3,750 research outputs found
Kinematical solution of the UHE-cosmic-ray puzzle without a preferred class of inertial observers
Among the possible explanations for the puzzling observations of cosmic rays
above the GZK cutoff there is growing interest in the ones that represent
kinematical solutions, based either on general formulations of particle physics
with small violations of Lorentz symmetry or on a quantum-gravity-motivated
scheme for the breakup of Lorentz symmetry. An unappealing aspect of these
cosmic-ray-puzzle solutions is that they require the existence of a preferred
class of inertial observers. Here I propose a new kinematical solution of the
cosmic-ray puzzle, which does not require the existence of a preferred class of
inertial observers. My proposal is a new example of a type of relativistic
theories, the so-called "doubly-special-relativity" theories, which have
already been studied extensively over the last two years. The core ingredient
of the proposal is a deformation of Lorentz transformations in which also the
Planck scale (in addition to the speed-of-light scale ) is described
as an invariant. Just like the introduction of the invariant requires a
deformation of the Galileian transformations into the Lorentz transformations,
the introduction of the invariant requires a deformation of the Lorentz
transformations, but there is no special class of inertial observers. The
Pierre Auger Observatory and the GLAST space telescope should play a key role
in future developments of these investigations. I also emphasize that the
doubly-special-relativity theory here proposed, besides being the first one to
provide a solution for the cosmic-ray puzzle, is also the first one in which a
natural description of macroscopic bodies is achieved, and may find
applications in the context of a recently-proposed dark-energy scenario.Comment: LaTex (revtex), 9 page
Observers and Measurements in Noncommutative Spacetimes
We propose a "Copenhagen interpretation" for spacetime noncommutativity. The
goal is to be able to predict results of simple experiments involving signal
propagation directly from commutation relations. A model predicting an energy
dependence of the speed of photons of the order E/E_Planck is discussed in
detail. Such effects can be detectable by the GLAST telescope, to be launched
in 2006.Comment: 10 pp; v2: equivalence of observers explicitely stated; v3: minor
changes, references and remarks added, burst spreading with energy emphasized
as a signature rather than nois
About Locality and the Relativity Principle Beyond Special Relativity
Locality of interactions is an essential ingredient of Special Relativity.
Recently, a new framework under the name of relative locality
\cite{AmelinoCamelia:2011bm} has been proposed as a way to consider Planckian
modifications of the relativistic dynamics of particles. We note in this paper
that the loss of absolute locality is a general feature of theories beyond
Special Relativity with an implementation of a relativity principle. We give an
explicit construction of such an implementation and compare it both with the
previously mentioned framework of relative locality and the so-called Doubly
Special Relativity theories.Comment: 10 pages, no figure
Kappa - Poincare dispersion relations and the black hole radiation
Following the methods developed by Corley and Jacobson, we consider
qualitatively the issue of Hawking radiation in the case when the dispersion
relation is dictated by quantum kappa-Poincare algebra. This relation
corresponds to field equations that are non-local in time, and, depending on
the sign of the parameter kappa, to sub- or superluminal signal propagation. We
also derive the conserved inner product, that can be used to count modes, and
therefore to obtain the spectrum of black hole radiation in this case.Comment: 11 pages, 2 figure
Quantum Gravity - Testing Time for Theories
The extreme smallness of both the Planck length, on the one side, and the
ratio of the gravitational to the electrical forces between, say, two
electrons, on the other side has led to a widespread belief that the realm of
quantum gravity is beyond terrestrial experiments. A series of classical and
quantum arguments are put forward to dispel this view. It is concluded that
whereas the smallness of the Planck length and the ratio of gravitational to
electrical forces, does play its own essential role in nature, it does not make
quantum gravity a science where humans cannot venture to probe her secrets. In
particular attention is drawn to the latest neutron and atomic interferometry
experiments, and to gravity wave interferometers. The latter, as Giovanni
Amelino-Camelia argues [Nature 398, 216 (1999)], can be treated as probes of
space-time fuzziness down to Planck length for certain quantum-gravity models
A bound on Planck-scale modifications of the energy-momentum composition rule from atomic interferometry
High sensitivity measurements in atomic spectroscopy were recently used in
Amelino-Camelia et. al. to constraint the form of possible modifications of the
energy-momentum dispersion relation resulting from Lorentz invariance violation
(LIV). In this letter we show that the same data can be used successfully to
set experimental bounds on deformations of the energy-momentum composition
rule. Such modifications are natural in models of deformed Lorentz symmetry
which are relevant in certain quantum gravity scenarios. We find the bound for
the deformation parameter to be a few orders of magnitude below the
Planck scale and of the same magnitude as the next-to-leading order effect
found in Amelino-Camelia et. al. We briefly discuss how it would be possible to
distinguish between these two scenarios.Comment: 5 pages, some comments and references adde
Large-scale non-locality in "doubly special relativity" with an energy-dependent speed of light
There are two major alternatives for violating the (usual) Lorentz invariance
at large (Planckian) energies or momenta - either not all inertial frames (in
the Planck regime) are equivalent (e.g., there is an effectively preferred
frame) or the transformations from one frame to another are (non-linearly)
deformed (``doubly special relativity''). We demonstrate that the natural (and
reasonable) assumption of an energy-dependent speed of light in the latter
method goes along with violations of locality/separability (and even
translational invariance) on macroscopic scales.
PACS: 03.30.+p, 11.30.Cp, 04.60.-m, 04.50.+h.Comment: 5 pages RevTeX, several modification
Distance Measurement and Wave Dispersion in a Liouville-String Approach to Quantum Gravity
Within a Liouville approach to non-critical string theory, we discuss
space-time foam effects on the propagation of low-energy particles. We find an
induced frequency-dependent dispersion in the propagation of a wave packet, and
observe that this would affect the outcome of measurements involving low-energy
particles as probes. In particular, the maximum possible order of magnitude of
the space-time foam effects would give rise to an error in the measurement of
distance comparable to that independently obtained in some recent heuristic
quantum-gravity analyses. We also briefly compare these error estimates with
the precision of astrophysical measurements.Comment: 20 pages, LaTe
Threshold configurations in the presence of Lorentz violating dispersion relations
A general characterization of lower and upper threshold configurations for
two particle reactions is determined under the assumptions that the single
particle dispersion relations E(p) are rotationally invariant and monotonic in
p, and that energy and momentum are conserved and additive for multiple
particles. It is found that at a threshold the final particle momenta are
always parallel and the initial momenta are always anti-parallel. The
occurrence of new phenomena not occurring in a Lorentz invariant setting, such
as upper thresholds and asymmetric pair production thresholds, is explained,
and an illustrative example is given.Comment: 5 pages, 3 figure
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