217,423 research outputs found
Dilaton Gravity with a Non-minmally Coupled Scalar Field
We discuss the two-dimensional dilaton gravity with a scalar field as the
source matter. The coupling between the gravity and the scalar, massless, field
is presented in an unusual form. We work out two examples of these couplings
and solutions with black-hole behaviour are discussed and compared with those
found in the literature
Differential Geometrical Formulation of Gauge Theory of Gravity
Differential geometric formulation of quantum gauge theory of gravity is
studied in this paper. The quantum gauge theory of gravity which is proposed in
the references hep-th/0109145 and hep-th/0112062 is formulated completely in
the framework of traditional quantum field theory. In order to study the
relationship between quantum gauge theory of gravity and traditional quantum
gravity which is formulated in curved space, it is important to find the
differential geometric formulation of quantum gauge theory of gravity. We first
give out the correspondence between quantum gauge theory of gravity and
differential geometry. Then we give out differential geometric formulation of
quantum gauge theory of gravity.Comment: 10 pages, no figur
And what if gravity is intrinsically quantic ?
Since the early days of search for a quantum theory of gravity the attempts
have been mostly concentrated on the quantization of an otherwise classical
system. The two most contentious candidate theories of gravity, sting theory
and quantum loop gravity are based on a quantum field theory - the latter is a
quantum field theory of connections on a SU(2) group manifold and former a
quantum field theory in two dimensional spaces. Here we argue that there is a
very close relation between quantum mechanics and gravity. Without gravity
quantum mechanics becomes ambiguous. We consider this observation as the
evidence for an intrinsic relation between these fundamental laws of nature. We
suggest a quantum role and definition for gravity in the context of a quantum
universe, and present a preliminary formulation for gravity in a system with a
finite number of particles.Comment: 8 pages, 1 figure. To appear in the proceedings of the DICE2008
conference, Castiglioncello, Tuscany, Italy, 22-26 Sep. 2008. V2: some typos
remove
The complete spectrum of the area from recoupling theory in loop quantum gravity
We compute the complete spectrum of the area operator in the loop
representation of quantum gravity, using recoupling theory. This result extends
previous derivations, which did not include the ``degenerate'' sector, and
agrees with the recently computed spectrum of the connection-representation
area operator.Comment: typos corrected in eqn.(21). Latex with IOP and epsf styles, 1 figure
(eps postscript file), 12 pages. To appear in Class. Quantum Gra
From Classical To Quantum Gravity: Introduction to Loop Quantum Gravity
We present an introduction to the canonical quantization of gravity performed
in loop quantum gravity, based on lectures held at the 3rd quantum geometry and
quantum gravity school in Zakopane in 2011. A special feature of this
introduction is the inclusion of new proposals for coupling matter to gravity
that can be used to deparametrize the theory, thus making its dynamics more
tractable. The classical and quantum aspects of these new proposals are
explained alongside the standard quantization of vacuum general relativity in
loop quantum gravity.Comment: 56 pages. Contribution to the Proceedings of the 3rd Quantum Geometry
and Quantum Gravity School in Zakopane (2011). v2: Typos corrected, various
small changes in presentation, version as published in Po
Quantum Gravity: Has Spacetime Quantum Properties?
The incompatibility between GR and QM is generally seen as a sufficient
motivation for the development of a theory of Quantum Gravity. If - so a
typical argumentation - QM gives a universally valid basis for the description
of all natural systems, then the gravitational field should have quantum
properties. Together with the arguments against semi-classical theories of
gravity, this leads to a strategy which takes a quantization of GR as the
natural avenue to Quantum Gravity. And a quantization of the gravitational
field would in some sense correspond to a quantization of geometry. Spacetime
would have quantum properties. But, this strategy will only be successful, if
gravity is a fundamental interaction. - What, if gravity is instead an
intrinsically classical phenomenon? Then, if QM is nevertheless fundamentally
valid, gravity can not be a fundamental interaction. An intrinsically classical
gravity in a quantum world would have to be an emergent, induced or residual,
macroscopic effect, caused by other interactions. The gravitational field (as
well as spacetime) would not have any quantum properties. A quantization of GR
would lead to artifacts without any relation to nature. The serious problems of
all approaches to Quantum Gravity that start from a direct quantization of GR
or try to capture the quantum properties of gravity in form of a 'graviton'
dynamics - together with the, meanwhile, rich spectrum of approaches to an
emergent gravity and/or spacetime - make this latter option more and more
interesting for the development of a theory of Quantum Gravity. The most
advanced emergent gravity (and spacetime) scenarios are of an
information-theoretical, quantum-computational type.Comment: 31 page
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