8 research outputs found
Weighting CMB and Galactic synchrotron polarisation
We review the present knowledge of the diffuse Galactic synchrotron emission
in polarisation. At microwave frequencies, we assess the expected contamination
to the CMB polarisation angular power spectrum, for and modes, as
expected after the WMAP first year measurements.Comment: 6 pages, 4 figures, proc. of the CMBnet workshop, 20-21 Feb. 2003,
Oxford, U
Inflation with a constant ratio of scalar and tensor perturbation amplitudes
The single scalar field inflationary models that lead to scalar and tensor
perturbation spectra with amplitudes varying in direct proportion to one
another are reconstructed by solving the Stewart-Lyth inverse problem to
next-to-leading order in the slow-roll approximation.
The potentials asymptote at high energies to an exponential form,
corresponding to power law inflation, but diverge from this model at low
energies, indicating that power law inflation is a repellor in this case. This
feature implies that a fine-tuning of initial conditions is required if such
models are to reproduce the observations. The required initial conditions might
be set through the eternal inflation mechanism.
If this is the case, it will imply that the spectral indices must be nearly
constant, making the underlying model observationally indistinguishable from
power law inflation.Comment: 20 pages, 7 figures. Major changes to the Introduction following
referee's comments. One figure added. Some other minor changes. No conclusion
was modifie
Determination of Inflationary Observables by Cosmic Microwave Background Anisotropy Experiments
Inflation produces nearly Harrison-Zel'dovich scalar and tensor perturbation
spectra which lead to anisotropy in the cosmic microwave background (CMB). The
amplitudes and shapes of these spectra can be parametrized by , , and where and are the scalar and
tensor contributions to the square of the CMB quadrupole and and
are the power-lawspectral indices. Even if we restrict ourselves to information
from angles greater than one third of a degree, three of these observables can
be measured with some precision. The combination can be
known to better than . The scalar index can be determined to
better than . The ratio can be known to about for and slightly better for smaller . The precision with which
can be measured depends weakly on and strongly on . For
can be determined with a precision of about . A
full-sky experiment with a beam using technology available today, similar
to those being planned by several groups, can achieve the above precision. Good
angular resolution is more important than high signal-to-noise ratio; for a
given detector sensitivity and observing time a smaller beam provides
significantly more information than a larger beam. The uncertainties in
and are roughly proportional to the beam size. We briefly discuss the
effects of uncertainty in the Hubble constant, baryon density, cosmological
constant and ionization history.Comment: 28 pages of uuencoded postscript with 8 included figures. A
postscript version is also available by anonymous ftp at
ftp://astro.uchicago.edu/pub/astro/knox/fullsim.p
Magnetic Fields in the Early Universe
This review concerns the origin and the possible effects of magnetic fields
in the early Universe. We start by providing to the reader with a short
overview of the current state of art of observations of cosmic magnetic fields.
We then illustrate the arguments in favour of a primordial origin of magnetic
fields in the galaxies and in the clusters of galaxies. We argue that the most
promising way to test this hypothesis is to look for possible imprints of
magnetic fields on the temperature and polarization anisotropies of the cosmic
microwave background radiation (CMBR). With this purpose in mind, we provide a
review of the most relevant effects of magnetic fields on the CMBR. A long
chapter of this review is dedicated to particle physics inspired models which
predict the generation of magnetic fields during the early Universe evolution.
Although it is still unclear if any of these models can really explain the
origin of galactic and intergalactic magnetic fields, we show that interesting
effects may arise anyhow. Among these effects, we discuss the consequences of
strong magnetic fields on the big-bang nucleosynthesis, on the masses and
couplings of the matter constituents, on the electroweak phase transition, and
on the baryon and lepton number violating sphaleron processes. Several
intriguing common aspects, and possible interplay, of magnetogenesis and
baryogenesis are also dicussed.Comment: 152 LaTeX pages, 6 figures., final version to appear in Phys. Re