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This paper attempts to connect two new gravitational mechanisms: the Verlinde's holographic model of gravity and the modification of inertia resulting from a Hubble-scale Casimir effect (MiHsC) of McCulloch. First we give a short survey about how the holographic scenario can give the correct dynamics of the universe. The introduction of a two-holographic screens one comparable to the Hubble horizon and a second screen that takes into account the contribution of all the matter between the test particle and the observer gives directly the modified Friedmann acceleration equation for the dynamical evolution of the universe. Improvements of this equation using the quantum corrections will realize the inflation at high energy scales and the late-time acceleration (i.e. the accelerated expansion of the universe nowadays) obviating the dark energy. From both models we can derive a version of Modified Newtonian Dynamics (MOND) observed in the dynamics of the astronomical objects obviating the dark matter and explaining other astronomical anomalies. A first connection between both theories is given at the end of the paper. [ABSTRACT FROM AUTHOR]

A novel mechanism of baryogenesis is proposed on the basis of the phase transition from the conformal invariant spacetime to the Einstein spacetime in quantum gravity. Strong-coupling gravitational excitations with dynamical mass about 1017 GeV are generated at the transition. They eventually decay into ordinary matters. We show that the low energy effective interactions between the gravitational potential describing the excitation and the non-conserving matter currents by the axial anomalies can explain matter asymmetry out of thermal equilibrium. [ABSTRACT FROM AUTHOR]

In this paper two consequences of the generalized uncertainty principle (GUP) are discussed in a heuristic manner. Both could be regarded as the evidences that prefer the cosmic censorship hypothesis (CCH). The first one is that the second law tends to decline the massless charged particles if the effects of the GUP on the thermodynamics of a de Sitter spacetime are considered. This weakens the threat to the horizon of an extreme charged black hole. The second one is that the uv/ir correspondence provides a constraint on the relation between the energy and the size of a system, which is incompatible to the naked singularities. [ABSTRACT FROM AUTHOR]

We give a brief and a critical review of the Barret-Crane spin foam models of quantum gravity. Then we describe two new spin foam models which are obtained by direct quantization of General Relativity and do not have some of the drawbacks of the Barret-Crane models. These are the model of spin foam invariants for the embedded spin networks in loop quantum gravity and the spin foam model based on the integration of the tetrads in the path integral for the Palatini action. [ABSTRACT FROM AUTHOR]

We propose a new approach to the quantum theory of gravitation, in which the point sets of regions of spacetime are replaced by objects in a category. The objects can be constructed as limits of spin foam models, thus directly connecting to approximations to general relativity which have already been studied, and leading to a mathematically natural interpretation of the meaning of the triangulations in the spin foam models. The physical motivation for our proposal is a connection between ideas about the limited amount of information which can flow from one region to another in General Relativity, an analysis of the problem of the infinities in QFT, and the relational or categorical approach to topology in abstract homotopy theory and algebraic geometry. [ABSTRACT FROM AUTHOR]

This paper explores the idea that within the framework of three-dimensional quantum gravity one can extend the notion of Feynman diagram to include the coupling of the particles in the diagram with quantum gravity. The paper concentrates on the non-trivial part of the gravitational response, which is to the large momenta propagating around a closed loop. By taking a limiting case one can give a simple geometric description of this gravitational response. This is calculated in detail for the example of a closed Feynman loop in the form of a trefoil knot. The results show that when the magnitude of the momentum passes a certain threshold value, non-trivial gravitational configurations of the knot play an important role. [ABSTRACT FROM AUTHOR]

We give a brief account of the description of the standard model in noncommutative geometry as well as the thermal time hypothesis, questioning their relevance for quantum gravity. [ABSTRACT FROM AUTHOR]

We argue that the model of a quantum computer with N qubits on a quantum space background, which is a fuzzy sphere with n = 2N elementary cells, can be viewed as the minimal model for quantum gravity. In fact, it is discrete, has no free parameters, is Lorentz-invariant, naturally realizes the holographic principle, and defines a subset of punctures of spin networks' edges of loop quantum gravity labelled by spins j = 2N-1-½. In this model, the discrete area spectrum of the cells, which is not equally spaced, is given in units of the minimal area of loop quantum gravity (for j = 1/2), and provides a discrete emission spectrum for quantum black holes. When the black hole emits one string of N bits encoded in one of the n cells, its horizon area decreases of an amount equal to the area of one cell. [ABSTRACT FROM AUTHOR]

We show how, in canonical quantum cosmology, the frame fixing induces a new energy density contribution having features compatible with the (actual) cold dark matter component of the Universe. First we quantize the closed Friedmann–Robertson–Walker (FRW) model in a synchronous reference and determine the spectrum of the super-Hamiltonian in the presence of ultra-relativistic matter and a perfect gas contribution. Then we include in this model small inhomogeneous (spherical) perturbations in the spirit of the Lemaitre–Tolman cosmology. The main issue of our analysis consists in outlining that, in the classical limit, the nonzero eigenvalue of the super-Hamiltonian can account for the present value of the dark matter critical parameter. Furthermore we obtain a direct correlation between the inhomogeneities in our dark matter candidate and those that appear in the ultra-relativistic matter. [ABSTRACT FROM AUTHOR]

We compute the boundary stress-energies of time-dependent asymptotically AdS spacetimes in five and seven dimensions, and find that their traces are equal to the respective four- and six-dimensional field-theoretic trace anomalies. This provides good supporting evidence in favor of the AdS/CFT correspondence in time-dependent backgrounds. [ABSTRACT FROM AUTHOR]

We use exact results in a new approach to quantum gravity to study the effect of quantum loop corrections on the behavior of the metric of spacetime near the Schwarzschild radius of a massive point particle in the standard model. We show that the classical conclusion that such a system is a black hole is obviated. Phenomenological implications are discussed. [ABSTRACT FROM AUTHOR]