Nuclear Theory·nucl-th

Friday·January 9, 2015

4 papers—2 primary·2 cross-listed

01
Critical Density and Impact of $Δ (1232)$ Resonance Formation in Neutron Stars
Bao-Jun Cai🇺🇸 · Farrukh J. Fattoyev🇺🇸 · Bao-An Li🇺🇸 · William G. Newton🇺🇸
The critical densities and impact of forming \D resonances in neutron stars are investigated within an extended nonlinear relativistic mean-field (RMF) model. The critical densities for the formation of four different charge states of \D are found to depend differently on the separate kinetic and potential parts of nuclear symmetry energy, the first example of a microphysical property of neutron stars to do so. Moreover, they are sensitive to the in-medium Delta mass $m_{Δ}$ and the completely unknown $Δ$ - $ρ$ coupling strength $g_{ρ Δ}$ . In the universal baryon-meson coupling scheme where the respective $Δ$ -meson and nucleon-meson coupling constants are assumed to be the same, the critical density for the first $Δ^{-} (1232)$ to appear is found to be \rc= $(2.08 \pm 0.02) ρ_{0}$ using RMF model parameters consistent with current constraints on all seven macroscopic parameters usually used to characterize the equation of state (EoS) of isospin-asymmetric nuclear matter (ANM) at saturation density $ρ_{0}$ . Moreover, the composition and the mass-radius relation of neutron stars are found to depend significantly on the values of the $g_{ρ Δ}$ and $m_{Δ}$ .
nucl-thastro-ph.SRnucl-exPRC(2015)·109 citations
02
Parity violation in neutron capture on the proton: determining the weak pion-nucleon coupling
J. de Vries🇩🇪 · N. Li🇩🇪 · Ulf-G. Meißner🇩🇪 · A. Nogga🇩🇪 · E. Epelbaum🇩🇪 · N. Kaiser🇩🇪
We investigate the parity-violating analyzing power in neutron capture on the proton at thermal energies in the framework of chiral effective field theory. By combining this analysis with a previous analysis of parity violation in proton-proton scattering, we are able to extract the size of the weak pion-nucleon coupling constant. The uncertainty is significant and dominated by the experimental error which is expected to be reduced soon.
nucl-thhep-phnucl-exPLB(2015)·18 citations
03
Constraining the density dependence of the nuclear symmetry energy from an X-ray bursting neutron star
Hajime Sotani🇯🇵 · Kei Iida🇯🇵 · Kazuhiro Oyamatsu🇯🇵
Neutrons stars lighter than the Sun are basically composed of nuclear matter of density up to around twice normal nuclear density. In our recent analyses, we showed that possible simultaneous observations of masses and radii of such neutron stars could constrain $η \equiv (K_{0} L^{2})^{1/3}$ , a combination of the incompressibility of symmetric nuclear matter $K_{0}$ and the density derivative of the nuclear symmetry energy $L$ that characterizes the theoretical mass-radius relation. In this paper, we focus on the mass-radius constraint of the X-ray burster 4U 1724-307 given by Suleimanov et al. (2011). We therefrom obtain the constraint that $η$ should be larger than around 130 MeV, which in turn leads to $L$ larger than around 110, 98, 89, and 78 MeV for $K_{0} = 180$ , 230, 280, and 360 MeV. Such a constraint on $L$ is more or less consistent with that obtained from the frequencies of quasi-periodic oscillations in giant flares observed in soft-gamma repeaters.
↳ astro-ph.HEnucl-thPRC(2015)·18 citations
04
Graphene as a Lattice Field Theory
Simon Hands🇬🇧 · Wes Armour🇬🇧 · Costas Strouthos🇨🇾
We introduce effective field theories for the electronic properties of graphene in terms of relativistic fermions propagating in 2+1 dimensions, and outline how strong inter-electron interactions may be modelled by numerical simulation of a lattice field theory. For strong enough coupling an insulating state can form via condensation of particle-hole pairs, and it is demonstrated that this is a theoretical possibility for monolayer graphene. For bilayer graphene the effect of an interlayer bias voltage can be modelled by the introduction of a chemical potential (akin to isopsin chemical potential in QCD) with no accompanying sign problem; simulations reveal the presence of strong interactions among the residual degrees of freedom at the resulting Fermi surface, which is disrupted by an excitonic condensate. We also present preliminary results for the quasiparticle dispersion, which permit direct estimates of both the Fermi momentum and the induced gap.
↳ cond-mat.str-elhep-latnucl-thPoS(2015)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE

Critical Density and Impact of Δ(1232) Resonance Formation in Neutron Stars

Parity violation in neutron capture on the proton: determining the weak pion-nucleon coupling

Constraining the density dependence of the nuclear symmetry energy from an X-ray bursting neutron star

Graphene as a Lattice Field Theory

Affiliations

Critical Density and Impact of $Δ (1232)$ Resonance Formation in Neutron Stars