1,245 research outputs found
Generalized Assisted Inflation
We obtain a new class of exact cosmological solutions for multi-scalar fields
with exponential potentials. We generalize the assisted inflation solutions
previously obtained, and demonstrate how they are modified when there exist
cross-couplings between the fields, such as occur in supergravity inspired
cosmological models.Comment: 5 page
Chaos in Anisotropic Pre-Inflationary Universes
We study the dynamics of anisotropic Bianchi type-IX models with matter and
cosmological constant. The models can be thought as describing the role of
anisotropy in the early stages of inflation. The concurrence of the
cosmological constant and anisotropy are sufficient to produce a chaotic
dynamics in the gravitational degrees of freedom, connected to the presence of
a critical point of saddle-center type in the phase space of the system. The
invariant character of chaos is guaranteed by the topology of the cylinders
emanating from unstable periodic orbits in the neighborhood of the
saddle-center. We discuss a possible mechanism for amplification of specific
wavelengths of inhomogeneous fluctuations in the models. A geometrical
interpretation is given for Wald's inequality in terms of invariant tori and
their destruction by increasing values of the cosmological constant.Comment: 14 pages, figures available under request. submitted to Physical
Review
Self-similar cosmological solutions with a non-minimally coupled scalar field
We present self-similar cosmological solutions for a barotropic fluid plus
scalar field with Brans-Dicke-type coupling to the spacetime curvature and an
arbitrary power-law potential energy. We identify all the fixed points in the
autonomous phase-plane, including a scaling solution where the fluid density
scales with the scalar field's kinetic and potential energy. This is related by
a conformal transformation to a scaling solution for a scalar field with
exponential potential minimally coupled to the spacetime curvature, but
non-minimally coupled to the barotropic fluid. Radiation is automatically
decoupled from the scalar field, but energy transfer between the field and
non-relativistic dark matter can lead to a change to an accelerated expansion
at late times in the Einstein frame. The scalar field density can mimic a
cosmological constant even for steep potentials in the strong coupling limit.Comment: 10 pages, 1 figure, revtex version to appear in Phys Rev D,
references adde
Dynamics of Assisted Inflation
We investigate the dynamics of the recently proposed model of assisted
inflation. In this model an arbitrary number of scalar fields with exponential
potentials evolve towards an inflationary scaling solution, even if each of the
individual potentials is too steep to support inflation on its own. By choosing
an appropriate rotation in field space we can write down explicitly the
potential for the weighted mean field along the scaling solution and for fields
orthogonal to it. This demonstrates that the potential has a global minimum
along the scaling solution. We show that the potential close to this attractor
in the rotated field space is analogous to a hybrid inflation model, but with
the vacuum energy having an exponential dependence upon a dilaton field. We
present analytic solutions describing homogeneous and inhomogeneous
perturbations about the attractor solution without resorting to slow-roll
approximations. We discuss the curvature and isocurvature perturbation spectra
produced from vacuum fluctuations during assisted inflation.Comment: 9 pages, 2 figures, latex with revtex and eps
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