* Astronomy

Blobrana · L

RE: Domain walls

Blobrana · L

Title: Where are the Walls?
Authors: Keith A. Olive, Marco Peloso, Adam J. Peterson

The reported spatial variation in the fine-structure constant at high redshift, if physical, could be due to the presence of dilatonic domains, and one or more domain walls inside our horizon. An absorption spectrum of an object in a different domain from our own would be characterised by a different value of alpha. We show that while a single wall solution is statically comparable to a dipole fit, and is a big improvement over a weighted mean (despite adding 3 parameters), a two-wall solution is a far better fit (despite adding 3 parameters over the single wall solution). We derive a simple model accounting for the two-domain wall solution. The goodness of these fits is however dependent on the extra random error which was argued to account for the large scatter in most of the data. When this error is omitted, all the above solutions are poor fits to the data. When included, the solutions that exhibit a spatial dependence agree with the data much more significantly than the Standard Model; however, the Standard Model itself is not a terrible fit to the data, having a p-value of ~ 20 %.

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Blobrana · L

Title: Scalar Domain Wall as the Universe
Authors: Yuta Toyozato, Kazuharu Bamba, Shin'ichi Nojiri

By using the formulation of the reconstruction, we construct models which have an exact solution describing the domain wall. The shape of the domain wall can be flat, de Sitter space-time, or anti-de Sitter space-time. In the constructed domain wall solutions, there often appears ghost with negative kinetic energy. We give, however, an example of the de Sitter domain wall solution without ghost, which could be a toy model of the inflation. We also investigate the localisation of the gravity as in the Randall-Sundrum model. It is shown that the four dimensional Newton law could be reproduced even in the de Sitter space-time domain wall solution.

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Title: Quantum fluctuations in planar domain-wall space-times: A possible origin of primordial preferred direction
Authors: Chih-Hung Wang, Yu-Huei Wu, Stephen D. H. Hsu

We study the gravitational effects of a planar domain wall on quantum fluctuations of a massless scalar field during inflation. By obtaining an exact solution of the scalar field equation in de Sitter space, we show that the gravitational effects of the domain wall break the rotational invariance of the primordial power spectrum without affecting the translational invariance. The strength of rotational violation is determined by one dimensionless parameter \beta, which is a function of two physical parameters, the domain wall surface tension \sigma and cosmological constant \Lambda. In the limit of small \beta, the leading effect of rotational violation of the primordial power spectrum is scale-invariant.

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Blobrana · L

Title: Casimir force for cosmological domain walls
Authors: Tomohiro Matsud

We calculate the vacuum fluctuations that may affect the evolution of cosmological domain walls. Considering domain walls, which are classically stable and have interaction with a scalar field, we show that explicit symmetry violation in the interaction may cause quantum bias that can solve the cosmological domain wall problem.

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