Nuclear Theory·nucl-th

Thursday·July 4, 2019

9 papers—6 primary·3 cross-listed

07
[Submitted on 2 Jul 2019] (cross-list from hep-ph)
Three-pion contribution to hadronic vacuum polarization
Martin Hoferichter🇺🇸 · Bai-Long Hoid🇩🇪 · Bastian Kubis🇩🇪
We address the contribution of the $3 π$ channel to hadronic vacuum polarization (HVP) using a dispersive representation of the $e^{+} e^{-} \to 3 π$ amplitude. This channel gives the second-largest individual contribution to the total HVP integral in the anomalous magnetic moment of the muon $(g - 2)_{μ}$ , both to its absolute value and uncertainty. It is largely dominated by the narrow resonances $ω$ and $ϕ$ , but not to the extent that the off-peak regions were negligible, so that at the level of accuracy relevant for $(g - 2)_{μ}$ an analysis of the available data as model independent as possible becomes critical. Here, we provide such an analysis based on a global fit function using analyticity and unitarity of the underlying $γ^{*} \to 3 π$ amplitude and its normalization from a chiral low-energy theorem, which, in particular, allows us to check the internal consistency of the various $e^{+} e^{-} \to 3 π$ data sets. Overall, we obtain $a_{μ}^{3 π} ∣_{\leq 1.8 GeV} = 46.2 (6) (6) \times 1 0^{- 10}$ as our best estimate for the total $3 π$ contribution consistent with all (low-energy) constraints from QCD. In combination with a recent dispersive analysis imposing the same constraints on the $2 π$ channel below $1 GeV$ , this covers nearly $80%$ of the total HVP contribution, leading to $a_{μ}^{HVP} = 692.3 (3.3) \times 1 0^{- 10}$ when the remainder is taken from the literature, and thus reaffirming the $(g - 2)_{μ}$ anomaly at the level of at least $3.4 σ$ . As side products, we find for the vacuum-polarization-subtracted masses $M_{ω} = 782.63 (3) (1) MeV$ and $M_{ϕ} = 1019.20 (2) (1) MeV$ , confirming the tension to the $ω$ mass as extracted from the $2 π$ channel.
Comments:
24 pages, 1 figure; Appendix B added; version published in JHEP
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1907.01556 [pdf]
JHEP(2019)·498 citations
08
[Submitted on 3 Jul 2019] (cross-list from hep-ph)
Thermal behaviors of light scalar resonances at low temperatures
Rui Gao🇨🇳 · Zhi-Hui Guo🇨🇳 · Jin-Yi Pang🇩🇪
We study the thermal properties of the lowest multiplet of the QCD light-flavor scalar resonances, including the $f_{0} (500) / σ$ , $K_{0}^{*} (700) / κ$ , $f_{0} (980)$ and $a_{0} (980)$ , in the framework of unitarized $U (3)$ chiral perturbation theory. After the successful fits to the meson-meson scattering inputs, such as the phase shifts and inelasticities, we obtain the unknown parameters and further calculate the resonance poles and their residues at zero temperature. By including the finite-temperature effects in the unitarized meson-meson scattering amplitudes, the thermal behaviors of the scalar resonance poles in the complex energy plane are studied. The masses of $σ$ and $κ$ are found to considerably decrease when increasing the temperatures, while their widths turn out to be still large when the temperatures reach around $200$ MeV. In contrast, both the masses and widths of the $f_{0} (980)$ and $a_{0} (980)$ are only slightly changed.
Comments:
25 pages, 6 figures. To match the published version in PRD. Thermal contributions from the tadpole diagrams are included. A numerical error when searching the thermal poles is corrected. The main conclusions remain unchanged
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1907.01787 [pdf]
PRD(2019)·18 citations
09
[Submitted on 3 Jul 2019] (cross-list from hep-ph)
Three regimes of QCD
L. Ya. Glozman🇦🇹
While the QCD Lagrangian as the whole is only chirally symmetric, its electric part has larger chiral-spin SU(2)_{CS} and SU(2N_F) symmetries. This allows separation of the electric and magnetic interactions in a given reference frame. Artificial truncation of the near-zero modes of the Dirac operator results in the emergence of the SU(2)_{CS} and SU(2N_F) symmetries in hadron spectrum. This implies that while the confining electric interaction is distributed among all modes of the Dirac operator, the magnetic interaction is located at least predominantly in the near-zero modes. Given this observation one could anticipate that above the pseudocritical temperature, where the near-zero modes of the Dirac operator are suppressed, QCD is SU(2)_{CS} and SU(2N_F) symmetric, which means absence of deconfinement in this regime. Solution of the N_F=2 QCD on the lattice with a chirally symmetric Dirac operator reveals that indeed in the interval Tc - 3Tc QCD is approximately SU(2)_{CS} and SU(2N_F) symmetric which implies that degrees of freedom are chirally symmetric quarks bound by the chromoelectric field into color-singlet objects without the chromomagnetic effects. This regime is referred to as a Stringy Fluid. At larger temperatures this emergent symmetry smoothly disappears and QCD approaches the Quark-Gluon Plasma regime with quasifree quarks. The Hadron Gas, the Stringy Fluid and the Quark-Gluon Plasma differ by symmetries, degrees of freedom and properties.
Comments:
15 pages. Will appear in IJMPA. Discussion of confinement - deconfinement has been expanded and new figures have been added
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1907.01820 [pdf]
Int.J.Mod.Phys.A(2021)·15 citations

Affiliations

first authorsco-authorsvia INSPIRE

Three-pion contribution to hadronic vacuum polarization

Thermal behaviors of light scalar resonances at low temperatures

Three regimes of QCD

Affiliations