Fri·Jul 15, 2011Friday·July 15, 2011

1. 01*

   Proton fraction in the inner neutron-star crust

   J. Piekarewicz🇺🇸 · G. Toledo Sanchez🇲🇽

   Monte Carlo simulations of neutron-rich matter of relevance to the inner neutron-star crust are performed for a system of A=5,000 nucleons. To determine the proton fraction in the inner crust, numerical simulations are carried out for a variety of densities and proton fractions. We conclude---as others have before us using different techniques---that the proton fraction in the inner stellar crust is very small. Given that the purported "nuclear pasta" phase in stellar crusts develops as a consequence of the long-range Coulomb interaction among protons, we question whether pasta formation is possible in such proton-poor environments. To answer this question, we search for physical observables sensitive to the transition between spherical nuclei and exotic pasta structures. Of particular relevance is the static structure factor S(k)---an observable sensitive to density fluctuations. However, no dramatic behavior was observed in S(k). We regard the identification of physical observables sensitive to the existence---or lack-thereof---of a pasta phase in proton-poor environments as an open problem of critical importance.

   ↳ nucl-thastro-ph.SRnucl-exPRC(2012)·30 citations
2. 02*

   Revealing baryon number fluctuations from proton number fluctuations in relativistic heavy ion collisions

   Masakiyo Kitazawa🇯🇵 · Masayuki Asakawa🇯🇵

   Baryon number cumulants are invaluable tools to diagnose the primordial stage of heavy ion collisions if they can be measured. In experiments, however, proton number cumulants have been measured as substitutes. In fact, proton number fluctuations are further modified in the hadron phase and different from those of baryon number. We show that the isospin distribution of nucleons at kinetic freezeout is binomial and factorized. This leads to formulas that express the baryon number cumulants sorely in terms of proron number fluctuations, which are experimentally observable.

   ↳ nucl-thhep-phnucl-exPRC(2012)·155 citations
3. 03*

   Shear viscosity to entropy density ratio in the Boltzmann-Uehling-Uhlenbeck model

   S. X. Li🇨🇳 · D. Q. Fang🇨🇳 · Y. G. Ma🇨🇳 · C. L. Zhou🇨🇳

   The ratio of shear viscosity ($\eta$) to entropy density ($s$) for an equilibrated system is investigated in intermediate energy heavy ion collisions below 100$A$ MeV within the framework of the Boltzmann-Uehling-Uhlenbeck (BUU) model . After the collision system almost reaches a local equilibration, the temperature, pressure and energy density are obtained from the phase space information and {$\eta /s$} is calculated using the Green-Kubo formulas. The results show that {$\eta$}/$s$ decreases with incident energy and tend towards a smaller value around 0.5, which is not so drastically different from the BNL Relativistic Heavy Ion Collider results in the present model.

   ↳ nucl-thhep-phnucl-exPRC(2011)·24 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.