119263588
Spinors and Voros star-product for Group Field Theory: First Contact
In the context of non-commutative geometries, we develop a group Fourier transform for the Lie group SU(2). Our method is based on the Schwinger representation of the Lie algebra su(2) in terms of spinors. It allows us to prove that the non-commutative R space dual to the SU(2) group is in fact of the Moyal-type and endowed with the Voros star-product when expressed in the spinor variables. Finally, from the perspective of quantum gravity, we discuss the application of these new tools to group field theories for spinfoam models and their interpretation as non-commutative field theories with quantum-deformed symmetries.
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.
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.
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.
120781216
Minimono: An ultracompact permanent magnet ion source for singly charged ions
Minimono is a 2.45 GHz electron cyclotron resonance ion source for singly charged ions which uses only permanent magnets. Measurements of ionization efficiencies, maximum currents extracted, and emittances for H+, 3,4He+, N+, Ne+, Ar+, Kr+, S+, and Si+ were carried out. In the case of buckminster fullerenes, C60+, C602+, and C603+ ions were extracted. The results obtained, the general mechanical simplicity of this ion source, and its low cost make this source attractive for the production of stable and radioactive ions.
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.
53503257
Recycling effect of germanium on ECR ion source
Abstract After running for three weeks with a 76 Ge beam provided by the ECR-4 ion source at GANIL we have investigated the recycling effect of an SF 6 plasma. The initial beam was produced by the classical method, using germanium dioxide in our micro-oven and helium as support gas. The overall ionization efficiency was measured and found to be around 3%. Without the oven, and using SF 6 instead of helium, the ECR-4 ion source has been able to produce a very stable beam during a two-week period. The intensity of 76 Ge 13+ (enrichment 88%) was increased to 40 e μA, and the overall ionization efficiency reached 40%. The oven method of production, the recycling effect and perspectives are described in this paper.
118397633
Low-energy dipole excitations in neon isotopes and N=16 isotones within the quasiparticle random-phase approximation and the Gogny force
Low-energy dipole excitations in neon isotopes and N=16 isotones are calculated with a fully consistent axially-symmetric-deformed quasiparticle random phase approximation (QRPA) approach based on Hartree-Fock-Bogolyubov (HFB) states. The same Gogny D1S effective force has been used both in HFB and QRPA calculations. The microscopical structure of these low-lying resonances, as well as the behavior of proton and neutron transition densities, are investigated in order to determine the isoscalar or isovector nature of the excitations. It is found that the N=16 isotones {sup 24}O, {sup 26}Ne, {sup 28}Mg, and {sup 30}Si are characterized by a similar behavior. The occupation of the 2s{sub 1/2} neutron orbit turns out to be crucial, leading to nontrivial transition densities and to small but finite collectivity. Some low-lying dipole excitations of {sup 28}Ne and {sup 30}Ne, characterized by transitions involving the {nu}1d{sub 3/2} state, present a more collective behavior and isoscalar transition densities. A collective proton low-lying excitation is identified in the {sup 18}Ne nucleus.
122846748
Giant resonances in {sup 238}U within the quasiparticle random-phase approximation with the Gogny force
Fully consistent axially-symmetric deformed quasiparticle random-phase approximation (QRPA) calculations have been performed, using the same Gogny D1S effective force for both the Hartree-Fock-Bogolyubov mean field and QRPA matrix. New implementation of this approach leads to the applicability of QRPA to heavy deformed nuclei. Giant resonances and low-energy collective states for monopole, dipole, quadrupole, and octupole modes are predicted for the heavy deformed nucleus {sup 238}U and compared with experimental data.