Nuclear Theory·nucl-th

Tuesday·June 2, 2015

8 papers—5 primary·3 cross-listed

01
[Submitted on 1 Jun 2015]
Pionless Effective Field Theory in Few-Nucleon Systems
Johannes Kirscher
A systematic description of low-energy observables in light nuclei is presented. The effective field theory formalism without pions is extended to: i) predictions with next-to-leading-order (non-perturbatively) accuracy for the 4-helium binding energy B({\alpha}), the triton charge radius, and the 3-helium-neutron scattering length; ii) phase shifts for neutron-deuteron scattering and {\alpha}-neutron low-energy scattering at leading order; iii) the ground states of the 5-helium (with and without Coulomb interaction) and 6-helium isotopes up to next-to-leading order; The convergence from leading- to next-to-leading order of the theory is demonstrated for correlations between: i) the triton binding energy B(t) and the triton charge radius; ii) B(t) and the 4-helium binding energy B({\alpha}); Furthermore, a correlation between B(t) and the scattering length in the singlet S-wave channel of neutron-helium-3 scattering is discovered, and a model-independent estimate for the trinucleon binding energy splitting is provided. The results provide evidence for the usefulness of the applied power-counting scheme, treating next-to-leading-order interactions nonperturbatively and four-nucleon interactions as, at least, one order higher. The 5- and 6-helium ground states are analyzed with a power-counting scheme which includes the momentum-dependent next-to-leading order vertices perturbatively. All calculations include a full treatment of the Coulomb interaction. The assessment of numerical uncertainties associated with the solution of the few-body equation of motion through the Resonating Group Method parallels the report of the results for light nuclei in order to establish this method as practical for the analysis of systems with up to six particles interacting via short-range interactions.
Comments:
103 pages, Ph.D. thesis, 2010
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1506.00347 [pdf]
8 citations
02
[Submitted on 1 Jun 2015]
Unified equation of state for neutron stars on a microscopic basis
B. K. Sharma🇪🇸 · M. Centelles🇪🇸 · X. Vinas🇪🇸 · M. Baldo🇮🇹 · G. F. Burgio🇮🇹
We derive a new equation of state (EoS) for neutron stars (NS) from the outer crust to the core based on modern microscopic Brueckner-Hartree-Fock (BHF) calculations using the Argonne $v_{18}$ potential plus three-body forces computed with the Urbana model. To deal with the inhomogeneous structures of matter in the NS crust, we use the recent Barcelona-Catania-Paris-Madrid (BCPM) nuclear energy density functional that is directly based on the same microscopic BHF calculations, and which is able to reproduce the ground-state properties of nuclei along the periodic table. The EoS of the outer crust requires the masses of neutron-rich nuclei, which are obtained through Hartree-Fock-Bogoliubov calculations with the BCPM functional when they are unknown experimentally. To compute the inner crust, Thomas-Fermi calculations in Wigner-Seitz cells are performed with the same functional. Existence of nuclear pasta is predicted in a range of average baryon densities between $≃$ 0.067 fm $^{- 3}$ and $≃$ 0.0825 fm $^{- 3}$ , where the transition to the core takes place. The NS core is computed from the nuclear EoS of the BHF calculation assuming non-exotic constituents (core of $n p e μ$ matter). In each region of the star, we discuss the comparison of the new EoS with previous EoSes for the complete NS structure, in particular, with the Lattimer-Swesty EoS and with the Shen et al. EoS widely used in astrophysical calculations. The new microscopically derived EoS fulfills at the same time a NS maximum mass of 2~ $M_{⊙}$ with a radius of 10 km, and a 1.5~ $M_{⊙}$ NS with a radius of 11.7 km.
Comments:
23 pages, 17 figures, revised version accepted for publication in Astronomy & Astrophysics
Subjects:
Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR)
arXiv:
1506.00375 [pdf]
Astron.Astrophys.(2015)·156 citations
03
[Submitted on 1 Jun 2015]
Non-extensive distributions for a relativistic Fermi Gas
Jacek Rożynek🇵🇱
Recently the non-extensive approach has been used in a variety of ways to describe dense nuclear matter. They differ in the methods of introducing the appropriate non-extensive single particle distributions inside a relativistic many-body system, in particular when one has to deal both with particles and antiparticles, as in the case of quark matter exemplified in the NJL approach. I present and discuss in detail the physical consequences of the methods used so far, which should be recognized before any physical conclusions can be reached from the results presented.
Comments:
Revision (the interchange) in formula (19) and (20)
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1506.00469 [pdf]
Physica A(2015)·6 citations
04
[Submitted on 1 Jun 2015]
Collective Modes in the Superfluid Inner Crust of Neutron Stars
Michael Urban · Micaela Oertel
The neutron-star inner crust is assumed to be superfluid at relevant temperatures. The contribution of neutron quasiparticles to thermodynamic and transport properties of the crust is therefore strongly suppressed by the pairing gap. Nevertheless, the neutron gas still has low-energy excitations, namely long-wavelength collective modes. We summarize different approaches to describe the collective modes in the crystalline phases of the inner crust and present an improved model for the description of the collective modes in the pasta phases within superfluid hydrodynamics.
Comments:
20 pages, 9 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1506.00483 [pdf]
IJMPE(2015)·7 citations
05
[Submitted on 1 Jun 2015]
The Possible Origin and Implications of the Shoulder in Reactor Neutrino Spectra
A.C. Hayes🇺🇸 · J. L. Friar🇺🇸 · G. T. Garvey🇺🇸 · Duligur Ibeling🇺🇸 · Gerard Jungman🇺🇸 · T. Kawano🇺🇸 · Robert W. Mills🇺🇸
We analyze within a nuclear database framework the shoulder observed in the antineutrino spectra in current reactor experiments. We find that the ENDF/B-VII.1 database predicts that the antineutrino shoulder arises from an analogous shoulder in the aggregate fission beta spectra. In contrast, the JEFF-3.1.1 database does not predict a shoulder for two out of three of the modern reactor neutrino experiments, and the shoulder that is predicted by JEFF-3.1.1 arises from $^{238}$ U. We consider several possible origins of the shoulder, and find possible explanations. For example, there could be a problem with the measured aggregate beta spectra, or the harder neutron spectrum at a light-water power reactor could affect the distribution of beta-decaying isotopes. In addition to the fissile actinides, we find that $^{238}$ U could also play a significant role in distorting the total antineutrino spectrum. Distinguishing these and quantifying whether there is an anomaly associated with measured reactor neutrino signals will require new short-baseline experiments, both at thermal reactors and at reactors with a sizable epithermal neutron component.
Comments:
Extension of previous version of the same manuscript, including an analysis of the Double Chooz neutrino experiment
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Instrumentation and Detectors (physics.ins-det)
arXiv:
1506.00583 [pdf]
PRD(2015)·122 citations
06
[Submitted on 23 May 2015] (cross-list from hep-ph)
Cherenkov and Fano effects at the origin of asymmetric vector mesons in nuclear media
I.M. Dremin🇷🇺
It is argued that the experimentally observed phenomenon of asymmetric vector mesons produced in nuclear media during high energy nucleus-nucleus collisions can be explained as Cherenkov and Fano effects. The mass distributions of lepton pairs created at meson decays decline from the traditional Breit-Wigner shape in the low-mass wing of the resonance. That is explained by the positive real part of the amplitude in this wing for classic Cherenkov treatment and further detalized in quantum mechanics as the interference of direct and continuum states in Fano effect. The corresponding parameters are found from the comparison with rho-meson data and admit reasonable explanation.
Comments:
7 pages, 1 figure
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1505.06297 [pdf]
0 citations
07
[Submitted on 30 May 2015] (cross-list from hep-th)
Matrix model and Holographic Baryons in the D0-D4 background
Si-wen Li🇨🇳 · Tuo Jia🇨🇳
We study on the spectrum and short-distance two-body force of holographic baryons by the matrix model, which is derived from Sakai-Sugimoto model in D0-D4 background (D0-D4/D8 system). The matrix model is derived by using the standard technique in string theory and it can describe multi-baryon system. We re-derive the action of the matrix model from open string theory on the wrapped baryon vertex, which is embedded in the D0- D4/D8 system. The matrix model offers a more systematic approach to the dynamics of the baryons at short distances. In our system, we find that the matrix model describe stable baryonic states only if $ζ = U_{Q_{0}}^{3} / U_{K K}^{3} < 2$ , where $U_{Q_{0}}^{3}$ is related to the number density of smeared D0-branes. This result in our paper is exactly the same as some previous presented results studied on this system as \cite{key-24 Baryons in D0-D4}. We also compute the baryon spectrum ( $k = 1$ case) and short-distance two-body force of baryons ( $k = 2$ case). The baryon spectrum is modified and could be able to fit the experimental data if we choose suitable value for $ζ$ . And the short-distance two-body force of baryons is also modified by the appearance of smeared D0-branes from the original Sakai-Sugimoto model. If $ζ > 2$ , we find that the baryon spectrum would be totally complex and an attractive force will appear in the short-distance interaction of baryons, which may consistently correspond to the existence of unstable baryonic states.
Comments:
19 pages
Subjects:
High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1506.00068 [pdf]
PRD(2015)·23 citations
08
[Submitted on 1 Jun 2015] (cross-list from hep-ph)
Mean pt scaling with m/nq at the LHC: Absence of (hydro) flow in small systems?
Antonio Ortiz🇲🇽
In this work, a study of the average transverse momentum (pt) as a function of the mid-rapidity charged hadron multiplicity (Nch) and hadron mass (m) in p-Pb and Pb-Pb collisions at LHC energies is presented. For the events producing low Nch, the average pt is found to scale with the reduced hadron mass, i.e., mass divided by the number of quark constituents (m/nq), this scaling also holds for inelastic pp collisions at RHIC and LHC energies. The scaling is broken in high multiplicity p-Pb and Pb-Pb collisions, where, for <Nch/deta> < 60 the average pt is higher for baryons than that for mesons, though they increase linearly with m/nq. This behavior is qualitatively well reproduced by Pythia 8, but not by hydro calculations, where an universal scaling with the hadron mass (and not with m/nq) is predicted for all the multiplicity event classes. Only the central (0-60%) Pb-Pb collisions behave as expected from hydro.
Comments:
8 pages, 6 figures. Minor changes were implemented in the text
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1506.00584 [pdf]
NPA(2015)·20 citations

Affiliations

first authorsco-authorsvia INSPIRE