The Equivalence Principle Revisited

A precise formulation of the strong Equivalence Principle is essential to the understanding of the relationship between gravitation and quantum mechanics. The relevant aspects are reviewed in a context including General Relativity, but allowing for the presence of torsion. For the sake of brevity, a concise statement is proposed for the Principle: "An ideal observer immersed in a gravitational field can choose a reference frame in which gravitation goes unnoticed". This statement is given a clear mathematical meaning through an accurate discussion of its terms. It holds for ideal observers (time-like smooth non-intersecting curves), but not for real, spatially extended observers. Analogous results hold for gauge fields. The difference between gravitation and the other fundamental interactions comes from their distinct roles in the equation of force.Comment: RevTeX, 18 pages, no figures, to appear in Foundations of Physic

Impact of soil tillage and land use on soil organic carbon decline under Mediterranean conditions

Soils under Mediterranean climate conditions frequently have low to very low levels of soil organic matter (SOM), as a result of low biomass production under the predominantly rainfed conditions and the intensive tillage operations commonly practiced. In order to assess both short and long-term impacts of soil tillage and land use on soil organic carbon, two sets of experiments were performed. One consisted in the identification and soil analysis of 3 pairs of sites under different soil types and land use over 5 to 30 years; in the second experiment a long-term fallow area was repeatedly submitted to different types of soil tillage management (mouldboard plough + disc harrow; non-inversion tine cultivation; no-till) over 3 years. Soil texture, bulk density and SOM were analysed along the whole soil profile in the first experiment, whereas bulk density and SOM to a depth of 30 cm was measured before the first tillage operations and at the end of the observation period in the second experiment. The results clearly indicate that tillage based land use, irrespective of the type of land use, caused a considerable decline in SOM content in the tilled soil layer. Very small and inconsistent differences in SOM between paired soil profiles were observed in the lower part of the profiles. In the second experiment with three types of tillage systems, SOM content decreased with tillage intensity. Avoidance of soil disturbance is an important step towards halting SOM decline under Mediterranean climate conditions

Decision Making for Inconsistent Expert Judgments Using Negative Probabilities

In this paper we provide a simple random-variable example of inconsistent information, and analyze it using three different approaches: Bayesian, quantum-like, and negative probabilities. We then show that, at least for this particular example, both the Bayesian and the quantum-like approaches have less normative power than the negative probabilities one.Comment: 14 pages, revised version to appear in the Proceedings of the QI2013 (Quantum Interactions) conferenc

Time-Reversal Symmetry Breaking and Decoherence in Chaotic Dirac Billiards

In this work, we perform a statistical study on Dirac Billiards in the extreme quantum limit (a single open channel on the leads). Our numerical analysis uses a large ensemble of random matrices and demonstrates the preponderant role of dephasing mechanisms in such chaotic billiards. Physical implementations of these billiards range from quantum dots of graphene to topological insulators structures. We show, in particular, that the role of finite crossover fields between the universal symmetries quickly leaves the conductance to the asymptotic limit of unitary ensembles. Furthermore, we show that the dephasing mechanisms strikingly lead Dirac billiards from the extreme quantum regime to the semiclassical Gaussian regime