50 research outputs found
Probing Lorentz and CPT violation with space-based experiments
Space-based experiments offer sensitivity to numerous unmeasured effects
involving Lorentz and CPT violation. We provide a classification of clock
sensitivities and present explicit expressions for time variations arising in
such experiments from nonzero coefficients in the Lorentz- and CPT-violating
Standard-Model Extension.Comment: 15 page
CPT, T, and Lorentz Violation in Neutral-Meson Oscillations
Tests of CPT and Lorentz symmetry using neutral-meson oscillations are
studied within a formalism that allows for indirect CPT and T violation of
arbitrary size and is independent of phase conventions. The analysis is
particularly appropriate for studies of CPT and T violation in oscillations of
the heavy neutral mesons D, B_d, and B_s. The general Lorentz- and CPT-breaking
standard-model extension is used to derive an expression for the parameter for
CPT violation. It varies in a prescribed way with the magnitude and orientation
of the meson momentum and consequently also with sidereal time. Decay
probabilities are presented for both uncorrelated and correlated mesons, and
some implications for experiments are discussed.Comment: 11 pages, references added, accepted in Physical Review
Threshold analyses and Lorentz violation
In the context of threshold investigations of Lorentz violation, we discuss
the fundamental principle of coordinate invariance, the role of an effective
dynamical framework, and the conditions of positivity and causality. Our
analysis excludes a variety of previously considered Lorentz-breaking
parameters and opens an avenue for viable dispersion-relation investigations of
Lorentz violation.Comment: 9 page
Signals for Lorentz Violation in Electrodynamics
An investigation is performed of the Lorentz-violating electrodynamics
extracted from the renormalizable sector of the general Lorentz- and
CPT-violating standard-model extension. Among the unconventional properties of
radiation arising from Lorentz violation is birefringence of the vacuum. Limits
on the dispersion of light produced by galactic and extragalactic objects
provide bounds of 3 x 10^{-16} on certain coefficients for Lorentz violation in
the photon sector. The comparative spectral polarimetry of light from
cosmologically distant sources yields stringent constraints of 2 x 10^{-32}.
All remaining coefficients in the photon sector are measurable in
high-sensitivity tests involving cavity-stabilized oscillators. Experimental
configurations in Earth- and space-based laboratories are considered that
involve optical or microwave cavities and that could be implemented using
existing technology.Comment: 23 pages REVTe
Lorentz and CPT Violation in Neutrinos
A general formalism is presented for violations of Lorentz and CPT symmetry
in the neutrino sector. The effective hamiltonian for neutrino propagation in
the presence of Lorentz and CPT violation is derived, and its properties are
studied. Possible definitive signals in existing and future
neutrino-oscillation experiments are discussed. Among the predictions are
direction-dependent effects, including neutrino-antineutrino mixing, sidereal
and annual variations, and compass asymmetries. Other consequences of Lorentz
and CPT violation involve unconventional energy dependences in oscillation
lengths and mixing angles. A variety of simple models both with and without
neutrino masses are developed to illustrate key physical effects. The
attainable sensitivities to coefficients for Lorentz violation in the
Standard-Model Extension are estimated for various types of experiments. Many
experiments have potential sensitivity to Planck-suppressed effects, comparable
to the best tests in other sectors. The lack of existing experimental
constraints, the wide range of available coefficient space, and the variety of
novel effects imply that some or perhaps even all of the existing data on
neutrino oscillations might be due to Lorentz and CPT violation.Comment: 25 pages REVTe
Quantum Theory of Noncommutative Fields
Generalizing the noncommutative harmonic oscillator construction, we propose
a new extension of quantum field theory based on the concept of "noncommutative
fields". Our description permits to break the usual particle-antiparticle
degeneracy at the dispersion relation level and introduces naturally an
ultraviolet and an infrared cutoff. Phenomenological bounds for these new
energy scales are given.Comment: LaTeX file, JHEP3.cls, subequations.sty; 12 pages, no figures. Final
version published in JHEP with some references adde
Vacuum Polarization Effects in the Lorentz and PCT Violating Electrodynamics
In this work we report new results concerning the question of dynamical mass
generation in the Lorentz and PCT violating quantum electrodynamics. A one loop
calculation for the vacuum polarization tensor is presented. The electron
propagator, "dressed" by a Lorentz breaking extra term in the fermion
Lagrangian density, is approximated by its first order: this scheme is shown to
break gauge invariance. Then we rather consider a full calculation to second
order in the Lorentz breaking parameter: we recover gauge invariance and use
the Schwinger-Dyson equation to discuss the full photon propagator. This allows
a discussion on a possible photon mass shift as well as measurable, observable
physical consequences, such as the Lamb-shift.Comment: Latex file, 19 pages, no figures, includes PACS number
Ghost Condensation and a Consistent Infrared Modification of Gravity
We propose a theoretically consistent modification of gravity in the
infrared, which is compatible with all current experimental observations. This
is an analog of Higgs mechanism in general relativity, and can be thought of as
arising from ghost condensation--a background where a scalar field \phi has a
constant velocity, = M^2. The ghost condensate is a new kind of
fluid that can fill the universe, which has the same equation of state, \rho =
-p, as a cosmological constant, and can hence drive de Sitter expansion of the
universe. However, unlike a cosmological constant, it is a physical fluid with
a physical scalar excitation, which can be described by a systematic effective
field theory at low energies. The excitation has an unusual low-energy
dispersion relation \omega^2 \sim k^4 / M^2. If coupled to matter directly, it
gives rise to small Lorentz-violating effects and a new long-range 1/r^2 spin
dependent force. In the ghost condensate, the energy that gravitates is not the
same as the particle physics energy, leading to the possibility of both sources
that can gravitate and antigravitate. The Newtonian potential is modified with
an oscillatory behavior starting at the distance scale M_{Pl}/M^2 and the time
scale M_{Pl}^2/M^3. This theory opens up a number of new avenues for attacking
cosmological problems, including inflation, dark matter and dark energy.Comment: 42 pages, LaTeX 2
Quasi-Particle Description of Strongly Interacting Matter: Towards a Foundation
We confront our quasi-particle model for the equation of state of strongly
interacting matter with recent first-principle QCD calculations. In particular,
we test its applicability at finite baryon densities by comparing with Taylor
expansion coefficients of the pressure for two quark flavours. We outline a
chain of approximations starting from the Phi-functional approach to QCD which
motivates the quasi-particle picture.Comment: Aug 2006. 6 pp. Invited Talk given at Hot Quarks 2006, Villasimius,
Sardinia, Italy, 15-20 May 200
Noncommutativity in Field Space and Lorentz Invariance Violation
The connection between Lorentz invariance violation and noncommutativity of
fields in a quantum field theory is investigated. A new dispersion relation for
a free field theory with just one additional noncommutative parameter is
obtained. While values for the noncommutative scale much larger than 10^{-20}
eV^{-1} are ruled out by the present experimental status, cosmic ray physics
would be compatible with and sensible to a noncommutativity arising from
quantum gravity effects. We explore the matter-antimatter asymmetry which is
naturally present in this framework.Comment: 10 pages, no figures. Final version to appear in Phys. Lett. B with
slight changes in the presentatio