Scalar Gravitational Theories with Variable Velocity of Light

We report a novel electrostatic self-excited resonator driven by DC voltage that achieves variable velocity-position characteristics via applying the pre-tension/pre-compression constraint. The resonator consists of a simply supported micro-beam, two plate electrodes, and two adjustable constraint bases, and it can be under pre-compression or pre-tension constraint by adjusting the distance L between two constraint bases (when beam length l > L, the resonator is under pre-compression and when l < L, it is under pre-tension). The oscillating velocity of the beam reaches the maximum value in the position around electrodes under the pre-compression constraint and reaches the maximum value in the middle position between two electrodes under the pre-tension condition. By changing the constraint of the microbeam, the position of the maximum velocity output of the oscillating beam can be controlled. The electrostatic self-excited resonator with a simple constraint structure under DC voltage has great potential in the field of propulsion of micro-robots, such as active rotation control of flapping wings.

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Non-Riemannian gravity actions from double field theory

Journal of High Energy Physics ◽

10.1007/jhep06(2021)173 ◽

2021 ◽

Vol 2021 (6) ◽

Author(s):

A. D. Gallegos ◽

U. Gürsoy ◽

S. Verma ◽

N. Zinnato

Keyword(s):

Field Theory ◽

Quantum Gravity ◽

Condensed Matter ◽

Equations Of Motion ◽

Technical Note ◽

Action Principle ◽

Relativistic Symmetry ◽

Gravitational Theories ◽

Double Field Theory

Abstract Non-Riemannian gravitational theories suggest alternative avenues to understand properties of quantum gravity and provide a concrete setting to study condensed matter systems with non-relativistic symmetry. Derivation of an action principle for these theories generally proved challenging for various reasons. In this technical note, we employ the formulation of double field theory to construct actions for a variety of such theories. This formulation helps removing ambiguities in the corresponding equations of motion. In particular, we embed Torsional Newton-Cartan gravity, Carrollian gravity and String Newton-Cartan gravity in double field theory, derive their actions and compare with the previously obtained results in literature.

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Entanglement entropy in cubic gravitational theories

Journal of High Energy Physics ◽

10.1007/jhep05(2021)186 ◽

2021 ◽

Vol 2021 (5) ◽

Author(s):

Elena Cáceres ◽

Rodrigo Castillo Vásquez ◽

Alejandro Vilar López

Keyword(s):

Entanglement Entropy ◽

Gravitational Theory ◽

Riemann Tensor ◽

Holographic Entanglement Entropy ◽

Gravitational Theories ◽

Entropy Functional ◽

Wide Range ◽

Splitting Problem ◽

Range Of Values

Abstract We derive the holographic entanglement entropy functional for a generic gravitational theory whose action contains terms up to cubic order in the Riemann tensor, and in any dimension. This is the simplest case for which the so-called splitting problem manifests itself, and we explicitly show that the two common splittings present in the literature — minimal and non-minimal — produce different functionals. We apply our results to the particular examples of a boundary disk and a boundary strip in a state dual to 4- dimensional Poincaré AdS in Einsteinian Cubic Gravity, obtaining the bulk entanglement surface for both functionals and finding that causal wedge inclusion is respected for both splittings and a wide range of values of the cubic coupling.

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