55,175 research outputs found
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
Antimatter, Lorentz Symmetry, and Gravity
A brief introduction to the Standard-Model Extension (SME) approach to
testing CPT and Lorentz symmetry is provided. Recent proposals for tests with
antimatter are summarized, including gravitational and spectroscopic tests.Comment: Presented at the 12th International Conference on Low Energy
Antiproton Physics, Kanazawa Japan, March 6-11, 2016, Accepted for
publication in JPS Conference Proceeding
Probing Relativity using Space-Based Experiments
An overview of space tests searching for small deviations from special
relativity arising at the Planck scale is given. Potential high-sensitivity
space-based experiments include ones with atomic clocks, masers, and
electromagnetic cavities. We show that a significant portion of the coefficient
space in the Standard-Model Extension, a framework that covers the full
spectrum of possible effects, can be accessed using space tests. Some remarks
on Lorentz violation in the gravitational sector are also given.Comment: 12 pages, invited talk at International Workshop, From Quantum to
Cosmos, Warrenton, VA, USA, May 22-24, 200
Matter-gravity couplings and Lorentz violation
The gravitational couplings of matter are studied in the presence of Lorentz
and CPT violation. At leading order in the coefficients for Lorentz violation,
the relativistic quantum hamiltonian is derived from the gravitationally
coupled minimal Standard-Model Extension. For spin-independent effects, the
nonrelativistic quantum hamiltonian and the classical dynamics for test and
source bodies are obtained. A systematic perturbative method is developed to
treat small metric and coefficient fluctuations about a Lorentz-violating and
Minkowski background. The post-newtonian metric and the trajectory of a test
body freely falling under gravity in the presence of Lorentz violation are
established. An illustrative example is presented for a bumblebee model. The
general methodology is used to identify observable signals of Lorentz and CPT
violation in a variety of gravitational experiments and observations, including
gravimeter measurements, laboratory and satellite tests of the weak equivalence
principle, antimatter studies, solar-system observations, and investigations of
the gravitational properties of light. Numerous sensitivities to coefficients
for Lorentz violation can be achieved in existing or near-future experiments at
the level of parts in 10^3 down to parts in 10^{15}. Certain coefficients are
uniquely detectable in gravitational searches and remain unmeasured to date.Comment: 59 pages two-column REVTe
Heavy spin-2 Dark Matter
We provide further details on a recent proposal addressing the nature of the
dark sectors in cosmology and demonstrate that all current observations related
to Dark Matter can be explained by the presence of a heavy spin-2 particle.
Massive spin-2 fields and their gravitational interactions are uniquely
described by ghost-free bimetric theory, which is a minimal and natural
extension of General Relativity. In this setup, the largeness of the physical
Planck mass is naturally related to extremely weak couplings of the heavy
spin-2 field to baryonic matter and therefore explains the absence of signals
in experiments dedicated to Dark Matter searches. It also ensures the
phenomenological viability of our model as we confirm by comparing it with
cosmological and local tests of gravity. At the same time, the spin-2 field
possesses standard gravitational interactions and it decays universally into
all Standard Model fields but not into massless gravitons. Matching the
measured DM abundance together with the requirement of stability constrains the
spin-2 mass to be in the 1 to 100 TeV range.Comment: Latex, 46 pages, 4 figures. Matches published versio
Recent Developments in Spacetime-Symmetry Tests in Gravity
Motivated by potentially detectable but minuscule signatures from Planckscale or other new physics, there has been a substantial increase in tests of spacetime symmetry in gravity in recent years. Some novel hypothetical effects that break local Lorentz symmetry and CPT symmetry in gravitational experiments as well as solar system and astrophysical observations have been studied in recent works. Much of this work uses the effective field theory framework, the Standard-Model Extension (SME), that includes gravitational couplings. In other cases, the parameters in specific hypothetical models of Lorentz violation in gravity have been tested
Overview of the SME: Implications and Phenomenology of Lorentz Violation
The Standard Model Extension (SME) provides the most general
observer-independent field theoretical framework for investigations of Lorentz
violation. The SME lagrangian by definition contains all Lorentz-violating
interaction terms that can be written as observer scalars and that involve
particle fields in the Standard Model and gravitational fields in a generalized
theory of gravity. This includes all possible terms that could arise from a
process of spontaneous Lorentz violation in the context of a more fundamental
theory, as well as terms that explicitly break Lorentz symmetry. An overview of
the SME is presented, including its motivations and construction. Some of the
theoretical issues arising in the case of spontaneous Lorentz violation are
discussed, including the question of what happens to the Nambu-Goldstone modes
when Lorentz symmetry is spontaneously violated and whether a Higgs mechanism
can occur. A minimal version of the SME in flat Minkowski spacetime that
maintains gauge invariance and power-counting renormalizability is used to
search for leading-order signals of Lorentz violation. Recent Lorentz tests in
QED systems are examined, including experiments with photons, particle and
atomic experiments, proposed experiments in space and experiments with a
spin-polarized torsion pendulum.Comment: 40 pages, Talk presented at Special Relativity: Will it Survive the
Next 100 Years? Potsdam, Germany, February, 200
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