Nuclear Theory·nucl-th

Thursday·February 1, 2018

10 papers—2 primary·8 cross-listed

01
Process-independent effective coupling. From QCD Green's functions to phenomenology
Jose Rodríguez-Quintero🇪🇸 · Daniele Binosi🇮🇹 · Cédric Mezrag🇮🇹 · Joannis Papavassiliou🇪🇸 · Craig D. Roberts🇺🇸
This article reports on a very recent proposal for a new type of process-independent QCD effective charge [Phys.Rev.D96(2017)054026] defined, as an anologue of the Gell-Mann-Low effective charge in QCD, on the ground of nothing but the knowledge of the gauge-field two-point Green's function, albeit modified within a particular computational framework; namely, the combination of pinch technique and background field method which makes possible a systematic rearranging of classes of diagrams in order to redefine the Green's function and have them obey linear QED-like Slavnov-Taylor identities. We have here calculated that effective charge, shown how strikingly well it compares to a process-dependent effective charge based on the Bjorken sum rule; and, finally, employed it in an exploratory calculation of the proton electromagnetic form factor in the hard scattering regime.
nucl-thFew Body Syst.(2018)·58 citations
02
The impact of $K^{+} Λ$ photoproduction on the resonance spectrum
D. Rönchen🇩🇪 · M. Döring🇺🇸 · U.-G. Meißner🇩🇪
The Jülich-Bonn coupled-channel framework is extended to $K^{+} Λ$ photoproduction. The spectrum of nucleon and $Δ$ resonances is extracted from simultaneous fits to several pion-induced reactions in addition to pion, eta and $K^{+} Λ$ photoproduction off the proton. More than 40,000 data points up to a center-of-mass energy of E $\sim$ 2.3 GeV including recently measured double-polarization observables are analyzed. The influence of the $γ p \to K^{+} Λ$ channel on the extracted resonance parameters and the appearance of states not seen in other channels is investigated. The Jülich-Bonn model includes effective three-body channels and guarantees unitarity and analyticity, which is a prerequisite for a reliable determination of the resonance spectrum in terms of poles and residues.
nucl-thhep-phnucl-exEPJA(2018)·60 citations
03
Anisotropic hydrodynamics with a scalar collisional kernel
Dekrayat Almaalol🇺🇸 · Michael Strickland🇺🇸
Prior studies of non-equilibrium dynamics using anisotropic hydrodynamics have used the relativistic Anderson-Witting scattering kernel or some variant thereof. In this paper, we make the first study of the impact of using a more realistic scattering kernel. For this purpose, we consider a conformal system undergoing transversally-homogenous and boost-invariant Bjorken expansion and take the collisional kernel to be given by the leading order 2 <-> 2 scattering kernel in scalar lambda phi^4. We consider both classical and quantum statistics in order to assess the impact of Bose enhancement on the dynamics. We also determine the anisotropic non-equilibrium attractor of a system subject to this collisional kernel. We find that, when the near-equilibrium relaxation-times in the Anderson-Witting and scalar collisional kernels are matched, the scalar kernel results in a higher degree of momentum-space anisotropy during the system's evolution, given the same initial conditions. Additionally, we find that taking into account Bose enhancement further increases the dynamically generated momentum-space anisotropy.
↳ hep-phnucl-thPRC(2018)·34 citations
04
An analysis of variational wave function for the pairing problem in strongly correlated system
Hsuan-Hao Fan · E. Krotscheck
We report a theoretical analysis of variational wave functions for the BCS pairing problem. Starting with a Jastrow-Feenberg (or, in a more recent language "fixed-node") wave function for the superfluid state, we develop the full optimized Fermi-Hypernetted Chain (FHNC-EL) equations which sum a local approximation of the parquet-diagrams. Close examination of the procedure reveals that it is essential to go beyond the usual Jastrow-Feenberg approximation to guarantee the correct stability range.
↳ cond-mat.quant-gascond-mat.str-elcond-mat.supr-connucl-thJ.Phys.Conf.Ser.(2018)·3 citations
05
Tribaryon configurations and the inevitable three nucleon repulsions at short distance
Aaron Park🇰🇷 · Woosung Park🇰🇷 · Su Houng Lee🇰🇷
We decompose the tribaryon configuration in terms of SU(3) flavor and spin state and analyse their color-spin-flavor wave function following Pauli principle. By comparing the color-color and color-spin interactions of compact tribaryon configuration against the lowest three nucleon threshold within a constituent quark model, we show that the three nucleon forces have to be repulsive at short distance for all possible quantum numbers and all values of the SU(3) symmetry breaking parameter. Our work identifies the origin of the repulsive nuclear three body forces including the hyperons at short distance that are called for from phenomenological considerations starting from nuclear matter to the maximum mass of a neutron star.
↳ hep-phnucl-thPRD(2018)·13 citations
06
Hyperfine interaction with the $^{229}$ Th nucleus and its low lying isomeric state
Robert A. Müller · Anna V. Maiorova · Stephan Fritzsche · Andrey V. Volotka · Randolf Beerwerth · Przemyslaw Glowacki · Johannes Thielking · David-Marcel Meier · Maksim Okhapkin · Ekkehard Peik · Andrey Surzhykov
The thorium nucleus with mass number $A = 229$ has attracted much interest because its extremely low lying first excited isomeric state at about $8$ eV opens the possibility for the development of a nuclear clock. However, neither the exact energy of this nuclear isomer nor properties, such as nuclear magnetic dipole and electric quadrupole moment are known to a high precision so far. The latter can be determined by investigating the hyperfine structure of thorium atoms or ions. Due to its electronic structure and the long lifetime of the nuclear isomeric state, Th $^{2 +}$ is especially suitable for such kind of studies. In this letter we present a combined experimental and theoretical investigation of the hyperfine structure of the $^{229}$ Th $^{2 +}$ ion in the nuclear ground and isomeric state. A very good agreement between theory and experiment is found for the nuclear ground state. Moreover, we use our calculations to confirm the recently presented experimental value for the nuclear magnetic dipole moment of the thorium nuclear isomer, which was in contradiction to previous theoretical studies.
↳ physics.atom-phnucl-thphysics.comp-phPRA(2018)·15 citations
07
N* Experiments and their Impact on Strong QCD Physics
Volker D. Burkert🇺🇸
I give a brief overview of experimental studies of the spectrum and the structure of the excited states of the nucleon and what we learn about their internal structure. The focus is on the effort to obtain a more complete picture of the light-quark baryon excitation spectrum employing electromagnetic beams, and on the study of the transition form factors and helicity amplitudes and their dependence on the magnitude of the photon virtuality $Q^{2}$ , especially for some of the most prominent resonances. The results were obtained in pion and eta electroproduction experiments off proton targets. They strengthen the connection of experiment and new results from modeling sQCD in DSE and Light Cone SR approaches. They also point to the nature of these states as 3-quark excitations at the core.
↳ nucl-exhep-phnucl-thFew Body Syst.(2018)·21 citations
08
On the chiral expansion of vector meson masses
Ruchipas Bavontaweepanya🇹🇭 · Xiao-Yu Guo🇩🇪 · Matthias F.M. Lutz🇩🇪
We study the chiral expansion of meson masses and decay constants using a chiral Lagrangian that was constructed previously based on the hadrogenesis conjecture. The one-loop self energies of the Goldstone bosons and vector mesons are evaluated. It is illustrated that a renormalizeable effective field theory arises once specific conditions on the low-energy constants are imposed. For the case where the hadrogenesis mass gap scale Lambda_{HG} is substantially larger than the chiral symmetry breaking scale Lambda_chi a partial summation scheme is required. All terms proportional to (M/\Lambda_\chi)^n can be summed by a suitable renormalization, where M is the chiral and large-N_c limit of the vector meson masses in QCD. The size of loop effects from vector meson degrees of freedom is illustrated for physical quarks masses. Naturally sized effects are observed that have significant impact on the chiral structure of low-energy QCD with three light flavours.
↳ hep-phnucl-thPRD(2018)·15 citations
09
Determine Arbitrary Feynman Integrals by Vacuum Integrals
Xiao Liu🇨🇳 · Yan-Qing Ma🇨🇳
By introducing an auxiliary parameter, we find a new representation for Feynman integrals, which defines a Feynman integral by analytical continuation of a series containing only vacuum integrals. The new representation therefore conceptually translates the problem of computing Feynman integrals to the problem of performing analytical continuations. As an application of the new representation, we use it to construct a novel reduction method for multi-loop Feynman integrals, which is expected to be more efficient than known integration-by-parts reduction method. Using the new method, we successfully reduced all complicated two-loop integrals in $g g \to H H$ process and $g g \to g g g$ process.
↳ hep-phhep-thnucl-thPRD(2019)·79 citations
10
Schwinger mechanism in the SU(3) Nambu--Jona-Lasinio model with an electric field
William R. Tavares🇧🇷 · Sidney S. Avancini🇧🇷
In this work we study the electrized quark matter under finite temperature and density conditions in the context of the SU(2) and SU(3) Nambu--Jona-Lasinio models. To this end, we evaluate the effective quark masses and the Schwinger quark-antiquark pair production rate. For the SU(3) NJL model we incorporate in the Lagrangian the 't Hooft determinant and we present a set of analytical expressions more convenient for numerical evaluations. We predict a decrease of the pseudocritical electric field with the increase of the temperature for both models and a more prominent production rate for the SU(3) model when compared to the SU(2).
↳ hep-phnucl-thPRD(2018)·11 citations

Affiliations

first authorsco-authorsvia INSPIRE