118728019
Spin Foam Models for Quantum Gravity and semi-classical limit
The spinfoam framework is a proposal for a regularized path integral for quantum gravity. Spinfoams define quantum space-time structures describing the evolution in time of the spin network states for quantum geometry derived from Loop Quantum Gravity (LQG). The construction of this covariant approach is based on the formulation of General Relativity as a topological theory plus the so-called simplicity constraints which introduce local degrees of freedom. The simplicity constraints are essential in turning the non-physical topological theory into 4d gravity. In this PhD manuscript, an original way to impose the simplicity constraints in 4d Euclidean gravity using harmonic oscillators is proposed and new coherent states, solutions of the constraints, are given. Moreover, a consistent spinfoam model for quantum gravity has to be connected to LQG and must have the right semi-classical limit. An explicit map between the spin network states of LQG and the boundary states of spinfoam models is given connecting the canonical and the covariant approaches. Finally, new techniques to compute semiclassical asymptotic expressions for the transition amplitudes of 3d quantum gravity and to extract semi-classical information from a spinfoam model are introduced. Explicit computations based on approximation methods and on the use of recurrence relations on spinfoam amplitudes have been performed. The results are relevant to derive quantum corrections to the dynamics of the gravitational field.
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.
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.
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.
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.
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.
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.
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.
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.
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.