Nuclear Theory·nucl-th

Thursday·September 20, 2018

8 papers—4 primary·4 cross-listed

05
A new parametrization for the scalar pion form factors
Stefan Ropertz🇩🇪 · Christoph Hanhart🇩🇪 · Bastian Kubis🇩🇪
We derive a new parametrization for the scalar pion form factors that allows us to analyze data over a large energy range via the inclusion of resonances, and at the same time to ensure consistency with the high-accuracy dispersive representations available at low energies. As an application the formalism is used to extract resonance properties of excited scalar mesons from data for $B ˉ_{s}^{0} \to J / ψ π π$ . In particular we find for the pole positions of $f_{0} (1500)$ and $f_{0} (2020)$ $1465 \pm 18 - i (50 \pm 9) MeV$ and $1910 \pm 50 - i (199 \pm 40) MeV$ , respectively. In addition, from their residues we calculate the respective branching ratios into $π π$ to be $(58 \pm 31) %$ and $(1.3 \pm 1.8) %$ .
↳ hep-phhep-exnucl-thEPJC(2018)·90 citations
06
Flavor symmetry breaking in the $Δ$ sea
J. J. Ethier🇳🇱 · W. Melnitchouk🇺🇸 · Fernanda Steffens🇩🇪 · A. W. Thomas🇦🇺
The discovery of a sizeable asymmetry in the $u ˉ$ and $d ˉ$ distributions in the proton was one of the more consequential experimental findings in hadron physics last century. Although widely believed to be related to the fundamental role of chiral symmetry in QCD, a definitive verification of this hypothesis has remained elusive. We propose a novel test of the role of chiral symmetry in generating the sea flavor asymmetry by comparing the $d ˉ - u ˉ$ content in the proton with that in the $Δ^{+}$ baryon, where a significant enhancement is expected around the opening of the $N π$ decay channel. Recent developments in lattice QCD suggest a promising way to test this prediction in the near future.
↳ hep-phhep-latnucl-thPRD(2019)·4 citations
07
Quasiparticle properties of nonequilibrium gluon plasma
Jarkko Peuron🇫🇮
We apply classical gluodynamics to early stages of ultrarelativistic heavy-ion collisions. We start by going through the space-time evolution of ultrarelativistic heavy-ion collisions in the color glass condensate framework and the basics of real-time gluodynamics on the lattice in the temporal gauge. We study the plasmon mass scale in three- and two-dimensional systems by comparing three different methods to measure the mass scale. The methods are a formula which can be derived from Hard Thermal Loop effective theory at leading order (HTL), the effective dispersion relation (DR) and measurement of the plasma oscillation frequency triggered by the introduction of a uniform electric field (UE) into the system. We observe that in both systems the plasmon mass scale decreases like a power law after an occupation number dependent initial transient time. In both cases the UE and HTL methods are in rough agreement, and in the three-dimensional case the two agree in the continuum limit. As a second way to study the quasiparticle properties, we derive, implement and test an algorithm which can be used to simulate linearized fluctuations on top of the classical background. The algorithm is derived by requiring conservation of Gauss' law and gauge invariance. We then apply the algorithm to spectral properties of overoccupied gluodynamics using linear response theory. We establish the existence of transverse and longitudinal quasiparticles by extracting their spectral functions. We also extract the dispersion relation, effective mass, plasmon mass and damping rate of the quasiparticles. Our results are consistent with the HTL effective theory, but we also observe effects beyond leading order HTL.
↳ hep-lathep-phnucl-th1 citation
08
Constraining the relativistic mean-field model equations of state with gravitational wave observations
Rana Nandi🇮🇳 · Prasanta Char🇮🇹 · Subrata Pal🇮🇳
The first detection of gravitational waves from the binary neutron star merger event GW170817 has started to provide important new constraints on the nuclear equation of state at high density. The tidal deformability bound of GW170817 combined with the observed two solar mass neutron star poses a serious challenge to theoretical formulations of realistic equations of state. We analyze a fully comprehensive set of relativistic nuclear mean-field theories by confronting them with the observational bounds and the measured neutron-skin thickness. We find that only a few models can withstand these bounds which predict a stiff overall equation of state but with a soft neutron-proton symmetry energy. Two possible indications are proposed: Circumstantial evidence of hadron-quark phase transition inside the star and new parametrizations that are consistent with ground state properties of finite nuclei and observational bounds. Based on extensive analysis of these sets, an upper limit on the radius of a $1.4 M_{⊙}$ neutron star of $R_{1.4} ≲ 12.9$ km is deduced.
↳ astro-ph.HEnucl-thPRC(2019)·69 citations

Affiliations

first authorsco-authorsvia INSPIRE

A new parametrization for the scalar pion form factors

Flavor symmetry breaking in the Δ sea

Quasiparticle properties of nonequilibrium gluon plasma

Constraining the relativistic mean-field model equations of state with gravitational wave observations

Affiliations

Flavor symmetry breaking in the $Δ$ sea