Nuclear Theory·nucl-th

Wednesday·February 14, 2018

8 papers—3 primary·5 cross-listed

01
$β$ -delayed fission in $r$ -process nucleosynthesis
M. R. Mumpower · T. Kawano · T. M. Sprouse · N. Vassh · E. M. Holmbeck · R. Surman · P. Moller
We present $β$ -delayed neutron emission and $β$ -delayed fission calculations for heavy, neutron-rich nuclei using the coupled Quasi-Particle Random Phase Approximation plus Hauser-Feshbach (QRPA+HF) approach. From the initial population of a compound nucleus after $β$ -decay, we follow the statistical decay taking into account competition between neutrons, $γ$ -rays, and fission. We find a region of the chart of nuclides where the probability of $β$ -delayed fission is $\sim 100$ %, that likely prevents the production of superheavy elements in nature. For a subset of nuclei near the neutron dripline, neutron multiplicity and the probability of fission are both large, leading to the intriguing possibility of multi-chance $β$ -delayed fission, a new decay mode for extremely neutron-rich heavy nuclei. In this new decay mode, $β$ -decay can be followed by multiple neutron emission leading to subsequent daughter generations which each have a probability to fission. We explore the impact of $β$ -delayed fission in rapid neutron capture process ( $r$ -process) nucleosynthesis in the tidal ejecta of a neutron star--neutron star merger and show that it is a key fission channel that shapes the final abundances near the second $r$ -process peak.
nucl-thastro-ph.SRApJ(2018)·92 citations
02
Strangeness $S = - 1$ hyperon-nucleon interactions: chiral effective field theory vs. lattice QCD
Jing Song🇨🇳 · Kai-Wen Li🇨🇳 · Li-Sheng Geng🇨🇳
Hyperon-nucleon interactions serve as basic inputs to studies of hypernuclear physics and dense (neutron) stars. Unfortunately, a precise understanding of these important quantities have lagged far behind that of the nucleon-nucleon interaction due to lack of high precision experimental data. Historically, hyperon-nucleon interactions are either formulated in quark models or meson exchange models. In recent years, lattice QCD simulations and chiral effective field theory approaches start to offer new insights from first principles. In the present work, we contrast the state of art lattice QCD simulations with the latest chiral hyperon-nucleon forces and show that the leading order relativistic chiral results can already describe the lattice QCD data reasonably well. Given the fact that the lattice QCD simulations are performed with pion masses ranging from the (almost) physical point to 700 MeV, such studies provide a highly non-trivial check on both the chiral effective field theory approaches as well as lattice QCD simulations. Nevertheless more precise lattice QCD simulations are eagerly needed to refine our understanding of hyperon-nucleon interactions.
nucl-thhep-lathep-phPRC(2018)·41 citations
03
Pseudorapidity distribution and decorrelation of anisotropic flow within CLVisc hydrodynamics
Long-Gang Pang🇨🇳 · Hannah Petersen🇩🇪 · Xin-Nian Wang🇨🇳
Studies of fluctuations and correlations of soft hadrons and hard and electromagnetic probes of the dense and strongly interacting medium require event-by-event hydrodynamic simulations of high-energy heavy-ion collisions that are computing intensive. We develop a (3+1)D viscous hydrodynamic model -- CLVisc that is parallelized on Graphics Processing Unit (GPU) using Open Computing Language (OpenCL) with 60 times performance increase for space-time evolution and more than 120 times for the Cooper-Frye particlization relative to that without GPU parallelization. The pseudo-rapidity dependence of anisotropic flow $v_{n} (η)$ are then computed in CLVisc with initial conditions given by the A Multi-Phase Transport (AMPT) model, with energy density fluctuations both in the transverse plane and along the longitudinal direction. Although the magnitude of $v_{n} (η)$ and the ratios between $v_{2} (η)$ and $v_{3} (η)$ are sensitive to the effective shear viscosity over entropy density ratio $η_{v} / s$ , the shape of the $v_{n} (η)$ distributions in $η$ do not depend on the value of $η_{v} / s$ . The decorrelation of $v_{n}$ along the pseudo-rapidity direction due to the twist and fluctuation of the event-planes in the initial parton density distributions is also studied. The decorrelation observable $r_{n} (η^{a}, η^{b})$ between $v_{n} {- η^{a}}$ and $v_{n} {η^{a}}$ with the auxiliary reference window $η^{b}$ is found not sensitive to $η_{v} / s$ when there is no initial fluid velocity. For small $η_{v} / s$ , the initial fluid velocity from mini-jet partons introduces sizable splitting of $r_{n} (η^{a}, η^{b})$ between the two reference rapidity windows $η^{b} \in [3, 4]$ and $η^{b} \in [4.4, 5.0]$ , as has been observed in experiment. The implementation of CLVisc and guidelines on how to efficiently parallelize scientific programs on GPUs are also provided.
nucl-thhep-phphysics.comp-phphysics.flu-dynPRC(2018)·213 citations
04
Particle-Hole Mirror Symmetries around the Half-Filled Shell: The Quantum Numbers and Algebraic Structure of Composite Fermions
W. C. Haxton · Daniel J. Haxton · Byungmin Kang
Composite fermions (CFs) of the fractional quantum Hall effect are described as spherical products of electron and vortex spinors, built from underlying L=1/2 ladder operators aligned so that the spinor angular momenta Le and Lv are maximal. We identify the CF's quantum numbers as the angular momentum L in (L_e L_v)L, its magnetic projection m_L, the electron number N, with L_v={N-1)/2, and magnetic \nu-spin, m_\nu=L_e-L_v. Translationally invariant FQHE states are formed by filling p subshells with their respective CFs, in order of ascending L for fixed L_e and L_v, beginning with the lowest allowed value, L=|m_\nu|. We show that this wave function has an exactly equivalent hierarchical form. FQHE states can be grouped into \nu-spin multiplets mirror symmetric around m_\nu=0, with N held constant. Electron particle-hole conjugation with respect to this vacuum is identified as the mirror symmetry relating FQHE states of the same N but distinct fillings \nu = p/(2p+1} and p/( 2p-1). Alternatively, mirror symmetric \nu-spin multiplets can be constructed in which the magnetic field strength is held fixed: the valence states are electron particle-vortex hole excitations. Particle-hole symmetry -- relating the N-particle FQHE state of filling \nu=p/(2p+1} to the $N ˉ$ -particle state of filling {p+1)/(2p+1} -- is shown to be equivalent to electron-vortex exchange. In this construction $N ˉ$ -N CFs of the higher density state occupy an extra zero-mode subshell. We link this structure, familiar from supersymmetric quantum mechanics, to the CF Pauli Hamiltonian, which we show is isospectral, quadratic in the \nu-spin raising and lowering operators, and four-fold degenerate. On linearization, it takes a Dirac form similar to that found in the integer quantum Hall effect (IQHE).
↳ cond-mat.str-elnucl-thphysics.atom-phPRB(2018)·1 citation
05
Neutrino Predictions from Generalized CP Symmetries of Charged Leptons
Peng Chen🇨🇳 · Salvador Centelles Chuliá🇪🇸 · Gui-Jun Ding🇨🇳 · Rahul Srivastava🇪🇸 · José W. F. Valle🇪🇸
We study the implications of generalized CP transformations acting on the mass matrices of charged leptons in a model-independent way. Generalized $e - μ$ , $e - τ$ and $μ - τ$ symmetries are considered in detail. In all cases the physical parameters of the lepton mixing matrix, three mixing angles and three CP phases can be expressed in terms of a restricted set of independent "theory" parameters that characterize a given choice of CP transformation. This leads to implications for neutrino oscillations as well as neutrinoless double beta decay experiments.
↳ hep-phhep-exnucl-exnucl-thJHEP(2018)·23 citations
06
Discriminating WIMP-nucleus response functions in present and future XENON-like direct detection experiments
A.Fieguth🇩🇪 · M.Hoferichter🇺🇸 · P.Klos🇩🇪 · J.Menéndez🇯🇵 · A.Schwenk🇩🇪 · C.Weinheimer🇩🇪
The standard interpretation of direct-detection limits on dark matter involves particular assumptions of the underlying WIMP-nucleus interaction, such as, in the simplest case, the choice of a Helm form factor that phenomenologically describes an isoscalar spin-independent interaction. In general, the interaction of dark matter with the target nuclei may well proceed via different mechanisms, which would lead to a different shape of the corresponding nuclear structure factors as a function of the momentum transfer $q$ . We study to what extent different WIMP-nucleus responses can be differentiated based on the $q$ -dependence of their structure factors (or "form factors"). We assume an overall strength of the interaction consistent with present spin-independent limits and consider an exposure corresponding to XENON1T-like, XENONnT-like, and DARWIN-like direct detection experiments. We find that, as long as the interaction strength does not lie too much below current limits, the DARWIN settings allow a conclusive discrimination of many different response functions based on their $q$ -dependence, with immediate consequences for elucidating the nature of dark matter.
↳ hep-phastro-ph.COhep-exnucl-thPRD(2018)·19 citations
07
Strong Matter: Rethinking Philosophically
Renxin Xu (PKU)🇨🇳
Normal condensed matter is merely of electromagnetic interaction. A novel state of strong-interaction matter is revisited.
↳ astro-ph.HEnucl-thSCPMA(2018)·18 citations
08
Exclusive vector meson photoproduction in fixed - target collisions at the LHC
V. P. Goncalves🇧🇷 · M. M. Jaime🇧🇷
The exclusive $ρ$ , $ω$ and $J /Ψ$ photoproduction in fixed - target collisions at the LHC is investigated. We estimate, for the first time, the rapidity and transverse momentum distributions of the vector meson photoproduction in $p H e$ , $p A r$ , $P b H e$ and $P b A r$ fixed - target collisions at the LHC using the STARlight Monte Carlo and present our results for the total cross sections. Predictions for the kinematical range probed by the LHCb detector are also presented. Our results indicate that the experimental analysis of this process in fixed - target collisions at the LHC is feasible. Such future analysis will probe the QCD dynamics in a kinematical range complementary to that studied in the collider mode.
↳ hep-phhep-exnucl-exnucl-thEPJC(2018)·15 citations

Affiliations

first authorsco-authorsvia INSPIRE