Nuclear Theory·nucl-th

Monday·January 16, 2017

10 papers—6 primary·4 cross-listed

07
Millisecond radio pulsars with known masses: parameter values and equation of state models
Sudip Bhattacharyya (TIFR, India) · Ignazio Bombaci (Universita di Pisa / INFN, Italy) · Debades Bandyopadhyay (SINP, India) · Arun V. Thampan (St. Joseph's College / IUCAA, India) · Domenico Logoteta (INFN, Italy)
The recent fast growth of a population of millisecond pulsars with precisely measured mass provides an excellent opportunity to characterize these compact stars at an unprecedented level. This is because the stellar parameter values can be accurately computed for known mass and spin rate and an assumed equation of state (EoS) model. For each of the 16 such pulsars and for a set of EoS models from nucleonic, hyperonic, strange quark matter and hybrid classes, we numerically compute fast spinning stable stellar parameter values considering the full effect of general relativity. This first detailed catalogue of the computed parameter values of observed millisecond pulsars provides a testbed to probe the physics of compact stars, including their formation, evolution and EoS. We estimate uncertainties on these computed values from the uncertainty of the measured mass, which could be useful to quantitatively constrain EoS models. We note that the largest value of the central density $ρ_{c}$ in our catalogue is $\sim 5.8$ times the nuclear saturation density $ρ_{sat}$ , which is much less than the expected maximum value $13 ρ_{sat}$ . We argue that the $ρ_{c}$ -values of at most a small fraction of compact stars could be much larger than $5.8 ρ_{sat}$ . Besides, we find that the constraints on EoS models from accurate radius measurements could be significantly biased for some of our pulsars, if stellar $s p innin g$ configurations are not used to compute the theoretical radius values.
↳ astro-ph.HEgr-qcnucl-thNew Astron.(2017)·22 citations
08
Chiral phase structure of three flavor QCD at vanishing baryon number density
A. Bazavov🇺🇸 · H.-T. Ding🇨🇳 · P. Hegde🇮🇳 · F. Karsch🇺🇸 · E. Laermann🇩🇪 · Swagato Mukherjee🇺🇸 · P. Petreczky🇺🇸 · C. Schmidt🇩🇪
We investigate the phase structure of QCD with 3 degenerate quark flavors as function of the degenerate quark masses at vanishing baryon number density. We use the Highly Improved Staggered Quarks on lattices with temporal extent $N_{t} = 6$ and perform calculations for six values of quark masses, which in the continuum limit correspond to pion masses in the range $80 MeV ≲ m_{π} ≲ 230$ MeV. By analyzing the volume and temperature dependence of the chiral condensate and chiral susceptibility we find no direct evidence for a first order phase transition in this range of pion mass values. Relying on the universal scaling behaviors of the chiral observables near an anticipated chiral critical point, we estimate an upper bound for the critical pion mass, $m_{π}^{c} ≲$ 50 MeV, below which a region of first order chiral phase transition is favored.
↳ hep-lathep-thnucl-thPRD(2017)·91 citations
09
Mesonic and nucleon fluctuation effects at finite baryon density
G. Fejos🇯🇵 · A. Hosaka🇯🇵
Mesonic and nucleon fluctuation effects are investigated in medium. We couple the nucleon field to the $2 + 1$ flavor meson model and investigate the finite temperature and density behavior of the system, in particular, the axial anomaly function. Somewhat contrary to earlier expectations we find that it tends to strengthen at finite density. At lower temperatures nucleon density fluctuations can cause a relative difference in the $U_{A} (1)$ axial anomaly of about $20%$ . This has important consequences on the mesonic spectra, especially on the $η - η^{'}$ system, as we observe no drop in the $η^{'}$ mass as a function of the baryochemical potential, irrespective of the temperature. Based on the details of chiral symmetry restoration, it is argued that there has to be a competition between underlying QCD effects of the anomaly and fluctuations of the low energy hadronic degrees of freedom, and the fate of the $U_{A} (1)$ coefficient should be decided by taking into account both effects simultaneously.
↳ hep-phnucl-thPRD(2017)·15 citations
10
Nucleon resonances $N (1875)$ and $N (2100)$ as strange partners of LHCb pentaquarks
Jun He🇨🇳
In this work, we investigate the possibility of interpreting two nucleon resonances, the $N (1875)$ and the $N (2100)$ , as hadronic molecular states from the $Σ^{*} K$ and $Σ K^{*}$ interactions, respectively. With the help of effective Lagrangians in which coupling constants are determined by the SU(3) symmetry, the $Σ^{*} K$ and $Σ K^{*}$ interactions are described by the vector-meson and pseudoscalar-meson exchanges. With the one-boson-exchange potential obtained, bound states from the $Σ^{*} K$ and $Σ K^{*}$ interactions are searched for in a quasipotential Bethe-Saltpeter equation approach. A bound state with quantum number $I (J^{P}) = 1/2 (3/ 2^{-})$ is produced from the $Σ^{*} K$ interaction, which can be identified as the $N (1875)$ listed in PDG. It can be seen as a strange partner of the LHCb pentaquark $P_{c} (4380)$ with the same quantum numbers in the molecular state picture. The $Σ K^{*}$ interaction also produces a bound state with quantum number $I (J^{P}) = 1/2 (3/ 2^{-})$ , which is related to experimentally observed $N (2100)$ in the $ϕ$ photoproduction. Our results suggest that the $N (2120)$ observed in the $K Λ (1520)$ photoproduction and the $N (2100)$ observed in the $ϕ$ photoproduction have different origins. The former is a conventional three-quark state while the latter is a $Σ K^{*}$ molecular state, which can be seen as a strange partner of the $P_{c} (4450)$ with different spin parity.
↳ hep-phhep-exnucl-exnucl-thPRD(2017)·69 citations

Affiliations

first authorsco-authorsvia INSPIRE

Millisecond radio pulsars with known masses: parameter values and equation of state models

Chiral phase structure of three flavor QCD at vanishing baryon number density

Mesonic and nucleon fluctuation effects at finite baryon density

Nucleon resonances N(1875) and N(2100) as strange partners of LHCb pentaquarks

Affiliations

Nucleon resonances $N (1875)$ and $N (2100)$ as strange partners of LHCb pentaquarks