Linearized supergravity with a dynamical preferred frame

We study supersymmetric extension of the Einstein-aether gravitational model where local Lorentz invariance is broken down to the subgroup of spatial rotations by a vacuum expectation value of a timelike vector field called aether. Embedding aether into a chiral vector superfield, we construct the most general action which describes dynamics of linear perturbations around the Lorentz-violating vacuum and is invariant under the linearized supergravity transformations. The analysis is performed both in the off-shell non-minimal superfield formulation of supergravity and in the “on-shell” approach invoking only physical component fields. The resulting model contains a single free coupling, in addition to the standard supergravity parameters. The spectrum of physical excitations features an enhanced on-shell gravity multiplet comprising four states with helicities 2, 3/2, 3/2 and 1 propagating with superluminal velocity. The remaining excitations propagate with the speed of light. We outline the observational constraints on the model following from its low-energy phenomenology.

Lorentz Violation in Torsional Antenna

A torsional-antenna and a log-periodic antenna are used as a source and an analyzer, respectively, to investigate the possible anomalies of an electro-magnetic field. An unexpected isotropic signal has been detected using those torsion angles, which correspond to a breakdown of the Local Lorentz Invariance, which was found in the past. This coincidence is interpreted as the recovery of a lost symmetry by torqueing the antenna, thus putting in evidence that this Lorentz violation is of angular nature. Introducing a new physical dimension—not only a mathematical dimension as a way to rearrange some equations—is here proposed as a general rule to recover the lost symmetry.

The causal set approach to quantum gravity

The causal set theory (CST) approach to quantum gravity postulates that at the most fundamental level, spacetime is discrete, with the spacetime continuum replaced by locally finite posets or “causal sets”. The partial order on a causal set represents a proto-causality relation while local finiteness encodes an intrinsic discreteness. In the continuum approximation the former corresponds to the spacetime causality relation and the latter to a fundamental spacetime atomicity, so that finite volume regions in the continuum contain only a finite number of causal set elements. CST is deeply rooted in the Lorentzian character of spacetime, where a primary role is played by the causal structure poset. Importantly, the assumption of a fundamental discreteness in CST does not violate local Lorentz invariance in the continuum approximation. On the other hand, the combination of discreteness and Lorentz invariance gives rise to a characteristic non-locality which distinguishes CST from most other approaches to quantum gravity. In this review we give a broad, semi-pedagogical introduction to CST, highlighting key results as well as some of the key open questions. This review is intended both for the beginner student in quantum gravity as well as more seasoned researchers in the field.

Degrees of freedom and problems in f(T) gravity

Torsion-based modified theories of gravity, such as [Formula: see text] gravity, are arguably one of the very few “true” modified gravities based on well-defined geometric structures. However, the original formulation explicitly works in a specific choice of frame, which has led to considerable amount of confusion in the literature about these theories breaking local Lorentz invariance. Pathological properties such as superluminal propagation and the lack of well-posedness of Cauchy problem were found to plague [Formula: see text] gravity. Recent effort to “covariantize” [Formula: see text] gravity has, however, renewed interests in this subject. In this proceeding paper, we review and discuss issues concerning the actual number of degrees of freedom in [Formula: see text] gravity, and how this might relate to the aforementioned pathologies.

An Experimental Configuration to Probe for Lorentz Symmetry Violation in Electrons Using Trapped Yb+ Ions

Since extensions of the standard model have been developed that predict violations of local Lorentz invariance (LLI), precision measurement groups have been working to reduce experimental bounds of the associated matrix element. Using an analogue of the Michelson-Morley test with trapped Ca+ ions, the current bound has been set at one part in 1018. However, by instead using Yb+ ions, which have highly stable electronic states for storing quantum information compared to their counterparts and exhibit enhanced effects of LLI breaking asymmetries, we can push the bounds to one part in 1023. In this article, we outline a configuration for such an experiment and offer solutions to experimental concerns. We develop an algorithm for state creation, manipulation, and measurement that minimizes measurement time and transition uncertainty. We also discuss necessary hardware for trapping and manipulating ions including a vacuum system, a Paul trap and the associated electrode voltage supplies, and an optics system for generating and applying transition pulses. The experiment is specifically designed to utilize the existing ion trap hardware in place at the Richerme lab at Indiana University Bloomington.