118825085
Pushing Further the Asymptotics of the 6j-symbol
In the context of spin-foam models for quantum gravity, we investigate the asymptotical behavior of the (6j)-symbol at next-to-leading order. This gives the first quantum gravity correction to the (3d) Regge action. We compute it analytically and check our results against numerical calculations. The (6j)-symbol is the building block of the Ponzano-Regge amplitudes for 3d quantum gravity, and the present analysis is directly relevant to deriving the quantum corrections to gravitational correlations in the spin-foam formalism.
119208355
Deformed phase space for 3d loop gravity and hyperbolic discrete geometries
We revisit the loop gravity space phase for 3D Riemannian gravity by algebraically constructing the phase space $T^*\mathrm{SU}(2)\sim\mathrm{ISO}(3)$ as the Heisenberg double of the Lie group $\mathrm{SO}(3)$ provided with the trivial cocyle. Tackling the issue of accounting for a non-vanishing cosmological constraint $\Lambda \ne 0$ in the canonical framework of 3D loop quantum gravity, $\mathrm{SL}(2,\mathbb{C})$ viewed as the Heisenberg double of $\mathrm{SU}(2)$ provided with a non-trivial cocyle is introduced as a phase space. It is a deformation of the flat phase space $\mathrm{ISO}(3)$ and reproduces the latter in a suitable limit. The $\mathrm{SL}(2,\mathbb{C})$ phase space is then used to build a new, deformed LQG phase space associated to graphs. It can be equipped with a set of Gauss constraints and flatness constraints, which form a first class system and Poisson-generate local 3D rotations and deformed translations. We provide a geometrical interpretation for this lattice phase space with constraints in terms of consistently glued hyperbolic triangles, i.e. hyperbolic discrete geometries, thus validating our construction as accounting for a constant curvature $\Lambda<0$. Finally, using ribbon diagrams, we show that our new model is topological.
119164220
Lifting SU(2) spin networks to projected spin networks
Projected spin network states are the canonical basis of quantum states of geometry for the recent EPRL-FK spinfoam models for quantum gravity introduced by Engle-Pereira-Rovelli-Livine and Freidel-Krasnov. They are functionals of both the Lorentz connection and the time-normal field. We analyze in detail the map from these projected spin networks to the standard SU(2) spin networks of loop quantum gravity. We show that this map is not one to one and that the corresponding ambiguity is parameterized by the Immirzi parameter. We conclude with a comparison of the scalar products between projected spin networks and SU(2) spin network states.
118371821
Holomorphic Simplicity Constraints for 4d Riemannian Spinfoam Models
Starting from the reformulation of the classical phase space of Loop Quantum Gravity in terms of spinor variables and spinor networks, we build coherent spin network states and show how to use them to write the spinfoam path integral for topological BF theory in terms of Gaussian integrals in the spinors. Finally, we use this framework to revisit the simplicity constraints reducing topological BF theory to 4d Riemannian gravity. These holomorphic simplicity constraints lead us to a new spinfoam model for quantum gravity whose amplitudes are defined as the evaluation of the coherent spin networks.
10412849
Discrete Gravity Models and Loop Quantum Gravity: a Short Review ?
We review the relation between Loop Quantum Gravity on a fixed graph and discrete models of gravity. We compare Regge and twisted geometries, and discuss discrete actions based on twisted geometries and on the discretization of the Plebanski action. We discuss the role of discrete geometries in the spin foam formalism, with particular attention to the definition of the simplicity constraints.
119310708
Deformed spinor networks for loop gravity: towards hyperbolic twisted geometries
In the context of a canonical quantization of general relativity, one can deform the loop gravity phase space on a graph by replacing the $$T^*\mathrm{SU}(2)$$T∗SU(2) phase space attached to each edge by $$\mathrm{SL}(2,{\mathbb C})$$SL(2,C) seen as a phase space. This deformation is supposed to encode the presence of a non-zero cosmological constant.Here we show how to parametrize this phase space in terms of spinor variables, thus obtaining deformed spinor networks for loop gravity, with a deformed action of the gauge group $$\mathrm{SU}(2)$$SU(2) at the vertices. These are to be formally interpreted as the generalization of loop gravity twisted geometries to a hyperbolic curvature.
120568906
QRPA CALCULATIONS FOR SPHERICAL AND DEFORMED NUCLEI WITH THE GOGNY FORCE
Fully consistent axially-symmetric-deformed Quasi-particle Random Phase Approximation (QRPA) calculations have been performed with the D1S Gogny force. Impact of the deformation in giant multipole resonances is discussed. QRPA and 5 Dimensional Collective Hamiltonian results are compared for low lying 2+ states in N = 16 isotones and Ni isotopes. Multipole resonances are also obtained for the heavy nucleus 238U.
94261474
METALLIC ION DEVELOPMENTS AT GANIL
Radioactive ion beams (RIB) are routinely produced at GANIL by fragmentation of the projectile. A possible way to improve the RIB intensity is to increase the primary beam intensity impinging the target. Although high intensities can be obtained with an ECR ion source for gaseous elements, it is more difficult for metallic elements due to the poor ionization efficiency of the source. This report deals with metallic ion beam production at high intensity. Experimental results for Ca, Ni and Fe are presented. The oven and the MIVOC methods are compared.
121772448
Challenging nuclear structure models through a microscopic description of proton inelastic scattering off 208Pb
A fully microscopic calculation of inelastic proton scattering off {sup 208}Pb is presented, and compared to experimental scattering data for incident proton energies between 65 and 201 MeV. By constructing the nucleon-nucleus interaction through the folding of nuclear structure information with a reliable nucleon-nucleon effective interaction that has no adjusted parameter, a consistent framework is built, for probing the influence of different descriptions of nuclear structure on nucleon inelastic scattering predictions. The absence of phenomenological normalization in this framework guarantees a unique and unambiguous interpretation of our calculations in terms of quality of the underlying nuclear structure description: a feature that had been reserved, until recently, to the electron probe. This tool is used to investigate the effect of long range correlations embedded in excited states, on calculated inelastic observables, demonstrating the sensitivity of nucleon scattering predictions to details of the nuclear structure.
120313109
Microscopic model approach to (n,xn) pre-equilibrium reactions for medium-energy neutrons
We report on microscopic model calculations of the first step of direct pre-equilibrium (n,xn) emission in neutron interaction with {sup 90}Zr and {sup 208}Pb below 20 MeV. Our model is based on both an accurate description of the target excited states, provided by the self-consistent random-phase approximation (RPA) method implemented with the Gogny D1S force, and well-established in-medium two-body forces to represent the residual nucleon-nucleon interaction for the inelastic processes. Two goals have been achieved: The present microscopic approach provides a unified description of collective state excitations and the pre-equilibrium one-step process, and our reaction model reproduces the available data fairly well, without any parameter adjustment.
121688592
High intensity metallic ion beams from an ECR ion source at GANIL
In recent years, progress concerning the production of high intensity of metallic ion beams (58Ni, 48Ca, 76Ge) at GANIL have been performed. The metallic ion from volatile compound method has been successfully used to produce a high intensity nickel beam with the ECR4 ion source: 20 e μA of 58Ni11+ at 24 kV extraction voltage. This beam has been maintained for 8 days and accelerated up to 74.5 MeV/u by our cyclotrons with a mean intensity of 0.13 pμA on target. This high intensity, required for experiment, led to the discovery of the doubly magic 48Ni isotope. The oven method has been first tested with natural metallic calcium on the ECR4 ion source, then used to produce a high power beam (740 W on target, i.e., 0.13 pμA accelerated up to 60 meV/u) of 48Ca still keeping a low consumption (0.09 mg/h). A germanium beam is now under development, using the oven method with germanium oxide. The ionization efficiencies have been measured and compared.