206 research outputs found
Phenomenological description of quantum gravity inspired modified classical electrodynamics
We discuss a large class of phenomenological models incorporating quantum
gravity motivated corrections to electrodynamics. The framework is that of
electrodynamics in a birefringent and dispersive medium with non-local
constitutive relations, which are considered up to second order in the inverse
of the energy characterizing the quantum gravity scale. The energy-momentum
tensor, Green functions and frequency dependent refraction indices are
obtained, leading to departures from standard physics. The effective character
of the theory is also emphasized by introducing a frequency cutoff. The
analysis of its effects upon the standard notion of causality is performed,
showing that in the radiation regime the expected corrections get further
suppressed by highly oscillating terms, thus forbiding causality violations to
show up in the corresponding observational effects.Comment: 14 pages, to be published in Obregon Festschrift 2006, Gen. Rel. and
Gra
Radiation in Lorentz violating electrodynamics
Synchrotron radiation is analyzed in the classical effective Lorentz
invariance violating model of Myers-Pospelov. Within the full far-field
approximation we compute the electric and magnetic fields, the angular
distribution of the power spectrum and the total emitted power in the m-th
harmonic, as well as the polarization. We find the appearance of rather
unexpected and large amplifying factors, which go together with the otherwise
negligible naive expansion parameter. This opens up the possibility of further
exploring Lorentz invariance violations by synchrotron radiation measurements
in astrophysical sources where these amplifying factors are important.Comment: Presented at the Second Mexican Meeting on Theoretical and
Experimental Physics, El Colegio Nacional, Mexico City, 6-10 September 200
Stochastic approach to inflation II: classicality, coarse-graining and noises
In this work we generalize a previously developed semiclassical approach to
inflation, devoted to the analysis of the effective dynamics of coarse-grained
fields, which are essential to the stochastic approach to inflation. We
consider general non-trivial momentum distributions when defining these fields.
The use of smooth cutoffs in momentum space avoids highly singular quantum
noise correlations and allows us to consider the whole quantum noise sector
when analyzing the conditions for the validity of an effective classical
dynamical description of the coarse-grained field. We show that the weighting
of modes has physical consequences, and thus cannot be considered as a mere
mathematical artifact. In particular we discuss the exponential inflationary
scenario and show that colored noises appear with cutoff dependent amplitudes.Comment: 18 pages, revtex, no figure
VEP oscillation solutions to the solar neutrino problem
We study the solar neutrino problem within the framework of a parametrized
post-Newtonian formulation for the gravitational interaction of the neutrinos,
which incorporates a violation to the equivalence principle (VEP). Using the
current data on the rates and the energy spectrum we find two possible
oscillation solutions, both for a large mixing angle. One of them involves the
MSW effect in matter and the other corresponds to vacuum oscillations. An
interesting characteristic of this mechanism is that it predicts a semi-annual
variation of the neutrino flux. Our analysis provides new constraints for some
VEP parameters.Comment: revtex, 18 pages, 11 figure
Microcausality and quantization of the fermionic Myers-Pospelov model
We study the fermionic sector of the Myers and Pospelov theory with a general
background . The spacelike case without temporal component is well defined
and no new ingredients came about, apart from the explicit Lorentz invariance
violation. The lightlike case is ill defined and physically discarded. However,
the other case where a nonvanishing temporal component of the background is
present, the theory is physically consistent. We show that new modes appear as
a consequence of higher time derivatives. We quantize the timelike theory and
calculate the microcausality violation which turns out to occur near the light
cone.Comment: 9 pages and 3 figures, new version accepted in EPJC, Volume 72, Issue
9, includes lee-wick review, microcausalit
Astrometry with The \u3cem\u3eHubble Space Telescope\u3c/em\u3e: A Parallax of the Central Star of the Planetary Nebula NGC 6853
We present an absolute parallax and relative proper motion for the central star of the planetary nebula NGC 6853 (the Dumbbell). We obtain these with astrometric data from the Fine Guidance Sensor 3, a white-light interferometer on the Hubble Space Telescope. Spectral classifications and VRIJHKT2M and DDO51 photometry of the stars making up the astrometric reference frame provide spectrophotometric estimates of their absolute parallaxes. Introducing these into our model as observations with error, we find πabs = 2.10 ± 0.48 mas for the DAO central star of NGC 6853. A weighted average with a previous ground-based USNO determination yields πabs = 2.40 ± 0.32. We assume that the extinction suffered by the reference stars nearest (in angular separation and distance) to the central star is the same as for the central star. Correcting for color differences, we find AV = 0.30 ± 0.06 for the central star, hence, an absolute magnitude MV = 5.48. A recent determination of the central star effective temperature aided in estimating the central star radius, R* = 0.055 ± 0.02 R⊙, a star that may be descending to the white dwarf cooling track
Global-change effects on early-stage decomposition processes in tidal wetlands – implications from a global survey using standardized litter
Tidal wetlands, such as tidal marshes and mangroves, are hotspots for carbon sequestration. The preservation of organic matter (OM) is a critical process by which tidal wetlands exert influence over the global carbon cycle and at the same time gain elevation to keep pace with sea-level rise (SLR). The present study assessed the effects of temperature and relative sea level on the decomposition rate and stabilization of OM in tidal wetlands worldwide, utilizing commercially available standardized litter. While effects on decomposition rate per se were minor, we show strong negative effects of temperature and relative sea level on stabilization, as based on the fraction of labile, rapidly hydrolyzable OM that becomes stabilized during deployment. Across study sites, OM stabilization was 29 % lower in low, more frequently flooded vs. high, less frequently flooded zones. Stabilization declined by ∼ 75 % over the studied temperature gradient from 10.9 to 28.5 ∘C. Additionally, data from the Plum Island long-term ecological research site in Massachusetts, USA, show a pronounced reduction in OM stabilization by > 70 % in response to simulated coastal eutrophication, confirming the potentially high sensitivity of OM stabilization to global change. We therefore provide evidence that rising temperature, accelerated SLR, and coastal eutrophication may decrease the future capacity of tidal wetlands to sequester carbon by affecting the initial transformations of recent OM inputs to soil OM
Garden and landscape-scale correlates of moths of differing conservation status: significant effects of urbanization and habitat diversity
Moths are abundant and ubiquitous in vegetated terrestrial environments and are pollinators, important herbivores of wild plants, and food for birds, bats and rodents. In recent years, many once abundant and widespread species have shown sharp declines that have been cited by some as indicative of a widespread insect biodiversity crisis. Likely causes of these declines include agricultural intensification, light pollution, climate change, and urbanization; however, the real underlying cause(s) is still open to conjecture. We used data collected from the citizen science Garden Moth Scheme (GMS) to explore the spatial association between the abundance of 195 widespread British species of moth, and garden habitat and landscape features, to see if spatial habitat and landscape associations varied for species of differing conservation status. We found that associations with habitat and landscape composition were species-specific, but that there were consistent trends in species richness and total moth abundance. Gardens with more diverse and extensive microhabitats were associated with higher species richness and moth abundance; gardens near to the coast were associated with higher richness and moth abundance; and gardens in more urbanized locations were associated with lower species richness and moth abundance. The same trends were also found for species classified as increasing, declining and vulnerable under IUCN (World Conservation Union) criteria
Neutrinos in a gravitational background: a test for the universality of the gravitational interaction
In this work we propose an extended formulation for the interaction between
neutrinos and gravitational fields. It is based on the parametrized
post-Newtonian aproach, and includes a violation of the universality of the
gravitational interaction which is non diagonal in the weak flavor space. We
find new effects that are not considered in the standard scenario for violation
of the equivalence principle. They are of the same order as the effects
produced by the Newtonian potential, but they are highly directional dependent
and could provide a very clean test of that violation. Phenomenological
consequences are briefly discussed.Comment: 18 pages, revtex, no figure
Mechanical metamaterials at the theoretical limit of isotropic elastic stiffness
Acknowledgements H.N.G.W. is grateful for support for this work by the ONR (grant number N00014-15-1-2933), managed by D. Shifler, and the DARPA MCMA programme (grant number W91CRB-10-1-005), managed by J. Goldwasser.Peer reviewedPostprintPostprintPostprintPostprin
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