Nuclear Theory·nucl-th

Tuesday·May 10, 2016

15 papers—9 primary·6 cross-listed

01
Quasiparticle anisotropic hydrodynamics for central collisions
Mubarak Alqahtani🇺🇸 · Mohammad Nopoush🇺🇸 · Michael Strickland🇺🇸
We use quasiparticle anisotropic hydrodynamics to study an azimuthally-symmetric boost-invariant quark-gluon plasma including the effects of both shear and bulk viscosities. In quasiparticle anisotropic hydrodynamics, a single finite-temperature quasiparticle mass is introduced and fit to the lattice data in order to implement a realistic equation of state. We compare results obtained using the quasiparticle method with the standard method of imposing the equation of state in anisotropic hydrodynamics and viscous hydrodynamics. Using these three methods, we extract the primordial particle spectra, total number of charged particles, and average transverse momentum for various values of the shear viscosity to entropy density ratio eta/s. We find that the three methods agree well for small shear viscosity to entropy density ratio, eta/s, but differ at large eta/s. We find, in particular, that when using standard viscous hydrodynamics, the bulk-viscous correction can drive the primordial particle spectra negative at large p_T which is clearly unphysical. Such a behavior is not seen in either anisotropic hydrodynamics approach, irrespective of the value of eta/s.
nucl-thhep-phPRC(2017)·56 citations
02
Cutoff regulators in chiral nuclear effective field theory
Bingwei Long🇨🇳 · Ying Mei🇨🇳
Three-dimensional cutoff regulators are frequently employed in multi-nucleon calculations, but they violate chiral symmetry and Lorentz invariance. A cutoff regularization scheme is proposed to compensate systematically at subleading orders for these symmetry violations caused by regulator artifacts. This is especially helpful when a soft momentum cutoff has to be used for technical reasons. It is also shown that dimensional regularization can still be used for some Feynman (sub)diagrams while cutoff regulators are used for the rest.
nucl-thhep-phPRC(2016)·13 citations
03
Importance of resonance widths in low-energy scattering of weakly-bound light-mass nuclei
P. R. Fraser · K. Massen-Hane · K. Amos · I. Bray · L. Canton · R. Fossion · A. S. Kadyrov · S. Karataglidis · J. P. Svenne · D. van der Knijff
What effect do particle-emitting resonances have on the scattering cross section? What physical considerations are necessary when modelling these resonances? These questions are important when theoretically describing scattering experiments with radioactive ion beams which investigate the frontiers of the table of nuclides, far from stability. Herein, a novel method is developed that describes resonant nuclear scattering from which centroids and widths in the compound nucleus are obtained when one of the interacting bodies has particle unstable resonances. The method gives cross sections without unphysical behavior that is found if simple Lorentzian forms are used to describe resonant target states. The resultant cross sections differ significantly from those obtained when the states in the coupled channel calculations are taken to have zero width, and compound-system resonances are better matched to observed values.
nucl-thPRC(2016)·7 citations
04
Structure of $^{23}$ Al from a multi-channel algebraic scattering model based on mirror symmetry
P. R. Fraser · A. S. Kadyrov · K. Massen-Hane · K. Amos · L. Canton · S. Karataglidis · D. van der Knijff · I. Bray
The proton-rich nucleus $^{23}$ Al has a ground state just 123 keV below the proton drip-line, and as a result comparatively little is known experimentally about its properties, as with many such nuclei. Theoretical investigations have tended to model exclusively the ground and first one to three excited states known. In this paper, we theoretically model most of the known spectrum, and predict what states may as yet be unobserved. We use the multichannel algebraic scattering (MCAS) method to describe states as resonances of a valence proton coupled to a $^{22}$ Mg rotor core. Six states with low-excitation energies and defined $J^{π}$ are matched, and we make the first prediction of the properties of four others and propound the possible existence of several more.
nucl-thJ.Phys.G(2016)·4 citations
05
Extension of the ratio method to low energy
F. Colomer · P. Capel · F. M. Nunes · R. C. Johnson
Background: The ratio method has been proposed as a means to remove the reaction model dependence in the study of halo nuclei. Purpose: Originally, it was developed for higher energies but given the potential interest in applying the method at lower energy, in this work we explore its validity at 20 MeV/nucleon. Method: The ratio method takes the ratio of the breakup angular distribution and the summed angular distribution (which includes elastic, inelastic and breakup) and uses this observable to constrain the features of the original halo wave function. In this work we use the Continuum Discretized Coupled Channel method and the Coulomb-corrected Dynamical Eikonal Approximation for the study. Results: We study the reactions of 11Be on 12C, 40Ca and 208Pb at 20 MeV/nucleon. We compare the various theoretical descriptions and explore the dependence of our result on the core-target interaction. Conclusions: Our study demonstrates that the ratio method is valid at these lower beam energies.
nucl-thnucl-exPRC(2016)·7 citations
06
Impacts of the tensor couplings of $ω$ and $ρ$ mesons and Coulomb exchange terms on super-heavy nuclei and their relation to symmetry energy
N. Liliani · A. M. Nugraha · J. P. Diningrum · A. Sulaksono
We have studied the effects of tensor coupling of $ω$ and $ρ$ meson terms, Coulomb exchange term in local density approximation and various isoscalar-isovector coupling terms of relativistic mean field model on the properties of nuclear matter, finite nuclei, and super-heavy nuclei. We found that for the same fixed value of symmetry energy $J$ or its slope $L$ the presence of tensor coupling of $ω$ and $ρ$ meson terms and Coulomb exchange term yields thicker neutron skin thickness of $^{208}$ Pb. We also found that the roles of tensor coupling of $ω$ and $ρ$ meson terms, Coulomb exchange term in local density approximation and various isoscalar-isovector coupling terms on the bulk properties of finite nuclei varies depending on the corresponding nucleus mass. However, on average, tensor coupling terms play a significant role in predicting the bulk properties of finite nuclei in a quite wide mass range especially in binding energies. We also observed that for some particular nuclei, the corresponding experimental data of binding energies is rather less compatible with the presence of Coulomb exchange term in local density approximation and they tend to disfavor the presence of isoscalar-isovector coupling term with too high $Λ$ value. Furthermore, we have found that these terms influence the detail properties of $^{292}$ 120 super-heavy nucleus such as binding energies, the magnitude of two nucleon gaps, single particle spectra, neutron densities, neutron skin thicknesses and mean square charge radii. However, the shell closure predictions of $^{208}$ Pb and $^{292}$ 120 nuclei is not affected by the presence of these terms.
nucl-thPRC(2016)·7 citations
07
Entropy Production and Effective Viscosity in Heavy-Ion Collisions
Yu. B. Ivanov🇷🇺 · A. A. Soldatov🇷🇺
Entropy production and an effective viscosity in central Au+Au collisions are estimated in a wide range of incident energies 3.3 GeV $\leq s_{N N} \leq$ 39 GeV. The simulations are performed within a three-fluid model employing three different equations of state with and without deconfinement transition, which are equally good in reproduction of the momentum-integrated elliptic flow of charged particles in the considered energy range. It is found that more that 80\% entropy is prodused during a short early collision stage which lasts $\sim$ 1 fm/c at highest considered energies $s_{N N} \geq$ 20 GeV. The estimated values of the viscosity-to-entropy ratio ( $η / s$ ) are approximately the same in all considered scenarios. At final stages of the system expansion they range from $\sim$ 0.05 at highest considered energies to $\sim$ 0.5 lowest ones. It is found that the $η / s$ ratio decreases with the temperature ( $T$ ) rise approximately as $\sim 1/ T^{4}$ and exhibits a rather weak dependence on the net-baryon density.
nucl-thhep-phEPJA(2016)·22 citations
08
Contribution of excited states to stellar weak-interaction rates in odd-A nuclei
Pedro Sarriguren
Weak-interaction rates, including beta-decay and electron capture, are studied in several odd-A nuclei in the pf-shell region at various densities and temperatures of astrophysical interest. Special attention is paid to the relative contribution to these rates of thermally populated excited states in the decaying nucleus. The nuclear structure involved in the weak processes is studied within a quasiparticle random-phase approximation with residual interactions in both particle-hole and particle-particle channels on top of a deformed Skyrme Hartree-Fock mean field with pairing correlations. In the range of densities and temperatures considered, it is found that the total rates do not differ much from the rates of the ground state fully populated. In any case, the changes are not larger than the uncertainties due to the nuclear model dependence of the rates.
nucl-thPRC(2016)·15 citations
09
Generalized-Seniority Pattern and Thermal Properties in Even Sn Isotopes
L. Y. Jia · Chong Qi
Even tin isotopes of mass number $A = 108 \sim 124$ are calculated with realistic interactions in the generalized-seniority approximation of the nuclear shell model. For each nucleus, we compute the lowest ten thousand states ( $5000$ of each parity) up to around $8$ MeV in excitation energy, by allowing as many as four broken pairs. The lowest fifty eigen energies of each parity are compared with the exact results of the large-scale shell-model calculation. The wavefunctions of the mid-shell nuclei show a clear pattern of the stepwise breakup of condensed coherent pairs with increasing excitation energy. We also compute in the canonical ensemble the thermal properties -- level density, entropy, and specific heat -- in relation to the thermal pairing phase transition.
nucl-thPRC(2016)·18 citations
10
Hyperons in neutron stars within Eddington-inspired Born-Infeld theory of gravity
A. I. Qauli🇮🇩 · M. Iqbal🇮🇩 · A. Sulaksono🇮🇩 · H. S. Ramadhan🇮🇩
We investigate the mass-radius relation of neutron star (NS) with hyperons inside its core by using the Eddington-inspired Born-Infeld (EiBI) theory of gravity. The equation of state of the star is calculated by using the relativistic mean field model under which the standard SU(6) prescription and hyperons potential depths are used to determine the hyperon coupling constants. We found that, for $4 \times 1 0^{6} m^{2} ≲ κ ≲ 6 \times 1 0^{6} m^{2}$ , the corresponding NS mass and radius predicted by the EiBI theory of gravity is compatible with observational constraints of maximum NS mass and radius. The corresponding $κ$ value is also compatible with the $κ$ range predicted by the astrophysical-cosmological constraints. We also found that the parameter $κ$ could control the size and the compactness of a neutron star.
↳ astro-ph.SRgr-qcnucl-thPRD(2016)·28 citations
11
Lectures on Bound states
Paul Hoyer🇫🇮
Even a first approximation of bound states requires contributions of all powers in the coupling. This means that the concept of "lowest order bound state" needs to be defined. In these lectures I discuss the "Born" (no loop, lowest order in $ℏ$ ) approximation. Born level states are bound by gauge fields which satisfy the classical field equations. As a check of the method, Positronium states of any momentum are determined as eigenstates of the QED Hamiltonian, quantized at equal time. Analogously, states bound by a strong external field $A^{μ} (x)$ are found as eigenstates of the Dirac Hamiltonian. Their Fock states have dynamically created $e^{+} e^{-}$ pairs, whose distribution is determined by the Dirac wave function. The linear potential of $D = 1 + 1$ dimensions confines electrons but repels positrons. As a result, the mass spectrum is continuous and the wave functions have features of both bound states and plane waves. The classical solutions of Gauss' law are explored for hadrons in QCD. A non-vanishing boundary condition at spatial infinity generates a constant \order{\alpha_s^0} color electric field between quarks of specific colors. Poincaré invariance limits the spectrum to color singlet $q q ˉ$ and $q q q$ states, which do not generate an external color field. This restricts the \order{\alpha_s^0} interactions between hadrons to string breaking dynamics as in dual diagrams. Light mesons lie on linear Regge and parallel daughter trajectories. There are massless states which may be significant for chiral symmetry breaking. Since the bound states are defined at equal time in all frames they have a non-trivial Lorentz covariance.
↳ hep-phnucl-th16 citations
12
From strong to weak coupling in holographic models of thermalization
Sašo Grozdanov🇳🇱 · Nikolaos Kaplis🇳🇱 · Andrei O. Starinets🇬🇧
We investigate the analytic structure of thermal energy-momentum tensor correlators at large but finite coupling in quantum field theories with gravity duals. We compute corrections to the quasinormal spectra of black branes due to the presence of higher derivative $R^{2}$ and $R^{4}$ terms in the action, focusing on the dual to $N = 4$ SYM theory and Gauss-Bonnet gravity. We observe the appearance of new poles in the complex frequency plane at finite coupling. The new poles interfere with hydrodynamic poles of the correlators leading to the breakdown of hydrodynamic description at a coupling-dependent critical value of the wave-vector. The dependence of the critical wave vector on the coupling implies that the range of validity of the hydrodynamic description increases monotonically with the coupling. The behavior of the quasinormal spectrum at large but finite coupling may be contrasted with the known properties of the hierarchy of relaxation times determined by the spectrum of a linearized kinetic operator at weak coupling. We find that the ratio of a transport coefficient such as viscosity to the relaxation time determined by the fundamental non-hydrodynamic quasinormal frequency changes rapidly in the vicinity of infinite coupling but flattens out for weaker coupling, suggesting an extrapolation from strong coupling to the kinetic theory result. We note that the behavior of the quasinormal spectrum is qualitatively different depending on whether the ratio of shear viscosity to entropy density is greater or less than the universal, infinite coupling value of $ℏ/4 π k_{B}$ . In the former case, the density of poles increases, indicating a formation of branch cuts in the weak coupling limit, and the spectral function shows the appearance of narrow peaks. We also discuss the relation of the viscosity-entropy ratio to conjectured bounds on relaxation time in quantum systems.
↳ hep-thcond-mat.str-elhep-phnucl-th+1JHEP(2016)·122 citations
13
A dynamical quasiparticle approach for the Quark-Gluon-Plasma bulk and transport properties
Hamza Berrehrah🇩🇪 · Elena Bratkovskaya🇩🇪 · Thorsten Steinert🇩🇪 · Wolfgang Cassing🇩🇪
The properties of quantum-chromo dynamics (QCD) nowadays are accessable by lattice QCD calculations at vanishing quark chemical potential $μ_{q}$ =0 but often lack a transparent physical interpretation. In this review we report about results from an extended dynamical quasiparticle model (DQPM $^{*}$ ) in which the effective parton propagators have a complex selfenergy that depends on the temperature $T$ of the medium as well as on the chemical potential $μ_{q}$ and the parton three-momentum $p$ with respect to the medium at rest. It is demonstrated that this approach allows for a good description of QCD thermodynamics with respect to the entropy density, pressure etc. above the critical temperature $T_{c} \approx$ 158 MeV. Furthermore, the quark susceptibility $χ_{q}$ and the quark number density $n_{q}$ are found to be reproduced simultaneously at zero and finite quark chemical potential. The shear and bulk viscosities $η, ζ$ , and the electric conductivity $σ_{e}$ from the DQPM $^{*}$ also turn out in close agreement with lattice results for $μ_{q}$ =0. The DQPM $^{*}$ , furthermore, allows to evaluate the momentum $p$ , $T$ and $μ_{q}$ dependencies of the partonic degrees of freedom also for larger $μ_{q}$ which are mandatory for transport studies of heavy-ion collisions in the regime 5 GeV $< s_{N N} <$ 10 GeV. We finally calculate the charm quark diffusion coefficient $D_{s}$ -- evaluated from the differential cross sections of partons in the medium for light and heavy quarks by employing the propagators and couplings from the DQPM -- and compare to the available lattice data. It is argued that the complete set of observables allows for a transparent interpretation of the properties of hot QCD.
↳ hep-phnucl-thIJMPE(2016)·68 citations
14
Effective field theory for large logarithms in radiative corrections to electron proton scattering
Richard J. Hill🇺🇸
Radiative corrections to elastic electron-proton scattering are analyzed in effective field theory. A new factorization formula identifies all sources of large logarithms in the limit of large momentum transfer, $Q^{2} ≫ m_{e}^{2}$ . Explicit matching calculations are performed through two-loop order. A renormalization analysis in soft-collinear effective theory is performed to systematically compute and resum large logarithms. Implications for the extraction of charge radii and other observables from scattering data are discussed. The formalism may be applied to other lepton-nucleon scattering and $e^{+} e^{-}$ annihilation processes.
↳ hep-phhep-exnucl-exnucl-th+1PRD(2017)·47 citations
15
Re-evaluation of the $^{16}$ O( $n$ , $γ$ ) $^{17}$ O cross section at astrophysical energies and its role as neutron poison in the $s$ process
Peter Mohr · Christian Heinz · Marco Pignatari · Iris Dillmann · Alberto Mengoni · Franz Kaeppeler
The doubly-magic nucleus $^{16}$ O has a small neutron capture cross section of just a few tens of microbarn in the astrophysical energy region. Despite of this, $^{16}$ O plays an important role as neutron poison in the astrophysical slow neutron capture ( $s$ ) process due to its high abundance. We present in this paper a re-evaluation of the available experimental data for $^{16}$ O( $n, γ$ ) $^{17}$ O and derive a new recommendation for the Maxwellian-averaged cross sections (MACS) between $k T$ = 5 $-$ 100 keV. Our new recommendations are lower up to $k T$ = 60 keV compared to the previously recommended values but up to 14\% higher at $k T$ = 100 keV. We explore the impact of this different energy dependence on the weak $s$ -process during core helium- ( $k T$ = 26 keV) and shell carbon burning ( $k T$ = 90 keV) in massive stars where $^{16}$ O is the most abundant isotope.
↳ astro-ph.SRnucl-exnucl-thApJ(2016)·14 citations

Affiliations

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