3,652 research outputs found
Testing kappa-Poincare' with neutral kaons
In recent work on experimental tests of quantum-gravity-motivated
phenomenological models, a significant role has been played by the so-called
``'' deformations of Poincar\'e symmetries. Sensitivity to values of
the relevant deformation length as small as has
been achieved in recent analyses comparing the structure of -Poincar\'e
symmetries with data on the gamma rays we detect from distant astrophysical
sources. We investigate violations of CPT symmetry which may be associated with
-Poincar\'e in the physics of the neutral-kaon system. A simple
estimate indicates that experiments on the neutral kaons may actually be more
-sensitive than corresponding astrophysical experiments, and may
already allow to probe values of of order the Planck length.Comment: 9 pages, LaTe
Quantum Measurements and the kappa--Poincare Group
The possible description of the vacuum of quantum gravity through the so
called kappa--Poincare group is analyzed considering some of the consequences
of this symmetry in the path integral formulation of nonrelativistic quantum
theory. This study is carried out with two cases, firstly, a free particle, and
finally, the situation of a particle immersed in a homogeneous gravitational
field. It will be shown that the kappa--Poincare group implies the loss of some
of the basic properties associated to Feynman's path integral. For instance,
loss of the group characteristic related to the time dependence of the
evolution operator, or the breakdown of the composition law for amplitudes of
events occurring successively in time. Additionally some similarities between
the present idea and the so called restricted path integral formalism will be
underlined. These analogies advocate the claim that if the kappa--Poincare
group contains some of the physical information of the quantum gravity vacuum,
then this vacuum could entail decoherence. This last result will also allow us
to consider the possibility of analyzing the continuous measurement problem of
quantum theory from a group--theoretical point of view, but now taking into
account the kappa--Poincare symmetries.Comment: Accepted in General Relativity and Gravitation. Dedicated to Alberto
Garcia on the occasion of his 60th. birthda
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
On the IR/UV mixing and experimental limits on the parameters of canonical noncommutative spacetimes
We investigate some issues that are relevant for the derivation of
experimental limits on the parameters of canonical noncommutative spacetimes.
By analyzing a simple Wess-Zumino-type model in canonical noncommutative
spacetime with soft supersymmetry breaking we explore the implications of
ultraviolet supersymmetry on low-energy phenomenology. The fact that new
physics in the ultraviolet can modify low-energy predictions affects
significantly the derivation of limits on the noncommutativity parameters based
on low-energy data. These are, in an appropriate sense here discussed,
``conditional limits''. We also find that some standard techniques for an
effective low-energy description of theories with non-locality at short
distance scales are only applicable in a regime where theories in canonical
noncommutative spacetime lack any predictivity, because of the strong
sensitivity to unknown UV physics. It appears useful to combine high-energy
data, from astrophysics, with the more readily available low-energy data.Comment: 14 page
Particle Creation from Vacuum by Lorentz Violation
It is shown that the vacuum state in presence of Lorentz violation can be
followed by a particle-full universe that represents the current status of the
universe. In this model the modification in dispersion relation (Lorentz
violation) is picked up representing the regime of quantum gravity. The result
can be interpreted such that the existence of the particles is an evidence for
quantum effects of gravity in the past. It is concluded that only the vacuum
state is sufficient to appear the matter fields spontaneously after the process
of semi-classical analysis.Comment: 9 pages, 2 figure
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
Spectral geometry of -Minkowski space
After recalling Snyder's idea of using vector fields over a smooth manifold
as `coordinates on a noncommutative space', we discuss a two dimensional
toy-model whose `dual' noncommutative coordinates form a Lie algebra: this is
the well known -Minkowski space.
We show how to improve Snyder's idea using the tools of quantum groups and
noncommutative geometry.
We find a natural representation of the coordinate algebra of
-Minkowski as linear operators on an Hilbert space study its `spectral
properties' and discuss how to obtain a Dirac operator for this space.
We describe two Dirac operators. The first is associated with a spectral
triple. We prove that the cyclic integral of M. Dimitrijevic et al. can be
obtained as Dixmier trace associated to this triple. The second Dirac operator
is equivariant for the action of the quantum Euclidean group, but it has
unbounded commutators with the algebra.Comment: 23 pages, expanded versio
Time Uncertainty in Quantum Gravitational Systems
It is generally argued that the combined effect of Heisenberg principle and
general relativity leads to a minimum time uncertainty. Most of the analyses
supporting this conclusion are based on a perturbative approach to
quantization. We consider a simple family of gravitational models, including
the Einstein-Rosen waves, in which the (non-linearized) inclusion of gravity
changes the normalization of time translations by a monotonic energy-dependent
factor. In these circumstances, it is shown that a maximum time resolution
emerges non-perturbatively only if the total energy is bounded. Perturbatively,
however, there always exists a minimum uncertainty in the physical time.Comment: (4 pages, no figures) Accepted for publication in Physical Review
Interplay between curvature and Planck-scale effects in astrophysics and cosmology
Several recent studies have considered the implications for astrophysics and
cosmology of some possible nonclassical properties of spacetime at the Planck
scale. The new effects, such as a Planck-scale-modified energy-momentum
(dispersion) relation, are often inferred from the analysis of some quantum
versions of Minkowski spacetime, and therefore the relevant estimates depend
heavily on the assumption that there could not be significant interplay between
Planck-scale and curvature effects. We here scrutinize this assumption, using
as guidance a quantum version of de Sitter spacetime with known Inonu-Wigner
contraction to a quantum Minkowski spacetime. And we show that, contrary to
common (but unsupported) beliefs, the interplay between Planck-scale and
curvature effects can be significant. Within our illustrative example, in the
Minkowski limit the quantum-geometry deformation parameter is indeed given by
the Planck scale, while in the de Sitter picture the parameter of quantization
of geometry depends both on the Planck scale and the curvature scalar. For the
much-studied case of Planck-scale effects that intervene in the observation of
gamma-ray bursts we can estimate the implications of "quantum spacetime
curvature" within robust simplifying assumptions. For cosmology at the present
stage of the development of the relevant mathematics one cannot go beyond
semiheuristic reasoning, and we here propose a candidate approximate
description of a quantum FRW geometry, obtained by patching together pieces
(with different spacetime curvature) of our quantum de Sitter. This
semiheuristic picture, in spite of its limitations, provides rather robust
evidence that in the early Universe the interplay between Planck-scale and
curvature effects could have been particularly significant.Comment: 26 pages
Lorentz invariance with an invariant energy scale
We propose a modification of special relativity in which a physical energy,
which may be the Planck energy, joins the speed of light as an invariant, in
spite of a complete relativity of inertial frames and agreement with Einstein's
theory at low energies. This is accomplished by a non-linear modification of
the action of the Lorentz group on momentum space, generated by adding a
dilatation to each boost in such a way that the Planck energy remains
invariant. The associated algebra has unmodified structure constants, and we
highlight the similarities between the group action found and a transformation
previously proposed by Fock. We also discuss the resulting modifications of
field theory and suggest a modification of the equivalence principle which
determines how the new theory is embedded in general relativity
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