Nuclear Theory·nucl-th

Friday·July 23, 2021

10 papers—6 primary·4 cross-listed

07
Gluon gravitational structure of hadrons of different spin
Dimitra A. Pefkou🇺🇸 · Daniel C. Hackett🇺🇸 · Phiala E. Shanahan🇺🇸
The gravitational form factors (GFFs) of hadrons encode the matrix elements of the energy momentum tensor of QCD. These quantities describe how energy, spin, and various mechanical properties of hadrons are carried by their quark and gluon constituents. We present the gluon GFFs of the pion, nucleon, $ρ$ meson, and $Δ$ baryon as functions of the squared momentum transfer $t$ in the region $0 \leq - t < 2 GeV^{2}$ , as determined in a lattice QCD study with pion mass $m_{π} = 450 (5) MeV$ . By fitting the extracted GFFs using multipole and z-parameter expansion functional forms, we extract various gluon contributions to the energy, pressure, and shear force distributions of the hadrons in the 3D and 2D Breit frames as well as in the infinite momentum frame. We also obtain estimates for the corresponding gluon mechanical and mass radii, as well as the forward-limit gluon contributions to the momentum fraction and angular momentum of the hadrons.
↳ hep-latnucl-thPRD(2022)·117 citations
08
Electromagnetic form factors of $Λ$ hyperon in the vector meson dominance model and a possible explanation of the near-threshold enhancement of the $e^{+} e^{-} \to Λ Λ ˉ$ reaction
Zhong-Yi Li🇨🇳 · An-Xin Dai🇨🇳 · Ju-Jun Xie🇨🇳
The near-threshold $e^{+} e^{-} \to Λ Λ ˉ$ reaction is studied with the assumption that the production mechanism is due to a near- $Λ Λ ˉ$ -threshold bound state. The cross section of $e^{+} e^{-} \to Λ Λ ˉ$ reaction is parametrized in terms of the electromagnetic form factors of $Λ$ hyperon, which are obtained with the vector meson dominance model. It is shown that the contribution to the $e^{+} e^{-} \to Λ Λ ˉ$ reaction from a new narrow state with quantum numbers $J^{P C} = 1^{--}$ is dominant for energies very close to threshold. The mass of this new state is around 2231 MeV, which is very close to the mass threshold of $Λ Λ ˉ$ , while its width is just a few MeV. This gives a possible solution to the problem that all previous calculations seriously underestimate the near-threshold total cross section of the $e^{+} e^{-} \to Λ Λ ˉ$ reaction. We also note that the near-threshold enhancement can be also reproduced by including these well established vector resonances $ω (1420)$ , $ω (1650)$ , $ϕ (1680)$ , or $ϕ (2170)$ with a Flatt $e ˊ$ form for their total decay width, and a strong coupling to the $Λ Λ ˉ$ channel.
↳ hep-phnucl-thChin.Phys.Lett.(2022)·27 citations
09
The $K ˉ N$ interaction in higher partial waves
Albert Feijoo🇨🇿 · Daniel Gazda🇨🇿 · Volodymyr Magas🇪🇸 · Angels Ramos🇪🇸
We present a chiral $K ˉ N$ interaction model that has been developed and optimized in order to account for the experimental data of inelastic $K ˉ N$ reaction channels that open at higher energies. In particular, we study the effect of the higher partial waves which originate directly from the chiral Lagrangian, as they could supersede the role of high-spin resonances employed in earlier phenomenological models to describe meson-baryon cross sections in the 2~GeV region. We present a detailed derivation of the partial wave amplitudes that emerge from the chiral SU(3) meson-baryon Lagrangian up to the d-waves and next-to-leading order in the chiral expansion. We implement a nonperturbative unitarization in coupled channels and optimize the model parameters to a large pool of experimental data in the relevant energy range where these new contributions are expected to be important. The obtained results are encouraging. They indicate the ability of the chiral higher partial waves to extend the description of the scattering data to higher energies and to account for structures in the reaction cross sections that cannot be accommodated by theoretical models limited to the s-waves.
↳ hep-phnucl-thSymmetry(2021)·13 citations
10
Self-consistent $O (4)$ model spectral functions from analytically continued FRG flows
Christopher Jung🇩🇪 · Jan-Hendrik Otto🇩🇪 · Ralf-Arno Tripolt🇦🇹 · Lorenz von Smekal🇩🇪
In this paper we explore practicable ways for self-consistent calculations of spectral functions from analytically continued functional renormalization group (aFRG) flow equations. As a particularly straightforward one we propose to include parametrizations of self-energies based on explicit analytic one-loop expressions. To exemplify this scheme we calculate the spectral functions of pion and sigma meson of the $O (4)$ model at vanishing temperature in the broken phase. Comparing the results with those from previous aFRG calculations, we explicitly demonstrate how self-consistency at all momenta fixes the tight relation between particle masses and decay thresholds. In addition, the two-point functions from our new semi-analytic FRG scheme have the desired domain of holomorphy built in and can readily be studied in the entire cut-complex frequency plane, on physical as well as other Riemann sheets. This is very illustrative and allows, for example, to trace the flow of the resonance pole of the sigma meson across an unphysical sheet. In order to assess the limitations due to the underlying one-loop structure, we also introduce a fully self-consistent numerical scheme based on spectral representations with scale-dependent spectral functions. The most notable improvement of this numerically involved calculation is that it describes the three-particle resonance decay of an off-shell pion, $π^{*} \to σ π \to 3 π$ . Apart from this further conceptual improvement, overall agreement with the results from the considerably simpler semi-analytic one-loop scheme is very encouraging, however. The latter can therefore provide a sound and practicable basis for self-consistent calculations of spectral functions in more realistic effective theories for warm and dense matter.
↳ hep-phnucl-thPRD(2021)·19 citations

Affiliations

first authorsco-authorsvia INSPIRE

Gluon gravitational structure of hadrons of different spin

Electromagnetic form factors of Λ hyperon in the vector meson dominance model and a possible explanation of the near-threshold enhancement of the e+e−→ΛΛˉ reaction

The KˉN interaction in higher partial waves

Self-consistent O(4) model spectral functions from analytically continued FRG flows

Affiliations

Electromagnetic form factors of $Λ$ hyperon in the vector meson dominance model and a possible explanation of the near-threshold enhancement of the $e^{+} e^{-} \to Λ Λ ˉ$ reaction

The $K ˉ N$ interaction in higher partial waves

Self-consistent $O (4)$ model spectral functions from analytically continued FRG flows