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Janusz Garecki

Publications and source records attributed to Janusz Garecki.

At least 19 recordsLinked to original sources
arXiv2021

Riemannian Structure imposed on Friedmann and more general spacetimes

In the paper we consider two Finsler-like Riemannian metrics, which can be in a natural way introduced into general relativity. One of those metrics $γ_{ab}$ is degenerate and the second $h_{ab}$ is nondegenerate. We are mainly interested with the metric $h_{ab}$ and comparing the geometric structure determined by this metric $h_{ab}$ with the geometric structure determined by the Lorentzian metric $g_{ab}$ of the underlying spacetime. Full comparison we have given for Friedmann Universis. The preliminary version of the paper was presented by one of us (J.G.) on conference POTOR 6 in Szczecin 2019. We think that the our introduction of the Riemannian metric $h_{ab}$ into spacetime is simpler and more general than to so-called Wick rotation.

physics.gen-ph↗
arXiv2019

General relativity with a positive cosmological constant $λ$ as a gauge theory

In the paper we show that the general relativity action (and Lagrangian) in recent Einstein-Palatini formulation is equivalent to the action (and Langrangian) of a gauge field. We begin with a bit of information of the Einstein-Palatini (EP) action, then we present how Einstein fields equations can be derived from it. In the next section, we consider Einstein-Palatini action integral for general relativity with a positive cosmological constant $Λ$ in terms of $\hat{F}$, the curvature of the affine connection's pulled back from de Sitter bundle to Lorentz bundle. We will see that in terms of $\hat{F}$ this action takes the form typical for a gauge field. Finally, we give a geometrical interpretation of the curvature $\hat{F}$.

gr-qc↗
arXiv2018

General relativity with nonzero cosmological constant as a gauge theory

We show in a new way that the general relativity action (and Lagrangian)in recent Einstein-Palatini formulation is equivalent in four dimensions to the action (and Lagrangian) of a gauge field. This paper is a continuation of the previous paper [17] and it also gives an amended version of the lecture delivered by one of the authors [M.D.] at Hypercomplex Seminar in Bedlewo.

gr-qc↗
arXiv2016

Do gravitational waves carry energy-momentum? A reappraisal

After direct detection gravitational radiation in 2015 many authors are publishing remakes of their old articles about this radiation. I decided to follow this line in my Lecture delivered at the Conference "Varcosmofun'16" (12-17 September 2016, Szczecin, Poland, EU). Namely, I have presented at this Conference an updated summary of my past articles on gravitational radiation. As a base for my presentation I have used mainly the article published in 2002 in Annalen der Physik \cite{Gar3} and the articles \cite{Gar4}. In these past articles I have showed that the real gravitational waves which possess a non-vanishing Riemann tensor always carry energy-momentum (and also angular momentum). Our proof have used canonical superenergy and supermomentum tensor for gravitational field in former articles and the averaged relative energy-momentum tensor in latter. In this article we confine to the energy-momentum only.

gr-qc↗
arXiv2016

Canonical superenergy and angular supermomentum complexes in general relativity and some of their applications

Many years ago we have introduced into general relativity, {\bf GR}, the canonical superenergy tensors, $S_i^{~k}$, and the canonical angular supermomentum tensors, $S^{ikl}=(-)S^{kil}$, matter and gravitation. We have obtained these tensors by special averaging of the differences of the canonical energy-momentum and canonical angular momentum. The averaging was performed in Riemann normal coordinates, {\bf RNC(P)}; {\bf P} is beginning of these coordinates. About four years ago we have observed that these tensors can also be obtained in other, simpler way, by using the canonical superenergy and angular super momentum complexes, $_K S_i^{~k}$, and, $_K S~^{ikl}=(-)_K S^{kil}$, respectively. Such complexes can be introduced into {\bf GR} in a natural way starting from canonical energy-momentum and angular momentum complexes. In this paper, at first, we define the canonical superenergy and angular supermomentum complexes in {\bf GR} and then, we apply them to analyze of a closed system, {\bf CS}, Trautman's radiative spacetimes, {\bf TRS}, and Friedman universes, {\bf FU}. Finally, we compare these complexes and the results obtained with their help with the canonical superenergy and angular supermomentum tensors and results obtained with them in past. In Appendix, for convenience, we summarize our old approach to canonical superenergy and angular supermomentum tensors.

gr-qc↗
arXiv2014

New approach to study gravitational stability of the solutions to the Einstein equations

Here we propose a new method to study gravitational stability of the solutions to the Einstein equations. This method uses the canonical superenergy density and it is different from approaches already used (Lyapunov's stability, dynamical systems). Our method is very alike to the procedure of finding the stable minima of the interior energy U for a dynamical system.

gr-qc↗
arXiv2011

Is torsion needed in a theory of gravity? A reappraisal

It is known that General Relativity ({\bf GR}) uses a Lorentzian Manifold $(M_4;g)$ as a geometrical model of the physical spacetime. The metric $g$ is required to satisfy Einstein's equations. Since the 1960s many authors have tried to generalize this model by introducing torsion. In this paper we discuss the present status of torsion in a theory of gravity. Our conclusion is that the general-relativistic model of the physical spacetime is sufficient for the all physical applications and it seems to be the best satisfactory.

gr-qc↗
arXiv2010

Teleparallel equivalent of general relativity: a critical review

After reminder some facts concerning general relativity ({\bf GR}) we pass to teleparallel gravity. We are confining the special model of the teleparallel gravity, which is popular recently, called {\it the teleparallel equivalent of general relativity} ({\bf TEGR}). We are finishing with conclusion and some general remarks.

gr-qc↗
arXiv2009

Statefinders and observational measurement of superenergy

The superenergy of the universe is a tensorial quantity and it is a general relativistic analogue of the Appell's energy of acceleration in classical mechanics. We propose the measurement of this quantity by the observational parameters such as the Hubble parameter, the deceleration parameter, the jerk and the snap (kerk) known as statefinders. We show that the superenergy of gravity requires only the Hubble and deceleration parameter to be measured, while the superenergy of matter requires also the measurement of the higher-order characteristics of expansion: the jerk and the snap. In such a way, the superenergy becomes another parameter characterizing the evolution of the universe.

gr-qc↗
arXiv2009

Conformal transformations and conformal invariance in gravitation

Conformal transformations are frequently used tools in order to study relations between various theories of gravity and the Einstein relativity. In this paper we discuss the rules of these transformations for geometric quantities as well as for the matter energy-momentum tensor. We show the subtlety of the matter energy-momentum conservation law which refers to the fact that the conformal transformation "creates" an extra matter term composed of the conformal factor which enters the conservation law. In an extreme case of the flat original spacetime the matter is "created" due to work done by the conformal transformation to bend the spacetime which was originally flat. We discuss how to construct the conformally invariant gravity theories and also find the conformal transformation rules for the curvature invariants $R^2$, $R_{ab}R^{ab}$, $R_{abcd}R^{abcd}$ and the Gauss-Bonnet invariant in a spacetime of an arbitrary dimension. Finally, we present the conformal transformation rules in the fashion of the duality transformations of the superstring theory. In such a case the transitions between conformal frames reduce to a simple change of the sign of a redefined conformal factor.

gr-qc↗
arXiv2007

Energy, angular momentum, superenergy and angular supermomentum in conformal frames

We find the rules of the conformal transformation for the energetic quantities such as the Einstein energy-momentum complex, the Bergmann-Thomson angular momentum complex, the superenergy tensor, and the angular supermomentum tensor of gravitation and matter. We show that the conformal transformation rules for the matter parts of both the Einstein complex and the Bergmann-Thomson complex are fairly simple, while the transformation rules for their gravitational parts are more complicated. We also find that the transformational rules of the superenergy tensor of matter and the superenergy tensor of gravity are quite complicated except for the case of a pure gravity. In such a special case the superenergy density as well as the sum of the superenergy density and the matter energy density are invariants of the conformal transformation. Besides, in that case, a conformal invariant is also the Bel-Robinson tensor which is a part of the superenergy tensor. As for the angular supermomentum tensor of gravity - it emerges that its transformational rule even for a pure gravity is quite complicated but this is not the case for the angular supermomentum tensor of matter. Having investigated some technicalities of the conformal transformations, we also find the conformal transformation rule for the curvature invariants and, in particular, for the Gauss-Bonnet invariant in a spacetime of arbitrary dimension.

hep-th↗
arXiv2007

On Energy of the Friedman Universes in Conformally Flat Coordinates

Recently many authors have calculated the energy of the Friedman universes by using double index energy-momentum complexes in Cartesian comoving coordinates $(t,x,y,z)$ and concluded that the flat and closed Friedman universes are energy-free. We show in this paper by using Einstein canonical energy-momentum complex and by doing calculations in conformally flat coordinates that such conclusion is incorrect. The results obtained in this paper are compatible with the results of the our previous paper \cite{Gar07} where we have used coordinate-independent averaged relative energy-momentum tensors to analyze Friedman universes.

gr-qc↗
arXiv2007

On Energy and Momentum of the Friedman and Some More General Universes

Recently some authors concluded that the energy and momentum of the Fiedman universes, flat and closed, are equal to zero locally and globally (flat universes) or only globally (closed universes). The similar conclusion was also done for more general only homogeneous universes (Kasner and Bianchi type I). Such conclusions originated from coordinate dependent calculations performed only in comoving Cartesian coordinates by using the so-called {\it energy-momentum complexes}. By using new coordinate independent expressions on energy and momentum one can show that the Friedman and more general universes {\it needn't be energetic nonentity}.

gr-qc↗
arXiv2006

Energy and momentum of the Friedmann and more general universes

Recently some authors concluded that the energy and momentum of the Fiedman universes, flat and closed, are equal to zero locally and globally (flat universes) or only globally (closed universes). The similar conclusion was also done for more general only homogeneous universes (Kasner and Bianchi type I). Such conclusions originated from coordinate dependent calculations performed only in comoving Cartesian coordinates by using the so-called {\it energy-momentum complexes}. But it is known that the energy-momentum complexes can be reasonably use only in precisely defined asymptotically flat spacetimes (at null or at spatial infinity) to calculate global energy and momentum. In this paper we show, by using new coordinate independent expressions on energy and momentum that the Friedman and more general universes {\it needn't be energetic nonentity}.

gr-qc↗