237 research outputs found
New Observational Bounds to Quantum Gravity Signals
We consider a new set of effects arising from the quantum gravity corrections
to the propagation of fields, associated with fluctuations of the spacetime
geometry. Using already existing experimental data, we can put bounds on these
effects that are more stringent by several orders of magnitude than those
expected to be obtained in astrophysical observations. In fact these results
can be already interpreted as questioning the whole scenario of linear (in
) corrections to the dispersion relations for free fields in Lorentz
violating theories.Comment: Latex, to be published in PR
Strangelet spectra from type II supernovae
We study in this work the fate of strangelets injected as a contamination in
the tail of a "strange matter-driven" supernova shock. A simple model for the
fragmentation and braking of the strangelets when they pass through the
expanding oxygen shell is presented and solved to understand the reprocessing
of this component. We find that the escaping spectrum is a scaled-down version
of the one injected at the base of the oxygen shell. The supernova source is
likely to produce low-energy particles of quite independently
of the initial conditions. However, it is difficult that ultrarrelativistic
strangelets (such as the hypothetical Centauro primaries) can have an origin in
those explosive events.Comment: RevTex file, 5 pp., no figure
Exact Philosophy of Space-Time
Starting from Bunge's (1977) scientific ontology, we expose a materialistic
relational theory of space-time, that carries out the program initiated by
Leibniz, and provides a protophysical basis consistent with any rigorous
formulation of General Relativity. Space-time is constructed from general
concepts which are common to any consistent scientific theory and they are
interpreted as emergent properties of the greatest assembly of things, namely,
the world.Comment: 13 pages, 3 figures. Version compatible with the published one. arXiv
admin note: substantial text overlap with arXiv:gr-qc/971006
Instability of hyper-compact Kerr-like objects
Viable alternatives to astrophysical black holes include hyper-compact
objects without horizon, such as gravastars, boson stars, wormholes and
superspinars. The authors have recently shown that typical rapidly-spinning
gravastars and boson stars develop a strong instability. That analysis is
extended in this paper to a wide class of horizonless objects with approximate
Kerr-like geometry. A detailed investigation of wormholes and superspinars is
presented, using plausible models and mirror boundary conditions at the
surface. Like gravastars and boson stars, these objects are unstable with very
short instability timescales. This result strengthens previous conclusions that
observed hyper-compact astrophysical objects with large rotation are likely to
be black holes.Comment: 15 pages, 3 figures. To be published in CQ
Stratigraphy and chronology of a 15ka sequence of multi-sourced silicic tephras in a montane peat bog, eastern North Island, New Zealand.
We document the stratigraphy, composition, and chronology of a succession of 16 distal, silicic tephra layers interbedded with lateglacial and Holocene peats and muds up to c. 15 000 radiocarbon years (c. 18 000 calendar years) old at a montane site (Kaipo Bog) in eastern North Island, New Zealand. Aged from 665 +/- 15 to 14 700 +/- 95 14C yr BP, the tephras are derived from six volcanic centres in North Island, three of which are rhyolitic (Okataina, Taupo, Maroa), one peralkaline (Tuhua), and two andesitic (Tongariro, Egmont). Correlations are based on multiple criteria: field properties and stratigraphic interrelationships, ferromagnesian silicate mineral assemblages, glass-shard major element composition (from electron microprobe analysis), and radiocarbon dating. We extend the known distribution of tephras in eastern North Island and provide compositional data that add to their potential usefulness as isochronous markers. The chronostratigraphic framework established for the Kaipo sequence, based on both site-specific and independently derived tephra-based radiocarbon ages, provides the basis for fine-resolution paleoenvironmental studies at a climatically sensitive terrestrial site from the mid latitudes of the Southern Hemisphere. Tephras identified as especially useful paleoenvironmental markers include Rerewhakaaitu and Waiohau (lateglacial), Konini (lateglacial-early Holocene), Tuhua (middle Holocene), and Taupo and Kaharoa (late Holocene)
Hyperextended Scalar-Tensor Gravity
We study a general Scalar-Tensor Theory with an arbitrary coupling funtion
but also an arbitrary dependence of the ``gravitational
constant'' in the cases in which either one of them, or both, do not
admit an analytical inverse, as in the hyperextended inflationary scenario. We
present the full set of field equations and study their cosmological behavior.
We show that different scalar-tensor theories can be grouped in classes with
the same solution for the scalar field.Comment: latex file, To appear in Physical Review
Cosmology, Oscillating Physics and Oscilllating Biology
According to recent reports there is an excess correlation and an apparent
regularity in the galaxy one-dimensional polar distribution with a
characteristic scale of 128 Mpc. This aparent spatial periodicity can
be naturally explained by a time oscillation of the gravitational constant .
On the other hand, periodic growth features of bivalve and coral fossiles
appear to show a periodic component in the time dependence of the number of
days per year. In this letter we show that a time oscillating gravitational
constant with similar period and amplitude can explain such a feature.Comment: 9 pages. latex using revtex. This revised version is supposed to be
free of e-mail nois
Accelerating Universe and Cosmological Perturbation in the Ghost Condensate
In the simplest Higgs phase of gravity called ghost condensation, an
accelerating universe with a phantom era (w<-1) can be realized without ghost
or any other instabilities. In this paper we show how to reconstruct the
potential in the Higgs sector Lagrangian from a given cosmological history
(H(t), \rho(t)). This in principle allows us to constrain the potential by
geometrical information of the universe such as supernova distance-redshift
relation. We also derive the evolution equation for cosmological perturbations
in the Higgs phase of gravity by employing a systematic low energy expansion.
This formalism is expected to be useful to test the theory by dynamical
information of large scale structure in the universe such as cosmic microwave
background anisotropy, weak gravitational lensing and galaxy clustering.Comment: 30 pages; typos corrected; version accepted for publication in JCA
Varying Fine Structure Constant and Black Hole Physics
Recent astrophysical observations suggest that the value of fine structure
constant may be slowly increasing with time. This may be
due to an increase of or a decrease of , or both. In this article, we
argue from model independent considerations that this variation should be
considered adiabatic. Then, we examine in detail the consequences of such an
adiabatic variation in the context of a specific model of quantized charged
black holes. We find that the second law of black hole thermodynamics is
obeyed, regardless of the origin of the variation, and that interesting
constraints arise on the charge and mass of black holes. Finally, we estimate
the work done on a black hole of mass due to the proposed
variation.Comment: 7 Pages, Revtex. Reference added, minor changes. Version to appear in
Class. Quant. Gra
Results of the Search for Strange Quark Matter and Q-balls with the SLIM Experiment
The SLIM experiment at the Chacaltaya high altitude laboratory was sensitive
to nuclearites and Q-balls, which could be present in the cosmic radiation as
possible Dark Matter components. It was sensitive also to strangelets, i.e.
small lumps of Strange Quark Matter predicted at such altitudes by various
phenomenological models. The analysis of 427 m^2 of Nuclear Track Detectors
exposed for 4.22 years showed no candidate event. New upper limits on the flux
of downgoing nuclearites and Q-balls at the 90% C.L. were established. The null
result also restricts models for strangelets propagation through the Earth
atmosphere.Comment: 14 pages, 11 EPS figure
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