6,516 research outputs found
Quantum gravity and minimum length
The existence of a fundamental scale, a lower bound to any output of a
position measurement, seems to be a model-independent feature of quantum
gravity. In fact, different approaches to this theory lead to this result. The
key ingredients for the appearance of this minimum length are quantum
mechanics, special relativity and general relativity. As a consequence,
classical notions such as causality or distance between events cannot be
expected to be applicable at this scale. They must be replaced by some other,
yet unknown, structure.Comment: 23 pages, RevTeX, few minor changes, published versio
Quantum wormholes and harmonic oscillators
The quantum state of a wormhole can be represented by a path integral over all asymptotically Euclidean four-geometries and all matter fields which have prescribed values, the arguments of the wave function, on a three-surface which divides the space time manifold into two disconnected parts. Minisuperspace models which consist of a homogeneous massless scalar field coupled to a Friedmann-Robertson-Walker space time are considered. Once the path integral over the lapse function is performed, the requirement that the space time be asymptotically Euclidean can be accomplished by fixing the asymptotic gravitational momentum in the remaining path integral. It is argued that there does not exist any wave function which corresponds to asymptotic field configurations such that the effective gravitational constant is negative in the asymptotic region. Then, the wormhole wave functions can be written as linear combinations of harmonic oscillator wave functions
The local degrees of freedom of higher dimensional pure Chern-Simons theories
The canonical structure of higher dimensional pure Chern-Simons theories is
analysed. It is shown that these theories have generically a non-vanishing
number of local degrees of freedom, even though they are obtained by means of a
topological construction. This number of local degrees of freedom is computed
as a function of the spacetime dimension and the dimension of the gauge group.Comment: 9 pages, RevTeX3.0 (LaTeX2.09), no figure
Quantum Non-Gravity and Stellar Collapse
Observational indications combined with analyses of analogue and emergent
gravity in condensed matter systems support the possibility that there might be
two distinct energy scales related to quantum gravity: the scale that sets the
onset of quantum gravitational effects (related to the Planck scale) and
the much higher scale signalling the breaking of Lorentz symmetry. We
suggest a natural interpretation for these two scales: is the energy
scale below which a special relativistic spacetime emerges, is the scale
below which this spacetime geometry becomes curved. This implies that the first
`quantum' gravitational effect around could simply be that gravity is
progressively switched off, leaving an effective Minkowski quantum field theory
up to much higher energies of the order of . This scenario may have
important consequences for gravitational collapse, inasmuch as it opens up new
possibilities for the final state of stellar collapse other than an evaporating
black hole.Comment: 6 pages, 2 figures. v2: Partially restructured; potentially
observable consequence added. Several clarifications + 3 new references. To
appear in Found. of Phy
Models of relativistic particle with curvature and torsion revisited
Models, describing relativistic particles, where Lagrangian densities depend
linearly on both the curvature and the torsion of the trajectories, are
revisited in D=3 space forms. The moduli spaces of trajectories are completely
and explicitly determined using the Lancret program. The moduli subspaces of
closed solitons in the three sphere are also determined.Comment: 13 page
Some not-so-common ideas about gravity
Most of the approaches to the construction of a theory of quantum gravity
share some principles which do not have specific experimental support up to
date. Two of these principles are relevant for our discussion: (i) the
gravitational field should have a quantum description in certain regime, and
(ii) any theory of gravity containing general relativity should be relational.
We study in general terms the possible implications of assuming deviations from
these principles, their compatibility with current experimental knowledge, and
how can they affect future experiments.Comment: 12 pages (+ references). Invited talk at DICE2014, Castiglioncello,
September 201
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