117 research outputs found
Quantum Cosmology from \cal{N} = 4 Super Yang - Mills Theory
We consider quantum \cal{N} = 4 super Yang-Mills theory interacting in a
covariant way with \cal{N} = 4 conformal supergravity. The induced large N
effective action for such a theory is calculated on a dilaton-gravitational
background using the conformal anomaly found via AdS/CFT correspondence.
Considering such an effective action as a quantum correction to the classical
gravity action we study quantum cosmology. In particular, the effect from
dilaton to the scale factor (which without dilaton corresponds to the
inflationary universe) is investigated. It is shown that, dependent on the
initial conditions for the dilaton, the dilaton may slow down, or accelerate,
the inflation process. At late times, the dilaton is decaying exponentially.Comment: 8 pages, LaTex, no figure
2D Dilaton-Maxwell Gravity as a Fixed Point of the Renormalization Group
A general model of dialton-Maxwell gravity in two dimensions is investigated.
The corresponding one-loop effective action and the generalized
-functions are obtained. A set of models that are fixed points of the
renormalization group equations are presented.Comment: 7 pages, LaTeX file, UB-ECM-PF 92/Mar1
DILATONIC GRAVITY NEAR TWO DIMENSIONS AND ASYMPTOTIC FREEDOM OF THE GRAVITATIONAL COUPLING CONSTANT
Two models of dilatonic gravity are investigated: (i) dilaton-Yang-Mills
gravity and (ii) higher-derivative dilatonic gravity. Both are renormalizable
in dimensions and have a smooth limit for . The corresponding one-loop effective actions and beta-functions are found.
Both theories are shown to possess a non-trivial ultraviolet fixed point ---for
all dilatonic couplings--- in which the gravitational constant is
asymptotically free. It is shown that in the regime of asymptotic freedom the
matter central charge can be significantly increased by two different
mechanisms ---as compared with pure dilatonic gravity, where .Comment: LaTeX, 10 pages, no figure
One-Loop Renormalization of Higher-Derivative 2D Dilaton Gravity
A theory of higher-derivative 2D dilaton gravity which has its roots in the
massive higher-spin mode dynamics of string theory is suggested. The
divergences of the effective action to one-loop are calculated, both in the
covariant and in the conformal gauge. Some technical problems which appear in
the calculations are discussed. An interpretation of the theory as a particular
D=2 higher-derivative -model is given. For a specific case of
higher-derivative 2D dilaton gravity, which is one loop multiplicatively
renormalizable, static configurations corresponding to black holes are shown to
exist.Comment: 12 pages, LaTeX fil
Renormalization-Group Improved Effective Potential for Finite Grand Unified Theories in Curved Spacetime
The renormalization-group improved effective potential ---to leading-log and
in the linear curvature approximation--- is constructed for ``finite'' theories
in curved spacetime. It is not trivial and displays a quite interesting,
exponential-like structure ---in contrast with the case of flat spacetime where
it coincides with the classical potential. Several possible cosmological
applications, as curvature-induced phase transitions and modifications of the
values of the gravitational and cosmological constants, are briefly discussed.Comment: 10 pages, LaTeX file, UB-ECM-PF 94/
The Effective Action in Gauged Supergravity on Hyperbolic Background and Induced Cosmological Constant
The one-loop effective action for 4-dimensional gauged supergravity with
negative cosmological constant, is investigated in space-times with compact
hyperbolic spatial section. The explicit expansion of the effective action as a
power series of the curvature on hyperbolic background is derived, making use
of heat-kernel and zeta-regularization techniques. The induced cosmological and
Newton constants are computed.Comment: 9 pages, UTF 23
One Loop Counterterms in 2D Dilaton-Maxwell Quantum Gravity
The renormalization structure of two-dimensional quantum gravity is
investigated, in a covariant gauge. One-loop divergences of the effective
action are calculated. All the surface divergent terms are taken into account,
thus completing previous one-loop calculations of the theory. It is shown that
the on-shell effective action contains only surface divergences. The off-shell
renormalizability of the theory is discussed and classes of renormalizable
dilaton and Maxwell potentials are found.Comment: 9 pages, LaTeX file, HUPD-92-1
Mellin-Barnes Representation for the Genus-g Finite Temperature String Theory
The Mellin-Barnes representation for the free energy of the genus- string
is constructed. It is shown that the interactions of the open bosonic string do
not modify the critical (Hagedorn) temperature. However,for the sectors having
a spinor structure, the critical temperature exists also for all and
depends on the windings. The appearance of a periodic structure is briefly
discussed.Comment: 9 pages, report UTF 294 (1993
A Novel Representation for the Free Energy in String Theory at Non-Zero Temperature
A novel representation ---in terms of a Laurent series--- for the free energy
of string theory at non-zero temperature is constructed. The examples of open
bosonic, open supersymmetric and closed bosonic strings are studied in detail.
In all these cases the Laurent series representation for the free energy is
obtained explicitly.
It is shown that the Hagedorn temperature arises in this formalism as the
convergence condition (specifically, the radius of convergence) of the
corresponding Laurent series. Some prospects for further applications are also
discussed. In particular, an attempt to describe string theory above the
Hagedorn temperature ---via Borel analytical continuation of the Laurent series
representation--- is provided.Comment: 21 pages, LaTeX file, HUPD-92-12, UB-ECM-PF 92/25, UFT 273-9
Induced wormholes due to quantum effects of spherically reduced matter in large N approximation
Using one-loop effective action in large N and s-wave approximation we
discuss the possibility to induce primordial wormholes at the early Universe.
An analytical solution is found for self-consistent primordial wormhole with
constant radius. Numerical study gives the wormhole solution with increasing
throat radius and increasing red-shift function. There is also some indication
to the possibility of a topological phase transition.Comment: LaTeX file, 2 eps figures, 9 pages, few misprints are corrected,
numerics are change
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