Nuclear Theory·nucl-th

Thursday·April 25, 2019

12 papers—7 primary·5 cross-listed

01
Quantifying Correlated Truncation Errors in Effective Field Theory
J. A. Melendez🇺🇸 · R. J. Furnstahl🇺🇸 · D. R. Phillips🇺🇸 · M. T. Pratola🇺🇸 · S. Wesolowski🇺🇸
Effective field theories (EFTs) organize the description of complex systems into an infinite sequence of decreasing importance. Predictions are made with a finite number of terms, which induces a truncation error that is often left unquantified. We formalize the notion of EFT convergence and propose a Bayesian truncation error model for predictions that are correlated across the independent variables, e.g., energy or scattering angle. Central to our approach are Gaussian processes that encode both the naturalness and correlation structure of EFT coefficients. Our use of Gaussian processes permits efficient and accurate assessment of credible intervals, allows EFT fits to easily include correlated theory errors, and provides analytic posteriors for physical EFT-related quantities such as the expansion parameter. We demonstrate that model-checking diagnostics---applied to the case of multiple curves---are powerful tools for EFT validation. As an example, we assess a set of nucleon-nucleon scattering observables in chiral EFT. In an effort to be self contained, appendices include thorough derivations of our statistical results. Our methods are packaged in Python code, called gsum, that is available for download on GitHub.
nucl-thhep-phnucl-exphysics.data-anPRC(2019)·189 citations
02
Time-Dependent Density Functional Theory for Fermionic Superfluids: from Cold Atomic Gases, to Nuclei and Neutron Stars Crust
Aurel Bulgac
In cold atoms and in the crust of neutron stars the pairing gap can reach values comparable with the Fermi energy. While in nuclei the neutron gap is smaller, it is still of the order of a few percent of the Fermi energy. The pairing mechanism in these systems is due to short range attractive interactions between fermions and the size of the Cooper pair is either comparable to the inter-particle separation or it can be as big as a nucleus, which is still relatively small in size. Such a strong pairing gap is the result of the superposition of a very large number of particle-particle configurations, which contribute to the formation of the Copper pairs. These systems have been shown to be the host of a large number of remarkable phenomena, in which the large magnitude of the pairing gap plays an essential role: quantum shock waves, quantum turbulence, Anderson-Higgs mode, vortex rings, domain walls, soliton vortices, vortex pinning in neutron star crust, unexpected dynamics of fragmented condensates and role of pairing correlations in collisions on heavy-ions, Larkin-Ovchinnikov phase as an example of a Fermi supersolid, role pairing correlations control the dynamics of fissioning nuclei, self-bound superfluid fermion droplets of extremely low densities.
nucl-thPhys.Status Solidi B(2019)·39 citations
03
Collinear true ternary fission as the consequence of the collective nuclear model
F. F. Karpeshin
The concept of collinear spontaneous true ternary fission of 252Cf is subject to critical analysis. The conclusion is that the collinear flight of the fragments turns out to be a natural and most probable mode. The collinearity arises in the model on the prescission stage as a result of the account of the principles of the collective Bohr's model. It is partly destroyed at the post-scission stage of spreading of the fragments due to their Coulomb interaction, with the allowance for the spin effects arising at the moment of scission. The final angular distribution of the fragments is calculated by means of the trajectory simulations. The calculated relative angle of the heavy and light fragments is kept 180 degrees with an uncertainty within 0.4 degree, which justifies search for a collinear tri-partition at the modern stage of experiment.
nucl-th1 citation
04
Pygmy resonances and symmetry energy
C.A. Bertulani
I present a brief summary of the first three decades of studies of pygmy resonances in nuclei and their relation to the symmetry energy of nuclear matter. I discuss the first experiments and theories dedicated to study the electromagnetic response in halo nuclei and how a low energy peak was initially identified as a candidate for the pygmy resonance. This is followed by the description of a collective state in medium heavy and heavy nuclei which was definitely identified as a pygmy resonance. The role of the slope parameter of the symmetry energy in determining the properties of neutron stars is stressed. The theoretical and experimental information collected on pygmy resonances, neutron skins, and the numerous correlations found with the slope parameter is briefly reviewed.
nucl-thEPJA(2019)·4 citations
05
Nuclear effects in electron- and neutrino-nucleus scattering within a relativistic quantum mechanical framework
Raúl González-Jiménez🇪🇸 · Alexis Nikolakopoulos🇧🇪 · Natalie Jachowicz🇧🇪 · José Manuel Udías🇪🇸
We study the impact of the description of the knockout nucleon wave function on electron- and neutrino-induced quasielastic and single-pion production cross sections. We work in a fully relativistic and quantum mechanical framework, where the relativistic mean-field model is used to describe the target nucleus. The focus is on Pauli blocking and the distortion of the final nucleon, these two nuclear effects are separated and analyzed in detail. We find that a proper quantum mechanical treatment of these effects is crucial to provide the correct magnitude and shape of the inclusive cross section. Also, this seems to be key to predict the right ratio of muon- to electron-neutrino cross sections at very forward scattering angles.
nucl-thPRC(2019)·76 citations
06
Self-consistent band calculation of slab phase in neutron-star crust
Yu Kashiwaba · Takashi Nakatsukasa (University of Tsukuba)
Fully self-consistent band calculation has been performed for slab phase in neutron-star inner crust, using the BCPM energy density functional. Optimized slab structure is calculated at given baryon density either with the fixed proton ratio or with the beta-equilibrium condition. Numerical results indicate the band gap of in order of keV to tens of keV, and the mobility of dripped neutrons are enhanced by the Bragg scattering, which leads to the macroscopic effective mass, $m ˉ_{z}^{*} / m_{n} = 0.65 \sim 0.75$ near the bottom of the inner crust in neutron stars. We also compare the results of the band calculation with those of the Thomas-Fermi approximation. The Thomas-Fermi approximation becomes invalid at low density with high proton ratio.
nucl-thastro-ph.GAPRC(2019)·30 citations
07
Influence of finite volume effect on the Polyakov Quark-Meson model
Niseem Magdy🇺🇸
In the current work, we study the influence of a finite volume on $2 + 1$ $S U (3)$ Polyakov Quark-Meson model (PQM) order parameters, (fluctuations) correlations of conserved charges and the quark-hadron phase boundary. Our study of the PQM model order parameters and the (fluctuations) correlations of conserved charges indicates a sizable shift of the quark-hadron phase boundary to higher values of baryon chemical potential ( $μ_{B}$ ) and temperature ( $T$ ) for decreasing the system volume. The detailed study of such effect could have important implications for the extraction of the (fluctuations) correlations of conserved charges of the QCD phase diagram from heavy ion data.
nucl-thhep-phUniverse(2019)·15 citations
08
Bayesian averaging of computer models with domain discrepancies: a nuclear physics perspective
Vojtech Kejzlar · Léo Neufcourt · Taps Maiti · Frederi Viens
This article studies Bayesian model averaging (BMA) in the context of competing expensive computer models in a typical nuclear physics setup. While it is well known that BMA accounts for the additional uncertainty of the model itself, we show that it also decreases the posterior variance of the prediction errors via an explicit decomposition. We extend BMA to the situation where the competing models are defined on non-identical study regions. Any model's local forecasting difficulty is offset by predictions obtained from the average model, thus extending individual models to the full domain. We illustrate our methodology via pedagogical simulations and applications to forecasting nuclear observables, which exhibit convincing improvements in both the BMA prediction error and empirical coverage probabilities.
↳ stat.MEnucl-thphysics.data-anstat.AP9 citations
09
Measurement of the mass difference and the binding energy of the hypertriton and antihypertriton
STAR Collaboration: J. Adam · L. Adamczyk · J. R. Adams · J. K. Adkins · G. Agakishiev · M. M. Aggarwal · Z. Ahammed · I. Alekseev · D. M. Anderson · R. Aoyama · A. Aparin · D. Arkhipkin and 337 other authors
According to the CPT theorem, which states that the combined operation of charge conjugation, parity transformation and time reversal must be conserved, particles and their antiparticles should have the same mass and lifetime but opposite charge and magnetic moment. Here, we test CPT symmetry in a nucleus containing a strange quark, more specifically in the hypertriton. This hypernucleus is the lightest one yet discovered and consists of a proton, a neutron, and a $Λ$ hyperon. With data recorded by the STAR detector{\cite{TPC,HFT,TOF}} at the Relativistic Heavy Ion Collider, we measure the $Λ$ hyperon binding energy $B_{Λ}$ for the hypertriton, and find that it differs from the widely used value{\cite{B_1973}} and from predictions{\cite{2019_weak, 1995_weak, 2002_weak, 2014_weak}}, where the hypertriton is treated as a weakly bound system. Our results place stringent constraints on the hyperon-nucleon interaction{\cite{Hammer2002, STAR-antiH3L}}, and have implications for understanding neutron star interiors, where strange matter may be present{\cite{Chatterjee2016}}. A precise comparison of the masses of the hypertriton and the antihypertriton allows us to test CPT symmetry in a nucleus with strangeness for the first time, and we observe no deviation from the expected exact symmetry.
↳ hep-exnucl-exnucl-thNat.Phys.(2020)·155 citations
10
Active Learning Algorithm for Computational Physics
Juan Yao · Yadong Wu · Jahyun Koo · Binghai Yan · Hui Zhai
In large-scale computation of physics problems, one often encounters the problem of determining a multi-dimensional function, which can be time-consuming when computing each point in this multi-dimensional space is already time-demanding. In the work, we propose that the active learning algorithm can speed up such calculations. The basic idea is to fit a multi-dimensional function by neural networks, and the key point is to make the query of labeled data economically by using a stratagem called "query by committee". We present the general protocol of this fitting scheme, as well as the procedure of how to further compute physical observables with the fitted functions. We show that this method can work well with two examples, which are quantum three-body problem in atomic physics and the anomalous Hall conductivity in condensed matter physics, respectively. In these examples, we show that one reaches an accuracy of few percent error for computing physical observables with less than $10%$ of total data points compared with uniform sampling. With these two examples, we also visualize that by using the active learning algorithm, the required data are added mostly in the regime where the function varies most rapidly, which explains the mechanism for the efficiency of the algorithm. We expect broad applications of our method on various kind of computational physics problems.
↳ cond-mat.quant-gascond-mat.mtrl-scinucl-thphysics.comp-phPRResearch(2020)·13 citations
11
Saturation momentum scale extracted from semi-inclusive transverse spectra in high-energy pp collisions
Takeshi Osada🇯🇵 · Takuya Kumaoka🇯🇵
Geometric scaling is well confirmed for transverse momentum distributions observed in proton-proton collisions at LHC energies. We introduced multiplicity dependence on a saturation momentum of the geometrical scaling, assuming the scaling holds for semi-inclusive distributions as well as for inclusive distributions. The saturation momentum is usually given by Bjorken's $x$ variable, but redefinition of the scaling variable can make the saturation momentum a function of collision energy $W$ . We treat the energy as a free parameter (denoted $W^{*}$ to distinguish it from $W$ ) and associate the energy-dependent saturation momentum $Q_{sat} (W^{*})$ with particle number density. By using $Q_{sat} (W^{*})$ for a scaling variable $τ$ , we show semi-inclusive distributions can be geometrically scaled. i.e., all semi-inclusive spectra observed at $W$ =0.90, 2.76 and 7.00 TeV overlap one universal function. The particle density dependences of mean transverse momentum $⟨ p_{T} ⟩$ for LHC energies scales in terms of $Q_{sat} (W^{*})$ . Furthermore, our model explains a scaling property of event-by-event $p_{T}$ fluctuation measure $C_{m} / ⟨ p_{T} ⟩$ at LHC energies for pp collisions, where $C_{m}$ is two-particle transverse momentum correlator. Our analysis of the $p_{T}$ fluctuation makes possible to evaluate a non-perturbative coefficient of the gluon correlation function.
↳ hep-phnucl-thPRC(2019)·12 citations
12
R-mode instability in compact stars
Cui Zhu🇨🇳 · Yu-bin Wang🇨🇳 · Xia Zhou🇨🇳
R-mode oscillations have been identified as viable and promising targets for continuous gravitational wave searches, meanwhile, it would allow us to probe the interior of compact stars directly. As well as emitting gravitational wave, r-modes would strongly affect the thermal and spin evolution of compact stars. In this paper, we reviewed the theory behind the gravitational wave driven r-mode instability in a rapidly rotating compact star. In particular, we will focus on r-mode instability window, r-mode evolution and detectability of r-mode.
↳ astro-ph.HEgr-qcnucl-thAIP Conf.Proc.(2019)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE