arXiv subjects

Tuomas Multamäki

Publications and source records attributed to Tuomas Multamäki.

3 recordsLinked to original sources

arXiv2009

Hamiltonian perturbation theory in f(R) gravity

Hamiltonian perturbation theory is used to analyse the stability of f(R) models. The Hamiltonian equations for the metric and its momentum conjugate are written for f(R) Lagrangian in the presence of perfect fluid matter. The perturbations examined are perpendicular to R. As perturbations are added to the metric and momentum conjugate to the induced metric instabilities are found, depending on the form of f(R). Thus the examination of these instabilities is a way to rule out certain f(R) models.

gr-qc↗

arXiv2008

Maximal symmetry and metric-affine f(R) gravity

The affine connection in a space-time with a maximally symmetric spatial subspace is derived using the properties of maximally symmetric tensors. The number of degrees of freedom in metric-affine gravity is thereby considerably reduced while the theory allows spatio-temporal torsion and remains non-metric. The Ricci tensor and scalar are calculated in terms of the connection and the field equations derived for the Einstein-Hilbert as wells as for f(R) Lagrangians. By considering specific forms of f(R), we demonstrate that the resulting Friedmann equations in Palatini formalism without torsion and metric-affine formalism with maximal symmetry are in general different in the presence of matter.

gr-qc↗

arXiv2004

How Long can Left and Right Handed Life Forms Coexist?

Reaction-diffusion equations based on a polymerization model are solved to simulate the spreading of hypothetic left and right handed life forms on the Earth's surface. The equations exhibit front-like behavior as is familiar from the theory of the spreading of epidemics. It is shown that the relevant time scale for achieving global homochirality is not, however, the time scale of front propagation, but the much longer global diffusion time. The process can be sped up by turbulence and large scale flows. It is speculated that, if the deep layers of the early ocean were sufficiently quiescent, there may have been the possibility of competing early life forms with opposite handedness.

q-bio.BM↗