Nuclear Theory·nucl-th

Friday·December 19, 2014

11 papers—2 primary·9 cross-listed

01
[Submitted on 18 Dec 2014]
Hyperon Puzzle of Neutron Stars with Skyrme Force Models
Yeunhwan Lim🇰🇷 · Chang Ho Hyun🇰🇷 · Kyujin Kwak🇰🇷 · Chang-Hwan Lee🇰🇷
We consider the so called hyperon puzzle of neutron star (NS). We employ Skyrme force models for the description of in-medium nucleon-nucleon, nucleon-Lambda hyperon ( $N Λ$ ), and Lambda-Lambda ( $ΛΛ$ ) interactions. A phenomenological finite-range force for the $ΛΛ$ interaction is considered as well. Equation of state (EoS) of NS matter is obtained in the framework of density functional theory, and Tolman-Oppenheimer-Volkoff equations are solved to obtain the mass-radius relations of NSs. It has been generally known that the existence of hyperons in the NS matter is not well supported by the recent discovery of large-mass NSs ( $M ≃ 2 M_{⊙}$ ) since hyperons make the EoS softer than the one without them. For the selected interaction models, $N Λ$ interactions reduce the maximum mass of NS by about 30~\%, while $ΛΛ$ interactions can give about 10~\% enhancement. Consequently, we find that some Skyrme force models predict the maximum mass of NS consistent with the observation of $2 M_{⊙}$ NSs, and at the same time satisfy observationally constrained mass-radius relations.
Comments:
24 pages, published in International Journal of Modern Physics E
Subjects:
Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1412.5722 [pdf]
IJMPE(2015)·42 citations
02
[Submitted on 18 Dec 2014]
UrQMD Study of the Effects of Centrality Definitions on Higher Moments of Net Protons at RHIC
Gary D. Westfall🇺🇸
A study using UrQMD is presented concerning the higher moments of net protons from Au+Au collisions at 7.7, 11.5, 14.6, 19.6, 27, 39, 62.4, and 200 GeV, concentrating on $C_{4} / C_{2} = κ σ^{2}$ . Higher moments of net protons are predicted to be a sensitive probe of the critical point of QCD. At the QCD critical point, particular ratios of the moments of net protons are predicted to differ from the Poisson baseline. Recently STAR has published the higher moments of net protons for Au+Au collisions at $s_{NN}$ = 7.7, 11.5, 19.6, 27, 39, 62.4, and 200 GeV. UrQMD quantitatively reproduces STAR's measured $C_{4} / C_{2} = κ σ^{2}$ for net protons for all Au+Au collisions more central than 30\% and at all centralities for $s_{NN}$ = 7.7 and 11.5 GeV. The effects are investigated of three different centrality definitions on the values of $C_{4} / C_{2} = κ σ^{2}$ from UrQMD calculations including the impact parameter given by UrQMD. It is shown that using a centrality definition based on multiplicity to calculate the higher moments of net protons gives a biased answer for $C_{4} / C_{2} = κ σ^{2}$ , except in the most central bin (0-5\%).
Comments:
7 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1412.5988 [pdf]
PRC(2015)·17 citations

Affiliations

first authorsco-authorsvia INSPIRE

Hyperon Puzzle of Neutron Stars with Skyrme Force Models

UrQMD Study of the Effects of Centrality Definitions on Higher Moments of Net Protons at RHIC

Affiliations