184 research outputs found
Some Remarks on the Semi-Classical Limit of Quantum Gravity
One of the most important issues in quantum gravity is to identify its
semi-classical regime. First the issue is to define for we mean by a
semi-classical theory of quantum gravity, then we would like to use it to
extract physical predictions. Writing an effective theory on a flat background
is a way to address this problem and I explain how the non-commutative
spacetime of deformed special relativity is the natural arena for such
considerations. On the other hand, I discuss how the definition of the
semi-classical regime can be formulated in a background independent fashion in
terms of quantum information and renormalisation of geometry.Comment: 5 pages, Proceedings of the Second International Workshop DICE2004
(Castello di Piombino, Tuscany) "From Decoherence and Emergent Classicality
to Emergent Quantum Mechanics
Lifting SU(2) Spin Networks to Projected Spin Networks
Projected spin network states are the canonical basis of quantum states of
geometry for the most recent EPR-FK spinfoam models for quantum gravity. They
are functionals of both the Lorentz connection and the time normal field. We
analyze in details the map from these projected spin networks to the standard
SU(2) spin networks of loop quantum gravity. We show that this map is not
one-to-one and that the corresponding ambiguity is parameterized by the Immirzi
parameter. We conclude with a comparison of the scalar products between
projected spin networks and SU(2) spin network states.Comment: 14 page
U(N) Coherent States for Loop Quantum Gravity
We investigate the geometry of the space of N-valent SU(2)-intertwiners. We
propose a new set of holomorphic operators acting on this space and a new set
of coherent states which are covariant under U(N) transformations. These states
are labeled by elements of the Grassmannian Gr(N,2), they possess a direct
geometrical interpretation in terms of framed polyhedra and are shown to be
related to the well-known coherent intertwiners.Comment: 23 page
Non-Commutativity of Effective Space-Time Coordinates and the Minimal Length
Considering that a position measurement can effectively involve a
momentum-dependent shift and rescaling of the "true" space-time coordinates, we
construct a set of effective space-time coordinates which are naturally
non-commutative. They lead to a minimum length and are shown to be related to
Snyder's coordinates and the five-dimensional formulation of Deformed Special
Relativity. This effective approach then provides a natural physical
interpretation for both the extra fifth dimension and the deformed momenta
appearing in this context.Comment: 5 page
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