30 research outputs found
S-matrix for s-wave gravitational scattering
In the s-wave approximation the 4D Einstein gravity with scalar fields can be
reduced to an effective 2D dilaton gravity coupled nonminimally to the matter
fields. We study the leading order (tree level) vertices. The 4-particle matrix
element is calculated explicitly. It is interpreted as scattering with
formation of a virtual black hole state. As one novel feature we predict the
gravitational decay of s-waves.Comment: 9 pages, 1 figure, added clarifying comments in the introduction, the
conclusion, and the virtual black hole sectio
Classical and Quantum Integrability of 2D Dilaton Gravities in Euclidean space
Euclidean dilaton gravity in two dimensions is studied exploiting its
representation as a complexified first order gravity model. All local classical
solutions are obtained. A global discussion reveals that for a given model only
a restricted class of topologies is consistent with the metric and the dilaton.
A particular case of string motivated Liouville gravity is studied in detail.
Path integral quantisation in generic Euclidean dilaton gravity is performed
non-perturbatively by analogy to the Minkowskian case.Comment: 27 p., LaTeX, v2: included new refs. and a footnot
Constraints, gauge symmetries, and noncommutative gravity in two dimensions
After an introduction into the subject we show how one constructs a canonical
formalism in space-time noncommutative theories which allows to define the
notion of first-class constraints and to analyse gauge symmetries. We use this
formalism to perform a noncommutative deformation of two-dimensional string
gravity (also known as Witten black hole).Comment: Based on lectures given at IFSAP-2004 (St.Petersburg), to be
submitted to Theor. Math. Phys., dedicated to Yu.V.Novozhilov on the occasion
of his 80th birthda
Positive specific heat of the quantum corrected dilaton black hole
Path integral quantization of dilaton gravity in two dimensions is applied to
the CGHS model to the first nontrivial order in matter loops. Our approach is
background independent as geometry is integrated out exactly. The result is an
effective shift of the Killing norm: the apparent horizon becomes smaller. The
Hawking temperature which is constant to leading order receives a quantum
correction. As a consequence, the specific heat becomes positive and
proportional to the square of the black hole mass.Comment: 18 pages, JHEP style, 1 eps figure, v2: extended the discussion,
added new formulas for mass change, added three new references (in particular
[35]
Area spectrum in Lorentz covariant loop gravity
We use the manifestly Lorentz covariant canonical formalism to evaluate
eigenvalues of the area operator acting on Wilson lines. To this end we modify
the standard definition of the loop states to make it applicable to the present
case of non-commutative connections. The area operator is diagonalized by using
the usual shift ambiguity in definition of the connection. The eigenvalues are
then expressed through quadratic Casimir operators. No dependence on the
Immirzi parameter appears.Comment: 12 pages, RevTEX; improved layout, typos corrected, references added;
changes in the discussion in sec. IIIB and
Comparison of relativity theories with observer-independent scales of both velocity and length/mass
We consider the two most studied proposals of relativity theories with
observer-independent scales of both velocity and length/mass: the one discussed
by Amelino-Camelia as illustrative example for the original proposal
(gr-qc/0012051) of theories with two relativistic invariants, and an
alternative more recently proposed by Magueijo and Smolin (hep-th/0112090). We
show that these two relativistic theories are much more closely connected than
it would appear on the basis of a naive analysis of their original
formulations. In particular, in spite of adopting a rather different formal
description of the deformed boost generators, they end up assigning the same
dependence of momentum on rapidity, which can be described as the core feature
of these relativistic theories. We show that this observation can be used to
clarify the concepts of particle mass, particle velocity, and
energy-momentum-conservation rules in these theories with two relativistic
invariants.Comment: 21 pages, LaTex. v2: Andrea Procaccini (contributing some results
from hia Laurea thesis) is added to the list of authors and the paper
provides further elements of comparison between DSR1 and DSR2, including the
observation that both lead to the same formula for the dependence of momentum
on rapidit
Dilaton Gravity in Two Dimensions
The study of general two dimensional models of gravity allows to tackle basic
questions of quantum gravity, bypassing important technical complications which
make the treatment in higher dimensions difficult. As the physically important
examples of spherically symmetric Black Holes, together with string inspired
models, belong to this class, valuable knowledge can also be gained for these
systems in the quantum case. In the last decade new insights regarding the
exact quantization of the geometric part of such theories have been obtained.
They allow a systematic quantum field theoretical treatment, also in
interactions with matter, without explicit introduction of a specific classical
background geometry. The present review tries to assemble these results in a
coherent manner, putting them at the same time into the perspective of the
quite large literature on this subject.Comment: 144 pages, 16 figures; v2,v3: added refs. and corrected typos, v4:
added 2 refs. and corrected typos (published version), v5: added note with
some relevant refs., v6: diligent students found still a couple of typos,
added 1 ref., v7: last update from Vienna (a couple of typos), v8: Leipzig
edition (a dozen typos), v9: MIT edition (4 typos, 1 ref.