Nuclear Theory·nucl-th

Thursday·June 4, 2015

10 papers—5 primary·5 cross-listed

06
High x Structure Function of the Virtually Free Neutron
Wim Cosyn🇧🇪 · Misak M. Sargsian🇺🇸
The pole extrapolation method is applied to the semi-inclusive inelastic electron scattering off the deuteron with tagged spectator protons to extract the high-x structure function of the neutron. This approach is based on the extrapolation of the measured cross sections at different momenta of the spectator proton to the non-physical pole of the bound neutron in the deuteron. The advantage of the method is in the possibility of suppression of the nuclear effects in a maximally model-independent way. The neutron structure functions obtained in this way demonstrate a surprising x dependence at $x \geq 0.6$ and $1.6 \leq Q^{2} \leq 3.38$ GeV $^{2}$ , indicating a possible rise of the neutron to proton structure function ratio. If the observed rise is valid in the true deep inelastic region then it may indicate new dynamics in the generation of high-x quarks in the nucleon. One such mechanism we discuss is the possible dominance of short-range isosinglet quark-quark correlations that can enhance the d-quark distribution in the proton.
↳ hep-phnucl-exnucl-thPRC(2016)·7 citations
07
Role of the $Λ_{c}^{+} (2940)$ in the $π^{-} p \to D^{-} D^{0} p$ reaction close to threshold
Ju-Jun Xie🇨🇳 · Yu-Bing Dong🇨🇳 · Xu Cao🇨🇳
We report on a theoretical study of the $π^{-} p \to D^{-} D^{0} p$ reaction near threshold within an effective Lagrangian approach. The production process is described by $t$ channel $D^{* 0}$ meson exchange, $s$ -channel nucleon pole, and $u$ channel $Σ_{c}^{++}$ exchange. In our work, the final $D^{0} p$ results from the ground $Λ_{c}^{+} (2286)$ state and also dominantly from the excited $Λ_{c}^{+} (2940)$ state which is assumed as a $D^{* 0} p$ molecular state with spin parity $J^{P} = \frac{1}{2}^{+}$ or $\frac{1}{2}^{-}$ . We calculate the total cross section of the $π^{-} p \to D^{-} D^{0} p$ reaction. It is shown that the spin parity assignment of $\frac{1}{2}^{-}$ for $Λ_{c}^{+} (2940)$ gives a sizable enhancement for the total cross section in comparison with a choice of $J^{p} = \frac{1}{2}^{+}$ . However, our theoretical result of the total cross section is sensitive to the value of the cutoff parameter involved in the form factor of the exchanged off-shell particles. Moreover, we also calculate the second order differential cross section and find it can be used to determine the parity of the $Λ_{c}^{+} (2940)$ . It is expected that our model calculations can be tested by future experiments at J-PARC in Japan.
↳ hep-phhep-exnucl-exnucl-thPRD(2015)·45 citations
08
Collective modes of p-wave superfluid Fermi gases in BEC phase
Francesco Matera · Matthias F. Wagner
The low-energy modes of a superfluid atomic Fermi gas at zero temperature are investigated. The Bose-Einstein-condensate (BEC) side of the superfluid phase is studied in detail. The atoms are assumed to be in only one internal state, so that for a sufficiently diluted gas the pairing of fermions can be considered effective in the l=1 channel only. In agreement with previous works on p-wave superfluidity in Fermi systems, it is found that the $p_{x} + i p_{y}$ phase represents the lowest energy state in both the Bardeen-Cooper-Schrieffer (BCS) and BEC sides. Our calculations show that at low energy three branches of collective modes can emerge, with different species of dispersion relations: a phonon-like mode, a single-particle-like mode and a gapped mode. A comparison with the Bogoliubov excitations of the corresponding spinor Bose condensate is made. They reproduce the dispersion relations of the excitation modes of the p-wave superfluid Fermi gas to a high accuracy.
↳ cond-mat.quant-gasnucl-thEur.Phys.J.D(2015)·1 citation
09
A covariant model for the nucleon spin structure
G. Ramalho🇧🇷
We present the results of the covariant spectator quark model applied to the nucleon structure function $f (x)$ measured in unpolarized deep inelastic scattering, and the structure functions $g_{1} (x)$ and $g_{2} (x)$ measured in deep inelastic scattering using polarized beams and targets ( $x$ is the Bjorken scaling variable). The nucleon is modeled by a valence quark-diquark structure with $S, P$ and $D$ components. The shape of the wave functions and the relative strength of each component are fixed by making fits to the deep inelastic scattering data for the structure functions $f (x)$ and $g_{1} (x)$ . The model is then used to make predictions on the function $g_{2} (x)$ for the proton and neutron.
↳ hep-phhep-exnucl-exnucl-thProceedings of New Trends in High-Energy …·0 citations
10
Thermodynamics and CP-odd transport in Holographic QCD with Finite Magnetic Field
Tara Drwenski🇳🇱 · Umut Gursoy🇳🇱 · Ioannis Iatrakis🇺🇸
We consider a bottom-up holographic model of QCD at finite temperature T and magnetic field B, and study dependence of thermodynamics and CP-odd transport on these variables. As the magnetic field couples to the flavor sector only, one should take the Veneziano limit where the number of flavors and colors are large while their ratio is kept fixed. We investigate the corresponding holographic background in the approximation where the ratio of flavors to colors is finite but small. We demonstrate that B-dependence of the entropy of QCD is in qualitative agreement with the recent lattice studies. Finally we study the CP-odd transport properties of this system. In particular, we determine the Chern-Simons decay rate at finite B and T, that is an important ingredient in the Chiral Magnetic Effect.
↳ hep-thhep-phnucl-thJHEP(2016)·28 citations

Affiliations

first authorsco-authorsvia INSPIRE

High x Structure Function of the Virtually Free Neutron

Role of the Λc+​(2940) in the π−p→D−D0p reaction close to threshold

Collective modes of p-wave superfluid Fermi gases in BEC phase

A covariant model for the nucleon spin structure

Thermodynamics and CP-odd transport in Holographic QCD with Finite Magnetic Field

Affiliations

Role of the $Λ_{c}^{+} (2940)$ in the $π^{-} p \to D^{-} D^{0} p$ reaction close to threshold