Nuclear Theory·nucl-th

Monday·March 14, 2016

8 papers—4 primary·4 cross-listed

01
New class of hybrid EoS and Bayesian M-R data analysis
D. Alvarez-Castillo🇷🇺 · A. Ayriyan🇷🇺 · S. Benic🇭🇷 · D. Blaschke🇷🇺 · H. Grigorian🇷🇺 · S. Typel🇩🇪
We explore systematically a new class of two-phase equations of state (EoS) for hybrid stars that is characterized by three main features : (1) stiffening of the nuclear EoS at supersaturation densities due to quark exchange effects (Pauli blocking) between hadrons, modelled by an excluded volume correction, (2) stiffening of the quark matter EoS at high densities due to multiquark interactions and (3) possibility for a strong first order phase transition with an early onset and large density jump. The third feature results from a Maxwell construction for the possible transition from the nuclear to a quark matter phase and its properties depend on the two parameters used for (1) and (2), respectively. Varying these two parameters one obtains a class of hybrid EoS that yields solutions of the Tolman-Oppenheimer-Volkoff (TOV) equations for sequences of hadronic and hybrid stars in the mass-radius diagram which cover the full range of patterns according to the Alford-Han-Prakash classification following which a hybrid star branch can be either absent, connected or disconnected with the hadronic one. The latter case often includes a tiny connected branch. The disconnected hybrid star branch, also called "third family", corresponds to high-mass twin stars characterized by the same gravitational mass but different radii. We perform a Bayesian analysis and demonstrate that the observation of such a pair of high-mass twin stars would have a sufficient discriminating power to favor hybrid EoS with a strong first order phase transition over alternative EoS.
nucl-thastro-ph.HEEPJA(2016)·127 citations
02
Dipole response in neutron-rich nuclei with new Skyrme interactions
H.Zheng · S.Burrello · M.Colonna · V.Baran
We investigate the isoscalar and isovector E1 response of neutron-rich nuclei, within a semi-classical transport model employing effective interactions for the nuclear mean-field. In particular, we adopt the recently introduced SAMi-J Skyrme interactions, whose parameters are specifically tuned to improve the description of spin-isospin properties of nuclei. Our analysis evidences a relevant degree of isoscalar/isovector mixing of the collective excitations developing in neutron-rich systems. Focusing on the low-lying strength emerging in the isovector response, we show that this energy region essentially corresponds to the excitation of isoscalar-like modes, which also contribute to the isovector response owing to their mixed character. Considering effective interactions which mostly differ in the isovector channels, we observe that these mixing effects increase with the slope L of the symmetry energy at saturation density, leading to a larger strength in the low-energy region of the isovector response. This result appears connected to the increase, with L, of the neutron/proton asymmetry at the surface of the considered nuclei, i.e., to the extension of the neutron skin.
nucl-thPRC(2016)·31 citations
03
Simultaneous chiral symmetry restoration and deconfinement - Consequences for the QCD phase diagram
Thomas Klahn🇵🇱 · Tobias Fischer🇵🇱 · Matthias Hempel🇨🇭
For studies of quark matter in astrophysical scenarios the thermodynamic bag model (tdBag) is commonly employed. Although successful, it does not account for dynamical chiral symmetry breaking (D $χ$ SB) and repulsions due to the vector interaction which is crucial to explain recent observations of massive, two solar mass neutron stars. In Klähn & Fischer (2015) we developed the novel vBag quark matter model which takes these effects into account. This article extends vBag to finite temperatures and isospin asymmetry. Another particular feature of vBag is the determination of the deconfinement bag constant $B_{dc}$ from a given hadronic equation of state (EoS) in order to ensure that chiral and deconfinement transitions coincide. We discuss consequences of this novel approach for the phase transition construction, the phase diagram, and implications for protoneutron stars.
nucl-thastro-ph.HEhep-phApJ(2017)·34 citations
04
Time-dependent density functional theory with twist-averaged boundary conditions
B. Schuetrumpf · W. Nazarewicz · P.-G. Reinhard
Time-dependent density functional theory is widely used to describe excitations of many-fermion systems. In its many applications, 3D coordinate-space representation is used, and infinite-domain calculations are limited to a finite volume represented by a box. For finite quantum systems (atoms, molecules, nuclei), the commonly used periodic or reflecting boundary conditions introduce spurious quantization of the continuum states and artificial reflections from boundary; hence, an incorrect treatment of evaporated particles. These artifacts can be practically cured by introducing absorbing boundary conditions (ABC) through an absorbing potential in a certain boundary region sufficiently far from the described system. But also the calculations of infinite matter (crystal electrons, quantum fluids, neutron star crust) suffer artifacts from a finite computational box. In this regime, twist- averaged boundary conditions (TABC) have been used successfully to diminish the finite-volume effects. In this work, we extend TABC to time-dependent framework and apply it to resolve the box artifacts for finite quantum systems using as test case small- and large-amplitude nuclear vibrations. We demonstrate that by using such a method, one can reduce finite volume effects drastically without adding any additional parameters. While they are almost equivalent in the linear regime, TABC and ABC differ in the nonlinear regime in their treatment of evaporated particles.
nucl-thphysics.comp-phPRC(2016)·32 citations
05
Spherical configuration of a super-dense hot compact object with particular EoS
E.P. Tito · V.I. Pavlov
The equation of state (EoS) $P = P (ρ, ...)$ -- pressure as a function of density and other thermodynamical quantities -- is what generates particularities of mass--radius distribution $M (R)$ for super--dense compact stellar bodies, the remnants of cosmic cataclysms. In view of recent nuclear experiments, we propose one particular EoS, which admits the critical state characterized by density $ρ_{c}$ and temperature $T_{c}$ , and which under certain conditions permits a radial distribution of the super--dense matter in "liquid" phase. We establish such conditions and demonstrate that a stable configuration is indeed possible (only) for temperatures smaller than the critical one. Using Tolman--Oppenheimer--Volkoff equations for hydrostatic equilibrium, we derive the mass--radius relation for the super--dense compact objects with masses smaller than the Sun, $M ≪ M_{⊙}$ . The obtained results are within the constraints established by both heavy--ion collision experiments and theoretical studies of neutron--rich matter.
↳ astro-ph.HEnucl-th0 citations
06
Measurements of $d_{2}^{n}$ and $A_{1}^{n}$ : Probing the neutron spin structure
D. Flay · M. Posik · D. S. Parno · K. Allada · W. Armstrong · T. Averett · F. Benmokhtar · W. Bertozzi · A. Camsonne · M. Canan · G. D. Cates · C. Chen and 79 other authors
We report on the results of the E06-014 experiment performed at Jefferson Lab in Hall A, where a precision measurement of the twist-3 matrix element $d_{2}$ of the neutron ( $d_{2}^{n}$ ) was conducted. This quantity represents the average color Lorentz force a struck quark experiences in a deep inelastic electron scattering event off a neutron due to its interaction with the hadronizing remnants. This color force was determined from a linear combination of the third moments of the spin structure functions $g_{1}$ and $g_{2}$ on $^{3}$ He after nuclear corrections had been applied to these moments. The kinematics included two average $Q^{2}$ bins of $3.2$ GeV $^{2}$ and $4.3$ GeV $^{2}$ , and Bjorken- $x$ $0.25 \leq x \leq 0.90$ covering the DIS and resonance regions. We found $d_{2}^{n}$ to be small and negative for $< Q^{2} >= 3.2$ GeV $^{2}$ , and smaller for $< Q^{2} >= 4.3$ GeV $^{2}$ , consistent with a lattice QCD calculation. The twist-4 matrix element $f_{2}^{n}$ was extracted by combining our $d_{2}^{n}$ with the world data on $Γ_{1}^{n} = \int_{0}^{1} g_{1}^{n} d x$ . We found $f_{2}^{n}$ to be roughly an order of magnitude larger than $d_{2}^{n}$ . Utilizing the extracted $d_{2}^{n}$ and $f_{2}^{n}$ data, we separated the color force into its electric and magnetic components, $F_{E}^{y, n}$ and $F_{B}^{y, n}$ , and found them to be equal and opposite in magnitude, in agreement with instanton model predictions but not with those from QCD sum rules. Additionally, we have extracted the neutron virtual photon-nucleon asymmetry $A_{1}^{n}$ , the structure function ratio $g_{1}^{n} / F_{1}^{n}$ , and the quark ratios $(Δ u + Δ u ˉ) / (u + u ˉ)$ and $(Δ d + Δ d ˉ) / (d + d ˉ)$ . These results were found to be consistent with DIS world data and with the prediction of the constituent quark model but at odds with those of perturbative QCD at large $x$ .
↳ nucl-exnucl-thPRD(2016)·64 citations
07
Pion-nucleon scattering in covariant baryon chiral perturbation theory with explicit Delta resonances
De-Liang Yao🇩🇪 · D. Siemens🇩🇪 · V. Bernard🇫🇷 · E. Epelbaum🇩🇪 · A. M. Gasparyan🇩🇪 · J. Gegelia🇩🇪 · H. Krebs🇩🇪 · Ulf-G. Meißner🇩🇪
We present the results of a third order calculation of the pion-nucleon scattering amplitude in a chiral effective field theory with pions, nucleons and delta resonances as explicit degrees of freedom. We work in a manifestly Lorentz invariant formulation of baryon chiral perturbation theory using dimensional regularization and the extended on-mass-shell renormalization scheme. In the delta resonance sector, the on mass-shell renormalization is realized as a complex-mass scheme. By fitting the low-energy constants of the effective Lagrangian to the $S$ - and $P$ -partial waves a satisfactory description of the phase shifts from the analysis of the Roy-Steiner equations is obtained. We predict the phase shifts for the $D$ and $F$ waves and compare them with the results of the analysis of the George Washington University group. The threshold parameters are calculated both in the delta-less and delta-full cases. Based on the determined low-energy constants, we discuss the pion-nucleon sigma term. Additionally, in order to determine the strangeness content of the nucleon, we calculate the octet baryon masses in the presence of decuplet resonances up to next-to-next-to-leading order in SU(3) baryon chiral perturbation theory. The octet baryon sigma terms are predicted as a byproduct of this calculation.
↳ hep-phnucl-thJHEP(2016)·125 citations
08
Properties of single cluster structure of $d^{*} (2380)$ in chiral SU(3) quark model
Qi-Fang Lü🇨🇳 · Fei Huang🇨🇳 · Yu-Bing Dong🇨🇳 · Peng-Nian Shen🇨🇳 · Zong-Ye Zhang🇨🇳
The structure of $d^{*} (2380)$ is re-studied with the single cluster structure in the chiral SU(3) quark model which has successfully been employed to explain the scattering and binding behaviors of baryonic systems. The mass and width are explicitly calculated with two types of trial wave functions. The result shows that the $(0 s)^{6} [6]_{or b}$ configuration is easy to convert to the configuration with the same $[6]_{or b}$ symmetry but $2ℏ ω$ excitation back and forth, however, it is seldom to turn into a two-cluster configuration with a (1s) relative motion in between. The resultant mass and width are about $2394$ MeV and $25$ MeV, respectively, and the stable size is about $0.75 f m$ , which are consistent with both the results in the two-cluster configuration calculation and the data measured by the COSY collaboration. It seems that the observed $d^{*}$ is a six-quark dominated exotic state with a spherical shape and breath mode in the coordinate space. Moreover, if $d^{*}$ does have $2ℏ ω$ excitation, the $d^{*} \to n p π π π$ decay mode might be a good place to distinguish the real structure of the observed phenomenon by COSY. The masses of various isospin-spin states of six-light-quark systems are also computed. It is shown that by considering the coupling with the configurations with $2ℏ ω$ excitations, only the mirror state with $I S$ = $30$ will be lower down to the place where whose mass is slightly higher than the value of the $ΔΔ$ threshold.
↳ hep-phnucl-thPhys. Rev. D 96, 014036 (2017)·1 citation

Affiliations

first authorsco-authorsvia INSPIRE