Nuclear Theory·nucl-th

Wednesday·May 6, 2015

12 papers—4 primary·8 cross-listed

05
The eta transition form factor from space- and time-like experimental data
R. Escribano🇪🇸 · P. Masjuan🇩🇪 · P. Sanchez-Puertas🇩🇪
The $η$ transition form factor is analysed for the first time in both space- and time-like regions at low and intermediate energies in a model-independent approach through the use of rational approximants. The $η \to e^{+} e^{-} γ$ experimental data provided by the A2 Collaboration in the very low energy region of the dilelectron invariant mass distribution allows for the extraction of the most precise up-to-date slope and curvature parameters of the form factors as well as their values at zero and infinity. The impact of these new results on the mixing parameters of the $η$ - $η^{'}$ system, together with the role played by renormalisation dependent effects, and on the determination of the $V P γ$ couplings from $V \to P γ$ and $P \to V γ$ radiative decays are also discussed.
↳ hep-phhep-exnucl-thEPJC(2015)·93 citations
06
Cross sections of $α$ -induced reactions for targets with masses $A \approx 20 - 50$ at low energies
Peter Mohr
A simple reduction scheme using so-called reduced energies $E_{red}$ and reduced cross sections $σ_{red}$ allows the comparison of heavy-ion induced reaction cross sections for a broad range of masses of projectile and target and over a wide energy range. A global behavior has been found for strongly bound projectiles whereas much larger reduced cross sections have been observed for weakly bound and halo projectiles. It has been shown that this simple reduction scheme works also well for $α$ -particle induced reactions on heavy target nuclei, but very recently significant deviations have been seen for $α$ + $^{33}$ S and $α$ + $^{23}$ Na. Motivated by these unexpected discrepancies, the present study analyses $α$ -induced reaction cross sections for targets with masses $A \approx 20 - 50$ . The study shows that the experimental data for $α$ -induced reactions on nuclei with $A \approx 20 - 50$ deviate slightly from the global behavior of reduced cross sections. However, in general the deviations evolve smoothly towards lower masses. The only significant outliers are the recent data for $^{33}$ S and $^{23}$ Na which are far above the general systematics, and some very old data may indicate that $^{36}$ Ar and $^{40}$ Ar are below the general trend. As expected, also the doubly-magic $^{40}$ Ca nucleus lies slightly below the results for its neighboring nuclei. Overall, the experimental data are nicely reproduced by a statistical model calculation utilizing the simple $α$ -nucleus potential by McFadden and Satchler. Simultaneously with the deviation of reduced cross sections $σ_{red}$ from the general behavior, the outliers $^{23}$ Na, $^{33}$ S, $^{36}$ Ar, and $^{40}$ Ar also show significant disagreement between experiment and statistical model calculation.
↳ nucl-exastro-ph.IMnucl-thEPJA(2015)·32 citations
07
Progress in vacuum susceptibilities and their applications to the chiral phase transition of QCD
Zhu-Fang Cui🇨🇳 · Feng-Yao Hou🇨🇳 · Yuan-Mei Shi🇨🇳 · Yong-Long Wang🇨🇳 · Hong-Shi Zong🇨🇳
The QCD vacuum condensates and various vacuum susceptibilities are all important parameters which characterize the nonperturbative properties of the QCD vacuum. In the QCD sum rules external field formula, various QCD vacuum susceptibilities play important roles in determining the properties of hadrons. In this paper, we review the recent progress in studies of vacuum susceptibilities together with their applications to the chiral phase transition of QCD. The results of the tensor, the vector, the axial-vector, the scalar, and the pseudo-scalar vacuum susceptibilities are shown in detail in the framework of Dyson-Schwinger equations.
↳ hep-phnucl-thAnnals Phys.(2015)·48 citations
08
Dissipative fluid dynamics for the dilute Fermi gas at unitarity: Anisotropic fluid dynamics
Marcus Bluhm · Thomas Schaefer (North Carolina State University)
We consider the time evolution of a dilute atomic Fermi gas after release from a trapping potential. A common difficulty with using fluid dynamics to study the expansion of the gas is that the theory is not applicable in the dilute corona, and that a naive treatment of the entire cloud using fluid dynamics leads to unphysical results. We propose to remedy this problem by including certain non-hydrodynamic degrees of freedom, in particular anisotropic components of the pressure tensor, in the theoretical description. We show that, using this method, it is possible to describe the crossover from fluid dynamics to ballistic expansion locally. We illustrate the use of anisotropic fluid dynamics by studying the expansion of the dilute Fermi gas at unitarity using different functional forms of the shear viscosity, including a shear viscosity which is solely a function of temperature, $η \sim (m T)^{3/2}$ , as predicted by kinetic theory in the dilute limit.
↳ cond-mat.quant-gasnucl-thPRA(2015)·40 citations
09
Phonons, pions and quasi-long-range order in spatially modulated chiral condensates
Yoshimasa Hidaka🇯🇵 · Kazuhiko Kamikado🇯🇵 · Takuya Kanazawa🇯🇵 · Toshifumi Noumi🇯🇵
We investigate low-energy fluctuations in the real kink crystal phase of dense quark matter within the Nambu--Jona-Lasinio model. The modulated chiral condensate breaks both the translational symmetry and chiral symmetry spontaneously, which leads to the appearance of phonons and pions that are dominant degrees of freedom in the infrared. Using the Ginzburg-Landau expansion near the Lifshitz point, we derive elastic free energies for phonons and pions in dependence on the temperature and chemical potential. We show that the one-dimensional modulation is destroyed by thermal fluctuations of phonons at nonzero temperature, and compute the exponent that characterizes the anisotropic algebraic decay of quasicondensate correlations at long distance. We also estimate finite-volume effects on the stability of the real kink crystal and briefly discuss the possibility of its existence in neutron stars.
↳ hep-phhep-thnucl-thPRD(2015)·80 citations
10
Neutrino-production of a charmed meson and the transverse spin structure of the nucleon
B. Pire🇫🇷 · L. Szymanowski🇵🇱
We calculate the amplitude for exclusive neutrino production of a charmed meson on an unpolarized target, in the colinear QCD approach where generalized parton distributions (GPDs) factorize from perturbatively calculable coefficient functions. We demonstrate that the transversity chiral odd GPDs contribute to the transverse cross section if the hard amplitude is calculated up to order mc/Q. We show how to access these GPDs through the azimuthal dependence of the nu N -> mu D N differential cross section.
↳ hep-phhep-exnucl-exnucl-thPRL(2015)·36 citations
11
Collectivity in high-multiplicity events of proton-proton collisions in the framework of String Percolation
I. Bautista🇲🇽 · A. Fernandez Tellez🇲🇽 · Premomoy Ghosh🇮🇳
We analyze high multiplicity proton-proton ( $pp$ ) collision data at the energies $s = 900$ GeV, $2.76$ TeV and $7$ TeV in the framework of the String Percolation Model (SPM) in terms of the ratio of shear viscosity and entropy density ( $η / s$ ) showing that the model allows the formation of strongly interacting collective medium in the high energy and high multiplicity events in p-p collisions.
↳ hep-phnucl-exnucl-th4 citations
12
Neutrino Nucleosynthesis of radioactive nuclei in supernovae
A. Sieverding🇩🇪 · L. Huther🇩🇪 · K. Langanke🇩🇪 · G. Martínez-Pinedo🇩🇪 · A. Heger🇦🇺
We study the neutrino-induced production of nuclides in explosive supernova nucleosynthesis for progenitor stars with solar metallicity and initial main sequence masses between 15 M $_{⊙}$ and 40 M $_{⊙}$ . We improve previous investigations i) by using a global set of partial differential cross sections for neutrino-induced charged- and neutral-current reactions on nuclei with charge numbers $Z < 76$ and ii) by considering modern supernova neutrino spectra which have substantially lower average energies compared to those previously adopted in neutrino nucleosynthesis studies. We confirm the production of $^{7}$ Li, $^{11}$ B, $^{138}$ La, and $^{180}$ Ta by neutrino nucleosynthesis, albeit at slightly smaller abundances due to the changed neutrino spectra. We find that for stars with a mass smaller than 20 M $_{⊙}$ , $^{19}$ F is produced mainly by explosive nucleosynthesis while for higher mass stars it is produced by the $ν$ process. We also find that neutrino-induced reactions, either directly or indirectly by providing an enhanced abundance of light particles, noticeably contribute to the production of the radioactive nuclides $^{22}$ Na and $^{26}$ Al. Both nuclei are prime candidates for gamma-ray astronomy. Other prime targets, $^{44}$ Ti and $^{60}$ Fe, however, are insignificantly produced by neutrino-induced reactions. We also find a large increase in the production of the long-lived nuclei $^{92}$ Nb and $^{98}$ Tc due to charged-current neutrino capture.
↳ astro-ph.HEnucl-th10 citations

Affiliations

first authorsco-authorsvia INSPIRE