Nuclear Theory·nucl-th

Wednesday·June 24, 2015

9 papers—5 primary·4 cross-listed

06
Cottingham formula and nucleon polarizabilities
J. Gasser🇨🇭 · M. Hoferichter🇨🇭 · H. Leutwyler🇨🇭 · A. Rusetsky🇩🇪
The difference between the electromagnetic self-energies of proton and neutron can be calculated with the Cottingham formula, which expresses the self-energies as an integral over the electroproduction cross sections---provided the nucleon matrix elements of the current commutator do not contain a fixed pole. We show that, under the same proviso, the subtraction function occurring in the dispersive representation of the virtual Compton forward scattering amplitude is determined by the cross sections. The representation in particular leads to a parameter-free sum rule for the nucleon polarizabilities. We evaluate the sum rule for the difference between the electric polarizabilities of proton and neutron by means of the available parameterizations of the data and compare the result with experiment.
↳ hep-phhep-latnucl-thEPJC(2015)·75 citations
07
Effects of a $N^{*}$ resonance with hidden charm in the $π^{-} p \to D^{-} Σ_{c}^{+}$ reaction near threshold
E. J. Garzon🇨🇳 · Ju-Jun Xie🇨🇳
We study the effect of a hidden charm nuclear excited state $N_{c c ˉ}^{*}$ in the $π^{-} p \to D^{-} Σ_{c}^{+}$ reaction near threshold using an effective Lagrangian approach. We calculate the background contribution of the $t$ and $u$ channels by the $D^{* 0}$ vector meson exchange and $Σ_{c}^{++}$ intermediate state, respectively. We show that the consideration of a $N_{c c ˉ}^{*}$ resonance provides an enhancement of the total cross section close to the reaction threshold. We also evaluate the differential cross section for different energies and we study the angle dependence. It is expected that our model calculations will be tested in future experiments.
↳ hep-phhep-exnucl-exnucl-thPRC(2015)·44 citations
08
Quantum fluctuations in the BCS-BEC crossover of two-dimensional Fermi gases
Lianyi He🇺🇸 · Haifeng Lv🇨🇳 · Gaoqing Cao🇨🇳 · Hui Hu🇦🇺 · Xia-Ji Liu🇦🇺
We present a theoretical study of the ground state of the BCS-BEC crossover in dilute two-dimensional Fermi gases. While the mean-field theory provides a simple and analytical equation of state, the pressure is equal to that of a noninteracting Fermi gas in the entire BCS-BEC crossover, which is not consistent with the features of a weakly interacting Bose condensate in the BEC limit and a weakly interacting Fermi liquid in the BCS limit. The inadequacy of the 2D mean-field theory indicates that the quantum fluctuations are much more pronounced than those in 3D. In this work, we show that the inclusion of the Gaussian quantum fluctuations naturally recovers the above features in both the BEC and the BCS limits. In the BEC limit, the missing logarithmic dependence on the boson chemical potential is recovered by the quantum fluctuations. Near the quantum phase transition from the vacuum to the BEC phase, we compare our equation of state with the known grand canonical equation of state of 2D Bose gases and determine the ratio of the composite boson scattering length $a_{B}$ to the fermion scattering length $a_{2D}$ . We find $a_{B} ≃ 0.56 a_{2D}$ , in good agreement with the exact four-body calculation. We compare our equation of state in the BCS-BEC crossover with recent results from the quantum Monte Carlo simulations and the experimental measurements and find good agreements.
↳ cond-mat.quant-gascond-mat.str-elcond-mat.supr-connucl-thPRA(2015)·29 citations
09
Anisotropic matching principle for the hydrodynamics expansion
Leonardo Tinti🇵🇱
Following the recent success of anisotropic hydrodynamics we propose a new, general prescription for the hydrodynamics expansion around an anisotropic background. The anisotropic distribution is fixing exactly the complete energy-momentum tensor, just like the effective temperature is fixing the proper energy density in the ordinary expansion around local equilibrium. This means that momen- tum anisotropies are already included at the leading order, allowing for large pressure anisotropies without the need of a next to leading order treatment. The first moment of the Boltzmann equation (local four-momentum conservation) provides the time evolution of the proper energy density and the four velocity. Differently from previous prescriptions, the dynamic equations for the pressure corrections are not derived from the zeroth or second moment of the Boltzmann equation, but they are taken directly from the exact evolution given by the Boltzmann equation. We check the effec- tiveness of this new approach by matching with the exact solution of the Boltzmann equation in the Bjorken limit with the collisional kernel treated in relaxation time approximation, finding an unprecedented agreement.
↳ hep-phnucl-thPRC(2016)·65 citations

Affiliations

first authorsco-authorsvia INSPIRE

Cottingham formula and nucleon polarizabilities

Effects of a N∗ resonance with hidden charm in the π−p→D−Σc+​ reaction near threshold

Quantum fluctuations in the BCS-BEC crossover of two-dimensional Fermi gases

Anisotropic matching principle for the hydrodynamics expansion

Affiliations

Effects of a $N^{*}$ resonance with hidden charm in the $π^{-} p \to D^{-} Σ_{c}^{+}$ reaction near threshold