80 research outputs found
Cosmological Implications of a Possible Class of Particles Able to Travel Faster than Light
We discuss the possible cosmological implications of a class of superluminal
particles, in a scenario where: a) Lorentz invariance is only an approximate
property of the equations of a sector of matter; b) several critical speeds of
matter in vacuum exist. The Big Bang scenario and the evolution of the very
early universe, as well as large scale structure, can be strongly influenced by
the new particles.Comment: 5 pages, to be published in the Proceedings of the Fourth
International Workshop on Theoretical and Phenomenological Aspects of
Underground Physics, Toledo (Spain) September 17-21 199
Invariance Violation Extends the Cosmic Ray Horizon ?
We postulate in the present paper that the energy-momentum relation is
modified for very high energy particles to violate Lorentz invariance and the
speed of photon is changed from the light velocity c. The violation effect is
amplified, in a sensitive way to detection, through the modified kinematical
constraints on the conservation of energy and momentum, in the absorption
process of gamma-rays colliding against photons of longer wavelengths and
converting into an electron-positron pair. For gamma-rays of energies higher
than 10 TeV, the minimum energy of the soft photons for the reaction and then
the absorption mean free path of gamma-rays are altered by orders of magnitude
from the ones conventionally estimated. Consideration is similarly applied to
high energy cosmic ray protons. The consequences may require the standard
assumptions on the maximum distance that very high energy radiation can travel
from to be revised.Comment: 14 pages, 1 figure, to be published in Ap J Letter
Inspecting absorption in the spectra of extra-galactic gamma-ray sources for insight into Lorentz invariance violation
We examine what the absorbed spectra of extra-galactic TeV gamma-ray sources,
such as blazars, would look like in the presence of Lorentz invariance
violation (LIV). Pair-production with the extra-galactic background light
modifies the observed spectra of such sources, and we show that a violation of
Lorentz invariance would generically have a dramatic effect on this absorption
feature. Inspecting this effect, an experimental task likely practical in the
near future, can provide unique insight on the possibility of LIV.Comment: Published in Phys. Rev.
Pre-Big Bang, fundamental Physics and noncyclic cosmologies
Contribution à la conférence ICFP 2012, International Conference on New Frontiers in Physics, Kolymbari, Crete 10-16 juin 2012International audienceDetailed analyses of WMAP and Planck data can have significant implications for noncyclic pre-Big Bang approaches incorporating a new fundamental scale beyond the Planck scale and, potentially, new ultimate constituents of matter with unconventional basic properties as compared to standard particles. Cosmic-ray experiments at the highest energies can also yield relevant information. Hopefully, future studies will be able to deal with alternatives: i) to standard physics for the structure of the physical vacuum, the nature of space-time, the validity of quantum field theory and conventional symmetries, the interpretation of string-like theories...; ii) to standard cosmology concerning the origin and evolution of our Universe, unconventional solutions to the cosmological constant problem, the validity of inflationary scenarios, the need for dark matter and dark energy... Lorentz-like symmetries for the properties of matter can then be naturally stable space-time configurations resulting from more general primordial scenarios that incorporate physics beyond the Planck scale and describe the formation and evolution of the physical vacuum. A possible answer to the question of the origin of half-integer spins can be provided by a primordial spinorial space-time with two complex coordinates instead of the conventional four real ones, leading to a really new cosmology. We discuss basic questions and phenomenological topics concerning noncyclic pre-Big Bang cosmologies and potentially related physics. (Contribution to the International Conference on New Frontiers in Physics, ICFP 2012, Kolymbari, Crete, June 10-16 2012
Self-consistency in Theories with a Minimal Length
The aim of this paper is to clarify the relation between three different
approaches of theories with a minimal length scale: A modification of the
Lorentz-group in the 'Deformed Special Relativity', theories with a
'Generalized Uncertainty Principle' and those with 'Modified Dispersion
Relations'. It is shown that the first two are equivalent, how they can be
translated into each other, and how the third can be obtained from them. An
adequate theory with a minimal length scale requires all three features to be
present.Comment: typos corrected, published with new title following referee's advic
Lorentz violation and Crab synchrotron emission: a new constraint far beyond the Planck scale
Special relativity asserts that physical phenomena appear the same for all
inertially moving observers. This symmetry, called Lorentz symmetry, relates
long wavelengths to short ones: if the symmetry is exact it implies that
spacetime must look the same at all length scales. Several approaches to
quantum gravity, however, suggest that there may be a Lorentz violating
microscopic structure of spacetime, for example discreteness,
non-commutativity, or extra dimensions. Here we determine a very strong
constraint on a type of Lorentz violation that produces a maximum electron
speed less than the speed of light. We use the observation of 100 MeV
synchrotron radiation from the Crab nebula to improve the previous limits by a
factor of 40 million, ruling out this type of Lorentz violation, and thereby
providing an important constraint on theories of quantum gravity.Comment: 12 pages. Presentation shortened and revised for letter to Nature.
New title "A strong astrophysical constraint on the violation of special
relativity by quantum gravity". Maximum observed synchrotron frequency
lowered, resulting in weakening the constraint from E_QG>4.5*10^27 GeV to
E_QG>10^26 GeV. The role of the effective field theory assumptions underlying
the analysis is highlighte
GRBs Neutrinos as a Tool to Explore Quantum Gravity induced Lorentz Violation
Lorentz Invariance Violation (LIV) arises in various quantum-gravity
theories. As the typical energy for quantum gravity is the Planck mass,
, LIV will, most likely, be manifested at very high energies that are
not accessible on Earth in the foreseeable future. One has to turn to
astronomical observations. Time of flight measurement from different
astronomical sources set current limits on the energy scale of possible LIV to
(for n=1 models) and (for n=2). According to
current models Gamma-Ray Bursts (GRBs) are accompanied by bursts of high energy
(\gsim 100TeV) neutrinos. At this energy range the background level of
currently constructed neutrino detectors is so low that a detection of a single
neutrino from the direction of a GRB months or even years after the burst would
imply an association of the neutrino with the burst and will establish a
measurement of a time of flight delay. Such time of flight measurements provide
the best way to observe (or set limits) on LIV. Detection of a single GRB
neutrino would open a new window on LIV and would improve current limits by
many orders of magnitude
Studies of Prototype CsI(Tl) Crystal Scintillators for Low-Energy Neutrino Experiments
Crystal scintillators provide potential merits for the pursuit of low-energy
low-background experiments. A CsI(Tl) scintillating crystal detector is being
constructed to study low-energy neutrino physics at a nuclear reactor, while
projects are underway to adopt this technique for dark matter searches. The
choice of the geometrical parameters of the crystal modules, as well as the
optimization of the read-out scheme, are the results of an R&D program.
Crystals with 40 cm in length were developed. The detector requirements and the
achieved performance of the prototypes are presented. Future prospects for this
technique are discussed.Comment: 32 pages, 14 figure
High-Energy gamma-ray Astronomy and String Theory
There have been observations, first from the MAGIC Telescope (July 2005) and
quite recently (September 2008) from the FERMI Satellite Telescope, on
non-simultaneous arrival of high-energy photons from distant celestial sources.
In each case, the highest energy photons were delayed, as compared to their
lower-energy counterparts. Although the astrophysics at the source of these
energetic photons is still not understood, and such non simultaneous arrival
might be due to non simultaneous emission as a result of conventional physics
effects, nevertheless, rather surprisingly, the observed time delays can also
fit excellently some scenarios in quantum gravity, predicting Lorentz violating
space-time "foam" backgrounds with a non-trivial subluminal vacuum refractive
index suppressed linearly by a quantum gravity scale of the order of the
reduced Planck mass. In this pedagogical talk, I discuss the MAGIC and FERMI
findings in this context and I argue on a theoretical model of space-time foam
in string/brane theory that can accommodate the findings of those experiments
in agreement with all other stringent tests of Lorentz invariance. However, I
stress the current ambiguities/uncertainties on the source mechanisms, which
need to be resolved first before definite conclusions are reached regarding
quantum gravity foam scenarios.Comment: 34 pages latex, 12 eps figures incorporated, uses special macros.
Based on invited plenary talk at DICE 2008 Conference (Castiglioncello,
Italy), September 22-26 200
Sources and sinks of nutrients and pollutants in Cullera Bay
[EN] Water quality plays a very important role in the ecological balance and economic development of coastal and estuarine areas. However, these areas have been progressively degraded in recent decades due to different factors, including an increase in nutrient and pollutant loads introduced into the system, which may cause eutrophication problems. This paper analyzes the water quality of one such area, Cullera Bay, located on the Spanish Mediterranean coast. This study focuses on the main sources and sinks of pollutant substances and the relationship between the distribution of these substances within the bay and local meteorological and oceanographic conditions. Two main sources of nutrients and pollutants were identified: the discharges of the Júcar River and the marine outfall, although other secondary sources are also present. The river discharge varies greatly depending on the season. The freshwater it carries is very rich in nutrients due to the presence of fertilizers and pesticides from its agricultural use. The domestic wastewater discharged through the marine outfall is occasionally untreated, particularly in the summer, when the tourist population increases and the capacity of the water treatment plant is exceeded. This study is based on data recorded during nine field campaigns carried out in the area in 2002 and 2003 and numerical simulations of hydrodynamics and pollutant dispersion. By analyzing the field data and the numerical simulation results, wind is identified as the main driving factor in the bay because the other possible driving factors either have negligible effects (tide), affect only a very localized area (waves, usual river discharges) or are infrequent (storm surges, river floods).The European Community funded this study as a part of the ECOSUD ‘‘Estuaries and Coastal Areas. Basis and Tools
for a More Sustainable Development’’ (reference no. ICA4-CT-2001-10027) and AQUAS ‘‘Water quality and sustainable
aquaculture. Links and implications’’ (reference no. INCOCT-2005-015105) projects. It was also funded by the Spanish
Ministry of Science and Technology, through the project ‘‘Desarrollo y optimizacio´n de te´cnicas para gestionar los vertidos
de aguas residuales de emisarios submarinos (ARTEMISA)’’(Reference no. REN2003-07585-C02-01/MAR).Sierra, J.; Mösso, C.; González Del Rio Rams, J.; Mestres, M.; Cupul, L.; Sánchez-Arcilla, A.; Rodilla Alamá, M.... (2007). Sources and sinks of nutrients and pollutants in Cullera Bay. Journal of Coastal Research. SI47:31-39. doi:10.2112/1551-5036-47.sp1.31S3139SI4
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