Øystein Elgarøy

Cosmological constraints on f(R) gravity theories within the Palatini approach

We investigate f(R) theories of gravity within the Palatini approach and show how one can determine the expansion history, H(a), for an arbitrary choice of f(R). As an example, we consider cosmological constraints on such theories arising from the supernova type la, large-scale structure formation, and cosmic microwave background observations. We find that the best fit to the data is a non-null leading order correction to the Einstein gravity. However, the current data exhibits no significant trend toward such corrections compared to the concordance ACDM model. Our results show that the oft-considered I/R models are not compatible with the data. The results demonstrate that background expansion alone can act as a good discriminator between modified gravity models when multiple data sets are used.

3 P 2 − 3 F 2 pairing in neutron matter with modern nucleon-nucleon potentials

We present results for the

On using the cosmic microwave background shift parameter in tests of models of dark energy

^3P_2 - ^3F_2

Nucleon-nucleon phase shifts and pairing in neutron matter and nuclear matter

pairing gap in neutron matter with several realistic nucleon-nucleon potentials, in particular with recent, phase-shift equivalent potentials. We find that their predictions for the gap cannot be trusted at densities above

SUPERFLUIDITY IN BETA -STABLE NEUTRON STAR MATTER

\rho\approx 1.7\rho_0

Neutrino mass, dark energy, and the linear growth factor

, where

Observational constraints on particle production during inflation

\rho_0

Model-space approach to 1S0 neutron and proton pairing in neutron star matter with the Bonn meson-exchange potentials

is the saturation density for symmetric nuclear matter. In order to make predictions above that density, potential models which fit the nucleon-nucleon phase shifts up to about 1 GeV are required.

Triplet pairing of neutrons in β-stable neutron star matter

Context. The so-called shift parameter is related to the position of the first acoustic peak in the power spectrum of the temperature anisotropies of the cosmic microwave background (CMB). It is an often used quantity in simple tests of dark energy models. However, the shift parameter is not directly measurable from the cosmic microwave background, and its value is usually derived from the data assuming a spatially flat cosmology with dark matter and a cosmological constant. Aims. To evaluate the effectiveness of the shift parameter as a constraint on dark energy models. Methods. We discuss the potential pitfalls in using the shift parameter as a test of non-standard dark energy models. Results. By comparing to full CMB fits, we show that combining the shift parameter with the position of the first acoustic peak in the CMB power spectrum improves the accuracy of the test considerably.

Can Planck-scale physics be seen in the cosmic microwave background?

We consider