Nuclear Theory·nucl-th

Thursday·August 24, 2017

11 papers—5 primary·6 cross-listed

01
Towards an understanding of discrete ambiguities in truncated partial wave analyses
Y. Wunderlich · A. Švarc · R. L. Workman · L. Tiator · R. Beck
It is well known that the observables in a single-channel scattering problem remain invariant once the amplitude is multiplied by an overall energy- and angle-dependent phase. This invariance is called the continuum ambiguity and acts on the infinite partial wave set. It has also long been known that, in the case of a truncated partial wave set, another invariance exists, originating from the replacement of the roots of partial wave amplitudes with their complex conjugate values. This discrete ambiguity is also known as the Omelaenko-Gersten-type ambiguity. In this paper, we show that for scalar particles, discrete ambiguities are just a subset of continuum ambiguities with a specific phase and thus mix partial waves, as the continuum ambiguity does. We present the main features of both, continuum and discrete ambiguities, and describe a numerical method which establishes the relevant phase connection.
nucl-thPRC(2017)·17 citations
02
Multipole modes of excitation in triaxially deformed superfluid nuclei
Kouhei Washiyama · Takashi Nakatsukasa
The five-dimensional quadrupole collective model based on energy density functionals (EDF) has often been employed to treat long-range correlations associated with shape fluctuations in nuclei. Our goal is to derive the collective inertial functions in the collective Hamiltonian by the local quasiparticle random phase approximation (QRPA) that correctly takes into account time-odd mean-field effects. Currently, practical framework to perform the QRPA calculation with the modern EDFs on the $(β, γ)$ deformation space is not available. Toward this goal, we develop an efficient numerical method to perform the QRPA calculation on the $(β, γ)$ deformation space based on the Skyrme EDF. We use the finite amplitude method (FAM) for efficient calculation of QRPA strength functions for multipole external fields. We construct a computational code of FAM-QRPA in the three-dimensional Cartesian coordinate space to handle triaxially deformed superfluid nuclei. We validate our new code by comparing our results with former QRPA calculations for axially symmetric nuclei. Isoscalar quadrupole strength functions in triaxial superfluid nuclei, $^{110}$ Ru and $^{190}$ Pt, are obtained within a reasonable computational cost. QRPA calculations for triaxially deformed superfluid nuclei based on the Skyrme EDF are achieved with the help of FAM. This is an important step toward the microscopic calculation of collective inertial functions of the local QRPA.
nucl-thPRC(2017)·16 citations
03
The equation of state for dense nucleonic matter from a metamodeling. I. Foundational aspects
J. Margueron🇺🇸 · R. Hoffmann Casali🇫🇷 · F. Gulminelli🇫🇷
A metamodeling for the nucleonic equation of state (EOS), inspired from a Taylor expansion around the saturation density of symmetric nuclear matter, is proposed and parameterized in terms of the empirical parameters. The present knowledge of nuclear empirical parameters is first reviewed in order to estimate their average values and associated uncertainties, and thus defining the parameter space of the metamodeling. They are divided into isoscalar and isovector type, and ordered according to their power in the density expansion. The goodness of the metamodeling is analyzed against the predictions of the original models. In addition, since no correlation among the empirical parameters is assumed a priori, all arbitrary density dependences can be explored, which might not be accessible in existing functionals. Spurious correlations due to the assumed functional form are also removed. This meta-EOS allows direct relations between the uncertainties on the empirical parameters and the density dependence of the nuclear equation of state and its derivatives, and the mapping between the two can be done with standard Bayesian techniques. A sensitivity analysis shows that the more influential empirical parameters are the isovector parameters $L_{sy m}$ and $K_{sy m}$ , and that laboratory constraints at super-saturation densities are essential to reduce the present uncertainties. The present metamodeling for the EOS for nuclear matter is proposed for further applications in neutron stars and supernova matter.
nucl-thPRC(2018)·331 citations
04
The equation of state for dense nucleonic matter from a meta-modeling. II. Predictions for neutron stars properties
J. Margueron🇺🇸 · R. Hoffmann Casali🇫🇷 · F. Gulminelli🇫🇷
Employing a recently proposed metamodeling for the nucleonic matter equation of state we analyze neutron star global properties such as masses, radii, momentum of inertia, and others. The impact of the uncertainty on empirical parameters on these global properties is analyzed in a Bayesian statistical approach. Physical constraints, such as causality and stability, are imposed on the equation of state and different hypotheses for the direct Urca (dUrca) process are investigated. In addition, only metamodels with maximum masses above 2 $M_{⊙}$ are selected. Our main results are the following: the equation of state exhibits a universal behavior against the dUrca hypothesis under the condition of charge neutrality and $β$ -equilibrium; neutron stars, if composed exclusively of nucleons and leptons, have a radius of 12.7 $\pm$ 0.4~km for masses ranging from 1 up to 2 $M_{⊙}$ ; a small radius lower than 11~km is very marginally compatible with our present knowledge of the nuclear empirical parameters; and finally, the most important empirical parameters which are still affected by large uncertainties and play an important role in determining the radius of neutrons stars are the slope and curvature of the symmetry energy ( $L_{sy m}$ and $K_{sy m}$ ) and, to a lower extent, the skewness parameters ( $Q_{s a t / sy m}$ ).
nucl-thPRC(2018)·200 citations
05
Electric dipole strength and dipole polarizability in $^{48}$ Ca within a fully self-consistent second random-phase approximation
Danilo Gambacurta🇷🇴 · Marcella Grasso🇫🇷 · Olivier Vasseur🇫🇷
The second random-phase-approximation model corrected by a subtraction procedure designed to cure double counting, instabilities, and ultraviolet divergences, is employed for the first time to analyze the dipole strength and polarizability in $^{48}$ Ca. All the terms of the residual interaction are included, leading to a fully self-consistent scheme. Results are illustrated with two Skyrme parametrizations, SGII and SLy4. Those obtained with the SGII interaction are particularly satisfactory. In this case, the low-lying strength below the neutron threshold is extremely well reproduced and the giant dipole resonance is described in a very satisfactory way especially in its spreading and fragmentation. Spreading and fragmentation are produced in a natural way within such a theoretical model by the coupling of 1 particle-1 hole and 2 particle-2 hole configurations. Owing to this feature, we may provide for the electric polarizability as a function of the excitation energy a curve with a similar slope around the centroid energy of the giant resonance compared to the corresponding experimental results. This represents a considerable improvement with respect to previous theoretical predictions obtained with the random-phase approximation or with several ab-initio models. In such cases, the spreading width of the excitation cannot be reproduced and the polarizability as a function of the excitation energy displays a stiff increase around the predicted centroid energy of the giant resonance.
nucl-thnucl-exPLB(2018)·32 citations
06
Revisiting the Equation of State of Hybrid Stars in the Dyson-Schwinger Equation Approach to QCD
Zhan Bai🇨🇳 · Huan Chen🇮🇹 · Yu-xin Liu🇨🇳
We investigate the equation of state(EoS) and the effect of the hadron-quark phase transition of strong interaction matter in compact stars. The hadron matter is described with the relativistic mean field theory,and the quark matter is described with the Dyson-Schwinger equation approach of QCD. The complete EoS of the hybrid star matter is constructed with not only the Gibbs construction but also the 3-window interpolation. The mass-radius relation of hybrid stars is also investigated. We find that, although the EoSs of both the hadron matter with hyperon and $Δ$ -baryon and the quark matter are generally softer than that of the nucleon matter, the 3-window interpolation construction may provide an EoS stiff enough for a hybrid star with mass exceeding 2 $M_{⊙}$ and, in turn, solve the so called "hyperon puzzle".
↳ hep-phastro-ph.HEnucl-thPRD(2018)·24 citations
07
Search for axion-like dark matter through nuclear spin precession in electric and magnetic fields
C. Abel🇬🇧 · N.J. Ayres🇬🇧 · G. Ban🇫🇷 · G. Bison🇨🇭 · K. Bodek🇵🇱 · V. Bondar🇧🇪 · M. Daum🇨🇭 · M. Fairbairn🇬🇧 · V.V. Flambaum🇦🇺 · P. Geltenbort🇫🇷 · K. Green🇬🇧 · W.C. Griffith🇬🇧 and 36 other authors
We report on a search for ultra-low-mass axion-like dark matter by analysing the ratio of the spin-precession frequencies of stored ultracold neutrons and $^{199}$ Hg atoms for an axion-induced oscillating electric dipole moment of the neutron and an axion-wind spin-precession effect. No signal consistent with dark matter is observed for the axion mass range $1 0^{- 24} eV \leq m_{a} \leq 1 0^{- 17} eV$ . Our null result sets the first laboratory constraints on the coupling of axion dark matter to gluons, which improve on astrophysical limits by up to 3 orders of magnitude, and also improves on previous laboratory constraints on the axion coupling to nucleons by up to a factor of 40.
↳ hep-phastro-ph.COnucl-exnucl-th+1PRX(2017)·330 citations
08
Thermodynamic and transport properties in Au + Au collisions at RHIC energies from the clustering of color strings
Pragati Sahoo🇮🇳 · Swatantra Kumar Tiwari🇮🇳 · Sudipan De🇮🇳 · Raghunath Sahoo🇮🇳 · Rolf P. Scharenberg🇺🇸 · Brijesh K. Srivastava🇺🇸
In this work, we have extracted the initial tempearture from the transverse momentum spectra of charged particles in $A u + A u$ collisions using STAR data at RHIC energies from $s_{N N}$ = 7.7 to 200 GeV. The initial energy density ( $ε$ ), shear viscosity to entropy density ratio ( $η / s$ ), trace anomaly ( $Δ$ ), the squared speed of sound ( $C_{s}^{2}$ ), entropy density, and bulk viscosity to entropy density ratio ( $ζ / s$ ) are obtained and compared with the lattice QCD calculations for (2+1) flavor. The initial temperatures obtained are compared with various hadronization and chemical freeze-out temperatures. The analysis of the data shows that the deconfinement to confinement transition possibly takes place between $s_{N N}$ = 11.5 and 19.6 GeV.
↳ hep-phhep-exhep-latnucl-ex+1Mod.Phys.Lett.A(2019)·30 citations
09
Analytic Boosted Boson Discrimination at the Large Hadron Collider
Andrew J. Larkoski🇺🇸 · Ian Moult🇺🇸 · Duff Neill🇺🇸
Jet substructure is playing a central role at the Large Hadron Collider (LHC) probing the Standard Model in extreme regions of phase space and providing innovative ways to search for new physics. Analytic calculations of experimentally successful observables are a primary catalyst driving developments in jet substructure, allowing for a deeper understanding of observables and for the exploitation of increasingly subtle features of jets. In this paper we present a field theoretic framework enabling systematically improvable calculations of groomed multi-prong substructure observables, which builds on recent developments in multi-scale effective theories. We use this framework to compute for the first time the full spectrum for groomed tagging observables at the LHC, carefully treating both perturbative and non-perturbative contributions in all regions. Our analysis enables a precision understanding which we hope will improve the reach and sophistication of jet substructure techniques at the LHC.
↳ hep-phnucl-th40 citations
10
$D D^{*}$ potentials in chiral perturbation theory and possible molecular states
Hao Xu🇨🇳 · Bo Wang🇨🇳 · Zhan-Wei Liu🇨🇳 · Xiang Liu🇨🇳
The $D D^{*}$ potentials are studied within the framework of heavy meson chiral effective field theory. We obtain the effective potentials of the $D D^{*}$ system up to $O (ϵ^{2})$ at the one-loop level. In addition to the one-pion exchange contribution, the contact and two-pion exchange interactions are also investigated in detail. Furthermore, we search for the possible molecular states by solving the Schrödinger equation with the potentials. We notice that the contact and two-pion exchange potentials are numerically non-negligible and important for the existence of a bound state. In our results, no bound state is found in the $I = 1$ channel within a wide range of cutoff parameter, while there exists a bound state in the $I = 0$ channel as the cutoff is near $m_{ρ}$ in our approach.
↳ hep-phhep-exhep-latnucl-thPRD(2019)·73 citations
11
Interplay between chiral symmetry breaking and the QCD Kondo effect
Kei Suzuki🇯🇵 · Shigehiro Yasui🇯🇵 · Kazunori Itakura🇯🇵
We investigate the interplay between the (light-light quark) chiral condensate and heavy-light quark condensate induced by the QCD Kondo effect, which is described by an effective Lagrangian with four-point interactions and the mean-field approximation. We find that the appearance of Kondo condensates decreases the critical chemical potential of the chiral condensate. In the region near the critical chemical potential, a coexistence phase with two kinds of condensates can appear. The behavior of such an interplay at finite temperature and with nonzero current light-quark mass is also discussed.
↳ hep-phnucl-thPRD(2017)·19 citations

Affiliations

first authorsco-authorsvia INSPIRE