427 research outputs found
Secondary B-mode polarization from Faraday rotation in clusters and galaxies
We revisit the polarisation induced by Faraday rotation when Cosmic Microwave
Background photons traverse magnetised plasma. We compute the secondary B-mode
angular power spectrum from Faraday rotation due to magnetic fields in galaxies
and galaxy clusters with masses ranging from to .
We investigate its dependence on the electron and the magnetic field profiles.
Namely, we consider both the beta-profile of electron density as well as an
electron density distribution based on the Navarro-Frenk-White dark matter
profile. We model the magnetic field structure in galaxies and clusters
motivated by recent observations. We further account for its redshift evolution
and we examine the importance of its coherence length. We find that the B-mode
polarisation from Faraday rotation depends on the normalisation parameter
. At 30 GHz for , the B-modes from
Faraday rotation range between and at in the case of a maximally coherent fields. For smaller
coherence lengths, those amplitudes are smaller and they peak at higher
multipoles.Comment: Accepted for publication in MNRA
Accretion, Primordial Black Holes and Standard Cosmology
Primordial Black Holes evaporate due to Hawking radiation. We find that the
evaporation time of primordial black holes increase when accretion of radiation
is included.Thus depending on accretion efficiency more and more number of
primordial black holes are existing today, which strengthens the idea that the
primordial black holes are the proper candidate for dark matter.Comment: 11 pages, 3 figure
The Search for a Primordial Magnetic Field
Magnetic fields appear wherever plasma and currents can be found. As such,
they thread through all scales in Nature. It is natural, therefore, to suppose
that magnetic fields might have been formed within the high temperature
environments of the big bang. Such a primordial magnetic field (PMF) would be
expected to arise from and/or influence a variety of cosmological phenomena
such as inflation, cosmic phase transitions, big bang nucleosynthesis, the
cosmic microwave background (CMB) temperature and polarization anisotropies,
the cosmic gravity wave background, and the formation of large-scale structure.
In this review, we summarize the development of theoretical models for
analyzing the observational consequences of a PMF. We also summarize the
current state of the art in the search for observational evidence of a PMF. In
particular we review the framework needed to calculate the effects of a PMF
power spectrum on the CMB and the development of large scale structure. We
summarize the current constraints on the PMF amplitude and the
power spectral index and discuss prospects for better determining these
quantities in the near future.Comment: 40 pages, 13 figures, Accepted for Physics Reports 23 Feb 2012.
Available online 3 March 2012. In press, corrected proo
Qweak: A Precision Measurement of the Proton's Weak Charge
The Qweak experiment at Jefferson Lab aims to make a 4% measurement of the
parity-violating asymmetry in elastic scattering at very low of a
longitudinally polarized electron beam on a proton target. The experiment will
measure the weak charge of the proton, and thus the weak mixing angle at low
energy scale, providing a precision test of the Standard Model. Since the value
of the weak mixing angle is approximately 1/4, the weak charge of the proton
is suppressed in the Standard Model, making it
especially sensitive to the value of the mixing angle and also to possible new
physics. The experiment is approved to run at JLab, and the construction plan
calls for the hardware to be ready to install in Hall C in 2007. The
theoretical context of the experiment and the status of its design are
discussed.Comment: 5 pages, 2 figures, LaTeX2e, to be published in CIPANP 2003
proceeding
Brans-Dicke Theory and primordial black holes in Early Matter-Dominated Era
We show that primordial black holes can be formed in the matter-dominated era
with gravity described by the Brans-Dicke theory. Considering an early
matter-dominated era between inflation and reheating, we found that the
primordial black holes formed during that era evaporate at a quicker than those
of early radiation-dominated era. Thus, in comparison with latter case, less
number of primordial black holes could exist today. Again the constraints on
primordial black hole formation tend towards the larger value than their
radiation-dominated era counterparts indicating a significant enhancement in
the formation of primordial black holes during the matter-dominaed era.Comment: 9 page
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