No Arabic abstract
We discuss generic properties of classical and quantum theories of gravity with a scalar field which are revealed at the vicinity of the cosmological singularity. When the potential of the scalar field is exponential and unbounded from below, the general solution of the Einstein equations has quasi-isotropic asymptotics near the singularity instead of the usual anisotropic Belinskii - Khalatnikov - Lifshitz (BKL) asymptotics. Depending on the strength of scalar field potential, there exist two phases of quantum gravity with scalar field: one with essentially anisotropic behavior of field correlation functions near the cosmological singularity, and another with quasi-isotropic behavior. The ``phase transition between the two phases is interpreted as the condensation of gravitons.
We discuss the asymptotic form of the static axially symmetric, globally regular and black hole solutions, obtained recently in Einstein-Yang-Mills and Einstein-Yang-Mills-dilaton theory.
In this work we show that Einstein gravity in four dimensions can be consistently obtained from the compactification of a generic higher curvature Lovelock theory in dimension $D=4+p$, being $pgeq1$. The compactification is performed on a direct product space $mathcal{M}_D=mathcal{M}_4timesmathcal{K}^p$, where $mathcal{K}^p$ is a Euclidean internal manifold of constant curvature. The process is carried out in such a way that no fine tuning between the coupling constants is needed. The compactification requires to dress the internal manifold with the flux of suitable $p$-forms whose field strengths are proportional to the volume form of the internal space. We explicitly compactify Einstein-Gauss-Bonnet theory from dimension six to Einstein theory in dimension four and sketch out a similar procedure for this compactification to take place starting from dimension five. Several black string/p-branes solutions are constructed, among which, a five dimensional asymptotically flat black string composed of a Schwarzschild black hole on the brane is particularly interesting. Finally, the thermodynamic of the solutions is described and we find that the consistent compactification modifies the entropy by including a constant term, which may induce a departure from the usual behavior of the Hawking-Page phase transition. New scenarios are possible in which large black holes dominate the canonical ensamble for all temperatures above the minimal value.
Recently it has been shown that infrared divergences in the conventional S-matrix elements of gauge and gravitational theories arise from a violation of the conservation laws associated with large gauge symmetries. These infrared divergences can be cured by using the Faddeev-Kulish (FK) asymptotic states as the basis for S-matrix elements. Motivated by this connection, we study the action of BMS supertranslations on the FK asymptotic states of perturbative quantum gravity. We compute the BMS charge of the FK states and show that it characterizes the superselection sector to which the state belongs. Conservation of the BMS charge then implies that there is no transition between different superselection sectors, hence showing that the FK graviton clouds implement the necessary vacuum transition induced by the scattering process.
After a brief exposition of the simplest class of affine theories of gravity in multidimensional space-times with symmetric connections, we consider the spherical and cylindrical reductions of these theories to two-dimensional dilaton-vecton gravity (DVG) field theories. The distinctive feature of these theories is the presence of a massive/tachyonic vector field (vecton) with essentially nonlinear coupling to the dilaton gravity. In the massless limit, the classical DVG theory can be exactly solved for a rather general coupling depending only on the field tensor and the dilaton. We show that the vecton field can be consistently replaced by a new effectively massive scalar field (scalaron) with an unusual coupling to dilaton gravity (DSG). Then we concentrate on considering the DVG models derived by reductions of D=3 and D=4 affine theories. In particular, we introduce the most general cylindrical reductions that are often ignored. The main subject of our study is the static solutions with horizons. We formulate the general conditions for the existence of the regular horizons and find the solutions of the static DVG/DSG near the horizons in the form of locally convergent power - series expansion. For an arbitrary regular horizon, we find a local generalization of the Szekeres - Kruskal coordinates. Finally, we consider one-dimensional integrable and nonintegrable DSG theories with one scalar. We analyze simplest models having three or two integrals of motion, respectively, and introduce the idea of a `topological portrait giving a unified qualitative description of static and cosmological solutions of some simple DSG models.
We performed the renormalization group analysis of the quantum Einstein gravity in the deep infrared regime for different types of extensions of the model. It is shown that an attractive infrared point exists in the broken symmetric phase of the model. It is also shown that due to the Gaussian fixed point the IR critical exponent $ u$ of the correlation length is 1/2. However, there exists a certain extension of the model which gives finite correlation length in the broken symmetric phase. It typically appears in case of models possessing a first order phase transitions as is demonstrated on the example of the scalar field theory with a Coleman-Weinberg potential.