Nuclear Theory·nucl-th

Tuesday·August 6, 2019

13 papers—6 primary·7 cross-listed

07
Spectral functions and critical dynamics of the $O (4)$ model from classical-statistical lattice simulations
Sören Schlichting🇩🇪 · Dominik Smith🇩🇪 · Lorenz von Smekal🇩🇪
We calculate spectral functions of the relativistic $O (4)$ model from real-time lattice simulations in classical-statistical field theory. While in the low and high temperature phase of the model, the spectral functions of longitudinal $(σ)$ and transverse $(π)$ modes are well described by relativistic quasi-particle peaks, we find a highly non-trivial behavior of the spectral functions in the cross over region, where additional structures appear. Similarly, we observe a significant broadening of the quasi-particle peaks, when the amount explicit $O (4)$ symmetry breaking is reduced. We further demonstrate that in the vicinity of the $O (4)$ critical point, the spectral functions develop an infrared power law associated with the critical dynamics, and comment on the extraction of the dynamical critical exponent $z$ from our simulations.
↳ hep-latcond-mat.stat-mechhep-phnucl-thNPB(2020)·36 citations
08
Hadron and Nuclear Physics on the Light Front
Stanley J. Brodsky🇺🇸 · Alexandre Deur🇺🇸
The QCD light-front (LF) Hamiltonian equation H_{LF}|\Psi> = M^2 |\Psi> derived from quantization at fixed LF time \tau = t+z/c provides a causal, frame-independent, method for computing hadron spectroscopy as well as dynamical observables such as structure functions, transverse momentum distributions, and distribution amplitudes. The LF formalism also leads to novel nuclear phenomena, such as "hidden color", "color transparency", "nuclear-bound quarkonium" and the shadowing and antishadowing of nuclear structure functions. For example, there are five distinct color-singlet Fock state representations of the six color-triplet quarks of the deuteron. The hidden color Fock states become manifest when the deuteron is probed when it has small transverse size, as in measurements of the deuteron form factor at large momentum transfer. The QCD Lagrangian with zero quark mass has no explicit mass scale. However, as shown by de Alfaro, Fubini, and Furlan (dAFF), a mass scale can appear in the equations of motion without affecting the conformal invariance of the Action. When one applies the dAFF procedure to the QCD LF Hamiltonian, it leads to a color confining potential \kappa^4 \zeta^2 for mesons, where \zeta^2 is the LF radial variable conjugate to the qbar-q invariant mass squared. The same result, including spin terms, is obtained using LF holography (AdS/QCD) -- the duality between LF dynamics and AdS_5 -- if one modifies the AdS_5 Action by the dilaton exp{+\kappa^2 z^2} in the fifth dimension z. If this procedure is generalized using superconformal algebra, the resulting LF eigensolutions provide unified Regge spectroscopy of mesons, baryons, and tetraquarks, including remarkable supersymmetric relations between the masses of mesons, baryons and tetraquarks with a universal Regge slope...
↳ hep-phhep-thnucl-thJPS Conf.Proc.(2020)·1 citation
09
Centrality dependence of Electrical and Hall conductivity at RHIC and LHC energies for a Conformal System
Bhaswar Chatterjee🇮🇳 · Rutuparna Rath🇮🇳 · Golam Sarwar🇮🇳 · Raghunath Sahoo🇮🇳
In this work, we study electrical conductivity and Hall conductivity in the presence of electromagnetic field using Relativistic Boltzmann Transport Equation with Relaxation Time Approximation. We evaluate these transport coefficients for a strongly interacting system consisting of nearly massless particles which is similar to Quark-Gluon Plasma and is likely to be formed in heavy-ion collision experiments. We explicitly include the effects of magnetic field in the calculation of relaxation time. The values of magnetic field are obtained for all the centrality classes of Au+Au collisions at $s_{NN} =$ 200 GeV and Pb+Pb collisions at $s_{NN} =$ 2.76 TeV. We consider the three lightest quark flavors and their corresponding antiparticles in this study. We estimate the temperature dependence of the electrical conductivity and Hall conductivity for different strengths of magnetic field. We observe a significant dependence of temperature on electrical and Hall conductivity in the presence of magnetic field.
↳ hep-phnucl-exnucl-thEPJA(2021)·11 citations
10
Modeling of Charged-Neutral Kaon Fluctuations as a Signature of DCC Production in A--A Collisions
Ranjit Nayak🇮🇳 · Sadhana Dash🇮🇳 · Basanata Nandi🇮🇳 · Claude Pruneau🇺🇸
Anomalous event-by-event fluctuations of the relative yields of neutral (K $_{s}^{0}$ ) and charged kaon (K $^{\pm}$ ) have been predicted to yield a signature for the formation of Disoriented Chiral Condensate (DCC) in relativistic heavy-ion collisions. In this work, we model the production and decay of DCCs in the context of heavy-ion collisions at the Large Hadron Collider, and estimate the sensitivity of large acceptance detectors, such as the ALICE detector, towards the identification of such anomalous decays. Our study is based on the robust statistical observable, $ν_{dyn}$ , known for its sensitivity to dynamical fluctuations. We first present simulations without DCCs, based on the HIJING and AMPT models, in order to establish an approximate reference for the magnitude of $ν_{dyn} (K^{\pm}, K_{s}^{0})$ and its centrality evolution in Pb--Pb collisions at the TeV energy scale. We next introduce simple phenomenological models of K $_{s}^{0}$ vs. K $^{\pm}$ event-by-event yield fluctuations, which we use to study the feasibility and sensitivity of detection of the production of DCCs in heavy-ion collisions. Although the precision of models such as HIJING and AMPT limit their use as absolute references and thus render anomalous fluctuations difficult to define precisely, our studies demonstrate that the magnitude of $ν_{dyn} (K^{\pm}, K_{s}^{0})$ is in fact very sensitive to the presence of small admixture of DCCs in normal non-DCC events. Consequently, while large values of $ν_{dyn} (K^{\pm}, K_{s}^{0})$ may not be sufficient to identify the existence of DCCs, nonetheless they constitute a first and necessary condition to signal their possible production in heavy-ion collisions.
↳ hep-phnucl-thPRC(2020)·11 citations
11
Nucleon resonances in $γ p \to ω p$ reaction
N.C. Wei🇨🇳 · F. Huang🇨🇳 · K. Nakayama🇺🇸 · D. M. Li🇨🇳
The most recent high-precision data on spin observables $Σ$ , $T$ , $P^{'}$ , $E$ , $F$ and $H$ reported by the CLAS Collaboration together with the previous data on differential cross sections and spin-density-matrix elements reported by the CLAS, A2, GRAAL, SAPHIR and CBELSA/TAPS Collaborations for the reaction $γ p \to ω p$ are analyzed within an effective Lagrangian approach. The reaction amplitude is constructed by considering the $t$ -channel $π$ and $η$ exchanges, the $s$ -channel nucleon and nucleon resonances exchanges, the $u$ -channel nucleon exchange and the generalized contact current. The latter accounts effectively for the interaction current and ensures that the full photoproduction amplitude is gauge invariant. It is shown that all the available CLAS data can be satisfactorily described by considering the $N (1520) 3/ 2^{-}$ , $N (1700) 3/ 2^{-}$ , $N (1720) 3/ 2^{+}$ , $N (1860) 5/ 2^{+}$ , $N (1875) 3/ 2^{-}$ , $N (1895) 1/ 2^{-}$ and $N (2060) 5/ 2^{-}$ resonances in the $s$ -channel. The parameters of these resonances are extracted and compared with those quoted by PDG.
↳ hep-phnucl-thPRD(2019)·23 citations
12
Pion off-shell electromagnetic form factors: data extraction and model analysis
Ho-Meoyng Choi🇰🇷 · T. Frederico🇧🇷 · Chueng-Ryong Ji🇺🇸 · J. P. B. C. de Melo🇧🇷
We investigate the pion electromagnetic half off-shell form factors, which parametrize the matrix element of the charged pion electromagnetic current with one leg off-mass-shell and the other leg on-mass-shell, using an exactly solvable manifestly covariant model of a $(3 + 1)$ dimensional fermion field theory. The model provides a 3D imaging of the two off-shell pion form factors $F_{1}$ and $F_{2}$ as a function of $(Q^{2}, t)$ , which are related to each other satisfying the Ward-Takahashi identity. The normalization of the renormalized charge form factor $F_{1}$ is fixed by $F_{1} (Q^{2} = 0, t = m_{π}^{2}) = 1$ while the other form factor $F_{2}$ vanishes, i.e. $F_{2} (Q^{2}, t = m_{π}^{2}) = 0$ for any value of $Q^{2}$ due to the time-reversal invariance of the strong interaction. We define the new form factor $g (Q^{2}, t) = F_{2} (Q^{2}, t) / (t - m_{π}^{2})$ and find that $g (Q^{2}, t)$ can be measurable in the on-mass-shell limit. In particular, $g (Q^{2} = 0, t = m_{π}^{2})$ is related with the pion charge radius. We also compare our form factors with the data extracted from the pion electroproduction reaction for both the off-shell region ( $t < 0$ ) and the on-shell limit ( $t \to m_{π}^{2}$ ).
↳ hep-phnucl-thPRD(2019)·14 citations
13
On the stability of two-flavor and three-flavor quark stars
Qianyi Wang🇨🇳 · Tong Zhao🇨🇳 · Hongshi Zong🇨🇳
Following our recenty proposed self-consistent mean-field approximation approach, we have done some researches on the chiral phase transition of strong interaction matter within the framework of Nambu-Jona-Lasinio (NJL) model. The chiral susceptibility and equation of state (EOS) are computed in this work for both two-flavor and three-flavor quark matter for contrast. The Pauli-Villars scheme, which can preserve gauge invariance, is used in this paper. Moreover, whether the three-flavor quark matter is more stable than the two-flavor quark matter or not in quark stars is discussed in this work. In our model, when the bag constant are the same, the two-flavor quark matter has a higher pressure than the three-flavor quark matter, which is different from what Witten proposed in his pioneering work.
↳ hep-phnucl-th10 citations

Affiliations

first authorsco-authorsvia INSPIRE

Spectral functions and critical dynamics of the O(4) model from classical-statistical lattice simulations

Hadron and Nuclear Physics on the Light Front

Centrality dependence of Electrical and Hall conductivity at RHIC and LHC energies for a Conformal System

Modeling of Charged-Neutral Kaon Fluctuations as a Signature of DCC Production in A--A Collisions

Nucleon resonances in γp→ωp reaction

Pion off-shell electromagnetic form factors: data extraction and model analysis

On the stability of two-flavor and three-flavor quark stars

Affiliations

Spectral functions and critical dynamics of the $O (4)$ model from classical-statistical lattice simulations

Nucleon resonances in $γ p \to ω p$ reaction