Nuclear Theory·nucl-th

Monday·November 23, 2015

11 papers—8 primary·3 cross-listed

01
Hot third family of compact stars and the possibility of core-collapse supernova explosions
Matthias Hempel🇨🇭 · Oliver Heinimann🇨🇭 · Andrey Yudin🇷🇺 · Igor Iosilevskiy🇷🇺 · Matthias Liebendörfer🇨🇭 · Friedrich-Karl Thielemann🇨🇭
A phase transition to quark matter can lead to interesting phenomenological consequences in core-collapse supernovae, e.g., triggering an explosion in spherically symmetric models. However, until now this explosion mechanism was only shown to be working for equations of state that are in contradiction with recent pulsar mass measurements. Here, we identify that this explosion mechanism is related to the existence of a third family of compact stars. For the equations of state investigated, the third family is only pronounced in the hot, early stages of the protocompact star and absent or negligibly small at zero temperature and thus represents a novel kind of third family. This interesting behavior is a result of unusual thermal properties induced by the phase transition, e.g., characterized by a decrease of temperature with increasing density for isentropes, and can be related to a negative slope of the phase transition line in the temperature-pressure phase diagram.
nucl-thastro-ph.HEastro-ph.SRPRD(2016)·37 citations
02
Distributions of the $S$ -matrix poles in Woods-Saxon and cut-off Woods-Saxon potentials
P. Salamon · Á. Baran · T. Vertse
The positions of the $l = 0$ $S$ -matrix poles are calculated in generalized Woods-Saxon (GWS) potential and in cut-off generalized Woods-Saxon (CGWS) potential. The solutions of the radial equations are calculated numerically for the CGWS potential and analytically for GWS using the formalism of Gy. Bencze \cite{[Be66]}. We calculate CGWS and GWS cases at small non-zero values of the diffuseness in order to approach the square well potential and to be able to separate effects of the radius parameter and the cut-off radius parameter. In the case of the GWS potential the wave functions are reflected at the nuclear radius therefore the distances of the resonant poles depend on the radius parameter of the potential. In CGWS potential the wave function can be reflected at larger distance where the potential is cut to zero and the derivative of the potential does not exist. The positions of most of the resonant poles do depend strongly on the cut-off radius of the potential, which is an unphysical parameter. Only the positions of the few narrow resonances in potentials with barrier are not sensitive to the cut-off distance. For the broad resonances the effect of the cut-off can not be corrected by using a suggested analytical form of the first order perturbation correction.
nucl-thNPA(2016)·8 citations
03
Phonon contributions to ab initio double mass differences of magic nuclei
E. E. Saperstein · M. Baldo · N. V. Gnezdilov · S. V. Tolokonnikov
Odd-even double mass differences (DMD) of magic nuclei are found within the approach starting from the free $N N$ interaction with account for particle-phonon coupling (PC) effects. We consider three PC effects: the phonon induced effective interaction, the renormalization of the "ends" due to the $Z$ -factor corresponding to the pole PC contribution to the nucleon mass operator and the change of the single-particle energies. The perturbation theory in $g_{L}^{2}$ , where $g_{L}$ is the vertex of the $L$ -phonon creation, is used for PC calculations. PC corrections to single-particle energies are found self-consistently with an approximate account for the tadpole diagram. Results for magic $^{40, 48}$ Ca, $^{56, 78}$ Ni, $^{100, 132}$ Sn and $^{208}$ Pb nuclei are presented. For lighter part of this set of nuclei, from $^{40}$ Ca till $^{56}$ Ni, the cases divide approximately in half between those where the PC corrections to DMD values make agreement with the data better and the ones with the opposite result. In the major part of the cases of worsening of description of DMD, a poor applicability of the perturbation theory for the induced interaction is the most probable reason of the phenomenon. For intermediate nuclei, $^{78}$ Ni and $^{100}$ Sn, there is no sufficiently accurate data on masses of nuclei necessary for finding DMD values. Finally, for heavier nuclei, $^{132}$ Sn and $^{208}$ Pb, PC corrections always make agreement with the experiment better.
nucl-thnucl-exPRC(2016)·9 citations
04
Applying Twisted Boundary Conditions for Few-body Nuclear Systems
Christopher Körber🇩🇪 · Thomas Luu🇩🇪
We describe and implement twisted boundary conditions for the deuteron and triton systems within finite-volumes using the nuclear lattice EFT formalism. We investigate the finite-volume dependence of these systems with different twists angles. We demonstrate how various finite-volume information can be used to improve calculations of binding energies in such a framework. Our results suggests that with appropriate twisting of boundaries, infinite-volume binding energies can be reliably extracted from calculations using modest volume sizes with cubic length $L \approx 8 - 14$ fm. Of particular importance is our derivation and numerical verification of three-body analogue of `i-periodic' twist angles that eliminate the leading order finite-volume effects to the three-body binding energy.
nucl-thhep-latPRC(2016)·21 citations
05
Meson assisted dibaryons
Avraham Gal🇮🇱
We discuss a new type of L=0 positive-parity dibaryons, pion-B-B', where the dominant binding mechanism is provided by resonating p-wave pion-baryon interactions. Recent calculations of such pion assisted dibaryons are reviewed with special emphasis placed on the non-strange I(JP)=1(2+) N-Delta dibaryon D_{12}(2150) studied recently at JLab, and on the 0(3+) Delta-Delta dibaryon D_{03}(2380) discovered recently by the WASA-at-COSY Collaboration. We review recent searches by the HADES Collaboration at GSI and by the E15 and E27 Experiments at J-PARC for a strangeness S=-1 I(JP)=1/2(0-) K-pp dibaryon and perhaps also for a strange I(JP)=3/2(2+) N-Sigma(1385) pion assisted dibaryon Y_{3/2(2+)}(2270). Charm C=+1 dibaryons, predicted with these same I(JP) values, are also briefly reviewed.
nucl-thhep-phnucl-exActa Phys.Polon.B(2016)·35 citations
06
Various aspects of the Deformation Dependent Mass model of nuclear structure
D. Petrellis · Dennis Bonatsos · N. Minkov
Recently, a variant of the Bohr Hamiltonian was proposed where the mass term is allowed to depend on the beta variable of nuclear deformation. Analytic solutions of this modified Hamiltonian have been obtained using the Davidson and the Kratzer potentials, by employing techniques from supersymmetric quantum mechanics. Apart from the new set of analytic solutions, the newly introduced Deformation-Dependent Mass (DDM) model offered a remedy to the problematic behaviour of the moment of inertia in the Bohr Hamiltonian, where it appears to increase proportionally to the square of beta. In the DDM model the moments of inertia increase at a much lower rate, in agreement with experimental data. The current work presents an application of the DDM-model suitable for the description of nuclei at the point of shape/phase transitions between vibrational and gamma-unstable or prolate deformed nuclei and is based on a method that was successfully applied before in the context of critical point symmetries.
nucl-thBulg.J.Phys.(2015)·1 citation
07
A possible evidence of observation of two mixed phases in nuclear collisions
K.A. Bugaev🇺🇦 · A.I. Ivanytskyi🇺🇦 · V.V. Sagun🇺🇦 · G.M. Zinovjev🇺🇦 · D.R. Oliinychenko🇺🇦 · V.S. Trubnikov🇺🇦 · E.G. Nikonov🇷🇺
Using an advanced version of the hadron resonance gas model we have found several remarkable irregularities at chemical freeze-out. The most prominent of them are two sets of highly correlated quasi-plateaus in the collision energy dependence of the entropy per baryon, total pion number per baryon, and thermal pion number per baryon which we found at center of mass energies 3.6-4.9 GeV and 7.6-10 GeV. The low energy set of quasi-plateaus was predicted a long time ago. On the basis of the generalized shock-adiabat model we demonstrate that the low energy correlated quasi-plateaus give evidence for the anomalous thermodynamic properties of the mixed phase at its boundary to the quark-gluon plasma. The question is whether the high energy correlated quasi-plateaus are also related to some kind of mixed phase. In order to answer this question we employ the results of a systematic meta-analysis of the quality of data description of 10 existing event generators of nucleus-nucleus collisions in the range of center of mass collision energies from 3.1 GeV to 17.3 GeV. These generators are divided into two groups: the first group includes the generators which account for the quark-gluon plasma formation during nuclear collisions, while the second group includes the generators which do not assume the quark-gluon plasma formation in such collisions. Comparing the quality of data description of more than a hundred of different data sets of strange hadrons by these two groups of generators, we find two regions of the equal quality of data description which are located at the center of mass collision energies 4.3-4.9 GeV and 10.-13.5 GeV. These two regions of equal quality of data description we interpret as regions of the hadron-quark-gluon mixed phase formation.
nucl-thEPJ Web Conf.(2016)·1 citation
08
Jet Hadronization via Recombination of Parton Showers in Vacuum and in Medium
Rainer J. Fries🇺🇸 · Kyongchol Han🇺🇸 · Che Ming Ko🇺🇸
We have studied the hadronization of jet parton showers based on the quark recombination model. This is achieved by letting gluons at the end of the perturbative shower evolution undergo a non-perturbative splitting into quark and antiquark pairs, then applying a Monte-Carlo version of instantaneous quark recombination, and finally subjecting remnant quarks (those which have not found a recombination partner) to Lund string fragmentation. When applied to parton showers from the PYTHIA Monte Carlo generator, the final hadron spectra from our calculation compare quite well to PYTHIA jets that have been hadronized with the default Lund string fragmentation. Modeling the quark gluon plasma produced in heavy ion collisions by a blast wave model, we have further studied medium effects on the hadronization of jet shower partons by also including their recombination with the thermal partons from the quark gluon plasma. We find that the latter leads to a significant enhancement of intermediate transverse momentum pions and protons at both RHIC and LHC. Our results thus suggest that medium modification of jet fragmentation provides a plausible explanation for the enhanced production of intermediate transverse momentum hadrons observed in experiments.
nucl-thnucl-exNucl.Part.Phys.Proc.(2016)·1 citation
09
Topological Susceptibility in Three-Flavor Quark Meson Model at Finite Temperature
Yin Jiang🇺🇸 · Tao Xia🇨🇳 · Pengfei Zhuang🇨🇳
We study $U_{A} (1)$ symmetry and its relation to chiral symmetry at finite temperature through the application of functional renormalization group to the $S U (3)$ quark meson model. Very different from the mass gap and mixing angel between $η$ and $η^{'}$ mesons which are defined at mean field level and behavior like the chiral condensates, the topological susceptibility includes a fluctuations induced part which becomes dominant at high temperature. As a result, the $U_{A} (1)$ symmetry is still considerably broken in the chiral symmetry restoration phase.
↳ hep-phhep-thnucl-thPRD(2016)·25 citations
10
Secondary electrons emitted during nuclear $β^{-}$ decay in few-electron atoms
Alexei M. Frolov · David M. Wardlaw
`Additional' ionization of light atoms and ions during nuclear $β^{-}$ decay is investigated. The procedure which can be used to determine the corresponding transition probabilities and the velocity/energy spectrum of secondary electrons is developed. Emission of very fast secondary electrons ( $δ -$ electrons) from $β^{-}$ -decaying atoms is also briefly discussed.
↳ physics.atom-phnucl-thPRC(2016)·1 citation
11
Nonperturbative contribution to the strange-antistrange asymmetry of the nucleon sea
Alfredo Vega🇺🇸 · Ivan Schmidt🇨🇱 · Thomas Gutsche🇩🇪 · Valery E. Lyubovitskij🇷🇺
We give predictions for the nonperturbative (intrinsic) contribution to the $s (x) - s ˉ (x)$ asymmetry of the nucleon sea. For this purpose we use different light-front wave functions inspired by the AdS/QCD formalism, together with a model of the nucleon in terms of meson-baryon fluctuations. The holographic wave functions for an arbitrary number of constituents, recently derived by us, give results quite close to known parametrizations that appear in the literature.
↳ hep-phnucl-thPRD(2016)·18 citations

Affiliations

first authorsco-authorsvia INSPIRE