Search results for "Quantum gravity"
showing 10 items of 126 documents
Dynamics for a 2-vertex Quantum Gravity Model
2010
We use the recently introduced U(N) framework for loop quantum gravity to study the dynamics of spin network states on the simplest class of graphs: two vertices linked with an arbitrary number N of edges. Such graphs represent two regions, in and out, separated by a boundary surface. We study the algebraic structure of the Hilbert space of spin networks from the U(N) perspective. In particular, we describe the algebra of operators acting on that space and discuss their relation to the standard holonomy operator of loop quantum gravity. Furthermore, we show that it is possible to make the restriction to the isotropic/homogeneous sector of the model by imposing the invariance under a global …
Reply to Comment on Measurement of quantum states of neutrons in the Earth's gravitational field
2003
Physical review / D 68(10), 108702 (2003). doi:10.1103/PhysRevD.68.108702
Asymptotic Safety in Quantum Einstein Gravity: Nonperturbative Renormalizability and Fractal Spacetime Structure
2007
The asymptotic safety scenario of Quantum Einstein Gravity, the quantum field theory of the spacetime metric, is reviewed and it is argued that the theory is likely to be nonperturbatively renormalizable. It is also shown that asymptotic safety implies that spacetime is a fractal in general, with a fractal dimension of 2 on sub-Planckian length scales.
Nonlocal quantum-field correlations and detection processes in quantum-field theory
2009
Quantum detection processes in quantum field theory (QFT) must play a key role in the description of quantum-field correlations, such as the appearance of entanglement, and of causal effects. We consider the detection in the case of a simple QFT model with a suitable interaction to exact treatment, consisting of a quantum scalar field coupled linearly to a classical scalar source. We then evaluate the response function to the field quanta of two-level pointlike quantum model detectors, and analyze the effects of the approximation adopted in standard detection theory. We show that the use of the RWA, which characterizes the Glauber detection model, leads in the detector response to nonlocal …
Quantum Thermodynamic Perturbation Theory for Fermions
1993
The quantum version of classical thermodynamic perturbation theory is applied to the ground state of a fluid of spin-1/2 fermions interacting via the Aziz interatomic potential, as a model for liquid 3He. Results from the rapidly-convergent sixth-order calculation about the unperturbed hard-sphere fluid for energy, density and sound velocity at the zero-pressure liquid equilibrium point, lie within a few percent of computer-simulation values and appreciably closer than the most elaborate recent variational calculation. The procedure explicitly avoids crossing phase boundaries and is relatively insensitive to varying the close-packing density up to a value somewhat below the maximum possible…
The Crossing Symmetric Bethe-Salpeter Equation
1972
As you may recall from the lectures of Prof. Sand-has [1], in non-relativistic quantum theory,the scattering amplitude satisfies the Lippmann-Schwinger equation, $$T = V + V{G_o}T$$ (1) It can be explicitly shown that if V=V+, T satisfies the elastic unitarity relation, Im T=TT+.
Asymptotic Safety, Fractals, and Cosmology
2013
These lecture notes introduce the basic ideas of the asymptotic safety approach to quantum Einstein gravity (QEG). In particular they provide the background for recent work on the possibly multi-fractal structure of the QEG space-times. Implications of asymptotic safety for the cosmology of the early Universe are also discussed.
U(N) invariant dynamics for a simplified loop quantum gravity model
2011
The implementation of the dynamics in Loop Quantum Gravity (LQG) is still an open problem. Here, we discuss a tentative dynamics for the simplest class of graphs in LQG: Two vertices linked with an arbitrary number of edges. We use the recently introduced U(N) framework in order to construct SU(2) invariant operators and define a global U(N) symmetry that will select the homogeneous/isotropic states. Finally, we propose a Hamiltonian operator invariant under area-preserving deformations of the boundary surface and we identify possible connections of this model with Loop Quantum Cosmology.
Focus on quantum Einstein gravity
2012
The gravitational asymptotic safety program summarizes the attempts to construct a consistent and predictive quantum theory of gravity within Wilson's generalized framework of renormalization. Its key ingredient is a non-Gaussian fixed point of the renormalization group flow which controls the behavior of the theory at trans-Planckian energies and renders gravity safe from unphysical divergences. Provided that the fixed point comes with a finite number of ultraviolet-attractive (relevant) directions, this construction gives rise to a consistent quantum field theory which is as predictive as an ordinary, perturbatively renormalizable one. This opens up the exciting possibility of establishin…