1,702 research outputs found
A New Test of the Einstein Equivalence Principle and the Isotropy of Space
Recent research has established that nonsymmetric gravitation theories like
Moffat's NGT predict that a gravitational field singles out an orthogonal pair
of polarization states of light that propagate with different phase velocities.
We show that a much wider class of nonmetric theories encompassed by the formalism predict such violations of the Einstein equivalence principle.
This gravity-induced birefringence of space implies that propagation through a
gravitational field can alter the polarization of light. We use data from
polarization measurements of extragalactic sources to constrain birefringence
induced by the field of the Galaxy. Our new constraint is times sharper
than previous ones.Comment: 21 pages, Latex, 3 Postscript figure
Clock-Comparison Tests of Lorentz and CPT Symmetry in Space
Clock-comparison experiments conducted in space can provide access to many
unmeasured coefficients for Lorentz and CPT violation. The orbital
configuration of a satellite platform and the relatively large velocities
attainable in a deep-space mission would permit a broad range of tests with
Planck-scale sensitivity.Comment: 4 page
Dirac theory within the Standard-Model Extension
The modified Dirac equation in the Lorentz-violating Standard-Model Extension
(SME) is considered. Within this framework, the construction of a hermitian
Hamiltonian to all orders in the Lorentz-breaking parameters is investigated,
discrete symmetries and the first-order roots of the dispersion relation are
determined, and various properties of the eigenspinors are discussed.Comment: 11 pages REVTe
Proposed astrophysical test of Lorentz invariance
Working in the context of a Lorentz-violating extension of the standard model
we show that estimates of Lorentz symmetry violation extracted from ultra-high
energy cosmic rays beyond the Greisen-Kuzmin-Zatsepin (GZK) cutoff allow for
setting bounds on parameters of that extension. Furthermore, we argue that a
correlated measurement of the difference in the arrival time of gamma-ray
photons and neutrinos emitted from active galactic nuclei or gamma-ray bursts
may provide a signature of possible violation of Lorentz symmetry. We have
found that this time delay is energy independent, however it has a dependence
on the chirality of the particles involved. We also briefly discuss the known
settings where the mechanism for spontaneous violation of Lorentz symmetry in
the context of string/M-theory may take place.Comment: Typos corrected. Version to appear in Phys. Rev.
Spacetime-varying couplings and Lorentz violation
Spacetime-varying coupling constants can be associated with violations of
local Lorentz invariance and CPT symmetry. An analytical supergravity cosmology
with time-varying fine-structure constant provides an explicit example.
Estimates are made for some experimental constraints.Comment: 4 page
One-Loop Renormalization of Lorentz-Violating Electrodynamics
We show that the general Lorentz- and CPT-violating extension of quantum
electrodynamics is one-loop renormalizable. The one-loop Lorentz-violating beta
functions are obtained, and the running of the coefficients for Lorentz and CPT
violation is determined. Some implications for theory and experiment are
discussed.Comment: 12 pages, accepted for publication in Physical Review
Finding Direction in the Search for Selection.
Tests for positive selection have mostly been developed to look for diversifying selection where change away from the current amino acid is often favorable. However, in many cases we are interested in directional selection where there is a shift toward specific amino acids, resulting in increased fitness in the species. Recently, a few methods have been developed to detect and characterize directional selection on a molecular level. Using the results of evolutionary simulations as well as HIV drug resistance data as models of directional selection, we compare two such methods with each other, as well as against a standard method for detecting diversifying selection. We find that the method to detect diversifying selection also detects directional selection under certain conditions. One method developed for detecting directional selection is powerful and accurate for a wide range of conditions, while the other can generate an excessive number of false positives
Lorentz and CPT tests with spin-polarized solids
Experiments using macroscopic samples of spin-polarized matter offer
exceptional sensitivity to Lorentz and CPT violation in the electron sector.
Data from existing experiments with a spin-polarized torsion pendulum provide
sensitivity in this sector rivaling that of all other existing experiments and
could reveal spontaneous violation of Lorentz symmetry at the Planck scale.Comment: 4 pages, accepted for publication in Physical Review Letter
CPT and Lorentz tests with muons
Precision experiments with muons are sensitive to Planck-scale CPT and
Lorentz violation that is undetectable in other tests. Existing data on the
muonium ground-state hyperfine structure and on the muon anomalous magnetic
moment could be analyzed to provide dimensionless figures of merit for CPT and
Lorentz violation at the levels of and .Comment: 4 pages, accepted for publication in Physical Review Letter
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