arXiv subjects

Jochen Weller

Publications and source records attributed to Jochen Weller.

78 records · Page 5Linked to original sources

arXiv2002

Future Supernovae observations as a probe of dark energy

We study the potential impact of improved future supernovae data on our understanding of the dark energy problem. We carefully examine the relative utility of different fitting functions that can be used to parameterize the dark energy models, and provide concrete reasons why a particular choice (based on a parameterization of the equation of state) is better in almost all cases. We discuss the details of a representative sample of dark energy models and show how future supernova observations could distinguish among these. As a specific example, we consider the proposed ``SNAP'' satellite which is planned to observe around 2000 supernovae. We show how a SNAP-class data set taken alone would be a powerful discriminator among a family of models that would be approximated by a constant equation of state for the most recent epoch of cosmic expansion. We show how this family includes most of the dark energy models proposed so far. We then show how an independent measurement of $Ω_{\rm m}$ can allow SNAP to probe the evolution of the equation of state as well, allowing further discrimination among a larger class of proposed dark energy models. We study the impact of the satellite design parameters on this method to distinguish the models and compare SNAP to alternative measurements. We establish that if we exploit the full precision of SNAP it provides a very powerful probe.

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arXiv2001

Opportunities for future supernova studies of cosmic acceleration

We investigate the potential of a future supernova dataset, as might be obtained by the proposed SNAP satellite, to discriminate among different ``dark energy'' theories that describe an accelerating Universe. We find that many such models can be distinguished with a fit to the effective pressure-to-density ratio, $w$, of this energy. More models can be distinguished when the effective slope, $dw/dz$, of a changing $w$ is also fit, but only if our knowledge of the current mass density, $Ω_m$, is improved. We investigate the use of ``fitting functions'' to interpret luminosity distance data from supernova searches, and argue in favor of a particular preferred method, which we use in our analysis.

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arXiv2000

Bubbles from dark energy ?

In a model recently proposed by Albrecht and Skordis it was suggested that the observed accelerated expansion of the universe could be caused by a scalar field which is trapped in a local minimum of an exponential potential modified by a polynomial prefactor. We show that scalar field cosmologies with this kind of local minimum in the potential are stable and do not decay to the true vacuum if they fulfill the observational constraints from the Type Ia Supernovae experiments. Further we briefly sketch how this potential could be related to a potential of interacting D-branes.

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arXiv1999

Inhomogeneous reionization and the polarization of the cosmic microwave background

In a universe with inhomogeneous reionization, the ionized patches create a second order signal in the cosmic microwave background polarization anisotropy. This signal originates in the coupling of the free electron fluctuation to the quadruple moment of the temperature anisotropy. We examine the contribution from a simple inhomogeneous reionization model and find that the signal from such a process is below the detectable limits of the Planck Surveyor mission. However t he signal is above the fundamental uncertainty limit from cosmic variance, so th at a future detection with a high accuracy experiment on sub-arcminute scales is possible.

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arXiv1999

Reionization by active sources and its effects on the cosmic microwave background

We investigate the possible effects of reionization by active sources on the cosmic microwave background. We concentrate on the sources themselves as the origin of reionization, rather than early object formation, introducing an extra period of heating motivated by the active character of the perturbations. Using reasonable parameters, this leads to four possibilities depending on the time and duration of the energy input: delayed last scattering, double last scattering, shifted last scattering and total reionization. We show that these possibilities are only very weakly constrained by the limits on spectral distortions from the COBE FIRAS measurements. We illustrate the effects of these reionization possibilities on the angular power spectrum of temperature anisotropies and polarization for simple passive isocurvature models and simple coherent sources, observing the difference between passive and active models. Finally, we comment on the implications of this work for more realistic active sources, such as causal white noise and topological defect models. We show for these models that non-standard ionization histories can shift the peak in the CMB power to larger angular scales.

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arXiv1999

Early structure formation with cold plus hot dark matter --- a success of strings plus inflation model

Quantum fluctuations created during inflation can account for the observed matter distribution in the linear regime if the universe has two components of dark matter, one which is cold and collisionless, and the other which is hot and free streams on small scales. However, this free streaming property of the hot component prevents early structure formation, and since objects, such as damped Lyman-$α$ systems, have been observed at high redshift, it is necessary to produce more power on small scales. Here, we show that the situation can be improved substantially in models where cosmic strings are formed at the end of inflation, and in which both inflation and strings participate in the generation of structure.

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