367 research outputs found
What's Behind Acoustic Peaks in the Cosmic Microwave Background Anisotropies
We give a brief review of the physics of acoustic oscillations in Cosmic
Microwave Background (CMB) anisotropies. As an example of the impact of their
detection in cosmology, we show how the present data on CMB angular power
spectrum on sub-degree scales can be used to constrain dark energy cosmological
models.Comment: 6 pages, proceedings to the TAUP2001 conference, LNGS, Italy, Sept.
200
Direct Detection of Dark Matter Rates for Various Wimps
The event rates for the direct detection of a dark matter candidate, which is
a Kaluza-Klein gauge boson, are evaluated for a number of nuclear targets.
Realistic form factors as well as spin ME and response functions are employed.Comment: 23 LaTex pages, 22 eps figure
Multiple Methods for Estimating the Bispectrum of the Cosmic Microwave Background with Application to the MAXIMA Data
We describe different methods for estimating the bispectrum of Cosmic
Microwave Background data. In particular we construct a minimum variance
estimator for the flat-sky limit and compare results with previously-studied
frequentist methods. Application to the MAXIMA dataset shows consistency with
primordial Gaussianity. Weak quadratic non-Gaussianity is characterised by a
tunable parameter , corresponding to non-Gaussianity at a level (ratio of non-Gaussian to Gaussian terms), and we find limits of
for the minimum-variance estimator and for the
usual frequentist estimator. These are the tightest limits on primordial
non-Gaussianity which include the full effects of the radiation transfer
function.Comment: 24 pages, 13 figure
A high-frequency study of the Sunyaev-Zel'dovich effect morphology in galaxy clusters
High-frequency, high-resolution imaging of the Sunyaev-Zel'dovich (SZ) effect
is an important technique to study the complex structures of the atmospheres of
merging galaxy clusters. Such observations are sensitive to the details of the
electron spectrum. We show that the morphology of the SZ intensity maps in
simulated galaxy clusters observed at 345 GHz, 600 GHz, and 857 GHz are
significantly different because of SZ relativistic corrections. These
differences can be revealed by high-resolution imaging instruments.
We calculate relativistically corrected SZ intensity maps of a simulated,
massive, merging galaxy cluster and of the massive, merging clusters 1E0657-558
(the Bullet Cluster) and Abell 2219. The morphologies of the SZ intensity maps
are remarkably different between 345 GHz and 857 GHz for each merging cluster.
We show that high-resolution imaging observations of the SZ intensity maps at
these frequencies, obtainable with the LABOCA and HERSCHEL-SPIRE instruments,
allow to fully exploit the astrophysical relevance of the predicted SZ
morphological effect.Comment: 9 pages, 14 figures, accepted for publication in MNRA
The Influence of Free Quintessence on Gravitational Frequency Shift and Deflection of Light with 4D momentum
Based on the 4D momentum, the influence of quintessence on the gravitational
frequency shift and the deflection of light are examined in modified
Schwarzschild space. We find that the frequency of photon depends on the state
parameter of quintessence : the frequency increases for and
decreases for . Meanwhile, we adopt an integral power number
() to solve the orbital equation of photon. The photon's
potentials become higher with the decrease of . The behavior of
bending light depends on the state parameter sensitively. In
particular, for the case of , there is no influence on the
deflection of light by quintessence. Else, according to the H-masers of GP-A
redshift experiment and the long-baseline interferometry, the constraints on
the quintessence field in Solar system are presented here.Comment: 12 pages, 2 figures, 4 tables. European Physical Journal C in pres
Cosmological limit on the neutrino mass
We have performed a careful analysis of constraints on the neutrino mass from
current cosmological data. Combining data from the cosmic microwave background
and the 2dF galaxy survey yields an upper limit on the sum of the three
neutrino mass eigenstates of \sum m_nu < 3 eV (95% conf.), without including
additional priors. Including data from SNIa observations, Big Bang
nucleosynthesis, and HST Hubble key project data on H_0 tightens the limit to
\sum m_nu < 2.5 eV (95% conf.). We also perform a Fisher matrix analysis which
illustrates the cosmological parameter degeneracies affecting the determination
of \sum m_nu.Comment: 6 pages, 2 figures, uses Revtex
Laparoscopic fistula excision and omentoplasty for high rectovaginal fistulas: a prospective study of 40 patients
AIM: The aim of this study is to prospectively evaluate 40 patients with a high rectovaginal fistula treated by a laparoscopic fistula division and closure, followed by an omentoplasty. PATIENTS AND METHODS: Forty patients with a rectovaginal fistula, between the middle third of the rectum and the posterior vaginal fornix, resulting from different causes (IBD, iatrogenic and birth trauma) were treated by a laparoscopic excision of the fistula and insertion of an omentoplasty in the rectovaginal septum. The patients completed the gastrointestinal quality of life index questionnaire (GIQLI) and the Cleveland Clinic incontinence score (CCIS). All tests were performed at regular intervals after treatment. RESULTS: In 38 (95%) patients with a median age of 53 years (range 33-72), the surgical procedure was feasible. In two patients, the fistula was closed without an omentoplasty, and a diverting stoma was performed. The median follow-up was 28 months (range 10-35). Two patients (5%) developed a recurrent fistula. In one patient, the interposed omentum became necrotic and was successfully treated laparoscopically. In another patient, an abscess developed, which needed drainage procedures. The mean CCIS was 9 (range 7-10) before treatment and 10 (range 7-13) after treatment (p = 0.5 Wilcoxon). The median GIQLI score was 85 (range 34-129) before treatment and 120 (range75-142) after treatment (p = 0.0001, Wilcoxon). CONCLUSIONS: Laparoscopic fistula excision combined with omentoplasty is a good treatment modality with a high healing rate for high rectovaginal fistulas and an acceptable complication rate
The Yuan-Tseh Lee Array for Microwave Background Anisotropy
The Yuan-Tseh Lee Array for Microwave Background Anisotropy (AMiBA) is the
first interferometer dedicated to studying the cosmic microwave background
(CMB) radiation at 3mm wavelength. The choice of 3mm was made to minimize the
contributions from foreground synchrotron radiation and Galactic dust emission.
The initial configuration of seven 0.6m telescopes mounted on a 6-m hexapod
platform was dedicated in October 2006 on Mauna Loa, Hawaii. Scientific
operations began with the detection of a number of clusters of galaxies via the
thermal Sunyaev-Zel'dovich effect. We compare our data with Subaru weak lensing
data in order to study the structure of dark matter. We also compare our data
with X-ray data in order to derive the Hubble constant.Comment: accepted for publication in ApJ (13 pages, 7 figures); a version with
high resolution figures available at
http://www.asiaa.sinica.edu.tw/~keiichi/upfiles/AMiBA7/pho_highreso.pd
Cosmological structure formation in a homogeneous dark energy background
There is now strong evidence that the current energy density of the Universe
is dominated by dark energy with an equation of state w<-1/3, which is causing
accelerated expansion. The build-up of structure within such Universes is
subject to significant ongoing study, particularly through the spherical
collapse model. This paper aims to review and consolidate progress for
cosmologies in which the dark energy component remains homogeneous on the
scales of the structures being modelled. The equations presented are designed
to allow for dark energy with a general time-varying equation of state w(a). In
addition to reviewing previous work, a number of new results are introduced: A
new fitting formula for the linear growth factor in constant w cosmologies is
given. A new formalism for determining the critical density for collapse is
presented based on the initial curvature of the perturbation. The commonly used
approximation to the critical density for collapse based on the linear growth
factor is discussed for a general dark energy equation of state. Virialisation
within such cosmologies is also considered, and the standard assumption that
energy is conserved between turn-around and virialisation is questioned and
limiting possiblities are presented.Comment: 13 pages, 9 figures, yet more typos corrected, A&A accepte
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