Nuclear Theory·nucl-th

Thursday·February 2, 2017

9 papers—6 primary·3 cross-listed

01
Relativistic approach to nuclear spin-isospin excitations including quasiparticle-vibration coupling
Caroline Robin · Elena Litvinova
The spin-isospin response of stable and exotic nuclei is investigated in the framework of the proton-neutron relativistic quasiparticle time-blocking approximation (pn-RQTBA). Based on the Covariant Density Functional Theory, this method extends the proton-neutron Relativistic Quasiparticle Random-Phase Approximation (pn-RQRPA) by including the coupling between single quasiparticles and collective nuclear vibrations. In the charge-exchange channel, this coupling generates a time-dependent effective interaction between proton and neutron quasiparticles. The particle-hole component of this interaction adds to the static pion and rho-meson exchange, while the particle-particle component provides a microscopic and consistent proton-neutron pairing interaction. We find that such dynamical effects induce fragmentation and spreading of the Gamow-Teller transition strength which are important for a better agreement with the experimental measurements and for an accurate description of $β$ -decay rates. The new developments include the coupling of single nucleons to isospin-flip vibrations in doubly-magic nuclei. We find that these phonons can have a non-negligible effect on $β$ -decay half-lives and "quenching" of the strength.
nucl-thPoS(2017)·2 citations
02
Solitonic Excitations in Collisions Of Superfluid Nuclei
Kazuyuki Sekizawa · Piotr Magierski · Gabriel Wlazłowski
We investigate the role of the pairing field dynamics in low-energy heavy ion reactions within the nuclear time-dependent density functional theory extended to superfluid systems. Recently, we have reported on unexpectedly large effects associated with the relative phase of the pairing field of colliding nuclei on the reaction outcomes, such as the total kinetic energy and the fusion cross section [P. Magierski, K. Sekizawa, and G. Wlazłowski, arXiv:1611.10261 [nucl-th]]. We have elucidated that the effects are due to creation of a "domain wall" or a "solitonic structure" of the pairing field in the neck region, which hinders energy dissipation as well as the neck formation, leading to significant changes of the reaction dynamics. The situation nicely mimics the one extensively studied experimentally with ultracold atomic gases, where two clouds of superfluid atoms possessing different phases of the pairing field are forced to merge, creating various topological excitations, quantum vortices and solitons, as well as Josephson currents. In this paper, we present unpublished results for a lighter system, namely, $^{44}$ Ca+ $^{44}$ Ca. It is shown that the pairing effects on the fusion hindrance are rather small in lighter systems, due to a strong tendency towards fusion, which is consistent with an earlier study.
nucl-thcond-mat.quant-gascond-mat.supr-connucl-exPoS(2017)·8 citations
03
Achieving high baryon densities in the fragmentation regions in heavy ion collisions at top RHIC energy
Ming Li🇺🇸 · Joseph I. Kapusta🇺🇸
Heavy ion collisions at extremely high energy, such as the top energy at RHIC, exhibit the property of transparency where there is a clear separation between the almost net-baryon-free central rapidity region and the net-baryon-rich fragmentation region. We calculate the net-baryon rapidity loss and the nuclear excitation energy using the energy-momentum tensor obtained from the McLerran-Venugopalan model. Nuclear compression during the collision is further estimated using a simple space-time picture. The results show that extremely high baryon densities, about twenty times larger than the normal nuclear density, can be achieved in the fragmentation regions.
nucl-thJ.Phys.Conf.Ser.(2017)·1 citation
04
Recent selected theory developments for NICA
David Blaschke🇷🇺
In this contribution I present a few selected topics of recent theoretical developments of relevance for the NICA facility under construction. In a first part, I discuss new aspects of the QCD phase diagram like the possible existence of a critical endpoint of first-order phase transitions from the perspective of generalizations of the 3-flavor PNJL model including the conjecture of a universal pressure for the onset of deconfinement in heavy-ion collisions and astrophysics. A second part is devoted to first results of the newly constructed event simulator (THESEUS) which is based on the particlization of the former three-fluid hydrodynamics code by Ivanov, Russkikh and Toneev that allows also to study the role of hadronic final state interactions. Possible signals of the mixed phase accessible at NICA are considered. In particular, the robustness of the baryon-stopping signal of deconfinement and the occurrence of antiflow for protons have been investigated for Au+Au collisions in the range of the NICA-MPD energy scan for $s \sim 6 \dots 8$ GeV. This signal is reflected also in the flow pattern of light nuclear clusters, in particular deuterons. The sharp peak for the $K^{+} / π^{+}$ ratio at $s \sim 8$ GeV (the "horn" effect) is not obtained in the present version of THESEUS and calls for improvement of the equation of state input. I report the recent progress in developing a generalized Beth-Uhlenbeck approach to a unified description of quark-hadron matter which includes now strangeness and reveals a new mechanism for explaining the $K^{+} / π^{+}$ ratio due to the pronounced occurrence of an anomalous mode in the $K^{+}$ at finite baryochemical potentials.
nucl-thhep-phEPJ Web Conf.(2017)·5 citations
05
The stifness of the supranuclear equation of state (once again)
J.E. Horvath🇧🇷 · R.A. de Souza🇧🇷
We revisit the present status of the stiffness of the supranuclear equations of state, particularly the solutions that increase the stiffness in the presence of hyperons, the putative transition to a quark matter phase and the robustness of massive compact star observations.
nucl-thastro-ph.SRJ.Phys.Conf.Ser.(2017)·3 citations
06
Two-Center Gaussian potential well for studying light nucleus in cluster structure
Nafiseh Roshanbakht · Mohammad Reza shojaei
The clustering phenomena is very important to determine structure of light nuclei and deformation of spherical shape is inevitable. Hence, we calculated the energy levels of two-center Gaussian potential well including spin-orbit coupling by solving the Schrödinger equation in the cylindrical coordinates. This model could predict the spin and parity of the light nucleus that have cluster structure consist of two identical clusters.
nucl-thAdv.High Energy Phys.(2017)·3 citations
07
Lattice QCD at nonzero temperature and density
Heng-Tong Ding🇨🇳
In this talk I review the current status of lattice QCD calculations at nonzero temperature and density. I focus on the QCD phase structure and bulk QCD thermodynamics at zero and nonzero chemical potentials.
↳ hep-lathep-phnucl-thPoS(2017)·35 citations
08
Exclusive neutrino-production of a charmed meson
B. Pire🇫🇷 · L. Szymanowski🇵🇱 · J. Wagner🇵🇱
We calculate the leading order in $α_{s}$ QCD amplitude for exclusive neutrino and antineutrino production of a $D$ pseudoscalar charmed meson on an unpolarized nucleon. We work in the framework of the collinear QCD approach where generalized parton distributions (GPDs) factorize from perturbatively calculable coefficient functions. We include both $O (m_{c})$ terms in the coefficient functions and $O (M_{D})$ mass term contributions in the heavy meson distribution amplitudes. We emphasize the sensitivity of specific observables on the transversity quark GPDs.
↳ hep-phhep-exnucl-exnucl-thPRD(2017)·31 citations
09
A self-consistent study of magnetic field effects on hybrid stars
V. Dexheimer🇺🇸 · B. Franzon🇩🇪 · S. Schramm🇩🇪
It is understood that strong magnetic fields affect the structure of neutron stars. Nevertheless, many calculations for magnetized neutron stars are still being performed using symmetric solutions of Einstein's equations. In this conference proceeding, we review why this is not the correct procedure and we also discuss the effects of magnetic fields on the stellar population and temperature profiles.
↳ astro-ph.HEastro-ph.SRnucl-thJ.Phys.Conf.Ser.(2017)·19 citations

Affiliations

first authorsco-authorsvia INSPIRE