317 research outputs found
Helical Magnetic Fields from Inflation
We analyze the generation of seed magnetic fields during de Sitter inflation
considering a non-invariant conformal term in the electromagnetic Lagrangian of
the form , where
is a pseudoscalar function of a non-trivial background field .
In particular, we consider a toy model, that could be realized owing to the
coupling between the photon and either a (tachyonic) massive pseudoscalar field
and a massless pseudoscalar field non-minimally coupled to gravity, where
follows a simple power-law behavior during
inflation, while it is negligibly small subsequently. Here, is a positive
dimensionless constant, the wavenumber, the conformal time, and
a real positive number. We find that only when and astrophysically interesting fields can be produced as
excitation of the vacuum, and that they are maximally helical.Comment: 17 pages, 1 figure, subsection IIc and references added; accepted for
publication in IJMP
The importance of viral load in the severity of acute bronchiolitis in hospitalized infants
OBJECTIVE: The relationship between viral load and the clinical evolution of bronchiolitis is controversial. Therefore, we aimed to analyze viral loads in infants hospitalized for bronchiolitis.
METHODS: We tested for the presence of human respiratory syncytial virus (HRSV) or human rhinovirus (HRV) using quantitative molecular tests of nasopharyngeal secretions and recorded severity outcomes.
RESULTS: We included 70 infants [49 (70%) HRSV, 9 (13%) HRV and 12 (17%) HRSV+HRV]. There were no differences among the groups according to the outcomes analyzed individually. Clinical scores showed greater severity in the isolated HRSV infection group. A higher isolated HRSV viral load was associated with more prolonged ventilatory support, oxygen therapy, and hospitalization days, even after adjustment for the age and period of nasopharyngeal secretion collection. In the co-infection groups, there was a longer duration of oxygen therapy when the HRSV viral load was predominant. Isolated HRV infection and co-infection with a predominance of HRV were not associated with severity.
CONCLUSION: Higher HRSV viral load in isolated infections and the predominance of HRSV in co-infections, independent of viral load, were associated with greater severity. These results contribute to the development of therapeutic and prophylactic approaches and a greater understanding of the pathophysiology of bronchiolitis
Reconstructing the Primordial Spectrum with CMB Temperature and Polarization
We develop a new method to reconstruct the power spectrum of primordial
curvature perturbations, , by using both the temperature and polarization
spectra of the cosmic microwave background (CMB). We test this method using
several mock primordial spectra having non-trivial features including the one
with an oscillatory component, and find that the spectrum can be reconstructed
with a few percent accuracy by an iterative procedure in an ideal situation in
which there is no observational error in the CMB data. In particular, although
the previous ``cosmic inversion'' method, which used only the temperature
fluctuations, suffered from large numerical errors around some specific values
of that correspond to nodes in a transfer function, these errors are found
to disappear almost completely in the new method.Comment: 18 pages, 17 figures, submitted to PR
Natural Inflation, Planck Scale Physics and Oscillating Primordial Spectrum
In the ``natural inflation'' model, the inflaton potential is periodic. We
show that Planck scale physics may induce corrections to the inflaton
potential, which is also periodic with a greater frequency. Such high frequency
corrections produce oscillating features in the primordial fluctuation power
spectrum, which are not entirely excluded by the current observations and may
be detectable in high precision data of cosmic microwave background (CMB)
anisotropy and large scale structure (LSS) observations.Comment: 20 pages, 11 figures. To appear in Int J Mod. Phys.
Statistical Properties of Gamma-Ray Burst Polarization
The emission mechanism and the origin and structure of magnetic fields in
gamma-ray burst (GRB) jets are among the most important open questions
concerning the nature of the central engine of GRBs. In spite of extensive
observational efforts, these questions remain to be answered and are difficult
or even impossible to infer with the spectral and lightcurve information
currently collected. Polarization measurements will lead to unambiguous answers
to several of these questions. Recent developments in X-ray and gamma-ray
polarimetry techniques have demonstrated a significant increase in sensitivity
enabling several new mission concepts, e.g. POET (Polarimeters for Energetic
Transients), providing wide field of view and broadband polarimetry
measurements. If launched, missions of this kind would finally provide
definitive measurements of GRB polarizations. We perform Monte Carlo
simulations to derive the distribution of GRB polarizations in three emission
models; the synchrotron model with a globally ordered magnetic field (SO
model), the synchrotron model with a locally random magnetic field (SR model),
and the Compton drag model (CD model). The results show that POET, or other
polarimeters with similar capabilities, can constrain the GRB emission models
by using the statistical properties of GRB polarizations. In particular, the
ratio of the number of GRBs for which the polarization degrees can be measured
to the number of GRBs that are detected (N_m/N_d) and the distributions of the
polarization degrees (Pi) can be used as the criteria. If N_m/N_d > 30% and Pi
is clustered between 0.2 and 0.7, the SO model will be favored. If instead
N_m/N_d < 15%, then the SR or CD model will be favored. If several events with
Pi > 0.8 are observed, then the CD model will be favored.Comment: Replaced with accepted version in ApJ. A few minor changes done.
References adde
Cosmology with CMB anisotropy
Measurements of CMB anisotropy and, more recently, polarization have played a
very important role allowing precise determination of various parameters of the
`standard' cosmological model. The expectation of the paradigm of inflation and
the generic prediction of the simplest realization of inflationary scenario in
the early universe have also been established -- `acausally' correlated initial
perturbations in a flat, statistically isotropic universe, adiabatic nature of
primordial density perturbations. Direct evidence for gravitational instability
mechanism for structure formation from primordial perturbations has been
established. In the next decade, future experiments promise to strengthen these
deductions and uncover the remaining crucial signature of inflation -- the
primordial gravitational wave background.Comment: Plenary talk at the IXth. International Workshop on High Energy
Physics Phenomenology (WHEPP-9), Institute of Physics, Bhubaneshwar, India.
Jan 3-14, 2006; To appear in the Proceedings to be published in Pramana; 12
pages, 2 figure
`Standard' Cosmological model & beyond with CMB
Observational Cosmology has indeed made very rapid progress in the past
decade. The ability to quantify the universe has largely improved due to
observational constraints coming from structure formation Measurements of CMB
anisotropy and, more recently, polarization have played a very important role.
Besides precise determination of various parameters of the `standard'
cosmological model, observations have also established some important basic
tenets that underlie models of cosmology and structure formation in the
universe -- `acausally' correlated initial perturbations in a flat,
statistically isotropic universe, adiabatic nature of primordial density
perturbations. These are consistent with the expectation of the paradigm of
inflation and the generic prediction of the simplest realization of
inflationary scenario in the early universe. Further, gravitational instability
is the established mechanism for structure formation from these initial
perturbations. The signature of primordial perturbations observed as the CMB
anisotropy and polarization is the most compelling evidence for new, possibly
fundamental, physics in the early universe. The community is now looking beyond
the estimation of parameters of a working `standard' model of cosmology for
subtle, characteristic signatures from early universe physics.Comment: 16 pages, 6 figures, Plenary talk, Proc. of GR-19, Mexico City,
Mexico (Jul 5-9, 2010). To appear in a special issue in Class. Q. Gra
Scale dependence of the primordial spectrum from combining the three-year WMAP, Galaxy Clustering, Supernovae, and Lyman-alpha forests
We probe the scale dependence of the primordial spectrum in the light of the
three-year WMAP (WMAP3) alone and WMAP3 in combination with the other
cosmological observations such as galaxy clustering and Type Ia Supernova
(SNIa). We pay particular attention to the combination with the Lyman
(Ly) forest. Different from the first-year WMAP (WMAP1), WMAP3's
preference on the running of the scalar spectral index on the large scales is
now fairly independent of the low CMB multipoles . A combination with the
galaxy power spectrum from the Sloan Digital Sky Survey (SDSS) prefers a
negative running to larger than 2, regardless the presence of low
CMB () or not. On the other hand if we focus on the
Power Law CDM cosmology with only six parameters (matter density
, baryon density , Hubble Constant , optical
depth , the spectral index, , and the amplitude, , of the
scalar perturbation spectrum) when we drop the low CMB contributions
WMAP3 is consistent with the Harrison-Zel'dovich-Peebles scale-invariant
spectrum ( and no tensor contributions) at . When assuming
a simple power law primordial spectral index or a constant running, in case one
drops the low contributions () WMAP3 is consistent
with the other observations better, such as the inferred value of .
We also find, using a spectral shape with a minimal extension of the running
spectral index model, LUQAS CROFT Ly and SDSS Ly exhibit
somewhat different preference on the spectral shape.Comment: 16 pages, 13 figures Revtex
Detailed optical and near-infrared polarimetry, spectroscopy and broadband photometry of the afterglow of GRB 091018: Polarisation evolution
[Abridged] A number of phenomena have been observed in GRB afterglows that
defy explanation by simple versions of the standard fireball model, leading to
a variety of new models. Polarimetry can be a major independent diagnostic of
afterglow physics, probing the magnetic field properties and internal structure
of the GRB jets. In this paper we present the first high quality multi-night
polarimetric light curve of a Swift GRB afterglow, aimed at providing a well
calibrated dataset of a typical afterglow to serve as a benchmark system for
modelling afterglow polarisation behaviour. In particular, our dataset of the
afterglow of GRB 091018 (at redshift z=0.971) comprises optical linear
polarimetry (R band, 0.13 - 2.3 days after burst); circular polarimetry (R
band) and near-infrared linear polarimetry (Ks band). We add to that high
quality optical and near-infrared broadband light curves and spectral energy
distributions as well as afterglow spectroscopy. The linear polarisation varies
between 0 and 3%, with both long and short time scale variability visible. We
find an achromatic break in the afterglow light curve, which corresponds to
features in the polarimetric curve. We find that the data can be reproduced by
jet break models only if an additional polarised component of unknown nature is
present in the polarimetric curve. We probe the ordered magnetic field
component in the afterglow through our deep circular polarimetry, finding
P_circ < 0.15% (2 sigma), the deepest limit yet for a GRB afterglow, suggesting
ordered fields are weak, if at all present. Our simultaneous R and Ks band
polarimetry shows that dust induced polarisation in the host galaxy is likely
negligible.Comment: 20 pages, 14 figures, 3 tables. Accepted for publication in MNRAS.
Some figures are reduced in quality to comply with arXiv size requirement
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