269 research outputs found
Fine Features in the Primordial Power Spectrum
A possible origin of the anomalous dip and bump in the primordial power
spectrum, which are reconstructed from WMAP data corresponding to the multipole
by using the inversion method, is investigated as a
consequence of modification of scalar field dynamics in the inflation era.
Utilizing an analytic formula to handle higher order corrections to the
slow-roll approximation, we evaluate the relation between a detailed shape of
inflaton potential and a fine structure in the primordial power spectrum. We
conclude that it is unlikely to generate the observed dip and bump in the power
spectrum by adding any features in the inflaton potential. Though we can make a
fine enough shape in the power spectrum by controlling the feature of the
potential, the amplitude of the dip and bump becomes too small in that case.Comment: 15 pages, 11 figures, submitted to JCA
Induced CMB quadrupole from pointing offsets
Recent claims in the literature have suggested that the {\it WMAP} quadrupole
is not primordial in origin, and arises from an aliasing of the much larger
dipole field because of incorrect satellite pointing. We attempt to reproduce
this result and delineate the key physics leading to the effect. We find that,
even if real, the induced quadrupole would be smaller than claimed. We discuss
reasons why the {\it WMAP} data are unlikely to suffer from this particular
systematic effect, including the implications for observations of point
sources. Given this evidence against the reality of the effect, the similarity
between the pointing-offset-induced signal and the actual quadrupole then
appears to be quite puzzling. However, we find that the effect arises from a
convolution between the gradient of the dipole field and anisotropic coverage
of the scan direction at each pixel. There is something of a directional
conspiracy here -- the dipole signal lies close to the Ecliptic Plane, and its
direction, together with the {\it WMAP} scan strategy, results in a strong
coupling to the component in Ecliptic co-ordinates. The dominant
strength of this component in the measured quadrupole suggests that one should
exercise increased caution in interpreting its estimated amplitude. The {\it
Planck} satellite has a different scan strategy which does not so directly
couple the dipole and quadrupole in this way and will soon provide an
independent measurement.Comment: 8 pages, 4 figure
Webometric analysis of departments of librarianship and information science: a follow-up study
This paper reports an analysis of the websites of UK departments of library and information science. Inlink counts of these websites revealed no statistically significant correlation with the quality of the research carried out by these departments, as quantified using departmental grades in the 2001 Research Assessment Exercise and citations in Google Scholar to publications submitted for that Exercise. Reasons for this lack of correlation include: difficulties in disambiguating departmental websites from larger institutional structures; the relatively small amount of research-related material in departmental websites; and limitations in the ways that current Web search engines process linkages to URLs. It is concluded that departmental-level webometric analyses do not at present provide an appropriate technique for evaluating academic research quality, and, more generally, that standards are needed for the formatting of URLs if inlinks are to become firmly established as a tool for website analysis
Neutrino and axion hot dark matter bounds after WMAP-7
We update cosmological hot dark matter constraints on neutrinos and hadronic
axions. Our most restrictive limits use 7-year data from the Wilkinson
Microwave Anisotropy Probe for the cosmic microwave background anisotropies,
the halo power spectrum (HPS) from the 7th data release of the Sloan Digital
Sky Survey, and the Hubble constant from Hubble Space Telescope observations.
We find 95% C.L. upper limits of \sum m_\nu<0.44 eV (no axions), m_a<0.91 eV
(assuming \sum m_\nu=0), and \sum m_\nu<0.41 eV and m_a<0.72 eV for two hot
dark matter components after marginalising over the respective other mass. CMB
data alone yield \sum m_\nu<1.19 eV (no axions), while for axions the HPS is
crucial for deriving m_a constraints. This difference can be traced to the fact
that for a given hot dark matter fraction axions are much more massive than
neutrinos.Comment: 9 pages, 3 figures, uses iopart.cls; v2: one additional figure,
references added, version accepted by JCA
Running Spectral Index from Inflation with Modulations
We argue that a large negative running spectral index, if confirmed, might
suggest that there are abundant structures in the inflaton potential, which
result in a fairly large (both positive and negative) running of the spectral
index at all scales. It is shown that the center value of the running spectral
index suggested by the recent CMB data can be easily explained by an inflaton
potential with superimposed periodic oscillations. In contrast to cases with
constant running, the perturbation spectrum is enhanced at small scales, due to
the repeated modulations. We mention that such features at small scales may be
seen by 21 cm observations in the future.Comment: 7 pages, 6 figures, v2: published in JCA
Educating Health Professionals about Disability: A Review of Interventions
Health professionals need to understand the human rights and health needs of disabled people. This review of evidence on interventions demonstrates that a range of often innovative approaches have been trialled. Lectures by faculty are less effective in changing attitudes than contact with disabled people themselves. Existing examples of good practice need to be scaled up, and better and more long-term evaluations of impact are required
Local Starbursts in a Cosmological Context
In this contribution I introduce some of the major issues that motivate the
conference, with an emphasis on how starbursts fit into the ``big picture''. I
begin by defining starbursts in several different ways, and discuss the merits
and limitations of these definitions. I will argue that the most physically
useful definition of a starburst is its ``intensity'' (star formation rate per
unit area). This is the most natural parameter to compare local starbursts with
physically similar galaxies at high redshift, and indeed I will argue that
local starbursts are unique laboratories to study the processes at work in the
early universe. I will describe how NASA's GALEX mission has uncovered a rare
population of close analogs to Lyman Break Galaxies in the local universe. I
will then compare local starbursts to the Lyman-Break and sub-mm galaxies high
redshift populations, and speculate that the multidimensional ``manifold'' of
starbursts near and far can be understood largely in terms of the
Schmidt/Kennicutt law and galaxy mass-metallicity relation. I will briefly
summarize he properties of starburst-driven galactic superwinds and their
possible implications for the evolution of galaxies and the IGM. These complex
multiphase flows are best studied in nearby starbursts, where we can study the
the hot X-ray gas that contains the bulk of the energy and newly produced
metals.Comment: Proceedings of the Conference "Starbursts: Fropm 30 Doradus to Lyman
Break Galaxies
Cosmological parameters from large scale structure - geometric versus shape information
The matter power spectrum as derived from large scale structure (LSS) surveys
contains two important and distinct pieces of information: an overall smooth
shape and the imprint of baryon acoustic oscillations (BAO). We investigate the
separate impact of these two types of information on cosmological parameter
estimation, and show that for the simplest cosmological models, the broad-band
shape information currently contained in the SDSS DR7 halo power spectrum (HPS)
is by far superseded by geometric information derived from the baryonic
features. An immediate corollary is that contrary to popular beliefs, the upper
limit on the neutrino mass m_\nu presently derived from LSS combined with
cosmic microwave background (CMB) data does not in fact arise from the possible
small-scale power suppression due to neutrino free-streaming, if we limit the
model framework to minimal LambdaCDM+m_\nu. However, in more complicated
models, such as those extended with extra light degrees of freedom and a dark
energy equation of state parameter w differing from -1, shape information
becomes crucial for the resolution of parameter degeneracies. This conclusion
will remain true even when data from the Planck surveyor become available. In
the course of our analysis, we introduce a new dewiggling procedure that allows
us to extend consistently the use of the SDSS HPS to models with an arbitrary
sound horizon at decoupling. All the cases considered here are compatible with
the conservative 95%-bounds \sum m_\nu < 1.16 eV, N_eff = 4.8 \pm 2.0.Comment: 18 pages, 4 figures; v2: references added, matches published versio
A circular polarimeter for the Cosmic Microwave Background
A primordial degree of circular polarization of the Cosmic Microwave
Background is not observationally excluded. The hypothesis of primordial
dichroism can be quantitatively falsified if the plasma is magnetized prior to
photon decoupling since the initial V-mode polarization affects the evolution
of the temperature fluctuations as well as the equations for the linear
polarization. The observed values of the temperature and polarization angular
power spectra are used to infer constraints on the amplitude and on the
spectral slope of the primordial V-mode. Prior to photon decoupling magnetic
fields play the role of polarimeters insofar as they unveil the circular
dichroism by coupling the V-mode power spectrum to the remaining brightness
perturbations. Conversely, for angular scales ranging between 4 deg and 10 deg
the joined bounds on the magnitude of circular polarization and on the magnetic
field intensity suggest that direct limits on the V-mode power spectrum in the
range of 0.01 mK could directly rule out pre-decoupling magnetic fields in the
range of 10-100 nG. The frequency dependence of the signal is located, for the
present purposes, in the GHz range.Comment: 28 pages, 12 included figures
Foreground removal from WMAP 7yr polarization maps using an MLP neural network
One of the fundamental problems in extracting the cosmic microwave background
signal (CMB) from millimeter/submillimeter observations is the pollution by
emission from the Milky Way: synchrotron, free-free, and thermal dust emission.
To extract the fundamental cosmological parameters from CMB signal, it is
mandatory to minimize this pollution since it will create systematic errors in
the CMB power spectra. In previous investigations, it has been demonstrated
that the neural network method provide high quality CMB maps from temperature
data. Here the analysis is extended to polarization maps. As a concrete
example, the WMAP 7-year polarization data, the most reliable determination of
the polarization properties of the CMB, has been analysed. The analysis has
adopted the frequency maps, noise models, window functions and the foreground
models as provided by the WMAP Team, and no auxiliary data is included. Within
this framework it is demonstrated that the network can extract the CMB
polarization signal with no sign of pollution by the polarized foregrounds. The
errors in the derived polarization power spectra are improved compared to the
errors derived by the WMAP Team.Comment: Accepted for publication in Astrophysics & Space Scienc
- âŠ