841 research outputs found
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
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
Could One Find Petroleum Using Neutrino Oscillations in Matter?
In neutrino physics, it is now widely believed that neutrino oscillations are
influenced by the presence of matter, modifying the energy spectrum produced by
a neutrino beam traversing the Earth. Here, we will discuss the reverse
problem, i.e. what could be learned about the Earth's interior from a single
neutrino baseline energy spectrum, especially about the Earth's mantle. We will
use a statistical analysis with a low-energy neutrino beam under very
optimistic assumptions. At the end, we will note that it is hard to find
petroleum with such a method, though it is not too far away from technical
feasibility.Comment: 6 pages, 4 figures, EPL LaTeX. Final version to be published in
Europhys. Let
Bounds on Lorentz and CPT Violation from the Earth-Ionosphere Cavity
Electromagnetic resonant cavities form the basis of many tests of Lorentz
invariance involving photons. The effects of some forms of Lorentz violation
scale with cavity size. We investigate possible signals of violations in the
naturally occurring resonances formed in the Earth-ionosphere cavity.
Comparison with observed resonances places the first terrestrial constraints on
coefficients associated with dimension-three Lorentz-violating operators at the
level of 10^{-20} GeV.Comment: 8 pages REVTe
Modelling silvicultural alternatives for conifer regeneration in boreal mixedwood stands (aspen/white spruce/balsam fir)
We model and compare the biological and financial constraints of four prescriptions that serve as alternatives to conventional clearcutting followed by planting in eastern and western boreal mixedwood stands. These alternative prescriptions for full or partial conifer stocking are (1) reliance on advance regeneration with or without augmentation by fill-planting; (2) understory scarification during a mast year; (3) direct seeding either aerially or with a scarifier-seeder; and (4) underplanting. Our main conclusions concerning the biological constraints are that (1) advance regeneration, mainly of balsam fir in the east and white spruce in the west, requires >26 000 and > 4000 trees/ha (because of different distributions), respectively, to achieve full conifer stocking; (2) reliance on a mast year requires at least 6 m2/ha of mature conifer basal area, but much less if some advance regeneration is present or only moderate stocking is desired; (3) aerial seeding with 35% scarification requires about a half-million seeds/ha to achieve full conifer stocking, while a scarifier-seeder would require only a third of this application rate; and (4) underplanting is constrained to aspen stands with >25% incident light at planting height. In all cases, alternative prescriptions become more feasible if only moderate or minimal stocking is the silvicultural objective. A costing exercise for the four prescriptions in comparison with a clearcut followed by planting shows that reliance on advance regeneration or understory planting are the cheapest alternatives to achieve full or partial conifer stocking. With the exception of full conifer stocking in situations where there is little advance regeneration (and where herbicides can be used), conventional plantations are never the cheapest approach. In such cases, fill planting and use of a scarifier-seeder become viable options. Aerial seeding and reliance on a mast year are the most expensive of the alternatives. We conclude, tentatively, that there is enough conifer basal area in most of the eastern boreal mixedwood of Canada to allow for the use of either or both a mast year and advance regeneration to achieve full or partial conifer stocking. By contrast, in the west conifer basal area will seldom be sufficient for natural seeding, and the density of advance regeneration is likewise often too low. Finally, because of light constraints, understory planting appears to have a much wider applicability in the west than in the east
Light and tree size influence belowground development in yellow birch and sugar maple
The effects of light and tree size on the root architecture and mycorrhiza of yellow birch (Betula alleghaniensis Britton) and sugar maple (Acer saccharum Marsh) growing in the understory of deciduous forests in southern Qu
Lorentz- and CPT-violating models for neutrino oscillations
A class of calculable global models for neutrino oscillations based on
Lorentz and CPT violation is presented. One simple example matches established
neutrino data from accelerator, atmospheric, reactor, and solar experiments,
using only two degrees of freedom instead of the usual five. A third degree of
freedom appears in the model, and it naturally generates the MiniBooNE
low-energy anomalies. More involved models in this class can also accommodate
the LSND anomaly and neutrino-antineutrino differences of the MINOS type. The
models predict some striking signals in various ongoing and future experiments.Comment: 17 pages two-column REVTe
Mountain maple and balsam fir early response to partial and clear-cut harvesting under aspen stands of northern Quebec
This study is a component of the Sylviculture et am
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