1,302 research outputs found
The Imprint of Gravitational Waves on the Cosmic Microwave Background
Long-wavelength gravitational waves can induce significant temperature
anisotropy in the cosmic microwave background. Distinguishing this from
anisotropy induced by energy density fluctuations is critical for testing
inflationary cosmology and theories of large-scale structure formation. We
describe full radiative transport calculations of the two contributions and
show that they differ dramatically at angular scales below a few degrees. We
show how anisotropy experiments probing large- and small-angular scales can
combine to distinguish the imprint due to gravitational waves.Comment: 11 pages, Penn Preprint-UPR-
Sterile Neutrinos as Dark Matter
The simplest model that can accomodate a viable nonbaryonic dark matter
candidate is the standard electroweak theory with the addition of right-handed
or sterile neutrinos. We reexamine this model and find that the sterile
neutrinos can be either hot, warm, or cold dark matter. Since their only direct
coupling is to left-handed or active neutrinos, the most efficient production
mechanism is via neutrino oscillations. If the production rate is always less
than the expansion rate, then these neutrinos will never be in thermal
equilibrium. However, enough of them may be produced so that they provide the
missing mass necessary for closure. We consider a single generation of neutrino
fields with a Dirac mass, , and a Majorana
mass for the right-handed components only, . For we show that the
number density of sterile neutrinos is proportional to so that the
energy density today is {\it independent of} . However is crucial in
determining the large scale structure of the Universe. In particular, leads to warm dark matter and a structure formation
scenario that may have some advantages over both the standard hot and cold dark
matter scenarios.Comment: 10 pages (1 figure available upon request) phyzzx,
FERMILAB-Pub-93/057-
Natural Inflation: Particle Physics Models, Power Law Spectra for Large Scale Structure, and Constraints from COBE
A pseudo-Nambu-Goldstone boson, with a potential of the form f \sim
M_{Pl}\Lambda \sim M_{GUT}f > 0.3 M_{Pl}P(k) \propto k^{n_s}n_s \simeq 1 - (M^2_{Pl}/8\pi f^2)n_s = 10 \la n_s \la 0.6-0.7b>2n_s
>0.6f > 0.3 M_{Pl}n_s > 0.7$; combined with other
bounds on large bubbles in extended inflation, this leaves little room for most
extended models.Comment: 42 pages, (12 figures not included but available from the authors
Anomalous Microwave Emission from the HII region RCW175
We present evidence for anomalous microwave emission in the RCW175 \hii
region. Motivated by 33 GHz 13\arcmin resolution data from the Very Small
Array (VSA), we observed RCW175 at 31 GHz with the Cosmic Background Imager
(CBI) at a resolution of 4\arcmin. The region consists of two distinct
components, G29.0-0.6 and G29.1-0.7, which are detected at high signal-to-noise
ratio. The integrated flux density is Jy at 31 GHz, in good
agreement with the VSA. The 31 GHz flux density is Jy
() above the expected value from optically thin free-free emission
based on lower frequency radio data and thermal dust constrained by IRAS and
WMAP data. Conventional emission mechanisms such as optically thick emission
from ultracompact \hii regions cannot easily account for this excess. We
interpret the excess as evidence for electric dipole emission from small
spinning dust grains, which does provide an adequate fit to the data.Comment: 5 pages, 2 figures, submmited to ApJ Letter
Multiscale Phenomenology of the Cosmic Web
We analyze the structure and connectivity of the distinct morphologies that
define the Cosmic Web. With the help of our Multiscale Morphology Filter (MMF),
we dissect the matter distribution of a cosmological CDM N-body
computer simulation into cluster, filaments and walls. The MMF is ideally
suited to adress both the anisotropic morphological character of filaments and
sheets, as well as the multiscale nature of the hierarchically evolved cosmic
matter distribution. The results of our study may be summarized as follows:
i).- While all morphologies occupy a roughly well defined range in density,
this alone is not sufficient to differentiate between them given their overlap.
Environment defined only in terms of density fails to incorporate the intrinsic
dynamics of each morphology. This plays an important role in both linear and
non linear interactions between haloes. ii).- Most of the mass in the Universe
is concentrated in filaments, narrowly followed by clusters. In terms of
volume, clusters only represent a minute fraction, and filaments not more than
9%. Walls are relatively inconspicous in terms of mass and volume. iii).- On
average, massive clusters are connected to more filaments than low mass
clusters. Clusters with M h have on average
two connecting filaments, while clusters with M
h have on average five connecting filaments. iv).- Density profiles
indicate that the typical width of filaments is 2\Mpch. Walls have less well
defined boundaries with widths between 5-8 Mpc h. In their interior,
filaments have a power-law density profile with slope ,
corresponding to an isothermal density profile.Comment: 28 pages, 22 figures, accepted for publication in MNRAS. For a
high-res version see http://www.astro.rug.nl/~weygaert/webmorph_mmf.pd
Protocol for the effect evaluation of Individual Placement and Support (IPS): a randomized controlled multicenter trial of IPS versus treatment as usual for patients with moderate to severe mental illness in Norway
Observational Constraints to Ricci Dark Energy Model by Using: SN, BAO, OHD, fgas Data Sets
In this paper, we perform a global constraint on the Ricci dark energy model
with both the flat case and the non-flat case, using the Markov Chain Monte
Carlo (MCMC) method and the combined observational data from the cluster X-ray
gas mass fraction, Supernovae of type Ia (397), baryon acoustic oscillations,
current Cosmic Microwave Background, and the observational Hubble function. In
the flat model, we obtain the best fit values of the parameters in regions: ,
, , . In the non-flat
model, the best fit parameters are found in
regions:,
, , ,
. Compared to the constraint results in
the model by using the same datasets, it is shown that
the current combined datasets prefer the model to the
Ricci dark energy model.Comment: 12 pages, 3 figure
Cosmic Concordance and Quintessence
We present a comprehensive study of the observational constraints on
spatially flat cosmological models containing a mixture of matter and
quintessence --- a time varying, spatially inhomogeneous component of the
energy density of the universe with negative pressure. Our study also includes
the limiting case of a cosmological constant. Low red shift constraints include
the Hubble parameter, baryon fraction, cluster abundance, age of the universe,
bulk velocity and shape of the mass power spectrum; intermediate red shift
constraints are due to type 1a supernovae, gravitational lensing, the Ly-a
forest, and the evolution of large scale structure; high red shift constraints
are based on cosmic microwave background temperature anisotropy. Mindful of
systematic errors, we adopt a conservative approach in applying these
constraints. We determine that quintessence models in which the matter density
parameter is 0.2 \ls \Omega_m \ls 0.5 and the effective, density-averaged
equation of state is -1 \le w \ls -0.2, are consistent with the most
reliable, current low red shift and CMB observations at the level.
Factoring in the constraint due to type 1a SNe, the range for the equation of
state is reduced to -1 \le w \ls -0.4, where this range represents models
consistent with each observational constraint at the 2 level or better
(concordance analysis). A combined maximum likelihood analysis suggests a
smaller range, -1 \le w \ls -0.6. We find that the best-fit and
best-motivated quintessence models lie near , , and spectral index , with an effective equation of state for ``tracker'' quintessence and for ``creeper''
quintessence. (abstract shortened)Comment: revised to match ApJ version; 33 pages; 20 figures, 4 in color; uses
emulateapj.st
Skewness in the Cosmic Microwave Background Anisotropy from Inflationary Gravity Wave Background
In the context of inflationary scenarios, the observed large angle anisotropy
of the Cosmic Microwave Background (CMB) temperature is believed to probe the
primordial metric perturbations from inflation. Although the perturbations from
inflation are expected to be gaussian random fields, there remains the
possibility that nonlinear processes at later epochs induce ``secondary''
non-gaussian features in the corresponding CMB anisotropy maps. The
non-gaussianity induced by nonlinear gravitational instability of scalar
(density) perturbations has been investigated in existing literature. In this
paper, we highlight another source of non-gaussianity arising out of higher
order scattering of CMB photons off the metric perturbations. We provide a
simple and elegant formalism for deriving the CMB temperature fluctuations
arising due to the Sachs-Wolfe effect beyond the linear order. In particular,
we derive the expression for the second order CMB temperature fluctuations. The
multiple scattering effect pointed out in this paper leads to the possibility
that tensor metric perturbation, i.e., gravity waves (GW) which do not exhibit
gravitational instability can still contribute to the skewness in the CMB
anisotropy maps. We find that in a flat universe, the skewness in
CMB contributed by gravity waves via multiple scattering effect is comparable
to that from the gravitational instability of scalar perturbations for equal
contribution of the gravity waves and scalar perturbations to the total rms CMB
anisotropy. The secondary skewness is found to be smaller than the cosmic
variance leading to the conclusion that inflationary scenarios do predict that
the observed CMB anisotropy should be statistically consistent with a gaussian
random distribution.Comment: 10 pages, Latex (uses revtex), 1 postscript figure included. Accepted
for publication in Physical Review
Keeping it in the family: Parental influences on young people's attitudes to police
Prior research finds young people are less satisfied with police than their older counterparts. Despite this, our understanding of youth attitudes to police is limited, as most research has focused on adult attitudes to police. This study adds to our understanding by examining the influence of parentâchild dynamics on youth attitudes to police. We predict that youth attitudes to police will be influenced by their parentsâ attitudes. A survey of 540 school students in South East Queensland reveals that perceived parental attitudes to police are associated with youth attitudes to police. However, this effect is partially mediated by maternal, but not paternal attachment. These findings suggest that youth attitudes to police are not simply influenced by contact with police and delinquency, but that familial context is important. Consequently, our theoretical understanding of youth attitudes to police must move beyond a focus upon police contact and delinquency
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