We will meet as usual at 11:30am in B1.19 (after coffee). This week Camilla Schelpe, Raquel Riberio and Hiro Funakoshi will respectively be leading the discussions on:
Cosmology of Chameleons with Power-Law Couplings
David F. Mota and Hans A. Winther
Strongly Coupled Perturbations in Two-Field Inflationary Models
Sera Cremonini, Zygmunt Lalak and Krzysztof Turzynski
Cosmological Constant from Decoherence
Claus Kiefer, Friedemann Queisser and Alexei A. Starobinsky
arXiv: 1010.5331
Claus Kiefer, Friedemann Queisser and Alexei A. Starobinsky
arXiv: 1010.5331
Full Details of This Week's Papers
Cosmology of Chameleons with Power-Law Couplings
David F. Mota and Hans A. Winther
In chameleon field theories a scalar field can couple to matter with gravitational strength and still evade local gravity constraints due to a combination of self-interactions and the couplings to matter. Originally, these theories were proposed with a constant coupling to matter, however, the chameleon mechanism also extends to the case where the coupling becomes field-dependent. We study the cosmology of chameleon models with power-law couplings and power-law potentials. It is found that these generalized chameleons, when viable, have a background expansion very close to LCDM, but can in some special cases enhance the growth of the linear perturbations at low redshifts. For the models we consider it is found that this region of the parameter space is ruled out by local gravity constraints. Imposing a coupling to dark matter only, the local constraints are avoided, and it is possible to have observable signatures on the linear matter perturbations.
Strongly Coupled Perturbations in Two-Field Inflationary Models
Sera Cremonini, Zygmunt Lalak and Krzysztof Turzynski
We study models of inflation with two scalar fields and non-canonical kinetic terms, focusing on the case in which the curvature and isocurvature perturbations are strongly coupled to each other. In the regime where a heavy mode can be identified and integrated out, we clarify the passage from the full two-field model to an effectively single-field description. However, the strong coupling sets a new scale in the system, and affects the evolution of the perturbations as well as the beginning of the regime of validity of the effective field theory. In particular, the predictions of the model are sensitive to the relative hierarchy between the coupling and the mass of the heavy mode. As a result, observables are not given unambiguously in terms of the parameters of an effectively single field model with non-trivial sound speed. Finally, the requirement that the sound horizon crossing occurs within the regime of validity of the effective theory leads to a lower bound on the sound speed. Our analysis is done in an extremely simple toy model of slow-roll inflation, which is chosen for its tractability, but is non-trivial enough to illustrate the richness of the dynamics in non-canonical multi-field models.
Cosmological Constant from Decoherence
Claus Kiefer, Friedemann Queisser and Alexei A. Starobinsky
arXiv: 1010.5331
We address the issue why a cosmological constant (dark energy) possesses a small positive value instead of being zero. Motivated by the cosmic landscape picture, we mimic the dark energy by a scalar field with potential wells and show that other degrees of freedom interacting with it can localize this field by decoherence in one of the wells. Dark energy can then acquire a small positive value. We also show that the additional degrees of freedom enhance the tunneling rate between the wells. The consideration is performed in detail for the case of two wells and then extended to a large number of wells.
No comments:
Post a Comment
To post a link to an arXiv article with ID xxxx.yyyy use:
<a href="http://arxiv.org/abs/xxxx.yyyy">arXiv:xxxx.yyyy</a>