151 research outputs found
Quantum spacetime and the renormalization group: Progress and visions
The quest for a consistent theory which describes the quantum microstructure
of spacetime seems to require some departure from the paradigms that have been
followed in the construction of quantum theories for the other fundamental
interactions. In this contribution we briefly review two approaches to quantum
gravity, namely, asymptotically safe quantum gravity and tensor models, based
on different theoretical assumptions. Nevertheless, the main goal is to find a
universal continuum limit for such theories and we explain how coarse-graining
techniques should be adapted to each case. Finally, we argue that although
seemingly different, such approaches might be just two sides of the same coin.Comment: 14 pages, 4 figures, Proceedings of "Progress and Visions in Quantum
Theory in View of Gravity: Bridging foundations of physics and mathematics",
Leipzig, 201
One Loop Graviton Self-Energy In A Locally De Sitter Background
The graviton tadpole has recently been computed at two loops in a locally de
Sitter background. We apply intermediate results of this work to exhibit the
graviton self-energy at one loop. This quantity is interesting both to check
the accuracy of the first calculation and to understand the relaxation effect
it reveals. In the former context we show that the self-energy obeys the
appropriate Ward identity. We also show that its flat space limit agrees with
the flat space result obtained by Capper in what should be the same gauge.Comment: 35 pages, plain TeX, 4 Postscript files, uses psfig.sty, revised June
1996 for publication in Physical Review
Covariant Pauli-Villars Regularization of Quantum Gravity at the One Loop Order
We study a regularization of the Pauli-Villars kind of the one loop
gravitational divergences in any dimension. The Pauli-Villars fields are
massive particles coupled to gravity in a covariant and nonminimal way, namely
one real tensor and one complex vector. The gauge is fixed by means of the
unusual gauge-fixing that gives the same effective action as in the context of
the background field method. Indeed, with the background field method it is
simple to see that the regularization effectively works. On the other hand, we
show that in the usual formalism (non background) the regularization cannot
work with each gauge-fixing.In particular, it does not work with the usual one.
Moreover, we show that, under a suitable choice of the Pauli-Villars
coefficients, the terms divergent in the Pauli-Villars masses can be corrected
by the Pauli-Villars fields themselves. In dimension four, there is no need to
add counterterms quadratic in the curvature tensor to the Einstein action
(which would be equivalent to the introduction of new coupling constants). The
technique also works when matter is coupled to gravity. We discuss the possible
consequences of this approach, in particular the renormalization of Newton's
coupling constant and the appearance of two parameters in the effective action,
that seem to have physical implications.Comment: 26 pages, LaTeX, SISSA/ISAS 73/93/E
Cosmological Acceleration from Virtual Gravitons
Intrinsic properties of the space itself and quantum fluctuations of its
geometry are sufficient to provide a mechanism for the acceleration of
cosmological expansion (dark energy effect). Applying
Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy approach to self-consistent
equations of one-loop quantum gravity, we found exact solutions that yield
acceleration. The permanent creation and annihilation of virtual gravitons is
not in exact balance because of the expansion of the Universe. The excess
energy comes from the spontaneous process of graviton creation and is trapped
by the background. It provides the macroscopic quantum effect of cosmic
acceleration.Comment: 6 pages, REVTeX
LC_2 formulation of supergravity
We formulate (N=1, d=11) supergravity in components in light-cone gauge
(LC_2) to order . In this formulation, we use judicious gauge choices
and the associated constraint relations to express the metric, three-form and
gravitino entirely in terms of the physical degrees of freedom in the theory.Comment: 11 page
Scalar-QED \beta-functions near Planck's Scale
The Renormalization Group Flow Equations of the Scalar-QED model near
Planck's scale are computed within the framework of the average effective
action. Exact Flow Equations, corrected by Einstein Gravity, for the running
self-interacting scalar coupling parameter and for the running v.e.v. of
, are computed taking into account threshold effects. Analytic
solutions are given in the infrared and ultraviolet limits.Comment: 19 pp, Latex; typos corrected and references added. To appear in the
Int. J. Mod. Phys.
Strong Coupling Quantum Gravity and Physics beyond the Planck Scale
We propose a renormalization prescription for the Wheeler-DeWitt equation of
(3+1)-dimensional Einstein gravity and also propose a strong coupling expansion
as an approximation scheme to probe quantum geometry at length scales much
smaller than the Planck length. We solve the Wheeler-DeWitt equation to the
second order in the expansion in a class of local solutions and discuss
problems arising in our approach.Comment: 27 pages, LaTeX file. To be published in Phys. Rev.
Cosmological Gravitational Wave in a Gravity with Quadratic Order Curvature Couplings
We present a set of equations describing the cosmological gravitational wave
in a gravity theory with quadratic order gravitational coupling terms which
naturally arise in quantum correction procedures. It is known that the
gravitational wave equation in the gravity theories with a general term
in the action leads to a second order differential equation with the only
correction factor appearing in the damping term. The case for a
term is completely different. The gravitational wave is described by a fourth
order differential equation both in time and space. However, curiously, we find
that the contributions to the background evolution are qualitatively the same
for both terms.Comment: 4 pages, revtex, no figure
Infinities within graviton scattering amplitudes
We present unitarity as a method for determining the infinities present in
graviton scattering amplitudes. The infinities are a combination of IR and UV.
By understanding the soft singularities we may extract the UV infinities and
relate these to counter-terms in the effective action. As an demonstration of
this method we rederive the UV infinities present at one-loop when gravity is
coupled to matter.Comment: revised versio
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