161 research outputs found
Generalization of a theorem of Gonchar
Let be two complex manifolds, let be two
nonempty open sets, let (resp. ) be an open subset of
(resp. ), and let be the 2-fold cross
Under a geometric condition on the boundary sets and we show that
every function locally bounded, separately continuous on continuous on
and separately holomorphic on
"extends" to a function continuous on a "domain of holomorphy" and
holomorphic on the interior of Comment: 14 pages, to appear in Arkiv for Matemati
Cosmological Parameters Degeneracies and Non-Gaussian Halo Bias
We study the impact of the cosmological parameters uncertainties on the
measurements of primordial non-Gaussianity through the large-scale non-Gaussian
halo bias effect. While this is not expected to be an issue for the standard
LCDM model, it may not be the case for more general models that modify the
large-scale shape of the power spectrum. We consider the so-called local
non-Gaussianity model and forecasts from planned surveys, alone and combined
with a Planck CMB prior. In particular, we consider EUCLID- and LSST-like
surveys and forecast the correlations among and the running of the
spectral index , the dark energy equation of state , the effective
sound speed of dark energy perturbations , the total mass of massive
neutrinos , and the number of extra relativistic degrees of
freedom . Neglecting CMB information on and scales /Mpc, we find that, if is assumed to be known, the
uncertainty on cosmological parameters increases the error on by
10 to 30% depending on the survey. Thus the constraint is
remarkable robust to cosmological model uncertainties. On the other hand, if
is simultaneously constrained from the data, the
error increases by . Finally, future surveys which provide a large
sample of galaxies or galaxy clusters over a volume comparable to the Hubble
volume can measure primordial non-Gaussianity of the local form with a
marginalized 1-- error of the order , after
combination with CMB priors for the remaining cosmological parameters. These
results are competitive with CMB bispectrum constraints achievable with an
ideal CMB experiment.Comment: 17 pages, 1 figure added, typos corrected, comments added, matches
the published versio
Direct and Indirect Detection of Dark Matter in D6 Flavor Symmetric Model
We study a fermionic dark matter in a non-supersymmetric extension of the
standard model with a family symmetry based on D6xZ2xZ2. In our model, the
final state of the dark matter annihilation is determined to be e+ e- by the
flavor symmetry, which is consistent with the PAMELA result. At first, we show
that our dark matter mass should be within the range of 230 GeV - 750 GeV in
the WMAP analysis combined with mu to e gamma constraint. Moreover we
simultaneously explain the experiments of direct and indirect detection, by
simply adding a gauge and D6 singlet real scalar field. In the direct detection
experiments, we show that the lighter dark matter mass ~ 230 GeV and the
lighter standard model Higgs boson ~ 115 GeV is in favor of the observed bounds
reported by CDMS II and XENON100. In the indirect detection experiments, we
explain the positron excess reported by PAMELA through the Breit-Wigner
enhancement mechanism. We also show that our model is consistent with no
antiproton excess suggested by PAMELA.Comment: 20 pages, 9 figures, 2 tables, accepted version for publication in
European Physical Journal
Some FRW Models of Accelerating Universe with Dark Energy
The paper deals with a spatially homogeneous and isotropic FRW space-time
filled with perfect fluid and dark energy components. The two sources are
assumed to interact minimally, and therefore their energy momentum tensors are
conserved separately. A special law of variation for the Hubble parameter
proposed by Berman (1983) has been utilized to solve the field equations. The
Berman's law yields two explicit forms of the scale factor governing the FRW
space-time and constant values of deceleration parameter. The role of dark
energy with variable equation of state parameter has been studied in detail in
the evolution of FRW universe. It has been found that dark energy dominates the
universe at the present epoch, which is consistent with the observations. The
physical behavior of the universe is discussed in detail.Comment: 10 pages, 5 figure
Constraints on the SZ Power Spectrum on Degree Angular Scales in WMAP Data
The Sunyaev-Zel'dovich (SZ) effect has a distinct spectral signature that
allows its separation from fluctuations in the cosmic microwave background
(CMB) and foregrounds. Using CMB anisotropies measured in Wilkinson Microwave
Anisotropy Probe's five-year maps, we constrain the SZ fluctuations at large,
degree angular scales corresponding to multipoles in the range from 10 to 400.
We provide upper bounds on SZ fluctuations at multipoles greater than 50, and
find evidence for a hemispherically asymmetric signal at ten degrees angular
scales. The amplitude of the detected signal cannot be easily explained with
the allowed number density and temperature of electrons in the Galactic halo.
We have failed to explain the excess signal as a residual from known Galactic
foregrounds or instrumental uncertainties such as 1/f-noise.Comment: 14 pages, 3 figures, 2 tables. Simple typos fixe
Limits on decaying dark energy density models from the CMB temperature-redshift relation
The nature of the dark energy is still a mystery and several models have been
proposed to explain it. Here we consider a phenomenological model for dark
energy decay into photons and particles as proposed by Lima (J. Lima, Phys.
Rev. D 54, 2571 (1996)). He studied the thermodynamic aspects of decaying dark
energy models in particular in the case of a continuous photon creation and/or
disruption. Following his approach, we derive a temperature redshift relation
for the CMB which depends on the effective equation of state and on
the "adiabatic index" . Comparing our relation with the data on the CMB
temperature as a function of the redshift obtained from Sunyaev-Zel'dovich
observations and at higher redshift from quasar absorption line spectra, we
find , adopting for the adiabatic index ,
in good agreement with current estimates and still compatible with
, implying that the dark energy content being constant in time.Comment: 8 pages, 1 figur
Reconstruction of the Dark Energy equation of state
One of the main challenges of modern cosmology is to investigate the nature
of dark energy in our Universe. The properties of such a component are normally
summarised as a perfect fluid with a (potentially) time-dependent
equation-of-state parameter . We investigate the evolution of this
parameter with redshift by performing a Bayesian analysis of current
cosmological observations. We model the temporal evolution as piecewise linear
in redshift between `nodes', whose -values and redshifts are allowed to
vary. The optimal number of nodes is chosen by the Bayesian evidence. In this
way, we can both determine the complexity supported by current data and locate
any features present in . We compare this node-based reconstruction with
some previously well-studied parameterisations: the Chevallier-Polarski-Linder
(CPL), the Jassal-Bagla-Padmanabhan (JBP) and the Felice-Nesseris-Tsujikawa
(FNT). By comparing the Bayesian evidence for all of these models we find an
indication towards possible time-dependence in the dark energy
equation-of-state. It is also worth noting that the CPL and JBP models are
strongly disfavoured, whilst the FNT is just significantly disfavoured, when
compared to a simple cosmological constant . We find that our node-based
reconstruction model is slightly disfavoured with respect to the CDM
model.Comment: 17 pages, 5 figures, minor correction
Large Scale Pressure Fluctuations and Sunyaev-Zel'dovich Effect
The Sunyaev-Zel'dovich (SZ) effect associated with pressure fluctuations of
the large scale structure gas distribution will be probed with current and
upcoming wide-field small angular scale cosmic microwave background
experiments. We study the generation of pressure fluctuations by baryons which
are present in virialized dark matter halos and by baryons present in small
overdensities. For collapsed halos, assuming the gas distribution is in
hydrostatic equilibrium with matter density distribution, we predict the
pressure power spectrum and bispectrum associated with the large scale
structure gas distribution by extending the dark matter halo approach which
describes the density field in terms of correlations between and within halos.
The projected pressure power spectrum allows a determination of the resulting
SZ power spectrum due to virialized structures. The unshocked photoionized
baryons present in smaller overdensities trace the Jeans-scale smoothed dark
matter distribution. They provide a lower limit to the SZ effect due to large
scale structure in the absence of massive collapsed halos. We extend our
calculations to discuss higher order statistics, such as bispectrum and
skewness in SZ data. The SZ-weak lensing cross-correlation is suggested as a
probe of correlations between dark matter and baryon density fields, while the
probability distribution functions of peak statistics of SZ halos in wide field
CMB data can be used as a probe of cosmology and non-Gaussian evolution of
large scale structure pressure fluctuations.Comment: 16 pages, 9 figures; Revised with expanded discussions. Phys. Rev. D.
(in press
Testing the Void against Cosmological data: fitting CMB, BAO, SN and H0
In this paper, instead of invoking Dark Energy, we try and fit various
cosmological observations with a large Gpc scale under-dense region (Void)
which is modeled by a Lemaitre-Tolman-Bondi metric that at large distances
becomes a homogeneous FLRW metric. We improve on previous analyses by allowing
for nonzero overall curvature, accurately computing the distance to the
last-scattering surface and the observed scale of the Baryon Acoustic peaks,
and investigating important effects that could arise from having nontrivial
Void density profiles. We mainly focus on the WMAP 7-yr data (TT and TE),
Supernova data (SDSS SN), Hubble constant measurements (HST) and Baryon
Acoustic Oscillation data (SDSS and LRG). We find that the inclusion of a
nonzero overall curvature drastically improves the goodness of fit of the Void
model, bringing it very close to that of a homogeneous universe containing Dark
Energy, while by varying the profile one can increase the value of the local
Hubble parameter which has been a challenge for these models. We also try to
gauge how well our model can fit the large-scale-structure data, but a
comprehensive analysis will require the knowledge of perturbations on LTB
metrics. The model is consistent with the CMB dipole if the observer is about
15 Mpc off the centre of the Void. Remarkably, such an off-center position may
be able to account for the recent anomalous measurements of a large bulk flow
from kSZ data. Finally we provide several analytical approximations in
different regimes for the LTB metric, and a numerical module for CosmoMC, thus
allowing for a MCMC exploration of the full parameter space.Comment: 70 pages, 12 figures, matches version accepted for publication in
JCAP. References added, numerical values in tables changed due to minor bug,
conclusions unaltered. Numerical module available at
http://web.physik.rwth-aachen.de/download/valkenburg
Chameleonic Generalized Brans--Dicke model and late-time acceleration
In this paper we consider Chameleonic Generalized Brans--Dicke Cosmology in
the framework of FRW universes. The bouncing solution and phantom crossing is
investigated for the model. Two independent cosmological tests: Cosmological
Redshift Drift (CRD) and distance modulus are applied to test the model with
the observation.Comment: 20 pages, 15 figures, to be published in Astrophys. Space Sci. (2011
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