Nuclear Theory·nucl-th

Thursday·December 6, 2018

10 papers—7 primary·3 cross-listed

01
QCD matter with a crossover and a first-order phase transition
Christopher J. Plumberg🇸🇪 · Thomas Welle🇺🇸 · Joseph I. Kapusta🇺🇸
We present a phenomenological parametrization of the phase diagram of QCD as a function of temperature $T$ and baryochemical potential $μ$ . The parametrization is constructed by introducing a switching function which controls the nature of the transition between the Hadron-Resonance Gas (HRG) and Quark-Gluon Plasma (QGP) phases of nuclear matter, such that the equation of state (EOS) possesses a rapid crossover at large $T$ and small $μ$ , a critical point placed anywhere along the phase transition line, and a first-order transition at small $T$ and large $μ$ . This EOS offers a convenient phenomenological tool for assessing the possible effects of the conjectured QCD critical point on heavy-ion observables.
nucl-thPoS(2018)·8 citations
02
Universality and the Coulomb interaction
C. H. Schmickler
We study the relationship between universal effects and the Coulomb interaction. Here, we present our approach and a first illustrative example. Understanding the relationship of universality and the Coulomb interaction is important for weakly bound nuclear few-body systems. The example nucleus we study is the excited state of $^{17}$ F which we model as a proton and an $^{16}$ O core. We use a Gaussian potential to represent short-range forces together with a Coulomb potential. Our calculation uses the Gaussian Expansion Method (GEM), which is a variational method well-suited to our problem. We find that we need to choose the range of the Gaussian potential in addition to the potential strength that reproduces the right scattering length. We propose to fit the range of the Gaussian potential such that the effective range is reproduced. We show that this approach leads to consistent results for $^{17}$ F.
nucl-thSpringer Proc.Phys.(2020)·1 citation
03
The 9Li(d,p) reaction, a specific probe of 10Li, paradigm of parity--inverted nuclei around N=6 closed shell
F. Barranco · G. Potel · E. Vigezzi · R.A. Broglia
We show, within the framework of renormalized nuclear field theory and of the induced reaction surrogate formalism, that the highly debated $^{10}$ Li structure, observed in a recent $^{9}$ Li(d,p) $^{10}$ Li one--neutron transfer experiment is consistent with or better, requires the presence of a virtual $1/ 2^{+}$ state of similar single--particle strength than that of the $1/ 2^{-}$ resonance at 0.45 $\pm$ 0.03 MeV. Based on continuum spectroscopy self-energy techniques, we find that the physical mechanism responsible for parity inversion in $_{3}^{10}$ Li is the same as that at the basis of the similar phenomenon observed in $_{4}^{11}$ Be and to that needed in $^{11}$ Li to have an important $s$ --wave ground state component. Furthermore, it is also consistent with the (normal) sequence of the $1 p_{1/2}$ and $2 s_{1/2}$ levels in the $N = 7$ isotones $_{5}^{12}$ B and $_{6}^{13}$ C.
nucl-thPRC(2020)·13 citations
04
Simple formula for leading $S U (3)$ irreducible representation for nucleons in an oscillator shell
V.K.B. Kota🇮🇳
Applications of rotational $S U (3)$ symmetry in nuclei, using Elliott's $S U (3)$ or pseudo- $S U (3)$ or proxy- $S U (3)$ model, often need just the lowest or leading $S U (3)$ irreducible representation (irrep) $(λ_{H}, μ_{H})$ . For nucleons in an oscillator shell $η$ , with $N = (η + 1) (η + 2) /2$ , we have the algebra $U (r N) \supset [U (N) \supset S U (3)] \otimes S U (r)$ ; $r = 2$ when there are only valence protons or neutrons and $r = 4$ for nucleons with isospin $T$ . Presented in this paper is a simple general formula for the leading $S U (3)$ irrep $(λ_{H}, μ_{H})$ in any given irrep ${f}$ of $U (N)$ . Results are provided for $(λ_{H}, μ_{H})$ irreps for $η$ values of interest in nuclei and for this for all allowed particle numbers. These results clearly show that prolate shape dominates over oblate shape in the shell model $S U (3)$ description.
nucl-th11 citations
05
Equation of state effects in core-collapse supernovae
Hannah Yasin · Sabrina Schäfer · Almudena Arcones · Achim Schwenk
We investigate the impact of different properties of the nuclear equation of state in core-collapse supernovae, with a focus on the proto-neutron-star contraction and its impact on the shock evolution. To this end, we introduce a range of equations of state that vary the nucleon effective mass, incompressibility, symmetry energy, and nuclear saturation point. This allows us to point to the different effects in changing these properties from the Lattimer and Swesty to the Shen et al. equations of state, the two most commonly used equations of state in simulations. In particular, we trace the contraction behavior to the effective mass, which determines the thermal nucleonic contributions to the equation of state. Larger effective masses lead to lower pressures at nuclear densities and a lower thermal index. This results in a more rapid contraction of the proto-neutron star and consequently higher neutrino energies, which aids the shock evolution to a faster explosion.
nucl-thastro-ph.HEnucl-exPRL(2020)·127 citations
06
Lower bound on the proton charge radius from electron scattering data
Franziska Hagelstein (AEC Bern)🇨🇭 · Vladimir Pascalutsa (JGU Mainz)🇩🇪
The proton charge-radius determinations from the electromagnetic form-factor measurements in electron-proton scattering require an extrapolation to zero momentum transfer ( $Q^{2} = 0$ ) which is prone to model-dependent assumptions. We show that the data at finite momentum transfer can be used to establish a rigorous lower bound on the proton charge radius. Using the available $e p$ data at low $Q^{2}$ , we obtain $R_{E} > 0.850 (1)$ fm as the lower bound on the proton radius. This reaffirms the discrepancy between the $e p$ and muonic-hydrogen values, while bypassing the model-dependent assumptions that go into the fitting and extrapolation of the $e p$ data.
nucl-thhep-phnucl-exPLB(2019)·7 citations
07
NLO Productions of $ω$ and $K_{S}^{0}$ with a Global Extraction of the Jet Transport Parameter in Heavy Ion collisions
Guo-Yang Ma🇨🇳 · Wei Dai🇨🇳 · Ben-Wei Zhang🇨🇳 · En-Ke Wang🇨🇳
In this work, we pave the way to calculate the productions of $ω$ and $K_{S}^{0}$ mesons at large $p_{T}$ in p+p and A+A collisions at the RHIC and the LHC. The $ω$ meson fragmentation functions (FFs) in vacuum at next-to-leading order (NLO) are obtained by evolving NLO DGLAP evolution equations with rescaled $ω$ FFs at initial scale $Q_{0}^{2} = 1.5$ GeV $^{2}$ from a broken SU(3) model, and the $K_{S}^{0}$ FFs in vacuum are taken from AKK08 parametrization directly. Within the framework of the NLO pQCD improved parton model, we make good descriptions of the experimental data on $ω$ and $K_{S}^{0}$ in p+p both at the RHIC and the LHC. With the higher-twist approach to take into account the jet quenching effect by medium modified FFs, the nuclear modification factors for $ω$ meson and $K_{S}^{0}$ meson at the RHIC and the LHC are presented with different sets of jet transport coefficient $q^_{0}$ . Then we make a global extraction of $q^_{0}$ at the RHIC and the LHC by confronting our model calculations with all available data on 6 identified mesons: $π^{0}$ , $η$ , $ρ^{0}$ , $ϕ$ , $ω$ , and $K_{S}^{0}$ . The minimum value of the total $χ^{2} / d . o . f$ for productions of these mesons gives the best value of $q^_{0} = 0.5 Ge V^{2} /fm$ for Au+Au collisions with $s_{NN} = 200$ GeV at the RHIC, and $q^_{0} = 1.2 Ge V^{2} /fm$ for Pb+Pb collisions with $s_{NN} = 2.76$ TeV at the LHC respectively, with the QGP spacetime evolution given by an event-by-event viscous hydrodynamics model IEBE-VISHNU. With these global extracted values of $q^_{0}$ , the nuclear modification factors of $π^{0}$ , $η$ , $ρ^{0}$ , $ϕ$ , $ω$ , and $K_{S}^{0}$ in A+A collisions are presented, and predictions of yield ratios such as $ω / π^{0}$ and $K_{S}^{0} / π^{0}$ at large $p_{T}$ in heavy-ion collisions at the RHIC and the LHC are provided.
nucl-thhep-phEPJC(2019)·30 citations
08
Interplay of dynamical and explicit chiral symmetry breaking effects on a quark
Fernando E. Serna🇧🇷 · Chen Chen🇧🇷 · Bruno El-Bennich🇧🇷
The relative contributions of explicit and dynamical chiral symmetry breaking in QCD models of the quark-gap equation are studied in dependence of frequently employed ansätze for the dressed interaction and quark-gluon vertex. The explicit symmetry breaking contributions are defined by a constituent-quark sigma term whereas the combined effects of explicit and dynamical symmetry breaking are described by a Euclidean constituent-mass solution. We extend this study of the gap equation to a quark-gluon vertex beyond the Abelian approximation complemented with numerical gluon- and ghost-dressing functions from lattice QCD. We find that the ratio of the sigma term over the Euclidean mass is largely independent of nonperturbative interaction and vertex models for current-quark masses, $m_{u, d} (μ) \leq m (μ) \leq m_{b} (μ)$ , and equal contributions of explicit and dynamical chiral symmetry breaking occur at $m (μ) \approx 400$ ~MeV. For massive solutions of the gap equation with lattice propagators this value decreases to about 200~MeV.
↳ hep-phnucl-thPRD(2019)·30 citations
09
Baryonic or quarkyonic matter?
Owe Philipsen🇩🇪 · Jonas Scheunert🇩🇪
During the last years it has become possible to address the cold and dense regime of QCD directly for sufficiently heavy quarks, where combined strong coupling and hopping expansions are convergent and a 3d effective theory can be derived, which allows to control the sign problem either in simulations or by fully analytic calculations. In this contribution we review the effective theory and study the $N_{c}$ -dependence of the nuclear liquid gas transition, as well as the equation of state of baryonic matter in the strong coupling limit. We find the transition to become more strongly first order with growing $N_{c}$ , suggesting that in the large $N_{c}$ limit its critical endpoint moves to high temperatures to connect with the deconfinement transition. Furthermore, to leading and next-to-leading order in the strong coupling and hopping expansions, respectively, the pressure is found to scale as $p \sim N_{c}$ . This suggests that baryonic and quarkyonic matter might be the same at nuclear densities. Further work is needed to see whether this result is stable under gauge corrections.
↳ hep-lathep-phnucl-thPoS(2018)·5 citations
10
The Roper resonance as a meson-baryon molecular state
B. Golli🇸🇮
The recently proposed mechanism for the formation of the Roper resonance, in which a dynamically generated state as well as a genuine three-quark resonant state play an equally important role, is confronted with the model proposed almost twenty years ago in which the Roper is pictured as a molecular state of the nucleon and the $σ$ meson.
↳ hep-phnucl-thBled Workshops Phys.(2018)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE