and extracted expansion coefficients to analyze the difference contributed by these factors. ...
↳ hep-phnucl-thPRC(2023)·9 citations
15
Neutron Star vs Quark Star in the Multimessenger Era
Zheng Cao🇨🇳 · Lie-Wen Chen🇨🇳
Neutron stars (NSs) which could contain exotic degrees of freedom in the core and the self-bound quark stars (QSs) made purely of absolutely stable deconfined quark matter are still two main candidates for the compact objects observed in pulsars and gravitational wave (GW) events in binary star mergers. We perform a Bayesian model-agnostic inference of the properties of NSs and QSs by combining multi-messenger data of GW170817, GW190425, PSR J0030+0451, PSR J0740+6620, PSR J1614-2230, PSR J0348+0432 as well as ab initio calculations from perturbative quantum chromodynamics and chiral effective field theory. We find the NS scenario is strongly favored against the QS scenario with a Bayes factor of NS over QS $B_{QS}^{NS} = 11.5$ . In addition, the peak of the squared sound velocity $c_{s}^{2} \sim 0.5 c^{2}$ around $3.5$ times nuclear saturation density $n_{0}$ observed in the NS case disappears in the QS case which suggests that the $c_{s}^{2}$ first increases and then saturates at $c_{s}^{2} \sim 0.5 c^{2}$ above $\sim 4 n_{0}$ . The sound velocity and trace anomaly are found to approach the conformal limit in the core of heavy NSs with mass $M ≳ 2 M_{⊙}$ , but not in the core of QSs.
↳ astro-ph.HEhep-phnucl-exnucl-th14 citations
16
Hybrid Renormalization for Quasi Distribution Amplitudes of A Light Baryon
Chao Han🇨🇳 · Yushan Su🇺🇸 · Wei Wang🇨🇳 · Jia-Lu Zhang🇨🇳
We develop a hybrid scheme to renormalize quasi distribution amplitudes of a light baryon on the lattice, which combines the self-renormalization and ratio scheme. By employing self-renormalization, the UV divergences and linear divergence at large spatial separations in quasi distribution amplitudes are removed without introducing extra nonperturbative effects, while making a ratio with respect to the zero-momentum matrix element can properly remove the UV divergences in small spatial separations. As a specific application, distribution amplitudes of the $Λ$ baryon made of $u d s$ are investigated, and the requisite equal-time correlators, which define quasi distribution amplitudes in coordinate space, are perturbatively calculated up to the next-to-leading order in strong coupling constant $α_{s}$ . These perturbative equal-time correlators are used to convert lattice QCD matrix elements to the continuum space during the renormalization process. Subsequently, quasi distribution amplitudes are matched onto lightcone distribution amplitudes by integrating out hard modes and the corresponding hard kernels are derived up to next-to-leading order in $α_{s}$ including the hybrid counterterms. These results are valuable in the lattice-based investigation of the lightcone distribution amplitudes of a light baryon from the first principles of QCD.
↳ hep-phhep-latnucl-thJHEP(2023)·25 citations
17
Resonance contributions to nucleon spin structure in Holographic QCD
Francesco Bigazzi🇮🇹 · Federico Castellani🇮🇹
We study polarized inelastic electron-nucleon scattering at low momentum transfer in the Witten-Sakai-Sugimoto model of holographic QCD, focusing on resonance production contributions to the nucleon spin structure functions. Our analysis includes both spin $3/2$ and spin $1/2$ low-lying nucleon resonances with positive and negative parity. We determine, in turn, the helicity amplitudes for nucleon-resonance transitions and the resonance contributions to the neutron and proton generalized spin polarizabilities. Extrapolating the model parameters to realistic QCD data, our analysis, triggered by recent experimental results from Jefferson Lab, agrees with the observation that the $Δ (1232)$ resonance gives the dominant contribution to the forward spin polarizabilities at low momentum transfer. The contribution is negative and tends to zero as the momentum transfer increases. As expected, the contribution of the $Δ (1232)$ to the longitudinal-transverse polarizabilities is instead negligible. The latter, for both nucleons, turn out the be negative functions with zero asymptote. The holographic results, at least for the proton where enough data are available, are in qualitative agreement with the resonance contributions to the spin polarizabilities extracted from experimental data on the helicity amplitudes.
↳ hep-phhep-thnucl-thJHEP(2024)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE