Nuclear Theory·nucl-th

Tuesday·October 27, 2020

16 papers—6 primary·10 cross-listed

01
Spin Susceptibility in Neutron Matter from Quantum Monte Carlo Calculations
Luca Riz · Francesco Pederiva · Diego Lonardoni · Stefano Gandolfi
The spin susceptibility in pure neutron matter is computed from auxiliary field diffusion Monte Carlo calculations over a wide range of densities. The calculations are performed for different spin asymmetries, while using twist-averaged boundary conditions to reduce finite-size effects. The employed nuclear interactions include both the phenomenological Argonne AV8 $^{'}$ +UIX potential and local interactions that are derived from chiral effective field theory up to next-to-next-to-leading order.
nucl-thParticles(2020)·5 citations
02
Machine learning-based inversion of nuclear responses
Krishnan Raghavan🇺🇸 · Prasanna Balaprakash🇺🇸 · Alessandro Lovato🇺🇸 · Noemi Rocco🇺🇸 · Stefan M. Wild🇺🇸
A microscopic description of the interaction of atomic nuclei with external electroweak probes is required for elucidating aspects of short-range nuclear dynamics and for the correct interpretation of neutrino oscillation experiments. Nuclear quantum Monte Carlo methods infer the nuclear electroweak response functions from their Laplace transforms. Inverting the Laplace transform is a notoriously ill-posed problem; and Bayesian techniques, such as maximum entropy, are typically used to reconstruct the original response functions in the quasielastic region. In this work, we present a physics-informed artificial neural network architecture suitable for approximating the inverse of the Laplace transform. Utilizing simulated, albeit realistic, electromagnetic response functions, we show that this physics-informed artificial neural network outperforms maximum entropy in both the low-energy transfer and the quasielastic regions, thereby allowing for robust calculations of electron scattering and neutrino scattering on nuclei and inclusive muon capture rates.
nucl-thPRC(2021)·31 citations
03
Coupled-channels treatment of $^{7} Be (p, γ)^{8} B$ in effective field theory
Renato Higa🇧🇷 · Pradeepa Premarathna🇺🇸 · Gautam Rupak🇺🇸
The E1 and M1 contributions to $^{7} Be (p, γ)^{8} B$ at low energies are calculated in halo effective field theory. The excited $^{7} Be^{⋆}$ core is included as an explicit degree of freedom in a coupled-channels calculation. The E1 transition is calculated up to next-to-next-to-leading order. The leading contribution from M1 transition that gives significant contribution in a narrow energy region around the $1^{+}$ resonance state of $^{8}$ B is included. We compare our results with previous halo effective field theory calculations that also included the $^{7} Be^{⋆}$ as an explicit degree of freedom. We disagree with these previous calculations in both the formal expressions and also in the analysis. Bayesian inference of the data gives $S_{17} (0) = 21.0 (7)$ eV b when combined with the expected theory error.
nucl-thastro-ph.SRnucl-exPRC(2022)·12 citations
04
Variational and parquet-diagram calculations for neutron matter. III. S-wave pairing
E. Krotscheck · J. Wang
We apply parquet-diagram summation methods for the calculation of the superfluid gap in $S$ -wave pairing in neutron matter for realistic nucleon-nucleon interactions such as the Argonne $v_{6}$ and the Reid $v_{6}$ potentials. It is shown that diagrammatic contributions that are outside the parquet class play an important role. These are, in variational theories, identified as so-called "commutator contributions". Moreover, using a particle-hole propagator appropriate for a superfluid system results in the suppression of the spin-channel contribution to the induced interaction. Applying these corrections to the pairing interaction, our results agree quite well with Quantum Monte Carlo data.
nucl-thPRC(2021)·7 citations
05
Constraining the density dependence of the symmetry energy with nuclear data and astronomical observations in the KIDS framework
Hana Gil · Young-Min Kim · Panagiota Papakonstantinou · Chang Ho Hyun
The KIDS framework for the nuclear equation of state (EoS) and energy density functional (EDF) offers the possibility to explore symmetry-energy (SE) parameters such as J (value at saturation density), L (slope), Ksym (curvature) and so on independently of each other and of assumptions about the effective mass. Here we examine the performance of EoSs with different SE parameters in reproducing nuclear properties and astronomical observations in an effort to constrain especially L and Ksym or the droplet-model counterpart Ktau. Assuming a standard EoS for symmetric matter, we explore several points on the hyperplane of (J,L,Ksym or Ktau) values. For each point, the corresponding EDF parameters and a pairing parameter are obtained for applications in spherical even-even nuclei. This is the first application of KIDS EDFs with pairing correlations. The EoSs are tested successively on properties of closed-shell nuclei, along the Sn isotopic chain, and on astronomical observations, in a step-by-step process of elimination and correction. A small regime of best-performing parameters is determined. The results strongly suggest that Ksym is negative and no lower than -200MeV, that Ktau lies between roughly -400 and -300MeV and that L lies between 40 and 65MeV with L<55MeV more likely. Correlations between symmetry-energy parameters are critically discussed. Predictions for the position of the neutron drip line and the neutron skin thickness of selected nuclei are reported. They are only weakly affected by the choice of effective mass values. Parts of the drip line can be sensitive to the SE parameters. The results underscore the role of Ktau and of precise astronomical input. Better constraints are possible with precise fits to nuclear energies and, in the future, more-precise input from astronomy.
nucl-thPRC(2021)·32 citations
06
$β$ -decay rates of $^{(115, 117)}$ Rh into $^{(115, 117)}$ Pd isotopes in the microscopic IBFM-2
J. Ferretti · J. Kotila · R. I. Magaña Vsevolodovna · E. Santopinto
The structure of odd- $A$ $^{(115, 117)}$ Rh and $^{(115, 117)}$ Pd isotopes is studied by means of the neutron-proton Interacting Boson-Fermion Model (IBFM-2). $J^{P} = \frac{1}{2}^{+}$ quantum number assignment for the $^{(115, 117)}$ Pd ground-states is critically discussed and the predicted energy levels are compared to the existing experimental data. The resulting nuclear wave functions are used to compute the $β$ -decay $f t$ values of the transitions from $^{(115, 117)}$ Rh to $^{(115, 117)}$ Pd in the microscopic IBFM-2 and the results compared with the data.
nucl-thPRC(2020)·14 citations
07
Investigating High-Energy Proton-Induced Reactions on Spherical Nuclei: Implications for the Pre-Equilibrium Exciton Model
Morgan B. Fox (1) · Andrew S. Voyles (1 and 2) · Jonathan T. Morrell (1) · Lee A. Bernstein (1 and 2) · Amanda M. Lewis (1) · Arjan J. Koning (3) · Jon C. Batchelder (1) · Eva R. Birnbaum (4) · Cathy S. Cutler (5) · Dmitri G. Medvedev (5) · Francois M. Nortier (4) · Ellen M. O'Brien (4) · Christiaan Vermeulen (4) ((1) Department of Nuclear Engineering, University of California, Berkeley (2) Lawrence Berkeley National Laboratory (3) International Atomic Energy Agency (4) Los Alamos National Laboratory (5) Brookhaven National Laboratory)
A number of accelerator-based isotope production facilities utilize 100- to 200-MeV proton beams due to the high production rates enabled by high-intensity beam capabilities and the greater diversity of isotope production brought on by the long range of high-energy protons. However, nuclear reaction modeling at these energies can be challenging because of the interplay between different reaction modes and a lack of existing guiding cross section data. A Tri-lab collaboration has been formed among the Lawrence Berkeley, Los Alamos, and Brookhaven National Laboratories to address these complexities by characterizing charged-particle nuclear reactions relevant to the production of established and novel radioisotopes. In the inaugural collaboration experiments, stacked-targets of niobium foils were irradiated at the Brookhaven Linac Isotope Producer (E $_{p}$ =200 MeV) and the Los Alamos Isotope Production Facility (E $_{p}$ =100 MeV) to measure $^{93}$ Nb(p,x) cross sections between 50 and 200 MeV. The measured cross-section results were compared with literature data as well as the default calculations of the nuclear model codes TALYS, CoH, EMPIRE, and ALICE. We developed a standardized procedure that determines the reaction model parameters that best reproduce the most prominent reaction channels in a physically justifiable manner. The primary focus of the procedure was to determine the best parametrization for the pre-equilibrium two-component exciton model. This modeling study revealed a trend toward a relative decrease for internal transition rates at intermediate proton energies (E $_{p}$ =20-60 MeV) in the current exciton model as compared to the default values. The results of this work are instrumental for the planning, execution, and analysis essential to isotope production.
↳ nucl-exnucl-thPRC(2021)·20 citations
08
Chiral symmetry breaking and chemical equilibrium in a heavy-ion collisions
Sourendu Gupta🇮🇳 · Jajati K. Nayak🇮🇳 · Sushant K. Singh🇮🇳
We examine the thermalization of an ensemble of the octet of pseudoscalar mesons, in the isospin symmetric limit, whose interactions are constrained through chiral symmetry, unitarity, and measurements. The reaction amplitudes generate all resonances up to masses of about 2 GeV, with twelve input parameters, namely f_pi, three masses, and eight low energy constants (LECs) of chiral perturbation theory. In linear response theory, we find that matter takes an extremely long time to thermalize. These long relaxation times are directly related to the fact that these mesons are pseudo-Goldstone bosons of chiral symmetry breaking. This result indicates that fireballs created with zero baryon number in heavy-ion collisions will drop out of chemical equilibrium once they enter the chiral symmetry broken phase.
↳ hep-phhep-exnucl-thPRD(2021)·4 citations
09
Vector mesons spectrum in a medium with a chiral imbalance induced by the vacuum of fermions
Vladimir Kovalenko🇷🇺 · Alexander Andrianov🇷🇺 · Vladimir Andrianov🇷🇺
The properties of the light vector mesons in the presence of local parity breaking medium with a chiral imbalance are considered in the vector-meson dominance model. Applying the finite lowest-order radiatively induced local effective Lagrangian, initially developed for the QED, for the vector $ρ$ and $ω$ mesons, we obtained the mass spectrum as a function of momentum and chiral chemical potential $μ_{5}$ . We showed that in addition to the Chern-Simons term, splitting the transverse polarisations of the mesons, there is another radiatively induced contribution that becomes important at momentum and $μ_{5}$ around a few hundred MeV.
↳ hep-phnucl-thJ.Phys.Conf.Ser.(2020)·4 citations
10
Wigner functions and quantum kinetic theory of polarized photons
Koichi Hattori🇯🇵 · Yoshimasa Hidaka🇯🇵 · Naoki Yamamoto🇯🇵 · Di-Lun Yang🇯🇵
We derive the Wigner functions of polarized photons in the Coulomb gauge with the $ℏ$ expansion applied to quantum field theory, and identify side-jump effects for massless photons. We also discuss the photonic chiral vortical effect for the Chern-Simons current and zilch vortical effect for the zilch current in local thermal equilibrium as a consistency check for our formalism. The results are found to be in agreement with those obtained from different approaches. Moreover, using the real-time formalism, we construct the quantum kinetic theory (QKT) for polarized photons. By further adopting a specific power counting scheme for the distribution functions, we provide a more succinct form of an effective QKT. This photonic QKT involves quantum corrections associated with self-energy gradients in the collision term, which are analogous to the side-jump corrections pertinent to spin-orbit interactions in the chiral kinetic theory for massless fermions. The same theoretical framework can also be directly applied to weakly coupled gluons in the absence of background color fields.
↳ hep-phastro-ph.HEcond-mat.otherhep-th+1JHEP(2021)·53 citations
11
Distribution of Energy-Momentum Tensor around a Static Quark in the Deconfined Phase of SU(3) Yang-Mills Theory
Ryosuke Yanagihara🇯🇵 · Masakiyo Kitazawa🇯🇵 · Masayuki Asakawa🇯🇵 · Tetsuo Hatsuda🇯🇵
Energy momentum tensor (EMT) characterizes the response of the vacuum as well as the thermal medium under the color electromagnetic fields. We define the EMT by means of the gradient flow formalism and study its spatial distribution around a static quark in the deconfined phase of SU(3) Yang-Mills theory on the lattice. Although no significant difference can be seen between the EMT distributions in the radial and transverse directions except for the sign, the temporal component is substantially different from the spatial ones near the critical temperature $T_{c}$ . This is in contrast to the prediction of the leading-order thermal perturbation theory. The lattice data of the EMT distribution also indicate the thermal screening at long distance and the perturbative behavior at short distance.
↳ hep-lathep-phnucl-thPRD(2020)·14 citations
12
Kinetic and Chemical Equilibration of Quark-Gluon Plasma
Xiaojian Du🇩🇪 · Sören Schlichting🇩🇪
We solve a leading-order QCD kinetic theory with light quarks and gluon degrees of freedom to study the non-equilibrium dynamics of the quark-gluon plasma (QGP). By including both elastic and inelastic scatterings for quarks and gluon, the model is proficient to describe kinetic and chemical equilibration of the QGP, and thus connects the initial (semi-) hard production of partons at early times with the hydrodynamic description of a near-thermalized quark-gluon plasma after the first fm/c of the collision. Within this approach, we investigate the time scales and mechanisms for kinetic and chemical equilibration of the QGP at zero and non-zero net-baryon density and elaborate on the connections to jet quenching physics and hydrodynamics.
↳ hep-phnucl-thPoS(2021)·1 citation
13
Di-lepton production from a single photon in strong magnetic fields: Vacuum dichroism
Koichi Hattori🇯🇵 · Hidetoshi Taya🇯🇵 · Shinsuke Yoshida🇨🇳
We study di-lepton production from a single photon in the presence of a strong constant magnetic field. By the use of the Ritus-basis formalism, we analytically evaluate the photon--to--di-lepton conversion vertex with fully taking into account the non-perturbative interactions between the produced fermions and the strong magnetic field. We show that the di-lepton spectrum becomes anisotropic with respect to the magnetic-field direction and depends on the photon polarization as a manifestation of the vacuum dichroism in a strong magnetic field. According to the energy conservation in the presence of the Landau quantization, not only the transverse momentum of the produced fermions but also the longitudinal momentum is discretized, and the di-lepton spectrum exhibits spike structures as functions of the incident photon energy and the magnetic field strength. We also show that the di-lepton production is strictly prohibited for massless fermions in the lowest Landau levels as an analogue of the so-called helicity suppression.
↳ hep-phastro-ph.HEnucl-thJHEP(2021)·41 citations
14
Condensates and pressure of two-flavor chiral perturbation theory at nonzero isospin and temperature
Prabal Adhikari🇺🇸 · Jens O. Andersen🇳🇴 · Martin A. Mojahed🇳🇴
We consider two-flavor chiral perturbation theory ( $χ$ PT) at finite isospin chemical potential $μ_{I}$ and finite temperature $T$ . We calculate the effective potential and the quark and pion condensates as functions of $T$ and $μ_{I}$ to next-to-leading order in the low-energy expansion in the presence of a pionic source. We map out the phase diagram in the $μ_{I}$ -- $T$ plane. Numerically, we find that the transition to the pion-condensed phase is second order in the region of validity of $χ$ PT, which is in agreement with model calculations and lattice simulations. Finally, we calculate the pressure to two-loop order in the symmetric phase for nonzero $μ_{I}$ and find that $χ$ PT seems to be converging very well.
↳ hep-phnucl-thEPJC(2021)·25 citations
15
QGP modification to single inclusive jets in a calibrated transport model
Weiyao Ke🇺🇸 · Xin-Nian Wang🇺🇸
We study inclusive jet suppression and modifications in the quark-gluon plasma (QGP) with a transport-based model. The model includes vacuum-like parton shower evolution at high-virtuality, a linearized transport for jet-medium interactions, and a simple ansatz for the jet-induced hydrodynamic response of the medium. Model parameters are calibrated to nuclear modification factors for inclusive hadron $R_{AA}^{h}$ and single inclusive jets $R_{AA}^{j}$ with cone size $R = 0.4$ in 0-10% central Au-Au and Pb-Pb collisions measured at the RHIC and LHC. The calibrated model consistently describes the cone-size dependent $R_{AA}^{j} (R)$ , modifications to inclusive jet fragmentation functions and jet shape. We discuss the origin of these modifications by analyzing the medium-induced jet energy flow in this model and elucidate the interplay of hard parton evolution and jet-induced medium response. In particular, we demonstrate that the excess of soft hadrons at $p_{T} \sim 2$ GeV/ $c$ in jet fragmentation function and jet shape at large $r = Δ η^{2} + Δ ϕ^{2}$ are consequences of both soft medium-induced gluon radiation and jet-induced medium excitation.
↳ hep-phnucl-thJHEP(2021)·73 citations
16
Systematizing and addressing theory uncertainties of unitarization with the Inverse Amplitude Method
Alexandre Salas-Bernárdez🇪🇸 · Felipe J. Llanes-Estrada🇪🇸 · Juan Escudero-Pedrosa (Univ. Complutense Madrid)🇪🇸 · Jose Antonio Oller (Univ. Murcia)🇪🇸
Effective Field Theories (EFTs) constructed as derivative expansions in powers of momentum, in the spirit of Chiral Perturbation Theory (ChPT), are a controllable approximation to strong dynamics as long as the energy of the interacting particles remains small, as they do not respect exact elastic unitarity. This limits their predictive power towards new physics at a higher scale if small separations from the Standard Model are found at the LHC or elsewhere. Unitarized chiral perturbation theory techniques have been devised to extend the reach of the EFT to regimes where partial waves are saturating unitarity, but their uncertainties have hitherto not been addressed thoroughly. Here we take one of the best known of them, the Inverse Amplitude Method (IAM), and carefully following its derivation, we quantify the uncertainty introduced at each step. We compare its hadron ChPT and its electroweak sector Higgs EFT applications. We find that the relative theoretical uncertainty of the IAM at the mass of the first resonance encountered in a partial-wave is of the same order in the counting as the starting uncertainty of the EFT at near-threshold energies, so that its unitarized extension should \textit{a priori} be expected to be reasonably successful. This is so provided a check for zeroes of the partial wave amplitude is carried out and, if they appear near the resonance region, we show how to modify adequately the IAM to take them into account.
↳ hep-phnucl-thSciPost Phys.(2021)·29 citations

Affiliations

first authorsco-authorsvia INSPIRE