Nuclear Theory·nucl-th

Monday·August 3, 2015

10 papers—6 primary·4 cross-listed

01
Range corrections in Proton Halo Nuclei
Emil Ryberg · Christian Forssén · H.-W. Hammer · Lucas Platter
We analyze the effects of finite-range corrections in halo effective field theory for S-wave proton halo nuclei. We calculate the charge radius to next-to-leading order and the astrophysical S-factor for low-energy proton capture to fifth order in the low-energy expansion. As an application, we confront our results with experimental data for the S-factor for proton capture on Oxygen-16 into the excited $1/ 2^{+}$ state of Fluorine-17. Our low-energy theory is characterized by a systematic low-energy expansion, which can be used to quantify an energy-dependent model error to be utilized in data fitting. Finally, we show that the existence of proton halos is suppressed by the need for two fine tunings in the underlying theory.
nucl-thAnnals Phys.(2016)·24 citations
02
Frustrated fragmentation and re-aggregation in nuclei: a non-equilibrium description in spallation
P. Napolitani🇫🇷 · M. Colonna🇮🇹
Heavy nuclei bombarded with protons and deuterons in the 1 GeV range have a large probability of undergoing a process of evaporation and fission; less frequently, the prompt emission of few intermediate-mass fragments can also be observed. We employ a recently developed microscopic approach, based on the Boltzmann-Langevin transport equation, to investigate the role of mean-field dynamics and phase-space fluctuations in these reactions. We find that the formation of few IMF's can be confused with asymmetric fission when relying on yield observables, but it can not be assimilated to the statistical decay of a compound nucleus when analysing the dynamics and kinematic observables: it can be described as a fragmentation process initiated by phase-space fluctuations, and successively frustrated by the mean-field resilience. As an extreme situation, which corresponds to non-negligible probability, the number of fragments in the exit channel reduces to two, so that fission-like events are obtained by re-aggregation processes. This interpretation, inspired by nuclear-spallation experiments, can be generalised to heavy-ion collisions from Fermi to relativistic energies, for situations when the system is closely approaching the fragmentation threshold.
nucl-thPRC(2015)·34 citations
03
Shear and Bulk Viscosities of Quark Matter from Quark-Meson Fluctuations in the Nambu--Jona-Lasinio model
Sabyasachi Ghosh🇧🇷 · Thiago C. Peixoto🇧🇷 · Victor Roy🇩🇪 · Fernando E. Serna🇧🇷 · Gastão Krein🇧🇷
We have calculated the temperature dependence of shear $η$ and bulk $ζ$ viscosities of quark matter due to quark-meson fluctuations. The quark thermal width originating from quantum fluctuations of quark- $π$ and quark- $σ$ loops at finite temperature is calculated with the formalism of real-time thermal field theory. Temperature-dependent constituent-quark and meson masses, and quark-meson couplings are obtained in the Nambu--Jona-Lasinio model. We found a non-trivial influence of the temperature-dependent masses and couplings on the Landau-cut structure of the quark self-energy. Our results for the ratios $η / s$ and $ζ / s$ , where $s$ is the entropy density (also determined in the Nambu--Jona-Lasinio model in the quasi-particle approximation), are in fair agreement with results of the literature obtained from different models and techniques. In particular, our result for $η / s$ has a minimum very close to the conjectured AdS/CFT lower bound, $η / s = 1/4 π$ .
nucl-thhep-phPRC(2016)·57 citations
04
Hyperons in nuclear matter from SU(3) chiral effective field theory
S. Petschauer🇩🇪 · J. Haidenbauer🇩🇪 · N. Kaiser🇩🇪 · Ulf-G. Meißner🇩🇪 · W. Weise🇩🇪
Brueckner theory is used to investigate the properties of hyperons in nuclear matter. The hyperon-nucleon interaction is taken from chiral effective field theory at next-to-leading order with SU(3) symmetric low-energy constants. Furthermore, the underlying nucleon-nucleon interaction is also derived within chiral effective field theory. We present the single-particle potentials of Lambda and Sigma hyperons in symmetric and asymmetric nuclear matter computed with the continuous choice for intermediate spectra. The results are in good agreement with the empirical information. In particular, our calculation gives a repulsive Sigma-nuclear potential and a weak Lambda-nuclear spin-orbit force.
nucl-thEPJA(2016)·88 citations
05
Longitudinal vector form factors in weak decays of nuclei
F. Simkovic🇷🇺 · S. Kovalenko🇨🇱 · M. I. Krivoruchenko🇷🇺
The longitudinal form factors of the weak vector current of particles with spin $J = 1/2$ and isospin $I = 1/2$ are determined by the mass difference and the charge radii of members of the isotopic doublets. The most promising reactions to measure these form factors are the reactions with large momentum transfers involving the spin-1/2 isotopic doublets with a maximum mass splitting. Numerical estimates of longitudinal form factors are given for nucleons and eight nuclear spin-1/2 isotopic doublets.
nucl-thhep-phAIP Conf.Proc.(2015)·0 citations
06
Exact calculations of a quasi-bound state in the $K ˉ K ˉ N$ system
N.V. Shevchenko🇨🇿 · J. Haidenbauer🇩🇪
Dynamically exact calculations of a quasi-bound state in the $K ˉ K ˉ N$ three-body system are performed using Faddeev-type AGS equations. As input two phenomenological and one chirally motivated $K ˉ N$ potentials are used, which describe the experimental information on the $K ˉ N$ system equally well and produce either a one- or two-pole structure of the $Λ (1405)$ resonance. For the $K ˉ K ˉ$ interaction separable potentials are employed that are fitted to phase shifts obtained from two theoretical models. The first one is a phenomenological $K ˉ K ˉ$ potential based on meson exchange, which is derived by SU(3) symmetry arguments from the Jülich $π π - K ˉ K$ coupled-channels model. The other interaction is a variant of the first one, which is adjusted to the $K K$ s-wave scattering length recently determined in lattice QCD simulations. The position and width of the $K ˉ K ˉ N$ quasi-bound state is evaluated in two ways: (i) by a direct pole search in the complex energy plane and (ii) using an "inverse determinant" method, where one needs to calculate the determinant of the AGS system of equations only for real energies. A quasi-bound state is found with binding energy $B_{K ˉ K ˉ N} = 12 - 26$ MeV and width $Γ_{K ˉ K ˉ N} = 61 - 102$ MeV, which could correspond to the experimentally observed $Ξ (1950)$ state.
nucl-thPRC(2015)·15 citations
07
Polyakov--Nambu--Jona-Lasinio model in finite volumes
Abhijit Bhattacharyya🇮🇳 · Sanjay K. Ghosh🇮🇳 · Rajarshi Ray🇮🇳 · Kinkar Saha🇮🇳 · Sudipa Upadhaya🇮🇳
We discuss the 2+1 flavor Polyakov loop enhanced Nambu--Jona-Lasinio model in a finite volume. The main objective is to check the volume scaling of thermodynamic observables for various temperatures and chemical potentials. We observe the possible violation of the scaling with system size in a considerable window along the whole transition region in the $T - μ_{q}$ plane.
↳ hep-phnucl-thEPL(2016)·27 citations
08
Massive photons: an infrared regularization scheme for lattice QCD+QED
Michael G. Endres🇺🇸 · Andrea Shindler🇩🇪 · Brian C. Tiburzi🇺🇸 · Andre Walker-Loud🇺🇸
Standard methods for including electromagnetic interactions in lattice quantum chromodynamics calculations result in power-law finite-volume corrections to physical quantities. Removing these by extrapolation requires costly computations at multiple volumes. We introduce a photon mass to alternatively regulate the infrared, and rely on effective field theory to remove its unphysical effects. Electromagnetic modifications to the hadron spectrum are reliably estimated with a precision and cost comparable to conventional approaches that utilize multiple larger volumes. A significant overall cost advantage emerges when accounting for ensemble generation. The proposed method may benefit lattice calculations involving multiple charged hadrons, as well as quantum many-body computations with long-range Coulomb interactions.
↳ hep-lathep-phnucl-thPRL(2016)·91 citations
09
The impact of quark masses on pQCD thermodynamics
Thorben Graf🇩🇪 · Juergen Schaffner-Bielich🇩🇪 · Eduardo S. Fraga🇧🇷
We present results for several thermodynamic quantities within the next-to-leading order calculation of the thermodynamic potential in perturbative QCD at finite temperature and chemical potential including non-vanishing quark masses. These results are compared to lattice data and to higher-order optimized perturbative calculations to investigate the trend brought about by mass corrections.
↳ hep-phnucl-thEPJA(2016)·22 citations
10
Flavor instabilities in the multi-angle neutrino line model
Sajad Abbar🇺🇸 · Huaiyu Duan🇺🇸 · Shashank Shalgar (UNM)🇺🇸
Neutrino flavor oscillations in the presence of ambient neutrinos is nonlinear in nature which leads to interesting phenomenology that has not been well understood. It was recently shown that, in the two-dimensional, two-beam neutrino Line model, the inhomogeneous neutrino oscillation modes on small distance scales can become unstable at larger neutrino densities than the homogeneous mode does. We develop a numerical code to solve neutrino oscillations in the multi-angle/beam Line model with a continuous neutrino angular distribution. We show that the inhomogeneous oscillation modes can occur at even higher neutrino densities in the multi-angle model than in the two-beam model. We also find that the inhomogeneous modes on sufficiently small scales can be unstable at smaller neutrino densities with ambient matter than without, although a larger matter density does shift the instability region of the homogeneous mode to higher neutrino densities in the Line model as it does in the one-dimensional supernova Bulb model. Our results suggest that the inhomogeneous neutrino oscillation modes can be difficult to treat numerically because the problem of spurious oscillations becomes more severe for oscillations on smaller scales.
↳ hep-phastro-ph.HEnucl-thPRD(2015)·57 citations

Affiliations

first authorsco-authorsvia INSPIRE