924 research outputs found
Renormalization group effects in the conformal sector of 4d quantom gravity with matter
We discuss the ``gravitationally dressed'' beta functions in the Gross--Neveu
model interacting with 2d Liouville theory and in gauge theory
interacting with the conformal sector of 4d quantum gravity. Among the effects
that we suggest may feel the gravitational dressing are the minimum of the
effective potential and the running of the gauge coupling.Comment: 7 pages, plain TEX, SISSA 45/94/E
Yang-Mills vacuum structure and quantum gravity
Using renormalization group methods we calculate the derivative expansion of
the effective Lagrangian for a covariantly constant gauge field in curved
spacetime. Curvature affects the vacuum, in particular it could induce phase
transitions between different vacua. We also consider the effect of quantum
fluctuations of the metric , in the context of a renormalizable theory.
In this case the critical curvature depends on the gravi tational coupling
constants.Comment: Latex file, 8 page
Conformal anomaly for dilaton coupled electromagnetic field
The derivation of the conformal anomaly for dilaton coupled electromagnetic
field in curved space is presented. The models of this sort naturally appear in
stringy gravity or after spherical reduction of multidimensional
Einstein-Maxwell theory. It is shown that unlike the case of minimal vector in
curved space or dilaton coupled scalar the anomaly induced effective action
cannot be derived. The reason is the same why anomaly induced effective action
cannot be constructed for interacting theories (like QED) in curved space.Comment: Latex file, 10 page
General dilatonic gravity with an asymptotically free gravitational coupling constant near two dimensions
We study a renormalizable, general theory of dilatonic gravity (with a
kinetic-like term for the dilaton) interacting with scalar matter near two
dimensions. The one-loop effective action and the beta functions for this
general theory are written down. It is proven that the theory possesses a
non-trivial ultraviolet fixed point which yields an asymptotically free
gravitational coupling constant (at ) in this regime.
Moreover, at the fixed point the theory can be cast under the form of a
string-inspired model with free scalar matter. The renormalization of the
Jackiw-Teitelboim model and of lineal gravity in dimensions is
also discussed. We show that these two theories are distinguished at the
quantum level. Finally, fermion-dilatonic gravity near two dimensions is
considered.Comment: LaTeX, 13 pages, no figure
Dark Energy: the equation of state description versus scalar-tensor or modified gravity
Dark energy dynamics of the universe can be achieved by equivalent
mathematical descriptions taking into account generalized fluid equations of
state in General Relativity, scalar-tensor theories or modified F(R) gravity in
Einstein or Jordan frames. The corresponding technique transforming equation of
state description to scalar-tensor or modified gravity is explicitly presented.
We show that such equivalent pictures can be discriminated by matching
solutions with data capable of selecting the true physical frame.Comment: LaTeX file, 10 pages, 3 figures, the fit of two equivalent models
with observational data is added, new reference
Gravitational Phase Transitions in Infrared Quantum Gravity
The conformal anomaly induced sector of four-dimensional quantum gravity
(infrared quantum gravity) ---which has been introduced by Antoniadis and
Mottola--- is here studied on a curved fiducial background. The one-loop
effective potential for the effective conformal factor theory is calculated
with accuracy, including terms linear in the curvature. It is proven that a
curvature induced phase transition can actually take place. An estimation of
the critical curvature for different choices of the parameters of the theory is
given.Comment: 9 pages, LaTeX file, 3 figures (not included), HUPD-92-10, UB-ECM-PF
92/2
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