One-loop effective scalar-tensor gravity

Non-minimal interactions are proven to be generated at the one-loop level in simple scalar-tensor gravity models. The John interaction from the Fab Four class is generated. The interaction affects the speed of gravitational waves in the contemporary Universe. Its role in low-energy phenomenology is discussed. Brans-Dicke-like interaction is generated in a non-minimal model. An opportunity to generate a dynamic low-energy Newton constant is addressed.Comment: Accepted to EPJ

Conformally Coupled General Relativity

Gravity model developed in the series of papers \cite{Arbuzov:2009zza,Arbuzov:2010fz,Pervushin:2011gz} is revisited. Model is based on Ogievetsky theorem that specifies structure of general coordinate transformation group. The theorem is implemented in the context of Noether theorem with the use of nonlinear representation technique. Canonical quantization is performed with the use of reparametrization-invariant time and ADM foliation techniques. Basic quantum features of the models are discussed. Mistakes occurred in the previous papers are corrected.Comment: 20 page

Effective theories of gravity

This thesis is devoted to the study of effective field theory methods for gravitational interactions. Effective field theories were developed in the context of particle physics. They provide a consistent framework to study low energy effects of some high energy fundamental theory. Applying these methods to quantum general relativity enables one to do calculations for processes taking place at energies below the Planck mass without a detailed knowledge of the ultra-violet complete theory of quantum gravity. Four related topics are considered in this thesis. We first study effects of quantum gravity in particle physics interactions. In particular, we focus on non-local operators involving fields of the standard model generated by quantum gravity. Bounds on the magnitude of the Wilson coefficients of non-local four fermion interactions are established. Secondly, we calculate the production rate of gravitational waves by binary systems using effective field theory methods. New massive gravitational modes, beyond the massless graviton, appear in the low energy spectrum of the quantum gravitational effctive field theory. These modes could be generated in binary inspirals. The third direction consists in a study of dark matter candidates within this effective gravity. The non-local operators generated by quantum gravitational interactions lead to new poles in the graviton propagator. These poles describe states with a non-vanishing decay widths. These states may contribute to the contemporary dark matter content provided that their lifetime is comparable with the current age of our universe. Correspondent constraints on the dark matter candidates are established. The last question addressed in this thesis consists in an implementation of effective field theory techniques to modified gravity models. One of the simplest stable extensions of general relativity is studied. The new interaction lying beyond general relativity significantly changes the correspondent effective theory. Implications of our results for gravitational interactions are discussed

Scalaron Decay in Perturbative Quantum Gravity

A certain quadratic gravity model provides a successfully inflationary scenario. The inflation is driven by the new scalar degree of freedom called scalaron. After the end of inflation the scalaron decays in matter and dark matter degrees of freedom reheating the Universe. We study new channels by which the scalaron can transfer energy to the matter sector. These channels are annihilation and decay via intermediate graviton states. Results are obtained within perturbative quantum gravity. In the heavy scalaron limit only scalar particles are produced by the annihilation channel. Scalaron decays in all types of particles are allowed. In the light scalaron limit decay channel is strongly suppressed. Boson production via the annihilation channel is expected to be dominant at the early stages of reheating, while fermion production will dominate later stages

FeynGrav 2.0

We present a new version of FeynGrav. The present version supports Feynman rules for matter with non-vanishing mass and $SU(N)$ Yang-Mills model. We revisit the gauge fixing procedure for gravity and derive interaction rules valid for an arbitrary gauge fixing parameter. We provide a few simple examples of calculations to illustrate package usage

Black Holes in Einstein-scalar-Gauss-Bonnet model probed with scattering amplitudes

We examined the quantum properties of scalar-tensor gravity with a coupling to the Gauss-Bonnet term, exploring both linear and quadratic couplings. We calculate the leading order corrections to the non-relativistic one-body gravitational potential and the metric studying the external gravitational field of a point-like scalar particle. The light-like scattering was studied and compared with the classical theory. We find that loop corrections are strongly suppressed and cannot significantly affect the black hole shadow for quadratic coupling. The leading order corrections are important for small-angle scattering and can contribute to the formation of the black hole shadow for the case of linear coupling.Comment: 23 pages, 4 figures. New references added in version

FeynGrav and Recent Progress in Computational Perturbative Quantum Gravity

The article reviews recent progress in computational quantum gravity caused by the framework that efficiently computes Feynman's rules. The framework is implemented in the FeynGrav package, which extends the functionality of the widely used FeynCalc package. FeynGrav provides all the tools to study quantum gravitational effects within the standard model. We review the framework, provide the theoretical background for the efficient computation of Feynman rules, and present the proof of its completeness. We review the derivation of Feynman rules for general relativity, Horndeski gravity, Dirac fermions, Proca field, electromagnetic field, and SU(N) Yang-Mills model. We conclude with a discussion of the current state of the FeynGrav package and discuss its further development

Massive gravitational waves from black hole inspirals in quantum gravity

We show that alongside the already observed gravitational waves,quantum gravity predicts the existence of two additional massive classical fields and thus two new massive waves. We set a limit on their masses using data from Eöt–Wash–like experiments. We point out that the existence of these new states is a model independent prediction of quantum gravity. We explain how these new classical fields could impact astrophysical processes and in particular the binary inspirals of black holes. We calculate the emission rate of these new states in binary inspirals astrophysical processes