1,720,982 research outputs found
Quantum reduced loop gravity: Universe on a lattice
No full textWe describe the quantum flat universe in Quantum Reduced Loop Gravity in terms of states based on cuboidal graphs with six-valent nodes. We investigate the action of the scalar constraint operator at each node, and we construct proper semiclassical states. This allows us to discuss the semiclassical effective dynamics of the quantum universe, which resembles that of Loop Quantum Cosmology. In particular, the regulator is identified with the third root of the inverse number of nodes within each homogeneous patch, while inverse-volume corrections are enhanced
Non Abelian gauge symmetries from the unobservability of extra-dimensions in a Kaluza-Klein approach
No full textQuantum-reduced loop gravity: Cosmology
No full textWe introduce a new framework for loop quantum gravity: mimicking the spin foam quantization procedure we propose to study the symmetric sectors of the theory imposing the reduction weakly on the full kinematical Hilbert space of the canonical theory. As a first application of quantum-reduced loop gravity we study the inhomogeneous extension of the Bianchi I model. The emerging quantum cosmological model represents a simplified arena on which the complete canonical quantization program can be tested. The achievements of this analysis could elucidate the relationship between loop quantum cosmology and the full theory. DOI: 10.1103/PhysRevD.87.08352
Quantum reduced loop gravity: Extension to scalar fields
No full textThe quantization of the Hamiltonian for a scalar field is performed in the framework of quantum reduced loop gravity. We outline how the regularization can be performed by using the analogous tools adopted in full loop quantum gravity, and the matrix elements of the resulting operator between basis states are analytic coefficients. These achievements open the way for a consistent analysis of the quantum gravity corrections to the classical dynamics of gravity in the presence of a scalar field in a cosmological setting
A new perspective on cosmology in Loop Quantum Gravity
No full textWe present a new cosmological model derived from Loop Quantum Gravity. The formulation is based on a projection of the kinematical Hilbert space of the full theory down to a subspace representing the proper arena for an inhomogeneous Bianchi I model. This procedure gives a direct link between the full theory and its cosmological sector, thus it allows to test the complete canonical quantization program and to shed light on the foundation of Loop Quantum Cosmology. Furthermore, the emerging quantum cosmological model represents a concrete implementation of a discrete quantum Universe and it opens new perspectives on the phenomenology of early cosmology
Quantum Reduced Loop Gravity
Full text linkQuantum Reduced Loop Gravity provides a promising framework for a consistent characterization of the early Universe dynamics. Inspired by BKL conjecture, a flat Universe is described as a collection of Bianchi I homogeneous patches. The resulting quantum dynamics is described by the scalar constraint operator, whose matrix elements can be analytically computed. The effective semiclassical dynamics is discussed, and the differences with Loop Quantum Cosmology are emphasized
Quantum reduced loop gravity: Semiclassical limit
No full textWe discuss the semiclassical limit of quantum reduced loop gravity, a recently proposed model to address the quantum dynamics of the early Universe. We apply loop quantum gravity (LQG) techniques in order to define the semiclassical states in the kinematical Hilbert space and we demonstrate that the expectation value of the euclidean scalar constraint coincides with the classical expression, i.e., one of the local Bianchi I dynamics. The result holds as a leading order expansion in the scale factors of the Universe and opens the way to study the subleading corrections to the semiclassical dynamics. We outline how by retaining a suitable finite coordinate length for holonomies that our effective Hamiltonian at the leading order coincides with the one expected from loop quantum cosmology (LQC). This result is an important step in fixing the correspondence between LQG and LQC
Quasi-linear model for the beam-plasma instability: analysis of the self-consistent evolution
Full text linkWe re-analyze the quasi-linear self-consistent dynamics for the beam-plasma instability, by comparing the theory predictions to numerical simulations of the corresponding Hamiltonian system. While the diffusive features of the asymptotic dynamics are reliably predicted, the early temporal mesoscale transport appears less efficient in reproducing the convective feature of the self-consistent scenario. As a result, we identify the origin of the observed discrepancy in the underlying quasi-linear model assumption that the distribution function is quasi-stationary. Furthermore, we provide a correction to the instantaneous quasi-linear growth rate based on a linear expansion of the distribution function time dependence, and we successfully test this revised formulation for the spectral evolution during the temporal mesoscale
Nonsingular cosmology from evolutionary quantum gravity
No full textWe provide a cosmological implementation of the evolutionary quantum gravity, describing an isotropic Universe, in the presence of a negative cosmological constant and a massive (preinflationary) scalar field. We demonstrate that the considered Universe has a nonsingular quantum behavior, associated to a primordial bounce, whose ground state has a high occupation number. Furthermore, in such a vacuum state, the super-Hamiltonian eigenvalue is negative, corresponding to a positive emerging dust energy density. The regularization of the model is performed via a polymer quantum approach to the Universe scale factor and the proper classical limit is then recovered, in agreement with a preinflationary state of the Universe. Since the dust energy density is redshifted by the Universe de Sitter phase and the cosmological constant does not enter the ground state eigenvalue, we get a late-time cosmology, compatible with the present observations, endowed with a turning point in the far future
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