Nuclear Theory·nucl-th

Friday·May 4, 2018

13 papers—7 primary·6 cross-listed

01
Pairing in Nuclei: Exact Solutions
A.B. Balantekin
Pairing plays an essential role in describing nuclear spectra and attempts to describe it has a long history in nuclear physics. Many theoretical tools were developed to treat the pairing problem either exactly or at various levels of approximation. In this contribution to the proceedings of a conference honoring the career of Taka Otsuka, recent developments in the exact solutions of the pairing problem are described.
nucl-thJPS Conf.Proc.(2018)·0 citations
02
Universal correlations in the nuclear symmetry energy, slope parameter, and curvature
Jeremy W. Holt · Yeunhwan Lim
From general Fermi liquid theory arguments, we derive correlations among the symmetry energy (J), its slope parameter (L), and curvature (K_sym) at nuclear matter saturation density. We argue that certain properties of these correlations do not depend on details of the nuclear forces used in the calculation. We derive as well a global parametrization of the density dependence of the symmetry energy that we show is more reliable, especially at low densities, than the usual Taylor series expansion around saturation density. We then benchmark these predictions against explicit results from chiral effective field theory.
nucl-thPLB(2018)·41 citations
03
Angular dependence of eta photoproduction in photon-induced reaction
Jun-Zhen Wang🇨🇳 · Bao-Chun Li🇨🇳
Photoproduction of eta mesons from nucleons can provide valuable information about the excitation spectrum of the nucleons. The angular dependence of photoproduction in the photon-induced reaction is investigated in the multi-source thermal model. The results are compared with experimental data from the decay mode. They are in good agreement with the experimental data. It is shown that the movement factor increases linearly with the photon beam energies. And, the deformation and translation of emission sources are visually given in the formalism.
nucl-thAdv.High Energy Phys.(2018)·0 citations
04
Localization of pairing correlations in nuclei within relativistic mean field models
R.-D. Lasseri🇫🇷 · J.-P. Ebran🇫🇷 · E. Khan🇫🇷 · N. Sandulescu🇷🇴
We analyze the localization properties of two-body correlations induced by pairing in the framework of relativistic mean field (RMF) models. The spatial properties of two-body correlations are studied for the pairing tensor in coordinate space and for the Cooper pair wave function. The calculations are performed both with Relativistic-Hatree-Bogoliubov (RHB) and RMF+Projected-BCS (PBCS) models and taking as examples the nuclei $^{66}$ Ni, $^{124}$ Sn and $^{200}$ Pb. It is shown that the coherence length have the same pattern as in previous non-relativistic HFB calculations, i.e., it is maximum in the interior of the nucleus and drops to a minimum in the surface region. In the framework of RMF+PBCS we have also analysed, for the particular case of $^{120}$ Sn, the dependence of the coherence length on the intensity of the pairing force. This analysis indicates that pairing is reducing the coherence length by about 25-30 $%$ compared to the RMF limit.
nucl-thPRC(2018)·3 citations
05
Extension of the ratio method to proton-rich nuclei
X. Y. Yun · F. Colomer · D. Y. Pang · P. Capel
The ratio method has been developed to improve the study of one-neutron halo nuclei through reactions. By taking the ratio of angular distributions for two processes, viz. breakup and elastic scattering, this new observable is nearly independent of the reaction mechanism and hence much more sensitive to the projectile structure than the cross sections for each single process. We study the extension of the ratio method to proton-rich nuclei and also explore the optimum experimental conditions for measuring this new observable. We compare accurate dynamical calculations of reactions for proton-rich projectiles to the prediction of the ratio method. We use the dynamical eikonal approximation that provides good results for this kind of reactions at intermediate energy. Our tests for 8B, an archteypical one-proton halo nucleus, on Pb, Ni, and C targets at 44 MeV/nucleon show that, the ratio works less well than for neutron halos due to the non-negligible Coulomb interaction between the valence proton and the target. Nevertheless, the ratio method still provides pertinent information about nuclear structure on the proton-rich side of the valley of stability. Interestingly the method is not affected if energy ranges-or bins-are considered in the projectile continuum. This makes the ratio easier to measure experimentally by increasing the breakup cross section. We also extend our analysis to 17F, 25Al, and 27P, whose study is of interest to both nuclear astrophysics and nuclear structure. We show that, albeit less precise than for one-neutron halo nuclei, nuclear-structure information can be inferred from the ratio method applied to exotic proton-rich nuclei. In particular, when the valence proton is loosely bound in an $s$ or $p$ orbital, viz. for proton halo nuclei, detailed structure information can be obtained through this new reaction observable.
nucl-thJ.Phys.G(2019)·3 citations
06
Monte Carlo approach to the excluded-volume hadron resonance gas in grand canonical and canonical ensembles
Volodymyr Vovchenko🇩🇪 · Mark I. Gorenstein🇩🇪 · Horst Stoecker🇩🇪
The Monte Carlo (MC) procedure for sampling the hadron yields within hadron resonance gas (HRG) model is presented. The effects of excluded-volume due to the finite hadron eigenvolumes and of exact charge conservation within the canonical ensemble (CE) formulation are simultaneously taken into account with the help of the importance sampling technique combined with the rejection sampling. The MC procedure allows one to calculate arbitrary moments of the event-by-event hadron yields. Note that the CE formulation for the excluded-volume HRG has not been considered before. The MC simulations coincide with the known analytic results in the thermodynamic limit for the excluded-volume HRG in the grand canonical ensemble and for the CE of non-interacting particles. The MC procedure is applied to study the simultaneous excluded-volume and CE effects. These effects are considered within the full HRG to calculate the particle number fluctuations and to estimate the finite size effects.
nucl-thhep-phPRC(2018)·18 citations
07
New exact solutions of relativistic hydrodynamics for longitudinally expanding fireballs
T. Csorgo🇭🇺 · G. Kasza🇭🇺 · M. Csanad🇭🇺 · Z. Jiang🇨🇳
We present new, exact, finite solutions of relativistic hydrodynamics for longitudinally expanding fireballs for arbitrary constant value of the speed of sound. These new solutions generalize earlier, longitudinally finite, exact solutions, from an unrealistic to a reasonable equation of state, characterized by a temperature independent (average) value of the speed of sound. Observables like the rapidity density and the pseudorapidity density are evaluated analytically, resulting in simple and easy to fit formulae that can be matched to the high energy proton-proton and heavy ion collision data at RHIC and LHC. In the longitudinally boost-invariant limit, these new solutions approach the Hwa-Bjorken solution and the corresponding rapidity distributions approach a rapidity plateaux.
nucl-thhep-exhep-phnucl-exUniverse(2018)·22 citations
08
Effective kinetic description of event-by-event pre-equilibrium dynamics in high-energy heavy-ion collisions
Aleksi Kurkela🇨🇭 · Aleksas Mazeliauskas🇩🇪 · Jean-François Paquet🇺🇸 · Sören Schlichting🇺🇸 · Derek Teaney🇺🇸
We develop a macroscopic description of the space-time evolution of the energy-momentum tensor during the pre-equilibrium stage of a high-energy heavy-ion collision. Based on a weak coupling effective kinetic description of the microscopic equilibration process (à la "bottom-up"), we calculate the non-equilibrium evolution of the local background energy-momentum tensor as well as the non-equilibrium linear response to transverse energy and momentum perturbations for realistic boost-invariant initial conditions for heavy ion collisions. We demonstrate how this framework can be used on an event-by-event basis to propagate the energy momentum tensor from far-from-equilibrium initial state models, e.g. IP-Glasma, to the time $τ_{hydro}$ when the system is well described by relativistic viscous hydrodynamics. The subsequent hydrodynamic evolution becomes essentially independent of the hydrodynamic initialization time $τ_{hydro}$ as long as $τ_{hydro}$ is chosen in an appropriate range where both kinetic and hydrodynamic descriptions overlap. We find that for $s_{N N} = 2.76 TeV$ central Pb-Pb collisions, the typical time scale when viscous hydrodynamics with shear viscosity over entropy ratio $η / s = 0.16$ becomes applicable is $τ_{hydro} \sim 1 fm/c$ after the collision.
↳ hep-phnucl-thPRC(2019)·248 citations
09
Eta Decay and Muonic Puzzles
Yu-Sheng Liu🇨🇳 · Ian C. Cloët🇺🇸 · Gerald A. Miller🇺🇸
New physics motivated by muonic puzzles (proton radius and muon $g - 2$ discrepancies) is studied. Using a light scalar boson $ϕ$ , assuming Yukawa interactions, accounts for these muonic puzzles simultaneously. Our previous work limits the existence of such a scalar boson's mass $m_{ϕ}$ from about 160 keV to 60 MeV. We improve this result by including the influence of all of the possible particles that couple to the $ϕ$ in computing the decay rate. Doing this involves including the strong interaction physics, involving quarks, necessary to compute the $η π ϕ$ vertex function. The Nambu-Jona-Lasinio model, which accounts for the spontaneous symmetry breaking that yields the constituent mass is employed to represent the relevant strong-interaction physics. We use the $η π ϕ$ vertex function to reanalyze the electron beam dump experiments. The result is that the allowed range of $m_{ϕ}$ lies between about 160 keV and 3.5 MeV. This narrow range represents an inviting target for ruling out or discovering this scalar boson. A possible UV completion of our phenomenological model is discussed.
↳ hep-phhep-exnucl-exnucl-th+1NPB(2019)·11 citations
10
Uncertainties in s-process nucleosynthesis in low mass stars determined from Monte Carlo variations
G. Cescutti · R. Hirschi · N. Nishimura · J. W. den Hartogh · T. Rauscher · A. St. J. Murphy · S. Cristallo
The main s-process taking place in low mass stars produces about half of the elements heavier than iron. It is therefore very important to determine the importance and impact of nuclear physics uncertainties on this process. We have performed extensive nuclear reaction network calculations using individual and temperature-dependent uncertainties for reactions involving elements heavier than iron, within a Monte Carlo framework. Using this technique, we determined the uncertainty in the main s-process abundance predictions due to nuclear uncertainties link to weak interactions and neutron captures on elements heavier than iron. We also identified the key nuclear reactions dominating these uncertainties. We found that $β$ -decay rate uncertainties affect only a few nuclides near s-process branchings, whereas most of the uncertainty in the final abundances is caused by uncertainties in neutron capture rates, either directly producing or destroying the nuclide of interest. Combined total nuclear uncertainties due to reactions on heavy elements are in general small (less than 50%). Three key reactions, nevertheless, stand out because they significantly affect the uncertainties of a large number of nuclides. These are $^{56}$ Fe(n, $γ$ ), $^{64}$ Ni(n, $γ$ ), and $^{138}$ Ba(n, $γ$ ). We discuss the prospect of reducing uncertainties in the key reactions identified in this study with future experiments.
↳ astro-ph.SRnucl-exnucl-thMNRAS(2018)·32 citations
11
Exclusive production of pions and the pion distribution amplitude
D. A. Fagundes🇧🇷 · E. G. S. Luna🇧🇷 · A. A. Natale🇧🇷 · M. Pelaez🇧🇷
Considering, as a limit case, an approximately flat pion distribution amplitude, which is determined from the hardest, in momentum space, solution of the Bethe-Salpeter equation for the pion wave function, we compute the pion transition form factor $F_{π γ γ^{*}} (Q^{2})$ and the pion form factor $F_{π} (Q^{2})$ , taking into account the LO as well as NLO form of the hard coefficient function entering the leading-twist factorization formula. We also compute the exclusive photoproduction of pions pairs at high energies, $γ γ \to π^{+} π^{-}$ , where perturbative QCD can be used to compute the hard scattering matrix elements. We verify that the existent data for exclusive pion production can be reasonably described as a function of such flat distribution amplitude.
↳ hep-phhep-exnucl-thJ.Phys.G(2020)·1 citation
12
The maximum mass of dark matter existing in compact stars based on the self-interacting fermionic model
X. D. Wang · B. Qi · N. B. Zhang · S. Y. Wang
By assuming that only gravitation acts between dark matter (DM) and normal matter (NM), we studied DM admixed neutron stars (DANSs) using the two-fluid TOV equations. The NM and DM of compact stars are simulated by the relativistic mean field (RMF) theory and non-self-annihilating self-interacting fermionic model, respectively. The effects of the particle mass of fermionic DM $m_{f}$ and the interaction strength parameter $y$ on the properties of DANSs are investigated in detail. $m_{f}$ and $y$ are considered as the free parameters due to the lack of information about the particle nature of DM so far. For a DANS, we suggest a simple universal relationship $M_{D}^{m a x} = (0.267 y + 0.627 - 3.21 \frac{M _{N}}{\M _{⊙}}) (\frac{1 \GeV}{m _{f}})^{2} \M_{⊙}$ for $y > 100$ , where $M_{D}^{m a x}$ is the maximum mass of DM existing in DANSs and $M_{N}$ is the mass of the neutron star without DM. For free fermion DM model ( $y$ =0), the relationship becomes $M_{D}^{m a x} = (0.627 - 0.027 \frac{M _{N}^{2}}{\M _{⊙}^{2}}) (\frac{1 \GeV}{m _{f}})^{2} \M_{⊙}$ . The radius of DM $R_{D}$ shows a linear relationship with $M_{D}^{m a x}$ in DANSs, namely $R_{D} = (7.02 \frac{M _{D}^{m a x}}{\M _{⊙}} + 1.36)$ ~km. These conclusions are independent of the different NM EOSs from RMF theory. Such a kind of universal relationship connecting the nature of DM particle and mass of stars might shed light on the constraining the nature of the DM by indirect method.
↳ astro-ph.COnucl-thInt.J.Mod.Phys.D(2019)·9 citations
13
Benchmarking the variational reduced density matrix theory in the doubly-occupied configuration interaction space with integrable pairing models
A. Rubio-Garcia · D. R. Alcoba · P. Capuzzi · J. Dukelsky
The variational reduced density matrix theory has been recently applied with great success to models within the truncated doubly-occupied configuration interaction space, which corresponds to the seniority zero subspace. Conservation of the seniority quantum number restricts the Hamiltonians to be based on the SU(2) algebra. Among them there is a whole family of exactly solvable Richardson-Gaudin pairing Hamiltonians. We benchmark the variational theory against two different exactly solvable models, the Richardson-Gaudin-Kitaev and the reduced BCS Hamiltonians. We obtain exact numerical results for the so-called PQGT N-representability conditions in both cases for systems that go from 10 to 100 particles. However, when random single-particle energies as appropriate for small superconducting grains are considered, the exactness is lost but still a high accuracy is obtained.
↳ cond-mat.str-elcond-mat.supr-connucl-thquant-phJ.Chem.Theor.Comput.(2018)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE