25,707 research outputs found
UV physics and the speed of sound during inflation
We consider inflation as an effective field theory and study the effects of
the addition to the Lagrangian of irrelevant operators with higher powers of
first derivatives on its dynamics and observables. We find that significant
deviations from the two-derivative dynamics are possible within the regime of
validity of the effective field theory. Focusing on monomial potentials we show
that the main effect of the terms under consideration is to reduce the speed of
sound thereby reducing the tensor fraction, while having little impact on the
scalar tilt. Crucially, these effects can arise even when the UV cut-off is
well above the inflationary Hubble parameter
Optimal reconstruction systems for erasures and for the q-potential
We introduce the -potential as an extension of the Benedetto-Fickus frame
potential, defined on general reconstruction systems and we show that protocols
are the minimizers of this potential under certain restrictions. We extend
recent results of B.G. Bodmann on the structure of optimal protocols with
respect to 1 and 2 lost packets where the worst (normalized) reconstruction
error is computed with respect to a compatible unitarily invariant norm. We
finally describe necessary and sufficient (spectral) conditions, that we call
-fundamental inequalities, for the existence of protocols with prescribed
properties by relating this problem to Klyachko's and Fulton's theory on sums
of hermitian operators
The impact on cosmology of a primordial scaling field
A scalar field with an exponential potential has the particular property that
it is attracted into a solution in which its energy scales as the dominant
component (radiation or matter) of the Universe, contributing a fixed fraction
of the total energy density. We briefly discuss the dynamics of such a scalar
field and its impact on Big Bang nucleosynthesis, the growth of large scale
structure and abundance of damped Lyman systems at high redshift.
Given the simplicity of the model, its theoretical motivation, and its success
in matching observations, we argue that it should be taken on par with other
currently viable models of structure formation.Comment: 3 pages, uses prcrc.sty, 2 figures, to be published in proceedings of
Dark Matter '9
Recommended from our members
Melanosuchus, M. niger
Number of Pages: 4Integrative BiologyGeological Science
Ricci focusing, shearing, and the expansion rate in an almost homogeneous Universe
The Universe is inhomogeneous, and yet it seems to be incredibly
well-characterised by a homogeneous relativistic model. One of the current
challenges is to accurately characterise the properties of such a model. In
this paper we explore how inhomogeneities may affect the overall optical
properties of the Universe by quantifying how they can bias the
redshift-distance relation in a number of toy models that mimic the real
Universe. The models that we explore are statistically homogeneous on large
scales. We find that the effect of inhomogeneities is of order of a few
percent, which can be quite important in precise estimation of cosmological
parameters. We discuss what lessons can be learned to help us tackle a more
realistic inhomogeneous universe.Comment: 22 pages, 8 figure
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