Nuclear Theory·nucl-th

Monday·March 18, 2019

10 papers—6 primary·4 cross-listed

01
Self-consistent calculation of the reactor antineutrino spectra including forbidden transitions
J. Petković · T. Marketin · G. Martínez-Pinedo · N. Paar
With the goal of determining the $θ_{13}$ neutrino oscillation mixing angle, the measurements of reactor antineutrino fluxes at the Double Chooz, RENO and Daya Bay experimental facilities have uncovered a systematic discrepancy between the number of observed events and theoretical expectations. In the \emph{ab initio} approach, the total reactor antineutrino spectrum is a weighted sum of spectra resulting from all $β$ branches of all fission products in the reactor core. At all three facilities a systematic deviation of the number of observed events from the number of predicted events was noticed, i.e., approximately 6\% of the predicted neutrinos were not observed. This discrepancy was named the reactor neutrino anomaly. In theoretical studies it is assumed that all the decays are allowed in shape, but a quarter of all transitions are actually forbidden and may have a complex energy dependence that will affect the total reactor antineutrino spectrum. In order to estimate the effect of forbidden transitions, we perform a fully self-consistent calculation of spectra from all contributing transitions and compare the results with a purely allowed approximation.
nucl-thJ.Phys.G(2019)·8 citations
02
Monopole moments and nuclear compressibility
G.F. Bertsch
The nuclear compressibility has a role in nuclear physics in several ways. Its relationship to the giant monopole is well known and has been subject of much theoretical work. Less well known is its affect on in nuclear structure, namely monopole transitions between low-lying states in the spectrum. Here I revisit the relationship between monopole and quadrupole moments in deformed nuclei. It has often been assumed without any microscopic justification that the nucleus can be treated as an incompressible fluid. An analytic formula is derived here for the resulting relationship between monopole and quadrupole moments. The formula is shown to be well satisfied within self-consistent mean-field theory calculated with several energy functionals. The formula can be tested when both monopole and quadrupole matrix elements of band-to-band transitions are known. Data is available for the decay of the first excited $K^{π} = 0^{+}$ band to the ground-state band in $^{156}$ Gd, and the extracted matrix elements are found to be consistent with the incompressible fluid picture.
nucl-th0 citations
03
Relating eccentricity fluctuations to density fluctuations in heavy-ion collisions
Rajeev S. Bhalerao🇮🇳 · Giuliano Giacalone🇫🇷 · Pablo Guerrero-Rodríguez🇪🇸 · Matthew Luzum🇧🇷 · Cyrille Marquet🇫🇷 · Jean-Yves Ollitrault🇫🇷
The magnitude of anisotropic flow in a nucleus-nucleus collision is determined by the energy density field, $ρ (x, y, z)$ , created right after the collision occurs. Specifically, elliptic flow, $v_{2}$ , and triangular flow, $v_{3}$ , are proportional to the anisotropy coefficients $ε_{2}$ and $ε_{3}$ , which are functionals of $ρ$ . We express the mean and the variance of $ε_{2}$ and $ε_{3}$ as a function of the 1- and 2-point functions of $ρ$ . These results generalize results obtained previously, that were valid only for central collisions, or only for identical point-like sources. We apply them to the color glass condensate effective theory, using the recently derived expression of the 2-point function.
nucl-thhep-phnucl-exActa Phys.Polon.B(2019)·12 citations
04
Time-dependent Hartree-Fock plus Langevin approach for hot fusion reactions to synthesize the $Z = 120$ superheavy element
K. Sekizawa · K. Hagino
We develop a novel approach to fusion reactions for syntheses of superheavy elements, which combines the time-dependent Hartree-Fock (TDHF) method with a dynamical diffusion model based on the Langevin equation. In this approach, the distance of the closest approach for the capture process is estimated within the TDHF approach, which is then plugged into the dynamical diffusion model as an initial condition. We apply this approach to hot fusion reactions leading to formation of the element $Z = 120$ , that is, the $^{48}$ Ca+ $^{254, 257}$ Fm, $^{51}$ V+ $^{249}$ Bk, and $^{54}$ Cr+ $^{248}$ Cm reactions. Our calculations indicate that the distances of the closest approach for these systems are similar to each other and thus the difference in the probabilities of evaporation residue formation among those reaction systems originates mainly from the evaporation process, which is sensitive to the fission barrier height and the excitation energy of a compound nucleus.
nucl-thnucl-exPRC(2019)·51 citations
05
$γ$ -rigid triaxial nuclei in the presence of a minimal length via a quantum perturbation method
S. Ait Elkorchi🇲🇦 · M. Chabab🇲🇦 · A. El Batoul🇲🇦 · A. Lahbas🇲🇦 · M. Oulne🇲🇦
In this work, we derive a closed solution of the Shr $o ¨$ dinger equation for Bohr Hamiltonien within the minimal length formalism. This formalism is inspired by Heisenberg algebra and a generlized uncertainty principle (GUP), applied to the geometrical collective Bohr- Mottelson model (BMM) of nuclei by means of deformed canonical commutation relation and the Pauli-Podolsky prescription. The problem is solved by means conjointly of asymptotic iteration method (AIM) and a quantum perturbation method (QPM) for transitional nuclei near the critical point symmetry Z(4) corresponding to phase transition from prolate to $γ$ -rigid triaxial shape. A scaled Davidson potentiel is used as a restoring potential in order to get physical minimum. The agreement between the obtained theoretical results and the experimental data is very satisfactory.
nucl-thNucl.Theor.(2018)·2 citations
06
Extension of Intra-Nuclear Cascade Model to Neutron Induced Nonelastic Cross-Sections in Low Energy Region
Masahiro Nakano🇯🇵 · Yusuke Uozumi🇯🇵
Two features, a slow slope and a sharp drop, in neutron induced total nonelastic cross-sections are analyzed within the framework of an intra-nuclear cascade (INC) model. First, to reproduce the slow slope from 100MeV to 10 MeV, the original INC is generalized in two points; a method to construct the ground state of the target nucleus, and a method of taking the effective two body cross-sections between two nucleons. Secondly, to analyze the origin of the sharp drop from 10MeV to nearly 1 MeV, the INC is extended to include quantum effects which are originated from the existence of the discrete states in the nuclear potential. It is shown that this extension leads to the sharp drops in the very low energy below around 10MeV. It is concluded that the INC model can be extended to explain the sharp drops in addition to the slow slope in neutron induced nonelastic cross-sections in the energy region from 100MeV down to 1 MeV.
nucl-thnucl-exPRC(2019)·8 citations
07
Cool baryon and quark matter in holographic QCD
Takaaki Ishii🇯🇵 · Matti Järvinen🇳🇱 · Govert Nijs🇳🇱
We establish a holographic bottom-up model which covers both the baryonic and quark matter phases in cold and dense QCD. This is obtained by including the baryons using simple approximation schemes in the V-QCD model, which also includes the backreaction of the quark matter to the dynamics of pure Yang-Mills. We examine two approaches for homogeneous baryon matter: baryons as a thin layer of noninteracting matter in the holographic bulk, and baryons with a homogeneous bulk gauge field. We find that the second approach exhibits phenomenologically reasonable features. At zero temperature, the vacuum, baryon, and quark matter phases are separated by strongly first order transitions as the chemical potential varies. The equation of state in the baryonic phase is found to be stiff, i.e., the speed of sound clearly exceeds the value $c_{s}^{2} = 1/3$ of conformal plasmas at high baryon densities.
↳ hep-phhep-thnucl-thJHEP(2019)·90 citations
08
A complete set of in-medium splitting functions to any order in opacity
Matthew D. Sievert🇺🇸 · Ivan Vitev🇺🇸 · Boram Yoon🇺🇸
In this Letter we report the first calculation of all $O (α_{s})$ medium-induced branching processes to any order in opacity. Our splitting functions results are presented as iterative solutions to matrix equations with initial conditions set by the leading order branchings in the vacuum. The flavor and quark mass dependence of the in-medium $q \to q g$ , $g \to g g$ , $q \to g q$ , $g \to q q ˉ$ processes is fully captured by the light-front wavefunction formalism and the color representation of the parent and daughter partons. We include the explicit solutions to second order in opacity as supplementary material and present numerical results in a realistic strongly-interacting medium produced in high center-of-mass energy heavy ion collisions at the Large Hadron Collider. Our numerical simulations show that the second order in opacity corrections can change the energy dependence of the in-medium shower intensity. We further find corrections to the longitudinal and angular distributions of the in-medium splitting kernels that may have important implications for jet substructure phenomenology.
↳ hep-phnucl-thPLB(2019)·74 citations
09
Nucleon axial, scalar, and tensor charges using lattice QCD at the physical pion mass
Nesreen Hasan🇩🇪 · Jeremy Green🇩🇪 · Stefan Meinel🇺🇸 · Michael Engelhardt🇺🇸 · Stefan Krieg🇩🇪 · John Negele🇺🇸 · Andrew Pochinsky🇺🇸 · Sergey Syritsyn🇺🇸
We report on lattice QCD calculations of the nucleon isovector axial, scalar, and tensor charges. Our calculations are performed on two 2+1-flavor ensembles generated using a 2-HEX-smeared Wilson-clover action at the physical pion mass and lattice spacings $a \approx$ 0.116 and 0.093 fm. We use a wide range of source-sink separations - eight values ranging from roughly 0.4 to 1.4 fm on the coarse ensemble and three values from 0.9 to 1.5 fm on the fine ensemble - which allows us to perform an extensive study of excited-state effects using different analysis and fit strategies. To determine the renormalization factors, we use the nonperturbative Rome-Southampton approach and compare RI'-MOM and RI-SMOM intermediate schemes to estimate the systematic uncertainties. Our final results are computed in the MS-bar scheme at scale 2 GeV. The tensor and axial charges have uncertainties of roughly 4%, $g_{T} = 0.972 (41)$ and $g_{A} = 1.265 (49)$ . The resulting scalar charge, $g_{S} = 0.927 (303)$ , has a much larger uncertainty due to a stronger dependence on the choice of intermediate renormalization scheme and on the lattice spacing.
↳ hep-lathep-phnucl-thPRD(2019)·73 citations
10
Sigma models on quantum computers
Andrei Alexandru🇺🇸 · Paulo F. Bedaque🇺🇸 · Henry Lamm🇺🇸 · Scott Lawrence (for the NuQS Collaboration)🇺🇸
We formulate a discretization of sigma models suitable for simulation by quantum computers. Space is substituted by a lattice, as usually done in lattice field theory, while the target space (a sphere) is replaced by the "fuzzy sphere", a construction well known from non-commutative geometry. Contrary to more naive discretizations of the sphere, in this construction the exact $O (3)$ symmetry is maintained, which suggests that the discretized model is in the same universality class as the continuum model. That would allow for continuum results to be obtained for very rough discretizations of the target space as long as the space discretization is made fine enough. The cost of performing time-evolution, measured as the number of CNOT operations necessary, is $12 L T /Δ t$ , where $L$ is the number of spatial sites, $T$ the maximum time extent and $Δ t$ the time spacing.
↳ hep-latcond-mat.str-elnucl-thphysics.comp-ph+1PRL(2019)·71 citations

Affiliations

first authorsco-authorsvia INSPIRE