Nuclear Theory·nucl-th

Tuesday·April 5, 2016

10 papers—8 primary·2 cross-listed

01
Spontaneous fission of superheavy nucleus $^{286}$ Fl
Dorin N. Poenaru · Radu A. Gherghescu
The decimal logarithm of spontaneous fission half-life of the superheavy nucleus $^{286}$ Fl experimentally determined is $lo g_{10} T_{f}^{e x p} (s) = - 0.632$ . We present a method to calculate the half-life based on the cranking inertia and the deformation energy, functions of two independent surface coordinates, using the best asymmetric two center shell model. In the first stage we study the statics. At a given mass asymmetry up to about $η = 0.5$ the potential barrier has a two hump shape, but for larger $η$ it has only one hump. The touching point deformation energy versus mass asymmetry shows the three minima, produced by shell effects, corresponding to three decay modes: spontaneous fission, cluster decay and $α$ ~decay. The least action trajectory is determined in the plane $(R, η)$ where $R$ is the separation distance of the fission fragments and $η$ is the mass asymmetry. We may find a sequence of several trajectories one of which gives the least action. The parametrization with two deformation coordinates $(R, η)$ and the radius of the light fragment, $R_{2}$ , exponentially decreasing with $R$ is compared with the simpler one, in which $R_{2}$ ~=constant. The latter is closer to the reality and reminds us about the alpha or cluster preformation at the nuclear surface.
nucl-thPRC(2016)·36 citations
02
Calculation of Spin Observables for Proton-Neutron Elastic Scattering in the Bethe-Salpeter Equation
Susumu Kinpara
Bethe-Salpeter equation is applied to $p$ - $n$ elastic scattering. The spin observables are calculated by the M matrix similar to $p$ - $p$ case. The parameters of the meson-exchange model are used with the cut-off for the pion exchange interaction. Change of the M matrix indicates breaking of the charge independence in the nucleon-nucleon system.
nucl-th1 citation
03
Self-consistent continuum random-phase approximation with finite-range interactions for charge-exchange excitations
V. De Donno · G. Co' · M. Anguiano · A. M. Lallena
The formalism of the continuum random-phase approximation theory which treats, without ap- proximations, the continuum part of the single-particle spectrum, is extended to describe charge- exchange excitations. Our approach is self-consistent, meaning that we use a unique, finite-range, interaction in the Hartree-Fock calculations which generate the single-particle basis and in the con- tinuum random-phase approximation which describes the excitation. We study excitations induced by the Fermi, Gamow-Teller and spin-dipole operators in doubly magic nuclei by using four Gogny- like finite-range interactions, two of them containing tensor forces. We focus our attention on the importance of the correct treatment of the continuum configuration space and on the effects of the tensor terms of the force.1
nucl-thPRC(2016)·12 citations
04
Evaluation of the forward Compton scattering off protons: II. Spin-dependent amplitude and observables
Oleksii Gryniuk🇩🇪 · Franziska Hagelstein🇩🇪 · Vladimir Pascalutsa (JGU Mainz)🇩🇪
The forward Compton scattering off the proton is determined by substituting the empirical total photoabsorption cross sections into dispersive sum rules. In addition to the spin-independent amplitude evaluated previously [Phys. Rev. D 92, 074031 (2015)], we obtain the spin-dependent amplitude over a broad energy range. The two amplitudes contain all the information about this process, and we, hence, can reconstruct the nonvanishing observables of the proton Compton scattering in the forward kinematics. The results are compared with predictions of chiral perturbation theory where available. The low-energy expansion of the spin-dependent Compton scattering amplitude yields the Gerasimov-Drell-Hearn (GDH) sum rule and relations for the forward spin polarizabilities (FSPs) of the proton. Our evaluation provides an empirical verification of the GDH sum rule for the proton, and yields empirical values of the proton FSPs. For the GDH integral, we obtain $204.5 (21.4)$ $μ$ b, in agreement with the sum rule prediction: $204.784481 (4)$ $μ$ b. For the FSPs, we obtain: $γ_{0} = - 92.9 (10.5) \times 1 0^{- 6}$ fm $^{4}$ , and $γ_{0} ˉ = 48.4 (8.2) \times 1 0^{- 6}$ fm $^{6}$ , improving on the accuracy of previous evaluations.
nucl-thhep-phnucl-exPRD(2016)·22 citations
05
Liquid gas phase transition in hypernuclei
S. Mallik🇮🇳 · G. Chaudhuri🇮🇳
The fragmentation of excited hypernuclear system formed in heavy ion collisions has been described by the canonical thermodynamical model extended to three component systems. The multiplicity distribution of the fragments has been analyzed in detail and it has been observed that the hyperons have the tendency to get attached to the heavier fragments. Another important observation is the phase coexistence of the hyperons, a phenomenon which is linked to liquid gas phase transition in strange matter.
nucl-thhep-exhep-phnucl-exPRC(2015)·6 citations
06
Effect of hyperons on phase coexistence in strange matter
P. Das🇮🇳 · S. Mallik🇮🇳 · G. Chaudhuri🇮🇳
The study of liquid gas phase transition in fragmentation of nuclei in heavy ion collisions has been extended to the strangeness sector using the statistical model for multifragmentation. Helmholtz's free energy, specific heat and few other thermodynamic observables have been analyzed in order to examine the occurence of phase transition in the strange matter. The bimodal behaviour of the largest cluster formed in fragmentation also strongly indicates coexistence of both the phases. The presence of hyperons strengthens the signals and also shifts the transition temperature to lower values.
nucl-thhep-exhep-phnucl-exPRC(2017)·2 citations
07
Application of the triaxial quadrupole-octupole rotor to the ground and negative-parity levels of actinide nuclei
M. S. Nadirbekov · N. Minkov · M. Strecker · W. Scheid
In this work we examine the possibility to describe yrast positive- and negative-parity excitations of deformed even-even nuclei through a collective rotation model in which the nuclear surface is characterized by triaxial quadrupole and octupole deformations. The nuclear moments of inertia are expressed as sums of quadrupole and octupole parts. By assuming an adiabatic separation of rotation and vibration degrees of freedom we suppose that the structure of the positive- and negative- parity bands may be determined by the triaxial-rigid-rotor motion of the nucleus. By diagonalizing the Hamiltonian in a symmetrized rotor basis with embedded parity we obtain a model description for the yrast positive- and negative-parity bands in several actinide nuclei. We show that the energy displacement between the opposite-parity sequences can be explained as the result of the quadrupole-octupole triaxiality.
nucl-thIJMPE(2016)·11 citations
08
Binding in light nuclei: Statistical NN uncertainties vs Computational accuracy
R. Navarro Perez · A. Nogga · J. E. Amaro · E. Ruiz Arriola
We analyse the impact of the statistical uncertainties of the the nucleon-nucleon interaction, based on the Granada-2013 np-pp database, on the binding energies of the triton and the alpha particle using a bootstrap method, by solving the Faddeev equations for $^{3}$ H and the Yakubovsky equations for $^{4}$ He respectively. We check that in practice about 30 samples prove enough for a reliable error estimate. An extrapolation of the well fulfilled Tjon-line correlation predicts the experimental binding of the alpha particle within uncertainties.
nucl-thphysics.comp-phphysics.data-anJ.Phys.Conf.Ser.(2016)·7 citations
09
Time-dependence of the holographic spectral function: Diverse routes to thermalisation
Souvik Banerjee🇳🇱 · Takaaki Ishii🇺🇸 · Lata Kh Joshi🇮🇳 · Ayan Mukhopadhyay🇦🇹 · P. Ramadevi🇮🇳
We develop a new method for computing the holographic retarded propagator in generic (non-)equilibrium states using the state/geometry map. We check that our method reproduces the thermal spectral function given by the Son-Starinets prescription. The time-dependence of the spectral function of a relevant scalar operator is studied in a class of non-equilibrium states. The latter are represented by AdS-Vaidya geometries with an arbitrary parameter characterising the timescale for the dual state to transit from an initial thermal equilibrium to another due to a homogeneous quench. For long quench duration, the spectral function indeed follows the thermal form at the instantaneous effective temperature adiabatically, although with a slight initial time delay and a bit premature thermalisation. At shorter quench durations, several new non-adiabatic features appear: (i) time-dependence of the spectral function is seen much before than that in the effective temperature (advanced time-dependence), (ii) a big transfer of spectral weight to frequencies greater than the initial temperature occurs at an intermediate time (kink formation) and (iii) new peaks with decreasing amplitudes but in greater numbers appear even after the effective temperature has stabilised (persistent oscillations). We find four broad routes to thermalisation for lower values of spatial momenta. At higher values of spatial momenta, kink formations and persistent oscillations are suppressed, and thermalisation time decreases. The general thermalisation pattern is globally top-down, but a closer look reveals complexities.
↳ hep-thcond-mat.str-elgr-qcnucl-thJHEP(2016)·19 citations
10
An Exponential Regulator for Rapidity Divergences
Ye Li🇺🇸 · Duff Neill🇺🇸 · Hua Xing Zhu🇺🇸
Finding an efficient and compelling regularization of soft and collinear degrees of freedom at the same invariant mass scale, but separated in rapidity is a persistent problem in high-energy factorization. In the course of a calculation, one encounters divergences unregulated by dimensional regularization, often called rapidity divergences. Once regulated, a general framework exists for their renormalization, the rapidity renormalization group (RRG), leading to fully resummed calculations of transverse momentum (to the jet axis) sensitive quantities. We examine how this regularization can be implemented via a multi-differential factorization of the soft-collinear phase-space, leading to an (in principle) alternative non-perturbative regularization of rapidity divergences. As an example, we examine the fully-differential factorization of a color singlet's momentum spectrum in a hadron-hadron collision at threshold. We show how this factorization acts as a mother theory to both traditional threshold and transverse momentum resummation, recovering the classical results for both resummations. Examining the refactorization of the transverse momentum beam functions in the threshold region, we show that one can directly calculate the rapidity renormalized function, while shedding light on the structure of joint resummation. Finally, we show how using modern bootstrap techniques, the transverse momentum spectrum is determined by an expansion about the threshold factorization, leading to a viable higher loop scheme for calculating the relevant anomalous dimensions for the transverse momentum spectrum.
↳ hep-phnucl-thNPB(2020)·173 citations

Affiliations

first authorsco-authorsvia INSPIRE