Nuclear Theory·nucl-th

Tuesday·November 21, 2017

19 papers—14 primary·5 cross-listed

01
Causality of fluid dynamics for high-energy nuclear collisions
Stefan Floerchinger🇩🇪 · Eduardo Grossi🇩🇪
Dissipative relativistic fluid dynamics is not always causal and can favor superluminal signal propagation under certain circumstances. On the other hand, high-energy nuclear collisions have a microscopic description in terms of QCD and are expected to follow the causality principle of special relativity. We discuss under which conditions the fluid evolutions for a radial expansion are hyperbolic and how the properties of the solutions are encoded in the associated characteristic curves. The expansion dynamics is causal in relativistic sense if the characteristic velocities are smaller than the speed of light. We obtain a concrete inequality from this constraint and discuss how it can be violated for certain initial conditions. We argue that causality poses a bound to the applicability of relativistic fluid dynamics. }
nucl-thhep-phJHEP(2018)·45 citations
02
Scaling within the Spectral Function approach
J. E. Sobczyk🇪🇸 · N. Rocco🇬🇧 · A. Lovato🇺🇸 · J. Nieves🇪🇸
Scaling features of the nuclear electromagnetic response functions unveil aspects of nuclear dynamics that are crucial for interpretating neutrino- and electron-scattering data. In the large momentum-transfer regime, the nucleon-density response function defines a universal scaling function, which is independent of the nature of the probe. In this work, we analyze the nucleon-density response function of $^{12}$ C, neglecting collective excitations. We employ particle and hole spectral functions obtained within two distinct many-body methods, both widely used to describe electroweak reactions in nuclei. We show that the two approaches provide compatible nucleon-density scaling functions that for large momentum transfers satisfy first-kind scaling. Both methods yield scaling functions characterized by an asymmetric shape, although less pronounced than that of experimental scaling functions. This asymmetry, only mildly affected by final state interactions, is mostly due to nucleon-nucleon correlations, encoded in the continuum component of the hole SF.
nucl-thhep-exnucl-exPRC(2018)·12 citations
03
Energy dependence of non-local potentials
A.E. Lovell · P.-L. Bacq · P. Capel · F.M. Nunes · L.J. Titus
Recently a variety of studies have shown the importance of including non-locality in the description of reactions. The goal of this work is to revisit the phenomenological approach to determining non-local optical potentials from elastic scattering. We perform a $χ^{2}$ analysis of neutron elastic scattering data off $^{40}$ Ca, $^{90}$ Zr and $^{208}$ Pb at energies $E \approx 5 - 40$ MeV, assuming a Perey and Buck or Tian, Pang, and Ma non-local form for the optical potential. We introduce energy and asymmetry dependencies in the imaginary part of the potential and refit the data to obtain a global parameterization. Independently of the starting point in the minimization procedure, an energy dependence in the imaginary depth is required for a good description of the data across the included energy range. We present two parameterizations, both of which represent an improvement over the original potentials for the fitted nuclei as well as for other nuclei not included in our fit. Our results show that, even when including the standard Gaussian non-locality in optical potentials, a significant energy dependence is required to describe elastic-scattering data.
nucl-thnucl-exPRC(2017)·22 citations
04
Methodology study of machine learning for the neutron star equation of state
Yuki Fujimoto🇯🇵 · Kenji Fukushima🇯🇵 · Koichi Murase🇯🇵
We discuss a methodology of machine learning to deduce the neutron star equation of state from a set of mass-radius observational data. We propose an efficient procedure to deal with a mapping from finite data points with observational errors onto an equation of state. We generate training data and optimize the neural network. Using independent validation data (mock observational data) we confirm that the equation of state is correctly reconstructed with precision surpassing observational errors. We finally discuss the relation between our method and Bayesian analysis with an emphasis put on generality of our method for underdetermined problems.
nucl-thastro-ph.HEhep-phPRD(2018)·77 citations
05
Container evolution for cluster structures in $^{16} O$
Y. Funaki
Background: $α +^{12} C$ clustering in $^{16} O$ has been of historical importance in nuclear clustering. In the last 15 years the $4 α$ condensate state has been proposed as a new-type cluster state. Purpose: The aim is to reveal a dynamical process of the formation of different kinds of cluster states, in terms of a "container" aspect of clusters, in $^{16} O$ . Method: The so-called THSR wave function for the $4 α$ clusters is extended to inclusion of two different containers occupied independently by the $^{12} C$ $(3 α)$ and $α$ clusters. Results: The five $J^{π} = 0^{+}$ states with $4 α$ tetrahedral shape, $α +^{12} C$ cluster structures, and the $4 α$ condensate character, are found to be represented, to good approximation, by single configurations of the extended THSR wave function with containers of appropriate shape and size. Conclusions: It is demonstrated in $^{16} O$ that the dynamical evolution of cluster structures can be caused by size and shape evolution of a container occupied with clusters. The $α$ condensate with gaslike $4 α$ configuration appears as a limit of the cluster formation.
nucl-thnucl-exPRC(2018)·31 citations
06
Nucleosynthesis of transuranium nuclides under conditions of Mike, Par and Barbell thermonuclear explosions
Yu.S. Lutostansky · V.I. Lyashuk
The creation of transuranium nuclides under pulsed neutron fluxes of thermonuclear explosions is investigated within the kinetic model of the astrophysical r process, taking into account the time dependence of the external parameters and the processes accompanying the beta decay of neutron-rich nuclei. Time-dependent neutron fluxes in the interval ~ 10e-6 s were modeled within the framework of the developed adiabatic binary model. The probabilities of beta-delayed processes were calculated on the base of the microscopic theory of finite Fermi systems. Calculations of transuranium nuclides yields Y(A) are made for three experimental USA thermonuclear explosions "Mike" (YM), "Par" (YP) and "Barbel" (YB). The root-mean-square deviations of the calculations compare to the experimental data (r.m.s.) are 91% for YM, 33% for YP, 29% for YB , which are significantly lower than for other known calculations. The exponential approximation of the experimental dependences Y(A) is carried out and the obtained values of r.m.s are equal to 56%, 86.8% and 60.2% for YM, YP and YB correspondingly, which is better or comparable with other calculations. An even-odd anomaly in the observed yields of heavy nuclei is explained by the predominant influence of processes accompanying the beta decay of heavy neutron-excess isotopes.
nucl-th0 citations
07
Toward electrodynamics of unconventional phases of dilute nuclear matter
Armen Sedrakian (FIAS) · John W. Clark (Washington U., St. Louis)
The phase diagram of isospin-asymmetrical nuclear matter may feature a number of unconventional phases, which include the translationally and rotationally symmetric, but isospin-asymmetrical BCS condensate, the current-carrying Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase, and the heterogeneous phase-separated phase. Because the Cooper pairs of the condensate carry a single unit of charge, these phases are charged superconductors and respond to electromagnetic gauge fields by either forming domains (type-I superconductivity) or quantum vortices (type-II superconductivity). We evaluate the Ginzburg-Landau (GL) parameter across the phase diagram and find that the unconventional phases of isospin-asymmetrical nuclear matter are good type-II superconductors and should form Abrikosov vortices with twice the quantum of magnetic flux. We also find that the LOFF phase at the boundary of the transition to the type-I state, with the GL parameter being close to the critical value $1/ 2$ .
nucl-thastro-ph.HEcond-mat.quant-gascond-mat.supr-conJ.Phys.Conf.Ser.(2018)·1 citation
08
New quasibound states of the compound nucleus in $α$ -particle capture by the nucleus
Sergei P. Maydanyuk (1 and2) · Peng-Ming Zhang (1) · Li-Ping Zou (1) ((1) Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, 730000, China, (2) Institute for Nuclear Research, National Academy of Sciences of Ukraine, Kiev, 03680, Ukraine)
We generalize the theory of nuclear decay and capture of Gamow that is based on tunneling through the barrier and internal oscillations inside the nucleus. In our formalism an additional factor is obtained, which describes distribution of the wave function of the $α$ particle inside the nuclear region. We discover new most stable states (called quasibound states) of the compound nucleus (CN) formed during the capture of $α$ particle by the nucleus. With a simple example, we explain why these states cannot appear in traditional calculations of the $α$ capture cross sections based on monotonic penetrabilities of a barrier, but they appear in a complete description of the evolution of the CN. Our result is obtained by a complete description of the CN evolution, which has the advantages of (1) a clear picture of the formation of the CN and its disintegration, (2) a detailed quantum description of the CN, (3) tests of the calculated amplitudes based on quantum mechanics (not realized in other approaches), and (4) high accuracy of calculations (not achieved in other approaches). These peculiarities are shown with the capture reaction of $α +^{44} Ca$ . We predict quasibound energy levels and determine fusion probabilities for this reaction. The difference between our approach and theory of quasistationary states with complex energies applied for the $α$ capture is also discussed. We show (1) that theory does not provide calculations for the cross section of $α$ capture (according to modern models of the $α$ capture), in contrast with our formalism, and (2) these two approaches describe different states of the $α$ capture (for the same $α$ -nucleus potential).
nucl-thhep-phnucl-exPRC(2017)·13 citations
09
Ab initio Translationally Invariant Nonlocal One-body Densities from No-core Shell-model Theory
M. Burrows · Ch. Elster · G. Popa · K.D. Launey · A. Nogga · P. Maris
[Background:] It is well known that effective nuclear interactions are in general nonlocal. Thus if nuclear densities obtained from {\it ab initio} no-core-shell-model (NCSM) calculations are to be used in reaction calculations, translationally invariant nonlocal densities must be available. [Purpose:] Though it is standard to extract translationally invariant one-body local densities from NCSM calculations to calculate local nuclear observables like radii and transition amplitudes, the corresponding nonlocal one-body densities have not been considered so far. A major reason for this is that the procedure for removing the center-of-mass component from NCSM wavefunctions up to now has only been developed for local densities. [Results:] A formulation for removing center-of-mass contributions from nonlocal one-body densities obtained from NCSM and symmetry-adapted NCSM (SA-NCSM) calculations is derived, and applied to the ground state densities of $^{4}$ He, $^{6}$ Li, $^{12}$ C, and $^{16}$ O. The nonlocality is studied as a function of angular momentum components in momentum as well as coordinate space [Conclusions:] We find that the nonlocality for the ground state densities of the nuclei under consideration increases as a function of the angular momentum. The relative magnitude of those contributions decreases with increasing angular momentum. In general, the nonlocal structure of the one-body density matrices we studied is given by the shell structure of the nucleus, and can not be described with simple functional forms.
nucl-thPRC(2018)·24 citations
10
Eigenvector continuation with subspace learning
Dillon Frame🇺🇸 · Rongzheng He🇺🇸 · Ilse Ipsen🇺🇸 · Daniel Lee🇺🇸 · Dean Lee🇺🇸 · Ermal Rrapaj🇨🇦
A common challenge faced in quantum physics is finding the extremal eigenvalues and eigenvectors of a Hamiltonian matrix in a vector space so large that linear algebra operations on general vectors are not possible. There are numerous efficient methods developed for this task, but they generally fail when some control parameter in the Hamiltonian matrix exceeds some threshold value. In this work we present a new technique called eigenvector continuation that can extend the reach of these methods. The key insight is that while an eigenvector resides in a linear space with enormous dimensions, the eigenvector trajectory generated by smooth changes of the Hamiltonian matrix is well approximated by a very low-dimensional manifold. We prove this statement using analytic function theory and propose an algorithm to solve for the extremal eigenvectors. We benchmark the method using several examples from quantum many-body theory.
nucl-thcond-mat.str-elcs.NAhep-lat+2PRL(2018)·181 citations
11
New trial wave function for nuclear cluster structure of nuclei
Bo Zhou🇯🇵
A new trial wave function is proposed for nuclear physics, in which an exact solution to the long-standing center-of-mass problem is given. In the new approach, the widths of the single-nucleon Gaussian wave packets and the widths of the relative Gaussian wave functions describing correlations of nucleons or clusters are treated as variables in the explicit intrinsic wave function of the nuclear system. As an example, this new wave function was applied to study the typical $^{20} Ne$ ( $α$ + $^{16} O$ ) cluster system. By removing exactly the spurious center-of-mass effect in a very simple way, the energy curve of $^{20} Ne$ was obtained by the variational calculations with the width of $α$ cluster, the width of $^{16} O$ cluster, and the size parameter of the nucleus. They are considered as the three crucial variational variables in describing the $^{20} Ne$ ( $α$ + $^{16} O$ ) cluster system. This shows that the new wave function can be a very interesting new tool for studying many-body and cluster effects in nuclear physics.
nucl-thPTEP(2018)·6 citations
12
Borromean Feshbach resonance in 11Li studied via 11Li(p,p')
Takuma Matsumoto · Junki Tanaka · Kazuyuki Ogata
A dipole resonance of 11Li is newly found by a 9Li + n + n three-body model analysis with the complex-scaling method. The resonance can be interpreted as a bound state in the 10Li + n system, that is, a Feshbach resonance in the 9Li + n + n system. As a characteristic feature of the Feshbach resonance of 11Li, the 10Li + n threshold is open above the 9Li + n + n one, which reflects a distinctive property of the Borromean system. A microscopic four-body reaction calculation for the 11Li(p,p') reaction at 6 MeV/nucleon is performed by taking into account the resonance and nonresonant continuum states of the three-body system. The angular distribution of the elastic and inelastic scattering as well as the breakup energy spectrum recently observed are reproduced well.
nucl-thPTEP(2019)·13 citations
13
Critical point of nuclear matter and beam energy dependence of net proton number fluctuations
Volodymyr Vovchenko🇩🇪 · Lijia Jiang🇩🇪 · Mark I. Gorenstein🇺🇦 · Horst Stoecker🇩🇪
The beam energy dependence of net baryon number susceptibilities is studied in the framework of the hadron resonance gas model with the attractive and repulsive van der Waals interactions between baryons. The collision energy dependences for the skewness $S σ$ and kurtosis $κ σ^{2}$ deviate significantly from the Poisson baseline and demonstrate the existence of rich structures at moderate collision energies. This behavior may result from the critical end point of the nuclear liquid-gas first order phase transition. In particular, $κ σ^{2}$ shows a non-monotonic energy dependence, and, in contrast to the standard scenario for the QCD critical point, it does not decrease at low collision energies. It is also found that the measurable net proton fluctuations differ significantly from the net baryon fluctuations when interactions between baryons cannot be neglected. The results are compared with the experimental net proton number fluctuations measured by the STAR collaboration.
nucl-thhep-phnucl-exPRC(2018)·37 citations
14
Evidence of the QCD tricritical endpoint existence at NICA-FAIR energies
K. A. Bugaev🇺🇦 · R. Emaus🇳🇴 · V. V. Sagun🇺🇦 · A. I. Ivanytskyi🇺🇦 · L. V. Bravina🇳🇴 · D. B. Blaschke🇵🇱 · E. G. Nikonov🇷🇺 · A. V. Taranenko🇷🇺 · E. E. Zabrodin🇳🇴 · G. M. Zinovjev🇺🇦
We present a summary of possible signals of the chiral symmetry restoration and deconfinement phase transitions which may be, respectively, probed at the center of mass collision energies at 4.3-4.9 GeV and above 8.7-9.2 GeV. It is argued that these signals may evidence for an existence of the tricritical endpoint of QCD phase diagram at the collision energy around 8.7-9.2 GeV. The equation of state of hadronic matter with the restored chiral symmetry is discussed and the number of bosonic and fermionic degrees of freedom is found.
nucl-thKnE Energ.Phys.(2018)·3 citations
15
Baryon interactions from lattice QCD with physical masses --- strangeness $S = - 1$ sector ---
Hidekatsu Nemura🇯🇵 · Sinya Aoki🇯🇵 · Takumi Doi🇯🇵 · Shinya Gongyo🇯🇵 · Tetsuo Hatsuda🇯🇵 · Yoichi Ikeda🇯🇵 · Takashi Inoue🇯🇵 · Takumi Iritani🇯🇵 · Noriyoshi Ishii🇯🇵 · Takaya Miyamoto🇯🇵 · Kenji Sasaki🇯🇵
We present our recent results of baryon interactions with strangeness $S = - 1$ based on Nambu-Bethe-Salpeter (NBS) correlation functions calculated from lattice QCD with almost physical quark masses corresponding to $(m_{π}, m_{K}) \approx (146, 525)$ MeV and large volume $(L a)^{4} = (96 a)^{4} \approx$ (8.1 fm) $^{4}$ . In order to perform a comprehensive study of baryon interactions, a large number of NBS correlation functions from NN to $ΞΞ$ are calculated simultaneously by using large scale computer resources. In this contribution, we focus on the strangeness $S = - 1$ channels of the hyperon interactions by means of HAL QCD method. Four sets of three potentials (the $^{3} S_{1} -^{3} D_{1}$ central, $^{3} S_{1} -^{3} D_{1}$ tensor, and the $^{1} S_{0}$ central potentials) are presented for the $Σ N - Σ N$ (the isospin $I = 3/2$ ) diagonal, the $Λ N - Λ N$ diagonal, the $Λ N \to Σ N$ transition, and the $Σ N - Σ N$ ( $I = 1/2$ ) diagonal interactions. Scattering phase shifts for $Σ N$ $(I = 3/2)$ system are presented.
↳ hep-latnucl-thEPJ Web Conf.(2018)·35 citations
16
Metric anisotropies and emergent anisotropic hydrodynamics
Ashutosh Dash · Amaresh Jaiswal
Expansion of a locally equilibrated fluid is considered in an anisotropic space-time given by Bianchi type I metric. Starting from isotropic equilibrium phase-space distribution function in the local rest frame, we obtain expressions for components of the energy-momentum tensor and conserved current, such as number density, energy density and pressure components. In the case of an axis-symmetric Bianchi type I metric, we show that they are identical to that obtained within the setup of anisotropic hydrodynamics. We further consider the case when Bianchi type I metric is a vacuum solution of Einstein equation: the Kasner metric. For axis-symmetric Kasner metric, we discuss the implications of our results in the context of anisotropic hydrodynamics.
↳ gr-qcnucl-thPRD(2018)·9 citations
17
First extraction of the scalar proton dynamical polarizabilities from real Compton scattering data
B. Pasquini (1, 2)🇮🇹 · P. Pedroni (2)🇮🇹 · S. Sconfietti (1, 2) ((1) U. Pavia, (2) INFN, Pavia)🇮🇹
We present the first attempt to extract the scalar dipole dynamical polarizabilities from proton real Compton scattering data below pion-production threshold. The theoretical framework combines dispersion relations technique, low-energy expansion and multipole decomposition of the scattering amplitudes. The results are obtained with statistical tools that have never been applied so far to Compton scattering data and are crucial to overcome problems inherent to the analysis of the available data set.
↳ hep-phhep-exnucl-exnucl-thPRC(2018)·27 citations
18
The state of matter in simulations of core-collapse supernovae -- Reflections and recent developments
Tobias Fischer🇵🇱 · Niels-Uwe Bastian🇵🇱 · David Blaschke🇵🇱 · Mateusz Cierniak🇵🇱 · Matthias Hempel🇨🇭 · Thomas Klähn · Gabriel Martínez-Pinedo🇩🇪 · William G. Newton🇺🇸 · Gerd Röpke🇷🇺 · Stefan Typel🇩🇪
In this review article we discuss selected developments regarding the role of the equation of state (EOS) in simulations of core-collapse supernovae. There are no first-principle calculations of the state of matter under supernova conditions since a wide range of conditions is covered, in terms of density, temperature and isospin asymmetry. Instead, model EOS are commonly employed in supernova studies. These can be divided into regimes with intrinsically different degrees of freedom: heavy nuclei at low temperatures, inhomogeneous nuclear matter where light and heavy nuclei coexist together with unbound nucleons, and the transition to homogeneous matter at high densities and temperatures. In this article we discuss each of these phases with particular view on their role in supernova simulations.
↳ astro-ph.HEnucl-thPubl.Astron.Soc.Austral.(2017)·49 citations
19
Quasiparticle anisotropic hydrodynamics for ultrarelativistic heavy-ion collisions
Mubarak Alqahtani🇺🇸 · Mohammad Nopoush🇺🇸 · Radoslaw Ryblewski🇵🇱 · Michael Strickland🇺🇸
In this proceedings contribution, we will review the basics of quasiparticle anisotropic hydrodynamics. Then, we will present some recent phenomenological results of 3+1d quasiparticle anisotropic hydrodynamics and Pb-Pb $2.76$ TeV collisions from the ALICE collaboration. We show that 3+1d quasiparticle anisotropic hydrodynamics model is able to describe the experimental results for Pb-Pb collisions at $2.76$ TeV quite well for many observables such as the spectra, the elliptic flow, and HBT radii in many centrality classes.
↳ hep-phnucl-thPoS(2018)·2 citations

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