Nuclear Theory·nucl-th

Monday·July 18, 2016

13 papers—9 primary·4 cross-listed

01
[Submitted on 14 Jul 2016]
Density-dependent effective baryon-baryon interaction from chiral three-baryon forces
Stefan Petschauer🇩🇪 · Johann Haidenbauer🇩🇪 · Norbert Kaiser🇩🇪 · Ulf-G. Meißner🇩🇪 · Wolfram Weise🇩🇪
A density-dependent effective potential for the baryon-baryon interaction in the presence of the (hyper)nuclear medium is constructed, based on the leading (irreducible) three-baryon forces derived within SU(3) chiral effective field theory. We evaluate the contributions from three classes: contact terms, one-pion exchange and two-pion exchange. In the strangeness-zero sector we recover the known result for the in-medium nucleon-nucleon interaction. Explicit expressions for the Lambda-nucleon in-medium potential in (asymmetric) nuclear matter are presented. Our results are suitable for implementation into calculations of (hyper)nuclear matter. In order to estimate the low-energy constants of the leading three-baryon forces we introduce the decuplet baryons as explicit degrees of freedom and construct the relevant terms in the minimal non-relativistic Lagrangian. With these, the constants are estimated through decuplet saturation. Utilizing this approximation we provide numerical results for the effect of the three-body force in symmetric nuclear matter and pure neutron matter on the Lambda-nucleon interaction. A moderate repulsion that increases with density is found in comparison to the free Lambda-nucleon interaction.
Comments:
25 pages, 15 figures, 4 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1607.04307 [pdf]
NPA(2017)·41 citations
02
[Submitted on 15 Jul 2016]
Carbon-oxygen-neon mass nuclei in superstrong magnetic fields
Martin Stein · Joachim Maruhn · Armen Sedrakian · P.-G. Reinhard
The properties of $\isotope [12] C$ , $\isotope [16] O$ , and $\isotope [20] N e$ nuclei in strong magnetic fields $B ≃ 1 0^{17}$ G are studied in the context of strongly magnetized neutron stars and white dwarfs. The SKY3D code is extended to incorporate the interaction of nucleons with the magnetic field and is utilized to solve the time-independent Hartree-Fock equations with a Skyrme interaction on a Cartesian three-dimensional grid. The numerical solutions demonstrate a number of phenomena, which include a splitting of the energy levels of spin-up and -down nucleons, spontaneous rearrangment of energy levels in $\isotope [16] O$ at a critical field, which leads to jump-like increases of magnetization and proton current in this nucleus, and evolution of the intrinsically deformed $\isotope [20] N e$ nucleus towards a more spherical shape under increasing field strength. Many of the numerical features can be understood within a simple analytical model based on the occupation by the nucleons of the lowest states of the harmonic oscillator in a magnetic field.
Comments:
v2: uses Revtex, 8 pages, 8 figures, matches published version
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
arXiv:
1607.04398 [pdf]
PRC(2016)·25 citations
03
[Submitted on 15 Jul 2016]
Dissecting nucleon transition electromagnetic form factors
Jorge Segovia🇩🇪 · Craig D. Roberts🇺🇸
In Poincaré-covariant continuum treatments of the three valence-quark bound-state problem, the force behind dynamical chiral symmetry breaking also generates nonpointlike, interacting diquark correlations in the nucleon and its resonances. We detail the impact of these correlations on the electromagnetically-induced nucleon- $Δ$ and nucleon-Roper transitions, providing a flavour-separation of the latter and associated predictions that can be tested at modern facilities.
Comments:
6 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1607.04405 [pdf]
PRC(2016)·44 citations
04
[Submitted on 15 Jul 2016]
Polarized proton-deuteron scattering as a test of time-reversal invariance
Yu.N. Uzikov🇷🇺 · J. Haidenbauer🇩🇪
Scattering of protons with transversal polarization $p_{y}^{p}$ on deuterons with tensor polarization $P_{x z}$ provides a null-test signal for time-reversal (T) invariance violating but parity (P) conserving effects. We calculate the corresponding null-test observable at beam energies 100-1000 MeV within the spin-dependent Glauber theory considering T-violating P-conserving nucleon-nucleon interactions. The S-wave component of the deuteron wave function as well as the D-wave are taken into account and the latter is found to play an important role for the magnitude and the energy dependence of the observable in question. Specifically, with inclusion of the D wave the maximum of the obtained signal is shifted to higher beam energies, i.e. to 700-800 MeV.
Comments:
6 pages, 3 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1607.04409 [pdf]
PRC(2016)·25 citations
05
[Submitted on 15 Jul 2016]
New phase space calculations for beta-decay half-lives
Sabin Stoica · Mihail Mirea · Ovidiu Nitescu · Jameel-Un Nabi · Mavra Ishfaq
We revisit the computation of the phase space factors (PSF) involved in the positron decay and electron capture (EC) processes for a large number of nuclei of experimental interest. To obtain the electron/positron wave functions needed in computation, we develop a code for solving accurately the Dirac equation with a nuclear potential derived from a realistic proton density distribution in the nucleus. The finite nuclear size (FNS) and screening effects are included through recipes which differ from those used in previous calculations. Comparing our results with former calculations employing approximate methods but computed with the same Q-values, we find a close agreement for positron decays, while for the EC process there are relevant differences. For the EC process we also find that the screening effect has a notable influence on the computed PSF values specially for light nuclei. Further, we re-computed the same PSF values but using the most recent Q-values reported in literature. In several cases these new Q-values differ significantly from the older ones, which results in large differences in the PSF values as compared with previous results. These new PSF values proposed here, can contribute to a more reliable calculation of the beta decay rates, which are key quantities in the study of nuclei far from the stability line, as well as to better understanding of the stellar evolution.
Comments:
9 pages, 1 figure
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1607.04426 [pdf]
Adv.High Energy Phys.(2016)·6 citations
06
[Submitted on 15 Jul 2016]
Breathing-like excited state of the Hoyle state in $^{12} C$
Bo Zhou · Akihiro Tohsaki · Hisashi Horiuchi · Zhongzhou Ren
The existence of the $0_{3}^{+}$ and $0_{4}^{+}$ states around 10 MeV excitation energy in $^{12} C$ is confirmed by a fully microscopic 3 $α$ cluster model. Firstly, a GCM (generator coordinate method) calculation is performed by superposing optimized 2 $α$ + $α$ THSR (Tohsaki-Horiuchi-Schuck-Röpke) wave functions with the radius-constraint method. The obtained two excited $0^{+}$ states above the Hoyle state are consistent with the recently observed states by experiment. Secondly, a variational calculation using the single 2 $α$ + $α$ THSR wave function orthogonalized to the ground and Hoyle states is made and it also supports the existence of the $0_{3}^{+}$ state obtained by the GCM calculation. The analysis of the obtained $0_{3}^{+}$ state is made by studying its 2 $α$ - $α$ reduced width amplitude, its 2 $α$ correlation function, and the large monopole matrix element between this state and the Hoyle state, which shows that this $0_{3}^{+}$ state is a breathing-like excited state of the Hoyle state. This character of the $0_{3}^{+}$ state is very different from the $0_{4}^{+}$ state which seems to have a bent-arm 3 $α$ structure.
Comments:
9 pages, 5 figures. Submitted to PRC on July 7, 2016
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1607.04468 [pdf]
PRC(2016)·45 citations
07
[Submitted on 28 Jun 2016]
Procedure for measuring particle's circular polarization variation with respect to the reaction plane in relativistic heavy-ion collisions
A.H. Tang🇺🇸 · G. Wang🇺🇸
The EM field pattern created by spectators in relativistic heavy-ion collisions plants a seed of positive (negative) magnetic helicity in the hemisphere above (below) the reaction plane. Owing to the chiral anomaly, the magnetic helicity interacts with the fermionic helicity of the collision system, and causes photons emitted in upper- and lower-hemispheres to have different preferences in the circular polarization. In this paper, we lay down a procedure to measure the variation of the circular polarization w.r.t the reaction plane in relativistic heavy-ion collisions for massless photons, as well as similar polarization patterns for vector mesons decaying into two daughters. We propose to study the yield differentially and compare the yield between upper- and lower-hemispheres in order to identify and quantify such effects.
Comments:
3 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1607.04489 [pdf]
PRC(2016)·2 citations
08
[Submitted on 15 Jul 2016]
Hamiltonian effective field theory study of the $N^{*} (1440)$ resonance in lattice QCD
Zhan-Wei Liu🇦🇺 · Waseem Kamleh🇦🇺 · Derek B. Leinweber🇦🇺 · Finn M. Stokes🇦🇺 · Anthony W. Thomas🇦🇺 · Jia-Jun Wu🇦🇺
We examine the phase shifts and inelasticities associated with the $N^{*} (1440)$ Roper resonance and connect these infinite-volume observables to the finite-volume spectrum of lattice QCD using Hamiltonian effective field theory. We explore three hypotheses for the structure of the Roper resonance. All three hypotheses are able to describe the scattering data well. In the third hypothesis the Roper resonance couples the low-lying bare basis-state component associated with the ground state nucleon with the virtual meson-baryon contributions. Here the non-trivial superpositions of the meson-baryon scattering states are complemented by bare basis-state components explaining their observation in contemporary lattice QCD calculations. The merit of this scenario lies in its ability to not only describe the observed nucleon energy levels in large-volume lattice QCD simulations but also explain why other low-lying states have been missed in today's lattice QCD results for the nucleon spectrum.
Comments:
14 pages, 14 figures; version to be published in Phys. Rev. D
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1607.04536 [pdf]
PRD(2017)·89 citations
09
[Submitted on 15 Jul 2016]
Nuclear Physics Around the Unitarity Limit
Sebastian König🇺🇸 · Harald W. Grießhammer🇺🇸 · H.-W. Hammer🇩🇪 · U. van Kolck🇫🇷
We argue that many features of the structure of nuclei emerge from a strictly perturbative expansion around the unitarity limit, where the two-nucleon S waves have bound states at zero energy. In this limit, the gross features of states in the nuclear chart are correlated to only one dimensionful parameter, which is related to the breaking of scale invariance to a discrete scaling symmetry and set by the triton binding energy. Observables are moved to their physical values by small, perturbative corrections, much like in descriptions of the fine structure of atomic spectra. We provide evidence in favor of the conjecture that light, and possibly heavier, nuclei are bound weakly enough to be insensitive to the details of the interactions but strongly enough to be insensitive to the exact size of the two-nucleon system.
Comments:
6 pages, 3 figures, published version, rewritten for clarity
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1607.04623 [pdf]
PRL(2017)·119 citations
10
[Submitted on 14 Jul 2016] (cross-list from hep-th)
Radial vibrations of BPS skyrmions
C. Adam🇪🇸 · M. Haberichter🇯🇵 · T. Romanczukiewicz🇵🇱 · A. Wereszczynski🇵🇱
We study radial vibrations of spherically symmetric skyrmions in the BPS Skyrme model. Concretely, we numerically solve the linearised field equations for small fluctuations in a skyrmion background, both for linearly stable oscillations and for (unstable) resonances. This is complemented by numerical solutions of the full nonlinear system, which confirm all the results of the linear analysis. In all cases, the resulting fundamental excitation provides a rather accurate value for the Roper resonance, supporting the hypothesis that the BPS Skyrme model already gives a reasonable approximate description of this resonance. Further, for many potentials additional higher resonances appear, again in agreement with known experimental results.
Comments:
Latex, 41 pages, 22 pdf figures; v2: minor changes
Subjects:
High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1607.04286 [pdf]
PRD(2016)·9 citations
11
[Submitted on 14 Jul 2016] (cross-list from hep-ph)
Synchrotron contribution to photon emission from quark-gluon plasma
B.G. Zakharov🇷🇺
We study the influence of the magnetic field on the photon emission from the quark-gluon plasma created in $AA$ collisions. We find that even for very optimistic assumption on the magnitude of the magnetic field for noncentral $AA$ collisions the effect of magnetic field is very small.
Comments:
5 pages, 2 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1607.04314 [pdf]
JETP Lett.(2016)·10 citations
12
[Submitted on 15 Jul 2016] (cross-list from hep-ph)
High Gluon Densities in Heavy Ions Collisions
Jean-Paul Blaizot🇫🇷
The early stages of heavy ion collisions are dominated by high density systems of gluons that carry each a small fraction $x$ of the momenta of the colliding nucleons. A distinguishing feature of such systems is the phenomenon of "saturation" which tames the expected growth of the gluon density as the energy of the collision increases. The onset of saturation occurs at a particular transverse momentum scale, the "saturation momentum", that emerges dynamically and that marks the onset of non-linear gluon interactions. At high energy, and for large nuclei, the saturation momentum is large compared to the typical hadronic scale, making high density gluons amenable to a description with weak coupling techniques. This paper reviews some of the challenges faced in the study of such dense systems of small $x$ gluons, and of the progress made in addressing them. The focus is on conceptual issues, and the presentation is both pedagogical, and critical. Examples where high gluon density could play a visible role in heavy ion collisions are briefly discussed at the end, for illustration purpose.
Comments:
Submitted to Reports on Progress in Physics
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1607.04448 [pdf]
Rept.Prog.Phys.(2017)·98 citations
13
[Submitted on 15 Jul 2016] (cross-list from astro-ph.HE)
Electrical conductivity tensor of dense plasma in magnetic fields
Arus Harutyunyan · Armen Sedrakian
Electrical conductivity of finite-temperature plasma in neutron star crusts is studied for applications in magneto-hydrodynamical description of compact stars. We solve the Boltzmann kinetic equation in relaxation time approximation taking into account the anisotropy of transport due to the magnetic field, the effects of dynamical screening in the scattering matrix element and corre- lations among the nuclei. We show that conductivity has a minimum at a non-zero temperature, a low-temperature decrease and a power-law increase with increasing temperature. Selected numerical results are shown for matter composed of carbon, iron, and heavier nuclei present in the outer crusts of neutron star.
Comments:
12 pages, 5 figures, supplemental material contains 21 tables. Proceedings of "The Modern Physics of Compact Stars and Relativistic Gravity 2015", 30 September 2015 - 3 October 2015 Yerevan, Armenia
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1607.04541 [pdf]
PoS(2016)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE