Thiemann transform for gravity with matter fields

The generalised Wick transform discovered by Thiemann provides a well-established relation between the Euclidean and Lorentzian theories of general relativity. We extend this Thiemann transform to the Ashtekar formulation for gravity coupled with spin-1/2 fermions, a non-Abelian Yang-Mills field, and a scalar field. It is proved that, on functions of the gravitational and matter phase space variables, the Thiemann transform is equivalent to the composition of an inverse Wick rotation and a constant complex scale transformation of all fields. This result holds as well for functions that depend on the shift vector, the lapse function, and the Lagrange multipliers of the Yang-Mills and gravitational Gauss constraints, provided that the Wick rotation is implemented by means of an analytic continuation of the lapse. In this way, the Thiemann transform is furnished with a geometric interpretation. Finally, we confirm the expectation that the generator of the Thiemann transform can be determined just from the spin of the fields and give a simple explanation for this fact.Comment: LaTeX 2.09, 14 pages, no figure

Astrophysical Bounds on Planck Suppressed Lorentz Violation

This article reviews many of the observational constraints on Lorentz symmetry violation (LV). We first describe the GZK cutoff and other phenomena that are sensitive to LV. After a brief historical sketch of research on LV, we discuss the effective field theory description of LV and related questions of principle, technical results, and observational constraints. We focus on constraints from high energy astrophysics on mass dimension five operators that contribute to LV electron and photon dispersion relations at order E/M_Planck. We also briefly discuss constraints on renormalizable operators, and review the current and future contraints on LV at order (E/M_Planck)^2.Comment: 30 pages, submitted to Lecture Notes in Physics, Quantum Gravity Phenomenology, eds. G.Amelino-Camelia, J. Kowalski-Glikman (Springer-Verlag

Modified Gravity via Spontaneous Symmetry Breaking

We construct effective field theories in which gravity is modified via spontaneous breaking of local Lorentz invariance. This is a gravitational analogue of the Higgs mechanism. These theories possess additional graviton modes and modified dispersion relations. They are manifestly well-behaved in the UV and free of discontinuities of the van Dam-Veltman-Zakharov type, ensuring compatibility with standard tests of gravity. They may have important phenomenological effects on large distance scales, offering an alternative to dark energy. For the case in which the symmetry is broken by a vector field with the wrong sign mass term, we identify four massless graviton modes (all with positive-definite norm for a suitable choice of a parameter) and show the absence of the discontinuity.Comment: 5 pages; revised versio

Phenomenological description of quantum gravity inspired modified classical electrodynamics

We discuss a large class of phenomenological models incorporating quantum gravity motivated corrections to electrodynamics. The framework is that of electrodynamics in a birefringent and dispersive medium with non-local constitutive relations, which are considered up to second order in the inverse of the energy characterizing the quantum gravity scale. The energy-momentum tensor, Green functions and frequency dependent refraction indices are obtained, leading to departures from standard physics. The effective character of the theory is also emphasized by introducing a frequency cutoff. The analysis of its effects upon the standard notion of causality is performed, showing that in the radiation regime the expected corrections get further suppressed by highly oscillating terms, thus forbiding causality violations to show up in the corresponding observational effects.Comment: 14 pages, to be published in Obregon Festschrift 2006, Gen. Rel. and Gra

A geometrical origin for the covariant entropy bound

Causal diamond-shaped subsets of space-time are naturally associated with operator algebras in quantum field theory, and they are also related to the Bousso covariant entropy bound. In this work we argue that the net of these causal sets to which are assigned the local operator algebras of quantum theories should be taken to be non orthomodular if there is some lowest scale for the description of space-time as a manifold. This geometry can be related to a reduction in the degrees of freedom of the holographic type under certain natural conditions for the local algebras. A non orthomodular net of causal sets that implements the cutoff in a covariant manner is constructed. It gives an explanation, in a simple example, of the non positive expansion condition for light-sheet selection in the covariant entropy bound. It also suggests a different covariant formulation of entropy bound.Comment: 20 pages, 8 figures, final versio

Geometric entropy, area, and strong subadditivity

The trace over the degrees of freedom located in a subset of the space transforms the vacuum state into a density matrix with non zero entropy. This geometric entropy is believed to be deeply related to the entropy of black holes. Indeed, previous calculations in the context of quantum field theory, where the result is actually ultraviolet divergent, have shown that the geometric entropy is proportional to the area for a very special type of subsets. In this work we show that the area law follows in general from simple considerations based on quantum mechanics and relativity. An essential ingredient of our approach is the strong subadditive property of the quantum mechanical entropy.Comment: Published versio

Benefícios do ômega 3 na prevenção de doença cardiovascular: Revisão integrativa de literatura

Introduction: Omega-3 polyunsaturated fatty acids such as alpha-linolenic acid (ALA), a fat found in plant foods, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), both found in fish, have been considered relevant substances for the maintenance of health, so that supplementation is being considered relevant for the reduction of cardiovascular risks. Objective: To identify and analyze the scientific evidence available in the literature on the contribution of omega 3 in the prevention and treatment of cardiovascular disease. Materials and Methods: Integrative literature review, with deference to materials published in the Scielo and PubMed databases, which considered as inclusion criteria articles published in the last 5 years, available in full, in English, Spanish, and Portuguese, which addressed the proposed theme; the exclusion criteria were editorials, letters to the editor, review studies, theses, dissertations, and duplicate articles that did not correspond to the theme. Results: Based on the aforementioned scientific evidence, the body's omega-3 indices are relevant to identify possible cardiovascular risk, so it can therefore be used as an objective for treatment when there is a possible risk for these manifestations. This risk factor can be modified by taking EPA and DHA. The standard 1 g/day dose of EPA and DHA recommended by cardiac societies is, however, probably far from ideal for everyone, as not only this standard dose but also diet, individual genetic history, body mass index, calorie intake and disposal, and other factors all together probably determine a person's level of omega-3 fatty acids. Therefore, it is suggested that the omega-3 index acts not only as a risk factor for cardiovascular disease, but that other contexts allied to the patient's lifestyle should be considered. Conclusion: Diet or supplementation of these nutrients may result in cardiovascular and other types of benefits to society as a whole

CPT Violation and Decoherence in Quantum Gravity

In these lectures I review, in as much pedagogical way as possible, various theoretical ideas and motivation for violation of CPT invariance in some models of Quantum Gravity, and discuss the relevant phenomenology. Since the subject is vast, I pay particular emphasis on the CPT Violating decoherence scenario for quantum gravity, due to space-time foam. In my opinion this seems to be the most likely scenario to be realised in Nature, should quantum gravity be responsible for the violation of this symmetry. In this context, I also discuss how the CPT Violating decoherence scenario can explain experimental ``anomalies'' in neutrino data, such as LSND results, in agreement with the rest of the presently available data, without enlarging the neutrino sector.Comment: 74 pages LATEX, Submitted to Lect. Notes Phys. (Springer), based on invited lectures at the 40th Winter School in Poland, February 200