arXiv subjects

Maciej Kolanowski

Publications and source records attributed to Maciej Kolanowski.

26 records · Page 2Linked to original sources

arXiv2021

Hamiltonian charges in the asymptotically de Sitter spacetimes

We generalize a notion of 'conserved' charges given by Wald and Zoupas to the asymptotically de Sitter spacetimes. Surprisingly, our construction is less ambiguous than the one encountered in the asymptotically flat context. An expansion around exact solutions possessing Killing vectors provides their physical meaning. In particular, we discuss a question of how to define energy and angular momenta of gravitational waves propagating on Kottler and Carter backgrounds. We show that obtained expressions have a correct limit as $Λ\to 0$. We also comment on the relation between this approach and the one based on the canonical phase space of initial data at $\mathcal{I}^+$.

gr-qc↗

arXiv2020

Energy of gravitational radiation in the de Sitter universe at the scri and at a horizon

In this note we investigate outcomes of a symplectic formula for the gravitational waves charges in the general relativity linearized around the de Sitter spacetime. We derive their explicit form at {\it scri} in the Bondi frame, compare with the connected Noether expression and analyze their gauge dependence which allows us to fix unambiguously boundary terms. We also discuss minimal requirements needed to impose on initial data to have finite values of charges. Furthermore, we analyze transformation laws of the energy upon the action of the de Sitter group and discuss its physical interpretation. Finally, we calculate its flux through a cosmological horizon instead of {\it scri}. We show that in the limit $Λ\to 0$, one recovers Trautman--Bondi formula strengthening recent proposal that one should choose a~null surface as a more natural boundary for the astrophysical systems in the presence of the cosmological constant.

gr-qc↗

arXiv2020

Casimir effect in conformally flat spacetimes

We discuss several approaches to determine the Casimir force in inertial frames of reference in different dimensions. On an example of a simple model involving mirrors in Rindler spacetime we show that Casimir's and Lifschitz's methods are inequivalent and only latter can be generalized to other spacetime geometries. For conformally coupled fields we derive the Casimir force in conformally flat spacetimes utilizing an anomaly and provide explicit examples in the Friedmann-Lemaitre-Robertson-Walker $(k=0)$ models.

quant-ph↗

arXiv2019

Dressed metric predictions revisited

It was recently shown that the volume operator of loop quantum cosmology (LQC) and all its positive powers are ill-defined on physical states. In this paper, we investigate how it effects predictions of cosmic microwave background (CMB) power spectra obtained within dressed metric approach for which expectations values of $\hat{a}$ are the key element. We find that almost every step in the procedure is ill-defined and relies heavily upon a (seemingly premature) numerical truncation. Thus, it suggests that more care is needed in making predictions regarding pre-inflationary physics. We propose a new scheme which contains only well-defined quantities. The surprising agreement of the hitherto models with observational data, especially at low angular momenta $l$ is explained.

gr-qc↗

arXiv2019

(Anti-)evaporation of Schwarzschild-de Sitter black holes revisited

It is widely believed that in the presence of a positive cosmological constant, heavy black holes can exhibit non-standard behaviour, namely there is a possibility that such objects would grow instead of evaporating. We point out that all those results (obtained in different frameworks) rely heavily upon the identification of the Nariai spacetime with the Schwarzschild--de Sitter (Kottler) black hole. In this note we argue that it is an incorrect assumption. As a result, previous treatments need revisiting. In particular, we show that within effective action approach, there is no solution corresponding to the Schwarzschild--de Sitter black hole.

gr-qc↗

arXiv2019

On backreaction effects in geometrical destabilisation of inflation

We study the geometrical instability arising in multi-field models of inflation with negatively-curved field space. We analyse how the homogeneous background evolves in presence of geometrical destabilisation, and show that, in simple models, a kinematical backreaction effect takes place that shuts off the instability. We also follow the evolution of the unstable scalar fluctuations. We show that they assist the kinematical backreaction while remaining in the perturbative regime. We conclude that, in the simplest models of geometrical destabilisation, inflation does not end prematurely, but rather proceeds along a modified, sidetracked, field-space trajectory.

astro-ph.CO↗

arXiv2018

The $1/N$ expansion of the symmetric traceless and the antisymmetric tensor models in rank three

We prove rigorously that the symmetric traceless and the antisymmetric tensor models in rank three with tetrahedral interaction admit a $1/N$ expansion, and that at leading order they are dominated by melon diagrams. This proves the recent conjecture of I. Klebanov and G. Tarnopolsky in JHEP 10 (2017) 037 [arXiv:1706.00839], which they checked numerically up to 8th order in the coupling constant.

hep-th↗

arXiv2017

Symmetries of the Trautman retarded radial coordinates

We consider spacetime described by observer that uses Trautman's retarded radial coordinates system. Given a metric tensor, we find all the symmetry maps. They set a 10 dimensional family of local diffeomorphisms of spacetime and can be parametrized by the Poincaré algebra. This result is similar to the symmetries of a Gauss observer using the Gauss simultaneous radial coordinates and experiencing the algebra deformation induced by the spacetime Riemann tensor. A new, surprising property of the retarded coordinates is that while the symmetries are differentiable, in general they are not differentiable twice. In other words, a family of smooth symmetries is smaller than in the Gaussian case. We demonstrate examples of that non-smoothness and find necessary conditions for the differentiability to the second order. We also discuss the consequences and relevance of that result for geometric relational observables program. One can interpret our result as that the retarded radial coordinates provide gauge conditions stronger that the Gaussian 4d radial gauge.

gr-qc↗