92 research outputs found
CMB Temperature Polarization Correlation and Primordial Gravitational Waves
We examine the use of the CMB's TE cross correlation power spectrum as a
complementary test to detect primordial gravitational waves (PGWs). The first
method used is based on the determination of the lowest multipole, ,
where the TE power spectrum, , first changes sign. The second
method uses Wiener filtering on the CMB TE data to remove the density
perturbations contribution to the TE power spectrum. In principle this leaves
only the contribution of PGWs. We examine two toy experiments (one ideal and
another more realistic) to see their ability to constrain PGWs using the TE
power spectrum alone. We found that an ideal experiment, one limited only by
cosmic variance, can detect PGWs with a ratio of tensor to scalar metric
perturbation power spectra at 99.9% confidence level using only the TE
correlation. This value is comparable with current constraints obtained by WMAP
based on the upper limits to the B-mode amplitude. We demonstrate
that to measure PGWs by their contribution to the TE cross correlation power
spectrum in a realistic ground based experiment when real instrumental noise is
taken into account, the tensor-to-scalar ratio, , should be approximately
three times larger.Comment: 13 pages, 13 figures, version matches published version. Combined
with 0710.365
Tracking Curvaton(s)?
The ratio of the curvaton energy density to that of the dominant component of
the background sources may be constant during a significant period in the
evolution of the Universe. The possibility of having tracking curvatons, whose
decay occurs prior to the nucleosynthesis epoch, is studied. It is argued that
the tracking curvaton dynamics is disfavoured since the value of the curvature
perturbations prior to curvaton decay is smaller than the value required by
observations. It is also argued, in a related context, that the minimal
inflationary curvature scale compatible with the curvaton paradigm may be
lowered in the case of low-scale quintessential inflation.Comment: 20 pages, 4figure
Low-scale Quintessential Inflation
In quintessential inflationary model, the same master field that drives
inflation becomes, later on, the dynamical source of the (present) accelerated
expansion. Quintessential inflationary models require a curvature scale at the
end of inflation around in order to explain the large scale
fluctuations observed in the microwave sky. If the curvature scale at the end
of inflation is much smaller than , the large scale adiabatic
mode may be produced thanks to the relaxation of a scalar degree of freedom,
which will be generically denoted, according to the recent terminology, as the
curvaton field. The production of the adiabatic mode is analysed in detail in
the case of the minimal quintessential inflationary model originally proposed
by Peebles and Vilenkin.Comment: 25 pages; 5 figure
Mammalian lectin arrays for screening host-microbe interactions
Many members of the C-type lectin family of glycan-binding receptors have been ascribed roles in the recognition of microorganisms and serve as key receptors in the innate immune response to pathogens. Other mammalian receptors have become targets through which pathogens enter target cells. These receptor roles have often been documented with binding studies involving individual pairs of receptors and micro-organisms. To provide a systematic overview of interactions between microbes and the large complement of C-type lectins, here we developed a lectin array and suitable protocols for labeling of microbes that could be used to probe this array. The array contains C-type lectins from cow, chosen as a model organism of agricultural interest for which the relevant pathogen–receptor interactions have not been previously investigated in detail. Screening with yeast cells and various strains of both Gram-positive and -negative bacteria revealed distinct binding patterns, which in some cases could be explained by binding to lipopolysaccharides or capsular polysaccharides, but in other cases suggested the presence of novel glycan targets on many of the microorganisms. These results are consistent with interactions previously ascribed to the receptors, but also highlight binding to additional sugar targets that have not previously been recognized. Our findings indicate that mammalian lectin arrays represent unique discovery tools for identifying both novel ligands and new receptor functions
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
Polarization of the Microwave Background in Reionized Models
I discuss the physics of polarization in models with early reionization. For
sufficiently high optical depth to recombination the polarization is boosted on
large scales while it is suppressed on smaller scales. New peaks appear in the
polarization power spectrum, their position is proportional to the square root
of the redshift at which the reionization occurs while their amplitude is
proportional to the optical depth. For standard scenarios the rms degree of
linear polarization as measured with a 7 degree FWHM antenna (like the one of
the Brown University experiment) is , , for an optical depth of 1, 0.5 or 0 respectively. For a 1 degree FWHM
antenna this same models give , and .
Detailed measurement of polarization on large angular scales could provide an
accurate determination of the epoch of reionization, which cannot be obtained
from temperature measurements alone.Comment: 19 pages, 12 figures, Revised to match PRD accepeted version.
Improved COBE normaliztion so some numerical results change slightl
An All-Sky Analysis of Polarization in the Microwave Background
Using the formalism of spin-weighted functions we present an all-sky analysis
of polarization in the Cosmic Microwave Background (CMB). Linear polarization
is a second-rank symmetric and traceless tensor, which can be decomposed on a
sphere into spin spherical harmonics. These are the analog of the
spherical harmonics used in the temperature maps and obey the same completeness
and orthogonality relations. We show that there exist two linear combinations
of spin multipole moments which have opposite parities and can be used
to fully characterize the statistical properties of polarization in the CMB.
Magnetic-type parity combination does not receieve contributions from scalar
modes and does not cross-correlate with either temperature or electric-type
parity combination, so there are four different power spectra that fully
characterize statistical properties of CMB. We present their explicit
expressions for scalar and tensor modes in the form of line of sight integral
solution and numerically evaluate them for a representative set of models.
These general solutions differ from the expressions obtained previously in the
small scale limit both for scalar and tensor modes. A method to generate and
analyze all sky maps of temperature and polarization is given and the optimal
estimators for various power spectra and their corresponding variances are
discussed.Comment: 15 pages, 1 figure, RevTeX, matches the accepted version (to appear
in Phys. Rev. D); code available at
http://arcturus.mit.edu:80/~matiasz/CMBFAST/cmbfast.htm
The Cosmological Constant
This is a review of the physics and cosmology of the cosmological constant.
Focusing on recent developments, I present a pedagogical overview of cosmology
in the presence of a cosmological constant, observational constraints on its
magnitude, and the physics of a small (and potentially nonzero) vacuum energy.Comment: 50 pages. Submitted to Living Reviews in Relativity
(http://www.livingreviews.org/), December 199
Statistics of Cosmic Microwave Background Polarization
We present a formalism for analyzing a full-sky temperature and polarization
map of the cosmic microwave background. Temperature maps are analyzed by
expanding over the set of spherical harmonics to give multipole moments of the
two-point correlation function. Polarization, which is described by a
second-rank tensor, can be treated analogously by expanding in the appropriate
tensor spherical harmonics. We provide expressions for the complete set of
temperature and polarization multipole moments for scalar and tensor metric
perturbations. Four sets of multipole moments completely describe isotropic
temperature and polarization correlations; for scalar metric perturbations one
set is identically zero, giving the possibility of a clean determination of the
vector and tensor contributions. The variance with which the multipole moments
can be measured in idealized experiments is evaluated, including the effects of
detector noise, sky coverage, and beam width. Finally, we construct
coordinate-independent polarization two-point correlation functions, express
them in terms of the multipole moments, and derive small-angle limits.Comment: 28 pages, RevTe
Relating Differently to Intrusive Images: The Impact of Mindfulness Based Cognitive Therapy (MBCT) on Intrusive Images in Patients With Severe Health Anxiety (Hypochondriasis).
Recurrent distressing intrusive images are a common experience in hypochondriasis. The aim of the current study was to assess the impact of Mindfulness-Based Cognitive Therapy (MBCT) for hypochondriasis on the occurrence and nature of distressing intrusive imagery in hypochondriasis. A semi-structured interview was used to assess intrusive imagery, and an adapted version of the Southampton Mindfulness Questionnaire (SMQ) was used to assess participants’ relationship with their intrusive images. A consecutive series of participants (N = 20) who were receiving MBCT for hypochondriasis as part of an ongoing research program were assessed prior to participating in an 8-week MBCT intervention, immediately following the intervention, and at three month follow-up. As compared to the baseline assessment, the frequency of intrusive images, the distress associated with them, and the intrusiveness of the images were all significantly reduced at the post-MBCT assessment. Participants’ adapted SMQ scores were significantly increased following the MBCT intervention, suggesting that participants’ relationship with their intrusive images had changed in that they had developed a more ‘mindful’ and compassionate response to the images when they did occur. Effect sizes from pre- to post-intervention were medium to large (Cohen’s d = 0.75 - 1.50). All treatment gains were maintained at 3 month follow-up. Results suggest that MBCT may be an effective intervention for addressing intrusive imagery in hypochondriasis
- …