Nuclear Theory·nucl-th

Tuesday·May 9, 2017

12 papers—9 primary·3 cross-listed

01
Wilsonian renormalization group versus subtractive renormalization in effective field theories for nucleon--nucleon scattering
E. Epelbaum🇩🇪 · J. Gegelia🇩🇪 · Ulf-G. Meißner🇩🇪
We compare the subtractive renormalization and the Wilsonian renormalization group approaches in the context of an effective field theory for the two-nucleon system. Based on an exactly solvable model of contact interactions, we observe that the standard Wilsonian renormalization group approach with a single cutoff parameter does not cover the whole space spanned by the renormalization scale parameters of the subtractive formalism. In particular, renormalization schemes corresponding to Weinberg's power counting in the case of an unnaturally large scattering length are beyond the region covered by the Wilsonian renormalization group approach. In the framework of pionless effective field theory, also extended by the inclusion of a long-range interaction of separable type, we demonstrate that Weinberg's power counting scheme is consistent in the sense that it leads to a systematic order-by-order expansion of the scattering amplitude.
nucl-thNPB(2017)·54 citations
02
Composition of nuclear matter with light clusters and Bose-Einstein condensation of $α$ particles
Xin-Hui Wu (Peking U.) · Si-Bo Wang (Peking U.) · Armen Sedrakian (FIAS) · Gerd Röpke (Rostock U.)
The Bose-Einstein condensation of $α$ partciles in the multicomponent environment of dilute, warm nuclear matter is studied. We consider the cases of matter composed of light clusters with mass numbers $A \leq 4$ and matter that in addition these clusters contains $\isotope [56] F e$ nuclei. We apply the quasiparticle gas model which treats clusters as bound states with infinite life-time and binding energies independent of temperature and density. We show that the $α$ particles can form a condensate at low temperature $T \leq 2$ MeV in such matter in the first case. When the $\isotope [56] F e$ nucleus is added to the composition the cluster abundances are strongly modified at low temperatures, with an important implication that the $α$ condensation at these temperatures is suppressed.
nucl-thastro-ph.HEcond-mat.quant-gascond-mat.supr-conJ.Low Temp.Phys.(2017)·16 citations
03
Photon production in Pb+Pb collisions at $s_{N N}$ =2.76 TeV
Yong-Ping Fu🇨🇳 · Qin Xi🇨🇳
We calculate the high energy photon production from the Pb+Pb collisions for different centrality classes at $s_{N N}$ =2.76 TeV Large Hadron Collider (LHC) energy. The jet energy loss in the jet fragmentation, jet-photon conversion and jet bremsstrahlung is considered by using the Wang-Huang-Sarcevic (WHS) and Baier-Dokshitzer-Mueller-Peigne-Schiff (BDMPS) models. We use the (1+1)-dimensional ideal relativistic hydrodynamics to study the collective transverse flow and space-time evolution of the quark gluon plasma (QGP). The numerical results agree well with the ALICE data of the direct photons from the Pb+Pb collisions ( $s_{N N}$ =2.76 TeV) for 0-20\%, 20-40\% and 40-80\% centrality classes.
nucl-thNPA(2018)·1 citation
04
Contact formalism for coupled channels
Ronen Weiss · Nir Barnea
The contact formalism, a useful tool for analyzing short-range correlations, is generalized here for systems with coupled channels, such as in nuclear physics. The relevant asymptotic form is presented and contact matrices are defined. Generally, for the case of two coupled channels, two two-body functions are included in the asymptotic form, resulting a 2 x 2 contact matrix. Nevertheless, it is shown that if the coupling terms of the potential are very weak or very strong, only a single two-body function is needed, resulting a single contact. This universal result is directly relevant to nuclear systems, and provides a theoretical explanation for the fact that proton-neutron short-range correlations can be described using the single bound-state deuteron wave function. It is achieved by applying an appropriate boundary condition on the two-body functions. This boundary condition can be interpreted as a mean field potential imposed on the correlated pair due to the residual system.
nucl-thcond-mat.quant-gasPRC(2017)·15 citations
05
New parameterization of the effective field theory motivated relativistic mean field model
Bharat Kumar🇮🇳 · S. K. Singh🇮🇳 · B. K. Agrawal🇮🇳 · S. K. Patra🇮🇳
A new parameter set is generated for finite and infinite nuclear system within the effective field theory motivated relativistic mean field (ERMF) formalism. The isovector part of the ERMF model employed in the present study includes the coupling of nucleons to the {\delta} and h̊o} mesons and the cross-coupling of h̊o} mesons to the {\sigma} and {\omega} mesons. The results for the finite and infinite nuclear systems obtained using our parameter set are in harmony with the available experimental data. We find the maximum mass of the neutron star to be 2.03M\odot? and yet a relatively smaller radius at the canonical mass, 12.69 km, as required by the available data.
nucl-thhep-phnucl-exNPA(2017)·88 citations
06
Weak quadrupole moments
Bryce G. C. Lackenby🇦🇺 · Victor V. Flambaum🇦🇺
Collective effects in deformed atomic nuclei present possible avenues of study on the non-spherical distribution of neutrons and the violation of the local Lorentz invariance. We introduce the weak quadrupole moment of nuclei, related to the quadrupole distribution of the weak charge in the nucleus. The weak quadrupole moment produces tensor weak interaction between the nucleus and electrons and can be observed in atomic and molecular experiments measuring parity nonconservation. The dominating contribution to the weak quadrupole is given by the quadrupole moment of the neutron distribution, therefore, corresponding experiments should allow one to measure the neutron quadrupoles. Using the deformed oscillator model and the Schmidt model we calculate the quadrupole distributions of neutrons, $Q_{n}$ , the weak quadrupole moments , $Q_{W}^{(2)}$ , and the Lorentz Innvariance violating energy shifts in $^{9}$ Be, $^{21}$ Ne , $^{27}$ Al, $^{131}$ Xe, $^{133}$ Cs, $^{151}$ Eu, $^{153}$ Eu, $^{163}$ Dy, $^{167}$ Er, $^{173}$ Yb, $^{177}$ Hf, $^{179}$ Hf, $^{181}$ Ta, $^{201}$ Hg and $^{229}$ Th.
nucl-thhep-phphysics.atom-phJ.Phys.G(2018)·10 citations
07
Single Charge-Exchange Reactions and the Neutron Density at the Surface of the Nucleus
Bui Minh Loc · Naftali Auerbach · Dao T. Khoa
In this work we study the charge-exchange reaction to Isobaric Analog State using two types of transition densities. We show that for projectiles that do not probe the interior of the nucleus but mostly the surface of this nucleus, distinct differences in the cross-section arise when the two types of transition densities are employed. We demonstrate this by considering the (3He,t) reaction.
nucl-thPRC(2017)·14 citations
08
Microscopic description of production cross sections including deexcitation effects
Kazuyuki Sekizawa
Background: At the forefront of the nuclear science, production of new neutron-rich isotopes is continuously pursued at accelerator laboratories all over the world. To explore the currently-unknown territories in the nuclear chart far away from the stability, reliable theoretical predictions are inevitable. Purpose: To provide a reliable prediction of production cross sections taking into account secondary deexcitation processes, both particle evaporation and fission, a new method called TDHF+GEMINI is proposed, which combines the microscopic time-dependent Hartree-Fock (TDHF) theory with a sophisticated statistical compound-nucleus deexcitation model, GEMINI++. Results: The method is applied for multinucleon transfer processes in low-energy heavy ion reactions. It is shown that the inclusion of secondary deexcitation processes, which are dominated by neutron evaporation in the present systems, substantially improves agreement with the experimental data. The magnitude of the evaporation effects is very similar to the one observed in GRAZING calculations. TDHF+GEMINI provides better description of the absolute value of the cross sections for channels involving transfer of more than one protons, compared with the GRAZING results. However, there remain discrepancies between the measurements and the calculated cross sections, indicating a limit of the theoretical framework that works with a single mean-field potential. Possible causes of the discrepancies are discussed. Conclusions: In order to perfectly reproduce experimental cross sections for multinucleon transfer processes, one should go beyond the standard self-consistent mean-field description. Nevertheless, the proposed method will provide valuable information to optimize production mechanisms of new neutron-rich nuclei through its microscopic, non-empirical predictions. (Shortened due to the word limit)
nucl-thnucl-exPRC(2017)·66 citations
09
Excited-state quantum phase transitions in a two-fluid Lipkin model
J.E. Garcia-Ramos · P. Perez-Fernandez · J.M. Arias
Background: Composed systems have became of great interest in the framework of the ground state quantum phase transitions (QPTs) and many of their properties have been studied in detail. However, in these systems the study of the so called excited-state quantum phase transitions (ESQPTs) have not received so much attention. Purpose: A quantum analysis of the ESQPTs in the two-fluid Lipkin model is presented in this work. The study is performed through the Hamiltonian diagonalization for selected values of the control parameters in order to cover the most interesting regions of the system phase diagram. [Method:] A Hamiltonian that resembles the consistent-Q Hamiltonian of the interacting boson model (IBM) is diagonalized for selected values of the parameters and properties such as the density of states, the Peres lattices, the nearest-neighbor spacing distribution, and the participation ratio are analyzed. Results: An overview of the spectrum of the two-fluid Lipkin model for selected positions in the phase diagram has been obtained. The location of the excited-state quantum phase transition can be easily singled out with the Peres lattice, with the nearest-neighbor spacing distribution, with Poincaré sections or with the participation ratio. Conclusions: This study completes the analysis of QPTs for the two-fluid Lipkin model, extending the previous study to excited states. The ESQPT signatures in composed systems behave in the same way as in single ones, although the evidences of their presence can be sometimes blurred. The Peres lattice turns out to be a convenient tool to look into the position of the ESQPT and to define the concept of phase in the excited states realm.
nucl-thquant-phPRC(2017)·19 citations
10
Sign problem in $Z_{3}$ -symmetric effective Polyakov-line model
Takehiro Hirakida🇯🇵 · Junpei Sugano🇯🇵 · Hiroaki Kouno🇯🇵 · Junichi Takahashi🇯🇵 · Masanobu Yahiro🇯🇵
As an effective model corresponding to $Z_{3}$ -symmetric QCD ( $Z_{3}$ -QCD), we construct a $Z_{3}$ -symmetric effective Polyakov-line model ( $Z_{3}$ -EPLM) by using the logarithmic fermion effective action. Since $Z_{3}$ -QCD tends to QCD in the zero temperature limit, $Z_{3}$ -EPLM also agrees with the ordinary effective Polyakov-line model (EPLM) there; note that ordinary EPLM does not possess $Z_{3}$ symmetry. Our main purpose is to discuss a sign problem appearing in $Z_{3}$ -EPLM. The action of $Z_{3}$ -EPLM is real, when the Polyakov line is not only real but also its $Z_{3}$ images. This suggests that the sign problem becomes milder in $Z_{3}$ -EPLM than in EPLM. In order to confirm this suggestion, we do lattice simulations for both EPLM and $Z_{3}$ -EPLM by using the reweighting method with the phase quenched approximation. In the low-temperature region, the sign problem is milder in $Z_{3}$ -EPLM than in EPLM. We also propose a new reweighting method. This makes the sign problem very weak in $Z_{3}$ -EPLM.
↳ hep-latPRD(2017)·14 citations
11
Flow equations for cold Bose gases
A. G. Volosniev · H.-W. Hammer
We derive flow equations for cold atomic gases with one macroscopically populated energy level. The generator is chosen such that the ground state decouples from all other states in the system as the renormalization group flow progresses. We propose a self-consistent truncation scheme for the flow equations at the level of three-body operators and show how they can be used to calculate the ground state energy of a general $N$ -body system. Moreover, we provide a general method to estimate the truncation error in the calculated energies. Finally, we test our scheme by benchmarking to the exactly solvable Lieb-Liniger model and find good agreement for weak and moderate interaction strengths.
↳ cond-mat.quant-gasnucl-thquant-phNew J.Phys.(2017)·9 citations
12
Thermalization of overpopulated systems in the 2PI formalism
Shoichiro Tsutsui🇯🇵 · Jean-Paul Blaizot🇯🇵 · Yoshitaka Hatta🇯🇵
Based on the two-particle irreducible (2PI) formalism to next-to-leading order in the $1/ N$ expansion, we study the thermalization of overpopulated systems in scalar $O (N)$ theories with moderate coupling. We focus in particular on the growth of soft modes, and examine whether this can lead to the formation of a transient Bose-Einstein condensate (BEC) when the initial occupancy is high enough. For the value of the coupling constant used in our simulations, we find that while the system rapidly approaches the condensation threshold, the formation of a BEC is eventually hindered by particle number changing processes.
↳ hep-phcond-mat.quant-gasnucl-thPRD(2017)·13 citations

Affiliations

first authorsco-authorsvia INSPIRE