207 research outputs found
Gravity Couplings in the Standard-Model Extension
The Standard-Model Extension (SME) is an action-based expansion describing
general Lorentz violation for known matter and fields, including gravity. In
this talk, I will discuss the Lorentz-violating gravity couplings in the SME.
Toy models that match the SME expansion, including vector and two-tensor
models, are reviewed. Finally I discuss the status of experiments and
observations probing gravity coefficients for Lorentz violation.Comment: 5 pages, Presented at the Fifth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, June 28-July 2, 201
Lorentz Violation and Gravity
In the last decade, a variety of high-precision experiments have searched for
miniscule violations of Lorentz symmetry. These searches are largely motivated
by the possibility of uncovering experimental signatures from a fundamental
unified theory. Experimental results are reported in the framework called the
Standard-Model Extension (SME), which describes general Lorentz violation for
each particle species in terms of its coefficients for Lorentz violation.
Recently, the role of gravitational experiments in probing the SME has been
explored in the literature. In this talk, I will summarize theoretical and
experimental aspects of these works. I will also discuss recent lunar laser
ranging and atom interferometer experiments, which place stringent constraints
on gravity coefficients for Lorentz violation.Comment: 5 pages, presented at the IAU Symposium No. 261: Relativity in
Fundamental Astronomy, Virginia Beach, VA, May 200
Testing Lorentz Symmetry with Gravity
In this talk, results from the gravitational sector of the Standard-Model
Extension (SME) are discussed. The weak-field phenomenology of the resulting
modified gravitational field equations is explored. The application of the
results to a variety of modern gravity experiments, including lunar laser
ranging, Gravity Probe B, binary pulsars, and Earth-laboratory tests, shows
promising sensitivity to gravitational coefficients for Lorentz violation in
the SME.Comment: 7 pages, presented at the Fourth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, August 200
Lorentz-Violating Electromagnetostatics
In this talk, the stationary limit of Lorentz-violating electrodynamics is
discussed. As illustrated by some simple examples, the general solution
includes unconventional mixing of electrostatic and magnetostatic effects. I
discuss a high-sensitivity null-type measurement, exploiting Lorentz-violating
electromagnetostatic effects, that could improve existing limits on parity-odd
coefficients for Lorentz violation in the photon sector.Comment: 6 pages, presented at the Third Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, August 200
Lorentz-violating gravitoelectromagnetism
The well-known analogy between a special limit of General Relativity and
electromagnetism is explored in the context of the Lorentz-violating
Standard-Model Extension (SME). An analogy is developed for the minimal SME
that connects a limit of the CPT-even component of the electromagnetic sector
to the gravitational sector. We show that components of the post-newtonian
metric can be directly obtained from solutions to the electromagnetic sector.
The method is illustrated with specific examples including static and rotating
sources. Some unconventional effects that arise for Lorentz-violating
electrostatics and magnetostatics have an analog in Lorentz-violating
post-newtonian gravity. In particular, we show that even for static sources,
gravitomagnetic fields arise in the presence of Lorentz violation.Comment: 11 pages, 2 color figures, version accepted in Physical Review
Local Lorentz-Symmetry Breaking and Gravity
The lagrangian-based Standard-Model Extension framework offers a broad
description of possible gravitational effects from local Lorentz violation. In
this talk, I review the status of the theoretical and phenomenological work in
this area. The extension of previous results in linearized gravity to the
nonlinear regime is discussed.Comment: 4 pages, presented at the Sixth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, June 17-21, 201
Anisotropic cubic curvature couplings
To complement recent work on tests of spacetime symmetry in gravity, cubic
curvature couplings are studied using an effective field theory description of
spacetime-symmetry breaking. The associated mass dimension 8 coefficients for
Lorentz violation studied do not result in any linearized gravity modifications
and instead are revealed in the first nonlinear terms in an expansion of
spacetime around a flat background. We consider effects on gravitational
radiation through the energy loss of a binary system and we study two-body
orbital perturbations using the post-Newtonian metric. Some effects depend on
the internal structure of the source and test bodies, thereby breaking the Weak
Equivalence Principle for self-gravitating bodies. These coefficients can be
measured in solar-system tests, while binary-pulsar systems and short-range
gravity tests are particularly sensitive.Comment: 11 page
Velocity-dependent inverse cubic force and solar system gravity tests
Higher mass dimension terms in an effective field theory framework for tests
of spacetime symmetries are studied. Using a post-Newtonian expansion method,
we derive the spacetime metric and the equations of motion for a binary system.
This reveals an inverse cubic force correction to General Relativity that
depends on the velocity of the bodies in the system. The results are studied in
the context of laboratory and space-based tests including the effects on
solar-system ephemeris, laser ranging observations, and gravimeter tests. This
work reveals the coefficient combinations for mass dimension 5 operators
controlling CPT violation for gravity that can be measured using analysis from
these tests. Other tests including light propagation can be used to probe these
coefficients. Sensitivity estimates are provided and the results are contrasted
with the minimal mass dimension 4 terms in the gravity sector.Comment: 10 pages, matches published versio
Testing the Gravitational Weak Equivalence Principle in the Standard-Model Extension with Binary Pulsars
The Standard-Model Extension provides a framework to systematically
investigate possible violation of the Lorentz symmetry. Concerning gravity, the
linearized version was extensively examined. We here cast the first set of
experimental bounds on the nonlinear terms in the field equation from the
anisotropic cubic curvature couplings. These terms introduce body-dependent
accelerations for self-gravitating objects, thus violating the gravitational
weak equivalence principle (GWEP). Novel phenomena, that are absent in the
linearized gravity, remain experimentally unexplored. We constrain them with
precise binary-orbit measurements from pulsar timing, wherein the high density
and large compactness of neutron stars are crucial for the test. It is the
first study that seeks GWEP-violating signals in a fully anisotropic framework
with Lorentz violation.Comment: 7 pages, 1 figure; accepted by PR
Relating Noncommutative SO(2,3) Gravity to the Lorentz-Violating Standard-Model Extension
We consider a model of noncommutative gravity that is based on a spacetime
with broken local SO(2,3) symmetry. We show that the torsion-free version of
this model is contained within the framework of the Lorentz-violating
Standard-Model Extension. We analyze in detail the relation between the
torsion-free, quadratic limits of the broken SO(2,3) model and the
Standard-Model Extension. As part of the analysis,we construct the relevant
geometric quantities to quadratic order in the metric perturbation around a
flat background.Comment: 10 pages, accepted in Symmetr
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