Contrary to general belief, quantum gravity can have important consequences for observations in present day experiments. It can predict parameters of the standard model of particle physics. Functional renormalisation permits the computation of fluctuation effects of the metric. Quantum gravity can be formulated as a non-perturbatively renormalisable quantum field theory, in close analogy to...

Over the past several years, a foremost development in cosmology has been the rise of the so-called Hubble tension. This refers to the disagreement between the measurements of the expansion rate of the universe - the Hubble constant (H0). Direct measurements of H0 using the astronomical "distance ladder" find H0 of about 67 km/s/Mpc, while the analysis of the cosmic microwave background...

We consider the charged massless Dirac fields in the background of $4$-dimensional Einstein-Born-Infeld dilaton black hole spacetime. We derive the analytical spin-half quasinormal modes, whose Dirac equations are obtained in terms of the hypergeometric functions. The stability analysis of those black holes under the charged Dirac perturbations is also discussed. Obtained results are...

General relativity (GR), i.e. Einstein theory of gravity, is recognized as one of the best physical theories -- with nice theoretical properties and significant phenomenological confirmations. Nevertheless, GR is not a complete theory of gravity and there are many attempts to modify it. One of the actual approaches towards more complete theory is nonlocal modified gravity. Nonlocal gravity...

Maxwell's action in vacua is scale-invariant. This causes singularity in the fields and infinite self-energy. By breaking this symmetry one may remove the singularity as well as make the self-energy finite. In the context of the spontaneously broken scale-invariant nonlinear electrodynamic with a magnetic dominance, we introduce black a hole solution.

We study the physical properties of...

Hidden symmetries provide a powerful tool for finding exact solutions in multifield cosmological models. I will show how, using such symmetries, one can find inflationary solutions in two-field models, which lead to the generation of primordial black holes. I will also discuss an exact solution in a two-field cosmological model, which describes dark energy. This solution is obtained with the...

We discuss cosmological perturbations of the scalar type in the spatially flat FRWL background during inflation. There are five independent scalar perturbations. Four of them are perturbations of the FRWL metric and the fifth one represents perturbations of a scalar field. As usual, a scalar field is used to describe dominant (perfect) cosmological fluid responsible for inflation [1].

These...

The DBI Langrangian (or a family of DBI Lagrangians) has been known and widely considered in many different fields of physics.

For instance, classical and quantum dynamics of tachyon systems have been examined, describing spatially homogeneous scalar fields, in the limit of classical and quantum mechanics.

Understanding and modelling of these systems are of particular importance in the...

We study pair production processes from vacuum of scalar particles and fermions in the presence of an external Coulomb field on de Sitter expanding universe assuming that, the quantum fields are minimally coupled with gravity. Our study is done in the chart with spherical space coordinates and the produced particles are described by the spherical wave solutions of the field equations. In this...

Fuzzy dark matter (FDM) is a rapidly growing area of research which aims to alleviate the shortcomings of the current leading cold dark matter (CDM) model. On large cosmic scales, FDM recreates the large scale structure generated by CDM simulations; the two diverge on smaller scales, where CDM suffers the most. Where CDM requires the addition of baryonic feedback and other physics, one of the...

The experimental search of non-conventional effects predicted by bottom-up approaches and theoretical models of quantum gravity is a quite recent field of research. Generically, it requires to consider probes of very high-energy and amplification mechanisms, conditions which are fulfilled by the propagation of the cosmic messengers. Advances in multi-messenger astronomy during the last decade...

We study the first order infrared behavior of "tame" hyperbolizable two-field cosmological models, defined as those classical two-field models whose scalar manifold is a connected, oriented and topologically finite hyperbolizable Riemann surface and whose scalar potential admits a positive and Morse extension to its end compactification. We achieve this by determining the universal forms of...

We introduce the notion of global and local thermodynamic equilibrium for any thermal system with well-defined first law. Our approach relies only on few key concepts, namely: Legendre transformation, Hessian matrices, Nambu brackets and thermodynamic curvature. In the extremal point, every convex (concave) potential must be in its global minimum (maximum). This allows one to impose standard...

Cosmological inflation provides solutions to some problems in standard cosmology. Many different scenarios of inflation have been proposed. The generally accepted and the most commonly used approach is that the inflationary phase can be described by a single scalar field. One of the interesting possible mechanisms for inflation is based on the dynamics driven by the tachyon field $\theta$ [1,...

A nonlocal gravity model

$ S = \frac 1{16\pi G} \int (R-2\Lambda+(R-4\Lambda)\mathcal{F}(\Box)(R-4\Lambda))\sqrt{-g} \mathrm d^4 x $

was recently introduced, and two exact cosmological solutions in flat space were presented.

One solution has similar properties to an interplay between the radiation and the dark energy, while the other one is a nonsingular time symmetric bounce. In this...

In the context of the spontaneously broken scale-invariant nonlinear electrodynamic introduced by Guendlmann et al with a magnetic dominance feature, we construct a thin-shell wormhole. The surface tension of the TSW is zero in static configuration implying the exotic matter present at the throat is a cloud of exotic dust. We apply the small-velocity perturbation as well as the radial linear...