1,317 research outputs found
Modified gravity with terms and cosmic acceleration
The modified gravity with or terms which grow at
small curvature is discussed. It is shown that such a model which has
well-defined newtonian limit may eliminate the need for dark energy and may
provide the current cosmic acceleration. It is demonstrated that terms
are important not only for early time inflation but also to avoid the
instabilities and the linear growth of the gravitational force. It is very
interesting that the condition of no linear growth for gravitational force
coincides with the one for scalar mass in the equivalent scalar-tensor theory
to be very large. Thus, modified gravity with term seems to be viable
classical theory.Comment: LaTeX file, 16 pages, discussion and references are adde
Conformal dynamics of quantum gravity with torsion
The trace anomaly induced dynamics of the conformal factor is investigated in
four-dimensional quantum gravity with torsion. The constraints for the coupling
constants of torsion matter interaction are obtained in the infrared stable
fixed point of the effective scalar theory.Comment: 10 pages, CPTH-A213.1292 -- HUPD-921
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
Instabilities and Anti-Evaporation of Reissner-Nordstr\"om Black Holes in modified gravity
We study the instabilities and related anti-evaporation of the extremal
Reissner-Nordstr\"om (RN) black hole in gravity. It is remarkable that
the effective electric charge can be generated for some solutions of
gravity without electromagnetic field. The anti-evaporation effect occurs but
it emerges only in the strong coupling limit of the effective gravitational
coupling. The instabilities of RN black hole are also investigated when the
electromagnetic sector is added to the action of gravity. We show the
anti-evaporation occurs in the Maxwell- gravity with the arbitrary
gravitational coupling constant although it does not occur in the
Maxwell-Einstein gravity. Furthermore, general spherically-symmetric solution
of gravity in the Einstein frame is obtained.Comment: LaTeX 11 pages, no figure, publication data: Physics Letters B 735,
376-382 (2014
Trace Anomaly Induced Effective Action and Hawking Radiation for 2d Dilatonic Supergravity
We construct the theory of 2d dilatonic supergravity(SG) with matter and
dilaton supermultiplets coupled to dilaton functions. Trace anomaly and induced
effective action for matter supermultiplet are calculated (what gives also
large-N effective action for dilatonic SG). Study of black holes and Hawking
radiation which turns out to be zero in supersymmetric CGHS model with dilaton
coupled matter is presented. In the same way one can study spherically
symmetric collapse for other 4d SG using simplified 2d approach.Comment: LaTeX file, 9 pag
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