531 research outputs found
Inflation after Planck and BICEP2
We discuss the inflationary paradigm, how it can be tested, and how various
models of inflation fare in the light of data from Planck and BICEP2. We
introduce inflation and reheating, and discuss temperature and polarisation
anisotropies in the cosmic microwave background radiation due to quantum
fluctuations during inflation. Fitting observations of the anisotropies with
theoretical realisations obtained by varying various parameters of the
curvature power spectrum and cosmological parameters enables one to obtain the
allowed ranges of these parameters. We discuss how to relate these parameters
to inflation models which allows one to rule in or out specific models of
inflation.Comment: Slightly longer version of a plenary review talk at the XXI DAE-BRNS
High Energy Physics Symposium at IIT Guwahati, Dec.8-12, 2014. 14 pages, 7
fig
A Cosmic Microwave Background feature consistent with a cosmic texture
The Cosmic Microwave Background provides our most ancient image of the
Universe and our best tool for studying its early evolution. Theories of high
energy physics predict the formation of various types of topological defects in
the very early universe, including cosmic texture which would generate hot and
cold spots in the Cosmic Microwave Background. We show through a Bayesian
statistical analysis that the most prominent, 5 degree radius cold spot
observed in all-sky images, which is otherwise hard to explain, is compatible
with having being caused by a texture. From this model, we constrain the
fundamental symmetry breaking energy scale to be phi_0 ~ 8.7 x 10^(15) GeV. If
confirmed, this detection of a cosmic defect will probe physics at energies
exceeding any conceivable terrestrial experiment.Comment: Accepted by Science. Published electronically via Science Express on
25 October 2007, http://www.sciencemag.org/cgi/content/abstract/114869
Strings and solitons in gauge theories
Imperial Users onl
The General Primordial Cosmic Perturbation
We consider the most general primordial cosmological perturbation in a
universe filled with photons, baryons, neutrinos, and a hypothetical cold dark
matter (CDM) component within the framework of linearized perturbation theory.
We give a careful discussion of the different allowed modes, distinguishing
modes which are regular at early times, singular at early times, or pure gauge.
As well as the familiar growing and decaying adiabatic modes and the baryonic
and CDM isocurvature modes we identify two {\it neutrino isocurvature} modes
which do not seem to have been discussed before. In the first, the ratio of
neutrinos to photons varies spatially but the net density perturbation
vanishes. In the second the photon-baryon plasma and the neutrino fluid have a
spatially varying relative bulk velocity, balanced so that the net momentum
density vanishes. Possible mechanisms which could generate the two neutrino
isocurvature modes are discussed. If one allows the most general regular
primordial perturbation, all quadratic correlators of observables such as the
microwave background anisotropy and matter perturbations are completely
determined by a real, symmetric matrix-valued function of
co-moving wavenumber. In a companion paper we examine prospects for detecting
or constraining the amplitudes of the most general allowed regular
perturbations using present and future CMB data.Comment: 18 pages, 2 Postscript figures, uses revtex. Revised 2-2000 Minor
errors corrected and some references adde
A Causal Source which Mimics Inflation
How unique are the inflationary predictions for the cosmic microwave
anisotropy pattern? In this paper, it is asked whether an arbitrary causal
source for perturbations in the standard hot big bang could effectively mimic
the predictions of the simplest inflationary models. A surprisingly simple
example of a `scaling' causal source is found to closely reproduce the
inflationary predictions. This letter extends the work of a previous paper
(ref. 6) to a full computation of the anisotropy pattern, including the Sachs
Wolfe integral. I speculate on the possible physics behind such a source.Comment: 4 pages, RevTex, 3 figure
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