arXiv subjects

Piret Kuusk

Publications and source records attributed to Piret Kuusk.

22 records · Page 2Linked to original sources

arXiv2006

The dynamics of scalar-tensor cosmology from RS two-brane model

We consider a Randall-Sundrum two-brane cosmological model in the low energy gradient expansion approximation by Kanno and Soda. It is a scalar-tensor theory with a specific coupling function and a specific potential. Upon introducing the FLRW metric and perfect fluid matter on both branes in the Jordan frame, the effective dynamical equation for the the A-brane (our Universe) scale factor decouples from the scalar field and B-brane matter leaving only a non-vanishing integration constant (the dark radiation term). We find exact solutions for the A-brane scale factor for four types of matter: cosmological constant, radiation, dust, and cosmological constant plus radiation. We perform a complementary analysis of the dynamics of the scalar field (radion) using phase space methods and examine convergence towards the limit of general relativity. In particular, we find that radion stabilizes at a certain finite value for suitable negative matter densities on the B-brane. Observational constraints from Solar system experiments (PPN) and primordial nucleosynthesis (BBN) are also briefly discussed.

gr-qc↗

arXiv2002

Long-wavelength approximation for string cosmology with barotropic perfect fluid

The field equations derived from the low energy string effective action with a matter tensor describing a perfect fluid with a barotropic equation of state are solved iteratively using the long-wavelength approximation, i.e. the field equations are expanded by the number of spatial gradients. In the zero order, a quasi-isotropic solution is presented and compared with the general solution of the pure dilaton gravity. Possible cosmological models are analyzed from the point of view of the pre-big bang scenario. The second order solutions are found and their growing and decaying parts are studied.

gr-qc↗

arXiv2001

Measurement of time in nonrelativistic quantum and classical mechanics

Possible theoretical frameworks for measurement of (arrival) time in the nonrelativistic quantum mechanics are reviewed. It is argued that the ambiguity between indirect measurements by a suitably introduced time operator and direct measurements by a physical clock particle has a counterpart in the corresponding classical framework of measurement of the Newtonian time based on the Hamiltonian mechanics.

quant-ph↗

arXiv1999

Geodesic multiplication and quantum kinematics in a Newtonian spacetime

We consider a quantum test particle in the background of a Newtonian gravitational field in the framework of Cartan's formulation of nonrelativistic spacetimes. We have proposed a novel quantization of a point particle which amounts to introducing its position operators as multiplication with the corresponding Riemann normal coordinates and momentum operators as infinitesimal right translation operators determined by geodesic multiplication of points of the spacetime. We present detailed calculations for the simplest model of a two-dimensional Newtonian spacetime.

gr-qc↗