2,715 research outputs found
Cosmology of Light Moduli
In string/M-theory with a large compactification radius, some axion-like
moduli can be much lighter than the gravitino. Generic moduli in gauge-mediated
supersymmetry breaking models also have a mass far below the weak scale.
Motivated by these, we examine the cosmological implications of light moduli
for the mass range from the weak scale to an extremely small scale of order
10^{-26} eV, and obtain an upper bound on the initial moduli misalignment for
both cases with and without a late entropy production.Comment: 23 pages including 3 pictex-figures, Late
Cosmology of Antisymmetric Tensor Field in D-brane Universe
We analyze homogeneous, anisotropic cosmology driven by a self-interacting
``massive'' antisymmetric tensor field which is present in string
theories with D-branes. Time-dependent magnetic field existing in the early
universe can lead to the Bianchi type I universe. Evolutions of such a tensor
field are solved exactly or numerically in the universe dominated by vacuum
energy, radiation, and field itself. The matter-like behavior of the
field (dubbed as ``-matter'') ensures that the anisotropy disappears at late
time and thus becomes unobservable in a reasonable cosmological scenario. Such
a feature should be contrasted to the cosmology of the conventional massless
antisymmetric tensor field.Comment: 13 page
String Cosmology of the D-brane Universe
We analyze homogeneous anisotropic cosmology driven by the dilaton and the
self-interacting ``massive'' antisymmetric tensor field which are indispensable
bosonic degrees with the graviton in the NS-NS sector of string theories with
D-branes. We found the attractor solutions for this system, which show the
overall features of general solutions, and confirmed it through numerical
analysis. The dilaton possesses the potential due to the presence of the
D-brane and the curvature of extra dimensions. In the presence of the
non-vanishing antisymmetric tensor field, the homogeneous universe expands
anisotropically while the D-brane term dominates. The isotropy is recovered as
the dilaton rolls down and the curvature term dominates. With the stabilizing
potential for the dilaton, the isotropy can also be recovered.Comment: 23 pages, 8 figures. Final version, to appear in Phys. Rev.
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