Nuclear Theory·nucl-th

Friday·May 5, 2017

8 papers—4 primary·4 cross-listed

01
Equilibration and hydrodynamics at strong and weak coupling
Wilke van der Schee🇺🇸
We give an updated overview of both weak and strong coupling methods to describe the approach to a plasma described by viscous hydrodynamics, a process now called hydrodynamisation. At weak coupling the very first moments after a heavy ion collision is described by the colour-glass condensate framework, but quickly thereafter the mean free path is long enough for kinetic theory to become applicable. Recent simulations indicate thermalization in a time $t \sim 40 (η / s)^{4/3} / T$ [1], with $T$ the temperature at that time and $η / s$ the shear viscosity divided by the entropy density. At (infinitely) strong coupling it is possible to mimic heavy ion collisions by using holography, which leads to a dual description of colliding gravitational shock waves. The plasma formed hydrodynamises within a time of $0.41/ T$ . A recent extension found corrections to this result for finite values of the coupling, when $η / s$ is bigger than the canonical value of $1/4 π$ , which leads to $t \sim (0.41 + 1.6 (η / s - 1/4 π)) / T$ [2]. Future improvements include the inclusion of the effects of the running coupling constant in QCD.
nucl-thhep-thNPA(2017)·5 citations
02
Fully self-consistent relativistic Brueckner-Hartree-Fock theory for finite nuclei
Shihang Shen · Haozhao Liang · Jie Meng · Peter Ring · Shuangquan Zhang
Starting from the relativistic form of the Bonn potential as a bare nucleon-nucleon interaction, the full Relativistic Brueckner-Hartree-Fock (RBHF) equations are solved for finite nuclei in a fully self-consistent basis. This provides a relativistic ab initio calculation of the ground state properties of finite nuclei without any free parameters and without three-body forces. The convergence properties for the solutions of these coupled equations are discussed in detail at the example of the nucleus $^{16}$ O. The binding energies, radii, and spin-orbit splittings of the doubly magic nuclei $^{4}$ He, $^{16}$ O, and $^{40}$ Ca are calculated and compared with the earlier RBHF calculated results in a fixed Dirac Woods-Saxon basis and other non-relativistic ab initio calculated results based on pure two-body forces.
nucl-thPRC(2017)·59 citations
03
"Sloppy" nuclear energy density functionals (II): Finite nuclei
Tamara Nikšić · Marko Imbrišak · Dario Vretenar
A study of parameter sensitivity of nuclear energy density functionals, initiated in the first part of this work \cite{NV.16}, is extended by the inclusion of data on ground-state properties of finite nuclei in the application of the manifold boundary approximation method (MBAM). Density functionals used in self-consistent mean-field calculations, and nuclear structure models based on them, are generally "sloppy" and exhibit an exponential range of sensitivity to parameter variations. Concepts of information geometry are used to identify the presence of effective functionals of lower dimension in parameter space associated with parameter combinations that can be tightly constrained by data. The MBAM is used in an iterative procedure that systematically reduces the complexity and the dimension of parameter space of a sloppy functional, with properties of nuclear matter and data on finite nuclei determining not only the values of model parameters, but also the optimal functional form of the density dependence.
nucl-thPRC(2017)·12 citations
04
The right choice of moment for anisotropic fluid dynamics
H. Niemi · E. Molnár · D. H. Rischke
We study anisotropic fluid dynamics derived from the Boltzmann equation based on a particular choice for the anisotropic distribution function within a boost-invariant expansion of the fluid in one spatial dimension. In order to close the conservation equations we need to choose an additional moment of the Boltzmann equation. We discuss the influence of this choice of closure on the time evolution of fluid-dynamical variables and search for the best agreement to the solution of the Boltzmann equation in the relaxation-time approximation.
nucl-thNPA(2017)·7 citations
05
Validity of the Weizsäcker-Williams Approximation and the Analysis of Beam Dump Experiments: Production of an axion, a dark photon, or a new axial-vector boson
Yu-Sheng Liu🇺🇸 · Gerald A. Miller🇺🇸
Beam dump experiments have been used to search for new particles, $ϕ$ , with null results interpreted in terms of limits on masses $m_{ϕ}$ and coupling constants $ϵ$ . However these limits have been obtained by using approximations [including the Weizsäcker-Williams (WW) approximation] or Monte-Carlo simulations. We display methods to obtain the cross section and the resulting particle production rates without using approximations on the phase space integral or Monte-Carlo simulations. In our previous work we examined the case of the new scalar boson production; in this paper we explore all possible new spin-0 and spin-1 particles. We show that the approximations cannot be used to obtain accurate values of cross sections. The corresponding exclusion plots differ by substantial amounts when seen on a linear scale. Furthermore, a new region ( $m_{ϕ} < 2 m_{e}$ ) of parameter space can be explored without using one of the common approximations, $m_{ϕ} ≫ m_{e}$ . We derive new expressions for the three photon decays of dark photon and four photon decays of new axial-vector bosons. As a result, the production cross section and exclusion region of different low mass ( $m_{ϕ} < 2 m_{e}$ ) bosons are very different. Moreover, our method can be used as a consistency check for Monte-Carlo simulations.
↳ hep-phhep-exnucl-exnucl-thPRD(2017)·111 citations
06
Chiral vortical effect in pionic superfluid vs spin alignment of baryons
Oleg V. Teryaev🇷🇺 · Valentin I. Zakharov🇷🇺
We consider chiral fluids, with (nearly) massless fermionic constituents, in the confining phase. Chiral vortical effect (CVE) is the flow of axial current along the axis of rotation of the fluid while the spin alignment is a non-vanishing correlation of polarizations of baryons with the axis of rotation. As the theoretical framework we use the model of pionic superfluidity induced by a non-vanishing isotopic chemical potential. We note that the average value of spin of virtual baryons reproduces the CVE. The role of defects, or vortices is crucial. The model does not apply directly to the quark-gluon plasma but might indicate existence of a mechanism to produce baryons with relatively large polarization in heavy-ion collisions.
↳ hep-thhep-phnucl-th7 citations
07
Exact self-duality in a modified Skyrme model
L. A. Ferreira🇧🇷
We propose a modification of the Skyrme model that supports a self-dual sector possessing exact non-trivial finite energy solutions. The action of such a theory possesses the usual quadratic and quartic terms in field derivatives, but the couplings of the components of the Maurer-Cartan form of the Skyrme model is made by a non-constant symmetric matrix, instead of the usual Killing form of the SU(2) Lie algebra. The introduction of such a matrix make the self-duality equations conformally invariant in three space dimensions, even though it may break the global internal symmetries of the original Skyrme model. For the case where that matrix is proportional to the identity we show that the theory possesses exact self-dual Skyrmions of unity topological charges.
↳ hep-thmath-phmath.MPnlin.SI+1JHEP(2017)·26 citations
08
A novel multiquark approach to hadron resonances
S. S. Afonin🇷🇺
A new approach to description of hadron spectroscopy is proposed. By assumption, the form of spectrum is dictated by the trace of energy momentum tensor in QCD. This provides the relativistic and renormalization invariance of hadron masses. The constructed scheme is applied to the light mesons for which two complementary interpretations are worked out. The first one represents an "atomic" structure of resonances above 1 GeV in which the quanta of non-perturbative gluon contributions are quantified via an effective formation of quasiparticles representing likely gluon analogues of positronium. This picture allows to build a "periodic table of the hadronic elements", i.e. to classify hadrons, in some sense, in analogy with Mendeleev table in chemistry. The classification does not require introduction of the orbital angular momentum associated with hadron constituents. The Regge and radial trajectories emerge in a natural way. The second interpretation is based on a "collisional" nature of some (or many) hadrons, specifically of scalar resonances below 1 GeV. Here the role of quasiparticles is played by another hadron. This picture in particular leads to a simple explanation of the puzzling scalar sector below 1 GeV with correct predictions for masses and dominant decay modes.
↳ hep-phhep-latnucl-th1 citation

Affiliations

first authorsco-authorsvia INSPIRE