Nuclear Theory·nucl-th

Friday·August 11, 2017

6 papers—2 primary·4 cross-listed

03
Cross sections for inelastic meson-meson scattering
Kai Yang🇨🇳 · Xiao-Ming Xu🇨🇳 · H. J. Weber🇺🇸
We study two kinds of inelastic meson-meson scattering. The first kind is inelastic 2-to-2 meson-meson scattering that is governed by quark interchange as well as quark-antiquark annihilation and creation. Cross-section formulas are provided to get unpolarized cross sections for $π K \to ρ K^{*}$ for $I = 1/2$ , $π K^{*} \to ρ K$ for $I = 1/2$ , $π K^{*} \to ρ K^{*}$ for $I = 1/2$ , and $ρ K \to ρ K^{*}$ for $I = 1/2$ . Near threshold, quark interchange dominates the reactions near the critical temperature. The second kind is 2-to-1 meson-meson scattering with the process that a quark in an initial meson and an antiquark in another initial meson annihilate into a gluon and subsequently the gluon is absorbed by the other antiquark or quark. The transition potential for the process is derived. Four Feynman diagrams at tree level contribute to the 2-to-1 meson-meson scattering. Starting from the $S$ -matrix element, the isospin-averaged unpolarized cross section with transition amplitudes is derived. The cross sections for $π π \to ρ$ and $π K \to K^{*}$ decrease with increasing temperature.
↳ hep-phnucl-thPRD(2017)·7 citations
04
Surmounting the sign problem in non-relativistic calculations: a case study with mass-imbalanced fermions
Lukas Rammelmüller🇩🇪 · William J. Porter🇺🇸 · Joaquín E. Drut🇺🇸 · Jens Braun🇩🇪
The calculation of the ground state and thermodynamics of mass-imbalanced Fermi systems is a challenging many-body problem. Even in one spatial dimension, analytic solutions are limited to special configurations and numerical progress with standard Monte Carlo approaches is hindered by the sign problem. The focus of the present work is on the further development of methods to study imbalanced systems in a fully non-perturbative fashion. We report our calculations of the ground-state energy of mass-imbalanced fermions using two different approaches which are also very popular in the context of the theory of the strong interaction (Quantum Chromodynamics, QCD): (a) the hybrid Monte Carlo algorithm with imaginary mass imbalance, followed by an analytic continuation to the real axis; and (b) the Complex Langevin algorithm. We cover a range of on-site interaction strengths that includes strongly attractive as well as strongly repulsive cases which we verify with non-perturbative renormalization group methods and perturbation theory. Our findings indicate that, for strong repulsive couplings, the energy starts to flatten out, implying interesting consequences for short-range and high-frequency correlation functions. Overall, our results clearly indicate that the Complex Langevin approach is very versatile and works very well for imbalanced Fermi gases with both attractive and repulsive interactions.
↳ cond-mat.quant-gashep-latnucl-thPRD(2017)·37 citations
05
$ρ$ -Meson Form Factors in the Point Form
Elmar P. Biernat🇦🇹 · Wolfgang Schweiger🇦🇹
We present a calculation of the electromagnetic form factors of the $ρ^{+}$ meson. Our formalism is based on the point-form of relativistic quantum mechanics. Electron- $ρ$ -meson scattering is formulated as a coupled-channel problem for a Bakamjian-Thomas mass operator, such that the dynamics of the exchanged photon is taken explicitly into account. The $ρ$ -meson current is extracted from on-shell matrix elements of the optical potential of the scattering process. As a consequence of the violation of cluster separability in the Bakamjian-Thomas framework, our current includes additional, unphysical contributions, which can be separated from the physical ones uniquely. Our results for the form factors are in good agreement with other approaches.
↳ hep-phnucl-thActa Phys.Polon.Supp.(2017)·1 citation
06
Two-photon exchange contribution to elastic $e^{-}$ -proton scattering: Full dispersive treatment of $π N$ states and comparison with data
O. Tomalak🇩🇪 · B. Pasquini🇮🇹 · M. Vanderhaeghen🇩🇪
We evaluate the two-photon exchange correction to the elastic electron-proton scattering cross section within a dispersive framework. Besides the elastic contribution, we account for all $π N$ intermediate state contributions using the phenomenological MAID fit as an input. We develop a novel method for the analytical continuation of the two-photon exchange amplitudes into the unphysical region and generalize our previous work to the momentum transfer region $0.064 GeV^{2} ≲ Q^{2} ≲ 1 GeV^{2}$ . We compare our results with recent OLYMPUS, CLAS and VEPP-3 data as well as with empirical fits and estimates in the forward angular region.
↳ hep-phnucl-exnucl-thPRD(2017)·41 citations

Affiliations

first authorsco-authorsvia INSPIRE

Cross sections for inelastic meson-meson scattering

Surmounting the sign problem in non-relativistic calculations: a case study with mass-imbalanced fermions

ρ-Meson Form Factors in the Point Form

Two-photon exchange contribution to elastic e−-proton scattering: Full dispersive treatment of πN states and comparison with data

Affiliations

$ρ$ -Meson Form Factors in the Point Form

Two-photon exchange contribution to elastic $e^{-}$ -proton scattering: Full dispersive treatment of $π N$ states and comparison with data