Nuclear Theory·nucl-th

Friday·January 22, 2016

11 papers—7 primary·4 cross-listed

01
Symmetry preserving truncations of the gap and Bethe-Salpeter equations
Daniele Binosi🇮🇹 · Lei Chang🇨🇳 · Joannis Papavassiliou🇪🇸 · Si-Xue Qin🇺🇸 · Craig D. Roberts🇺🇸
Ward-Green-Takahashi (WGT) identities play a crucial role in hadron physics, e.g. imposing stringent relationships between the kernels of the one- and two-body problems, which must be preserved in any veracious treatment of mesons as bound-states. In this connection, one may view the dressed gluon-quark vertex, $Γ_{μ}^{a}$ , as fundamental. We use a novel representation of $Γ_{μ}^{a}$ , in terms of the gluon-quark scattering matrix, to develop a method capable of elucidating the unique quark-antiquark Bethe-Salpeter kernel, $K$ , that is symmetry-consistent with a given quark gap equation. A strength of the scheme is its ability to expose and capitalise on graphic symmetries within the kernels. This is displayed in an analysis that reveals the origin of $H$ -diagrams in $K$ , which are two-particle-irreducible contributions, generated as two-loop diagrams involving the three-gluon vertex, that cannot be absorbed as a dressing of $Γ_{μ}^{a}$ in a Bethe-Salpeter kernel nor expressed as a member of the class of crossed-box diagrams. Thus, there are no general circumstances under which the WGT identities essential for a valid description of mesons can be preserved by a Bethe-Salpeter kernel obtained simply by dressing both gluon-quark vertices in a ladder-like truncation; and, moreover, adding any number of similarly-dressed crossed-box diagrams cannot improve the situation.
nucl-thhep-phPRD(2016)·119 citations
02
Real-time Kadanoff-Baym approach to nuclear response functions
H. S. Köhler · N. H. Kwong
Linear density response functions are calculated for symmetric nuclear matter of normal density by time-evolving two-time Green's functions in real time. Of particular interest is the effect of correlations. The system is therefore initially time-evolved with a collision term calculated in a direct Born approximation as well as with full (RPA) ring-summation until fully correlated. An external time-dependent potential is then applied. The ensuing density fluctuations are recorded to calculate the density response. This method was previously used by Kwong and Bonitz for studying plasma oscillations in a correlated electron gas. The energy-weighted sum-rule for the response function is guaranteed by using conserving self-energy insertions as the method then generates the full vertex-functions. These can alternatively be calculated by solving a Bethe -Salpeter equation as done in some previous works. The (first order) mean field is derived from a momentum-dependent (non-local) interaction while $2^{n d}$ order self-energies are calculated using a particle-hole two-body effective (or 'residual') interaction given by a gaussian \it local \rm potential. We present numerical results for the response function $S (ω, q_{0})$ for $q_{0} = 0.2, 0.4$ and $0.8 fm^{- 1}$ . Comparison is made with the nucleons being un-correlated i.e. with only the first order mean field included, the 'HF+RPA' approximation. We briefly discuss the relation of our work with the Landau quasi-particle theory as applied to nuclear systems by Sjöberg and followers using methods developped by Babu and Brown, with special emphasis on the 'induced' interaction.
nucl-thJ.Phys.Conf.Ser.(2016)·1 citation
03
Quadrupole and monopole transition properties of $0_{2}^{+}$ in Gd isotopes
Masayuki Matsuzaki · Tomoya Ueno
The longstanding problem of characterization of the $0_{2}^{+}$ states in Gd isotopes is revisited by adopting the Nilsson $+$ BCS mean field and the random-phase approximation. The interband electric quadrupole transition strengths varying almost two orders of magnitude are nicely reproduced at the same time as other observables. These results indicate that the $0_{2}^{+}$ states, in particular, those in lighter isotopes are well described as $β$ vibrations excited on top of deformed ground states without recourse to the shape-coexistence picture.
nucl-thPTEP(2016)·3 citations
04
Isoscalar-isovector proton-neutron pairing and quartet condensation in N=Z nuclei
M. Sambataro · N. Sandulescu
We show that the correlations generated in the ground state of $N = Z$ nuclei by the isovector and isoscalar pairing forces can be treated with high precision as a condensate of alpha-like quartets. To treat these correlations, the quartet condensation model (QCM) is extended to the treatment of spherically symmetric isovector $(T = 1, J = 0)$ and isoscalar $(T = 0, J = 1)$ pairing forces . Within QCM we discuss the competition between $T = 1$ and $T = 0$ pairing correlations in the case of a two-level model and for $N = Z$ nuclei with nucleons moving in the open shells above $^{16}$ O, $^{40}$ Ca and $^{100}$ Sn. We show that in $N = Z$ systems isovector and isoscalar proton-neutron pairing correlations always coexist.
nucl-thPRC(2016)·21 citations
05
The mechanism of solute-enriched clusters formation in neutron-irradiated pressure vessel steels: the case of Fe-Cu model alloys
A.V. Subbotina · S.V. Panyukov
Mechanism of solute-enriched clusters formation in neutron-irradiated pressure vessel steels is proposed and developed in case of Fe-Cu model alloys. We show that the obtained results are in a good agreement with available experimental data on the parameters of clusters enriched with the alloying elements. The suggested solute-drag mechanism is analogous to the well-known zone-refining process. Our model explains why the formation of solute-enriched clusters does not happen in austenitic stainless steels with fcc lattice structure. It also allows to quantify the method of evaluation of neutron irradiation dose for the process of RPV steels hardening.
nucl-thcond-mat.mtrl-sciphysics.atm-clus0 citations
06
Partial Conservation Law in a Schematic Single j Shell Model
Wesley Pereira · Ricardo Garcia · Larry Zamick · Alberto Escuderos · Kai Neergård
We report the discovery of a partial conservation law obeyed by a schematic Hamiltonian of two protons and two neutrons in a j shell. In our Hamiltonian the interaction matrix element of two nucleons with combined angular momentum J is linear in J for even J and constant for odd J. It turns out that in some stationary states the sum J_p + J_n of the angular momenta J_p and J_n of the proton and neutron pairs is conserved. The energies of these states are given by a linear function of J_p + J_n. The systematics of their occurrence is described and explained.
nucl-thIJMPE(2017)·1 citation
07
Probing the hadron-quark mixed phase at high isospin and baryon density - Sensitive observables
Massimo Di Toro🇮🇹 · Maria Colonna🇮🇹 · Vincenzo Greco🇮🇹 · Guo-Yun Shao🇨🇳
We discuss the isospin effect on the possible phase transition from hadronic to quark matter at high baryon density and finite temperatures. The two-Equation of State (Two-EoS) model is adopted to describe the hadron-quark phase transition in dense matter formed in heavy-ion collisions. For the hadron sector we use Relativistic Mean Field (RMF) effective models, already tested on heavy ion collision (HIC). For the quark phase we consider various effective models, the MIT-Bag static picture, the Nambu--Jona-Lasinio (NJL) approach with chiral dynamics and finally the NJL coupled to the Polyakov-loop field (PNJL), which includes both chiral and (de)confinement dynamics. The idea is to extract mixed phase properties which appear robust with respect to the model differences. In particular we focus on the phase transitions of isospin asymmetric matter, with two main results: i) an earlier transition to a mixed hadron-quark phase, at lower baryon density/chemical potential with respect to symmetric matter; ii) an "Isospin Distillation" to the quark component of the mixed phase, with predicted effects on the final hadron production. Possible observation signals are suggested to probe in heavy-ion collision experiments at intermediate energies, in the range of the NICA program.
nucl-thhep-phEPJA(2016)·3 citations
08
Specific Heat of Matter Formed in Relativistic Nuclear Collisions
Sumit Basu🇮🇳 · Sandeep Chatterjee🇮🇳 · Rupa Chatterjee🇮🇳 · Tapan K. Nayak🇮🇳 · Basanta K. Nandi🇮🇳
We report the excitation energy dependence of specific heat (\cv) of hadronic matter at freeze-out in Au+Au and Cu+Cu collisions at the Relativistic Heavy Ion Collider energies by analyzing the published data on event-by-event mean transverse momentum (\meanpt) distributions. The \meanpt~distributions in finite \pt~ranges are converted to distributions of effective temperatures, and dynamical fluctuations in temperature are extracted by subtracting widths of the corresponding mixed event distributions. The heat capacity per particle at the kinetic freeze-out surface is presented as a function of collision energy, which shows a sharp rise in \cv~below \sNN~=~62.4~GeV. We employ the Hadron Resonance Gas (HRG) model to estimate \cv~at the chemical and kinetic freeze-out surfaces. The experimental results are compared to the HRG and other theoretical model calculations. HRG results show good agreement with data. Model predictions for \cv~at the Large Hadron Collider energy are presented.
↳ nucl-exhep-phnucl-thPRC(2016)·37 citations
09
Charmonia in a Contact Interaction
Marco A. Bedolla🇲🇽 · J.J. Cobos-Martínez🇲🇽 · Adnan Bashir🇲🇽
For the flavour-singlet heavy quark system of charmonia, we compute the masses of the ground state mesons in four different channels: pseudo-scalar ( $η_{c} (1 S)$ ), vector ( $J /Ψ (1 S)$ ), scalar ( $χ_{c_{0}} (1 P)$ ) and axial vector ( $χ_{c_{1}} (1 P)$ ), as well as the weak decay constants of the $η_{c} (1 S)$ and $J /Ψ (1 S)$ and the charge radius of $η_{c} (1 S)$ . The framework for this analysis is provided by a symmetry-preserving Schwinger-Dyson equation (SDEs) treatment of a vector $\times$ vector contact interaction (CI). The results found for the meson masses and the weak decay constants, for the spin-spin combinations studied, are in fairly good agreement with experimental data and earlier model calculations based upon Schwinger-Dyson and Bethe-Salpeter equations (BSEs) involving sophisticated interaction kernels. The charge radius of $η_{c} (1 S)$ is consistent with the results from refined SDE studies and lattice Quantum Chromodynamics (QCD).
↳ hep-phnucl-thPRD(2015)·58 citations
10
Phase diagram and nucleation in the Polyakov-loop-extended Quark-Meson truncation of QCD with the unquenched Polyakov-loop potential
Rainer Stiele🇫🇷 · Juergen Schaffner-Bielich🇩🇪
Unquenching of the Polyakov-loop potential showed to be an important improvement for the description of the phase structure and thermodynamics of strongly-interacting matter at zero quark chemical potentials with Polyakov-loop extended chiral models. This work constitutes the first application of the quark backreaction on the Polyakov-loop potential at nonzero density. The observation is that it links the chiral and deconfinement phase transition also at small temperatures and large quark chemical potentials. The build up of the surface tension in the Polyakov-loop extended Quark-Meson model is explored by investigating the two and 2+1-flavour Quark-Meson model and analysing the impact of the Polyakov-loop extension. In general, the order of magnitude of the surface tension is given by the chiral phase transition. The coupling of the chiral and deconfinement transition with the unquenched Polyakov-loop potential leads to the fact that the Polyakov-loop contributes at all temperatures.
↳ hep-phnucl-thPRD(2016)·32 citations
11
Nonperturbative True Muonium on the Light Front with TMSWIFT
Henry Lamm🇺🇸 · Richard F. Lebed🇺🇸
The true muonium $(μ μ ˉ)$ bound state presents an interesting test of light-cone quantization techniques. In addition to exhibiting the standard problems of handling non-perturbative calculations, true muonium requires correct treatment of $e e ˉ$ Fock-state contributions. Having previously produced a crude model of true muonium using the method of iterated resolvents, our current work has focused on the inclusion of the box diagrams to improve the cutoff-dependent issues of the model. Further, a parallel computer code, TMSWIFT, allowing for smaller numerical uncertainties, has been developed. This work focuses on the current state of these efforts to develop a model of true muonium that is testable at near-term experiments.
↳ hep-phnucl-thphysics.comp-phFew Body Syst.(2016)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE