224 research outputs found
Cyclic Universe \`{a} la string theory
We shall present a model of the "cyclic universe" that can be constructed
only by assuming a minimal set of properties of string theory. We clarify our
viewpoint of the cyclic universe and show some attempts to mateliarize the idea
as field theoretical manner.Comment: Proceeding of International Workshop "Frontier of Quantum Physics"
February 17(Thu.)-19(Sat.) 200
A new mechanism of realizing inflationary universe with recourse to backreaction of quantized free fields -- Inflation without inflaton --
It is shown that the inflationary era in early universe is realized due to
the effect of backreaction of quantized matter fields. In fact we start by
quantizing a free scalar field in the Friedmann-Robertson-Walker space-time,
and the field is fluctuating quantum mechanically around the bottom of the mass
potential. We then obtain the vacuum expectation value of the energy density of
the scalar field as a functional of the scale factor of the universe. By
plugging it into the Einstein equation, a self-consistent equation is
established in which the matter fields determine the time evolution of the
universe. We solve this equation by setting few conditions and find the
following solution: the universe expands \`{a} la de Sitter with e-folding
number and then it turns to shrink with a decreasing Hubble
parameter which rapidly goes to zero.Comment: 25 pages, 5 figure
CMB Fluctuations and String Compactification Scales
We propose a mechanism for the generation of temperature fluctuations of
cosmic microwave background. We consider a large number of fields, such as
Kaluza-Klein modes and string excitations. Each field contributes to the
gravitational potential by a small amount, but an observable level of
temperature fluctuations is achieved by summing up the contribution of
typically of order 10^{14} fields. Tensor fluctuations are hardly affected by
these fields. Our mechanism is based on purely quantum effects, and is
different from the "slow-roll" or "curvaton" scenario. Using the observed data,
we find constraints on the parameters of this model, such as the size of the
extra dimensions and the string scale. Our model predicts a particular pattern
of non-gaussianity with a small magnitude.Comment: 4 pages, 2 figures; v2: Corrected a mistake in eq. (11), which does
not affect the subsequent context. Added a comment on inflaton fluctuations
at the end of the paper. Final version to appear in Phys. Lett.
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