The Elusive Part of the Standard-Model Extension Gravitational Sector

In the minimal gravitational sector of the Standard-Model Extension, there is a coefficient whose physical consequences are unknown, and the reason behind this lack of effects is still puzzling. This contribution summarizes several studies where the goal was to find a fundamental explanation of this puzzle. So far, no evidence of such a fundamental explanation has been found, suggesting that this coefficient could actually produce physical effects. Nevertheless, while looking for this fundamental reason, several relevant lessons have been revealed.Comment: Presented at the Seventh Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, June 20-24, 201

Quantum particles and an effective spacetime geometry

Spacetime geometry is supposed to be measured by identifying the trajectories of free test particles with geodesics. In practice, this cannot be done because, being described by Quantum Mechanics, particles do not follow trajectories. As a first step to study how it is possible to read spacetime geometry with quantum particles, we model these particles with classical extended objects. We propose to represent such extended objects by its covariant center of mass, which generically does not follow a geodesic of the background metric. We present a scheme that allows to extract some of components of an "effective" connection, namely, the connection that would be obtained if the locus of the center of mass is regarded as a geodesic. We discuss some issues that arise when trying to obtain all the components of the effective connection and its possible implications.Comment: Presented at the IX Workshop of the Mexican Gravity Divisio

Searching for spacetime granularity: analyzing a concrete experimental setup

In this work we show that the spin pendulum techniques developed by the E\:{o}t-Wash group could be used to put very stringent bounds on the free parameters of a Lorentz invariant phenomenological model of quantum gravity. The model is briefly described as well as the experimental setup that we have in mind.Comment: 9 pages. For the proceedings of the VIII School of the Gravitation and Mathematical Physics Division of the Mexican Physical Society 'Speakable and unspeakable in gravitational physics: testing gravity from submillimeter to cosmic scale'