arXiv subjects

Milovan Vasilić

Publications and source records attributed to Milovan Vasilić.

5 recordsLinked to original sources

arXiv2018

Searching for MOND in scalar-tensor theories of gravity

In this paper, I study spherically symmetric solutions in a simple class of geometric sigma models of the Universe. This class of models is a subclass of the wider class of scalar-tensor theories of gravity. The purpose of this work is to examine how the additional scalar degree of freedom modifies Newtonian gravitational force. The general solution for spherically symmetric metric far from the point source is obtained in a weak field approximation. As it turns out, it is parametrized by the mass of the source, and an additional function of time. One particular model is examined as an example. It is shown that there are solutions that accommodate MOND regime at some distances from the source. Unfortunately, the obtained interval of distances turns out to be smaller than it is needed. An additional analysis shows that genuine MOND, that explains galactic curves of all nearby galaxies, cannot be obtained.

gr-qc↗

arXiv2017

A class of regular bouncing cosmologies

In this paper, I construct a class of everywhere regular geometric sigma models that possess bouncing solutions. Precisely, I show that every bouncing metric can be made a solution of such a model. My previous attempt to do so by employing one scalar field has failed due to the appearance of harmful singularities near the bounce. In this work, I use four scalar fields to construct a class of geometric sigma models which are free of singularities. The models within the class are parametrized by their background geometries. I prove that, whatever background is chosen, the dynamics of its small perturbations is classically stable on the whole time axes. Contrary to what one expects from the structure of the initial Lagrangian, the physics of background fluctuations is found to carry 2 tensor, 2 vector and 2 scalar degrees of freedom. The graviton mass, that naturally appears in these models, is shown to be several orders of magnitude smaller than its experimental bound. I provide three simple examples to demonstrate how this is done in practice. In particular, I show that graviton mass can be made arbitrarily small.

gr-qc↗

arXiv2017

Pseudo-Riemannian Universe from Euclidean bulk

I develop the idea that our world is a brane-like object embedded in Euclidean bulk. In its ground state, the brane constituent matter is assumed to be homogeneous and isotropic, and of negligible influence on the bulk geometry. The analysis of this paper is model independent, in the sense that action functional of bulk fields is not specified. Instead, the behavior of the brane is derived from the universally valid conservation equation of the bulk stress tensor. The present work studies the behavior of a $3$-sphere in the $5$-dimensional Euclidean bulk. The sphere is made of bulk matter characterized by the equation of state $p=αρ$. It is shown that stability of brane vibrations requires $α< 0$. Then, the stable brane perturbations obey Klein-Gordon-like equation with an effective metric of Minkowski signature. The argument is given that it is this effective metric that is detected in physical measurements. The corresponding effective Universe is analyzed for all the values of $α<0$. In particular, the effective metric is shown to be a solution of Einstein's equations coupled to an effective perfect fluid. The effective energy density and pressure at the present epoch are calculated. So are the age of the Universe, and the effective cosmological constant. All the results are presented in two tables. As an illustration, one simple choice of the brane constituent matter is studied in detail.

gr-qc↗

arXiv2017

Geometric sigma model of the Universe

The purpose of this work is to demonstrate how an arbitrarily chosen background of the Universe can be made a solution of a simple geometric sigma model. Geometric sigma models are purely geometric theories in which spacetime coordinates are seen as scalar fields coupled to gravity. Although they look like ordinary sigma models, they have the peculiarity that their complete matter content can be gauged away. The remaining geometric theory possesses a background solution that is predefined in the process of constructing the theory. The fact that background configuration is specified in advance is another peculiarity of geometric sigma models. In this paper, I construct geometric sigma models based on different background geometries of the Universe. Whatever background geometry is chosen, the dynamics of its small perturbations is shown to posses a generic classical stability. This way, any freely chosen background metric is made a stable solution of a simple model. Three particular models of the Universe are considered as examples of how this is done in practice.

gr-qc↗

arXiv2012

Oscillations of neutrino velocity

In this paper, we consider the problem of quantum measurement of neutrino velocity. We show, that the well known neutrino flavor oscillations are always accompanied by the oscillations of neutrino velocity. In particular, the velocity of a freely moving neutrino is demonstrated to periodically exceed the speed of light. Unfortunately, the superluminal effect turns out to be too small to be experimentally detected. It is also shown that neutrino velocity significantly depends on the energy, size and shape of the neutrino wave packet. Owing to the big experimental error of the recent experiments, these dependences remained unnoticeable. Finally, we have shown that the recent claims that superluminal neutrinos should loose energy during their flight is not true. Instead, our formula suggests the approximate conservation of energy along neutrino trajectory. All these results have been obtained without violation of special theory of relativity.

hep-ph↗