On the triviality of certain non-Riemannian models of gravitation

We prove in the Tucker-Wang approach to non-Riemannian Gravity that a general homogeneous Lagrangian density in the general connection with order of homogeneity of at least two, gives no contribution to the generalised Einstein equations. Using this result other important cases are also considered.Comment: 12 pages, Latex, final version for Physics Letters

Effective Levi-Civita Dilaton theory from Metric Affine Dilaton Gravity

We show how a Metric Affine theory of Dilaton gravity can be reduced to an effective Riemannian Dilaton gravity model. A simple generalization of the Obukhov-Tucker-Wang theorem to Dilaton gravity is then presented.Comment: 9 pages, Latex, revised final version for Physics Letters

Non-Invariant Ground States, Thermal Average, and generalized Fermionic Statistics

We present an approach to generalised fermionic statistics which relates the existence of a generalised statistical behaviour to non-invariant ground states. Considering the thermal average of an operatorial generalization of the Heisenberg algebra, we get an occupation number which depends on the degree of mixing between symmetric and antisymmetric sectors of the ground state. A natural prescription is given for the construction of a supersymmetric statistics. We also show that the structure of the vacuum, and therefore the statistical behaviour of the system, can be accounted for in terms of a second order phase transition.Comment: 11 pages, accepted in Physics Letters

On the solutions of the Cartan equation in Metric Affine Gravity

In the Tucker-Wang approach to Metric Affine gravity we review some particular solutions of the Cartan equation for the non-riemannian part of the connection. As application we show how a quite general non Riemannian model gives a Proca type equation for the trace of the nonmetricity 1-forms Q

Isomorphism between Non-Riemannian gravity and Einstein-Proca-Weyl theories extended to a class of Scalar gravity theories

We extend the recently proved relation between certain models of Non-Riemannian gravitation and Einstein- Proca-Weyl theories to a class of Scalar gravity theories. This is used to present a Black-Hole Dilaton solution with non-Riemannian connection.Comment: 13 pages, tex file, accepted in Class. Quant. Gra

Electrical conductivity of SiO2 at extreme conditions and planetary dynamos

Ab intio molecular dynamics simulations show that the electrical conductivity of liquid SiO2 is semimetallic at the conditions of the deep molten mantle of early Earth and super-Earths, raising the possibility of silicate dynamos in these bodies. Whereas the electrical conductivity increases uniformly with increasing temperature, it depends nonmonotonically on compression. At very high pressure, the electrical conductivity decreases on compression, opposite to the behavior of many materials. We show that this behavior is caused by a novel compression mechanism: the development of broken charge ordering, and its influence on the electronic band gap

Exotic Statistics for Ordinary Particles in Quantum Gravity

Objects exhibiting statistics other than the familiar Bose and Fermi ones are natural in theories with topologically nontrivial objects including geons, strings, and black holes. It is argued here from several viewpoints that the statistics of ordinary particles with which we are already familiar are likely to be modified due to quantum gravity effects. In particular, such modifications are argued to be present in loop quantum gravity and in any theory which represents spacetime in a fundamentally piecewise-linear fashion. The appearance of unusual statistics may be a generic feature (such as the deformed position-momentum uncertainty relations and the appearance of a fundamental length scale) which are to be expected in any theory of quantum gravity, and which could be testable.Comment: Awarded an honourable mention in the 2008 Gravity Research Foundation Essay Competitio

1.1 Platelet Activation and Cognitive Impairment in Elderly Patients with Metabolic Syndrome

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Electronic conductivity of solid and liquid (Mg, Fe)O computed from first principles

Ferropericlase (Mg, Fe)O is an abundant mineral of Earth's lower mantle and the liquid phase of the material was an important component of the early magma ocean. Using quantum-mechanical, finite-temperature density-functional theory calculations, we compute the electronic component of the electrical and thermal conductivity of (Mg0.75, Fe0.25)O crystal and liquid over a wide range of planetary conditions: 0–200 GPa, 2000–4000 K for the crystal, and 0–300 GPa, 4000–10,000 K for the liquid. We find that the crystal and liquid are semi-metallic over the entire range studied: the crystal has an electrical conductivity exceeding 103 S/m, whereas that of the liquid exceeds 104 S/m. Our results on the crystal are in reasonable agreement with experimental measurements of the electrical conductivity of ferropericlase once we account for the dependence of conductivity on iron content. We find that a harzburgite-dominated mantle with ferropericlase in combination with Al-free bridgmanite agrees well with electromagnetic sounding observations, while a pyrolitic mantle with a ferric-iron rich bridgmanite composition yields a lower mantle that is too conductive. The electronic component of thermal conductivity of ferropericlase with XFe=0.19 is negligible (<1 W/m/K). The electrical conductivity of the crystal and liquid at conditions of the core-mantle boundary are similar to each other (3×104 S/m). A crystalline or liquid ferropericlase-rich layer of a few km thickness thus accounts for the high conductance that has been proposed to explain anomalies in Earth's nutation. The electrical conductivity of liquid ferropericlase exceeds that of liquid silica by more than an order of magnitude at conditions of a putative basal magma ocean, thus strengthening arguments that the basal magma ocean could have produced an ancient dynamo