217 research outputs found
CPT and Lorentz violation as signatures for Planck-scale physics
In recent years, the breakdown of spacetime symmetries has been identified as
a promising research field in the context of Planck-scale phenomenology. For
example, various theoretical approaches to the quantum-gravity problem are
known to accommodate minute violations of CPT invariance. This talk covers
various topics within this research area. In particular, some mechanisms for
spacetime-symmetry breaking as well as the Standard-Model Extension (SME) test
framework will be reviewed; the connection between CPT and Lorentz invariance
in quantum field theory will be exposed; and various experimental CPT tests
with emphasis on matter--antimatter comparisons will be discussed.Comment: 6 page
Gravitational Redshift, Equivalence Principle, and Matter Waves
We review matter wave and clock comparison tests of the gravitational
redshift. To elucidate their relationship to tests of the universality of free
fall (UFF), we define scenarios wherein redshift violations are coupled to
violations of UFF ("type II"), or independent of UFF violations ("type III"),
respectively. Clock comparisons and atom interferometers are sensitive to
similar effects in type II and precisely the same effects in type III
scenarios, although type III violations remain poorly constrained. Finally, we
describe the "Geodesic Explorer," a conceptual spaceborne atom interferometer
that will test the gravitational redshift with an accuracy 5 orders of
magnitude better than current terrestrial redshift experiments for type II
scenarios and 12 orders of magnitude better for type III.Comment: Work in progress. 11 page
Limits on isotropic Lorentz violation in QED from collider physics
We consider the possibility that Lorentz violation can generate differences
between the limiting velocities of light and charged matter. Such effects would
lead to efficient vacuum Cherenkov radiation or rapid photon decay. The absence
of such effects for 104.5 GeV electrons at the Large Electron Positron collider
and for 300 GeV photons at the Tevatron therefore constrains this type of
Lorentz breakdown. Within the context of the standard-model extension, these
ideas imply an experimental bound at the level of -5.8 x 10^{-12} <=
\tilde{\kappa}_{tr}-(4/3)c_e^{00} <= 1.2 x 10^{-11} tightening existing
laboratory measurements by 3-4 orders of magnitude. Prospects for further
improvements with terrestrial and astrophysical methods are discussed.Comment: Replaced with final version published in PR
Atom Interferometers and the Gravitational Redshift
From the principle of equivalence, Einstein predicted that clocks slow down
in a gravitational field. Since the general theory of relativity is based on
the principle of equivalence, it is essential to test this prediction
accurately. Muller, Peters and Chu claim that a reinterpretation of decade old
experiments with atom interferometers leads to a sensitive test of this
gravitational redshift effect at the Compton frequency. Wolf et al dispute this
claim and adduce arguments against it. In this article, we distill these
arguments to a single fundamental objection: an atom is NOT a clock ticking at
the Compton frequency. We conclude that atom interferometry experiments
conducted to date do not yield such sensitive tests of the gravitational
redshift. Finally, we suggest a new interferometric experiment to measure the
gravitational redshift, which realises a quantum version of the classical clock
"paradox".Comment: 18 pages, one figure, improved discussion, corrected typo
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