465 research outputs found
DSR as an explanation of cosmological structure
Deformed special relativity (DSR) is one of the possible realizations of a
varying speed of light (VSL). It deforms the usual quadratic dispersion
relations so that the speed of light becomes energy dependent, with preferred
frames avoided by postulating a non-linear representation of the Lorentz group.
The theory may be used to induce a varying speed of sound capable of generating
(near) scale-invariant density fluctuations, as discussed in a recent Letter.
We identify the non-linear representation of the Lorentz group that leads to
scale-invariance, finding a universal result. We also examine the higher order
field theory that could be set up to represent it
Primordial fluctuations without scalar fields
We revisit the question of whether fluctuations in hydrodynamical,
adiabatical matter could explain the observed structures in our Universe. We
consider matter with variable equation of state w=p_0/\ep_0 and a concomitant
(under the adiabatic assumption) density dependent speed of sound, . We
find a limited range of possibilities for a set up when modes start inside the
Hubble radius, then leaving it and freezing out. For expanding Universes,
power-law w(\ep_0) models are ruled out (except when ,
requiring post-stretching the seeded fluctuations); but sharper profiles in
do solve the horizon problem. Among these, a phase transition in is
notable for leading to scale-invariant fluctuations if the initial conditions
are thermal. For contracting Universes all power-law w(\ep_0) solve the
horizon problem, but only one leads to scale-invariance: w\propto \ep_0^2 and
c_s\propto \ep_0. This model bypasses a number of problems with single scalar
field cyclic models (for which is large but constant)
Comments on "Note on varying speed of light theories"
In a recent note Ellis criticizes varying speed of light theories on the
grounds of a number of foundational issues. His reflections provide us with an
opportunity to clarify some fundamental matters pertaining to these theories
Multipole invariants and non-Gaussianity
We propose a framework for separating the information contained in the CMB
multipoles, , into its algebraically independent components. Thus
we cleanly separate information pertaining to the power spectrum,
non-Gaussianity and preferred axis effects. The formalism builds upon the
recently proposed multipole vectors (Copi, Huterer & Starkman 2003; Schwarz &
al 2004; Katz & Weeks 2004), and we elucidate a few features regarding these
vectors, namely their lack of statistical independence for a Gaussian random
process. In a few cases we explicitly relate our proposed invariants to
components of the -point correlation function (power spectrum, bispectrum).
We find the invariants' distributions using a mixture of analytical and
numerical methods. We also evaluate them for the co-added WMAP first year map
Evidence for non-Gaussianity in the CMB
In a recent Letter we have shown how COBE-DMR maps may be used to disprove
Gaussianity at a high confidence level. In this report we digress on a few
issues closely related to this Letter. We present the general formalism for
surveying non-Gaussianity employed. We present a few more tests for
systematics. We wonder about the theoretical implications of our result.Comment: Proceedings of the Planck meeting, Santender 9
Inflation and the quantum measurement problem
We propose a solution to the quantum measurement problem in inflation. Our model treats Fourier modes of cosmological perturbations as analogous to particles in a weakly interacting Bose gas. We generalize the idea of a macroscopic wave function to cosmological fields, and construct a self-interaction Hamiltonian that focuses that wave function. By appropriately setting the coupling between modes, we obtain the standard adiabatic, scale-invariant power spectrum. Because of central limit theorem, we recover a Gaussian random field, consistent with observations
The Multipole Vectors of WMAP, and their frames and invariants
We investigate the Statistical Isotropy and Gaussianity of the CMB
fluctuations, using a set of multipole vector functions capable of separating
these two issues. In general a multipole is broken into a frame and
ordered invariants. The multipole frame is found to be suitably sensitive to
galactic cuts. We then apply our method to real WMAP datasets; a coadded masked
map, the Internal Linear Combinations map, and Wiener filtered and cleaned
maps. Taken as a whole, multipoles in the range or show
consistency with statistical isotropy, as proved by the Kolmogorov test applied
to the frame's Euler angles. This result in {\it not} inconsistent with
previous claims for a preferred direction in the sky for . The
multipole invariants also show overall consistency with Gaussianity apart from
a few anomalies of limited significance (98%), listed at the end of this paper.Comment: 9 pages. Submitted to MNRA
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