152 research outputs found
Cosmological constraints on unparticle dark matter
In unparticle dark matter (unmatter) models the equation of state of the
unmatter is given by , where is the scaling factor.
Unmatter with such equations of state would have a significant impact on the
expansion history of the universe. Using type Ia supernovae (SNIa), the baryon
acoustic oscillation (BAO) measurements and the shift parameter of the cosmic
microwave background (CMB) to place constraints on such unmatter models we find
that if only the SNIa data is used the constraints are weak. However, with the
BAO and CMB shift parameter data added strong constraints can be obtained. For
the UDM model, in which unmatter is the sole dark matter, we find that
at 95% C.L. For comparison, in most unparticle physics models it is
assumed . For the CUDM model, in which unmatter co-exists with
cold dark matter, we found that the unmatter can at most make up a few percent
of the total cosmic density if , thus it can not be the major component
of dark matter.Comment: Replaced with revised version. BAO data is added to make a tighter
constraint. Version accepted for publication on Euro.Phys.J.
Cosmological constraints from galaxy clustering
In this manuscript I review the mathematics and physics that underpins recent
work using the clustering of galaxies to derive cosmological model constraints.
I start by describing the basic concepts, and gradually move on to some of the
complexities involved in analysing galaxy redshift surveys, focusing on the 2dF
Galaxy Redshift Survey (2dFGRS) and the Sloan Digital Sky survey (SDSS).
Difficulties within such an analysis, particularly dealing with redshift space
distortions and galaxy bias are highlighted. I then describe current
observations of the CMB fluctuation power spectrum, and consider the importance
of measurements of the clustering of galaxies in light of recent experiments.
Finally, I provide an example joint analysis of the latest CMB and large-scale
structure data, leading to a set of parameter constraints.Comment: 30 pages, 13 figures. Lecture given at Third Aegean Summer School,
The invisible universe: Dark matter and Dark energ
Large-scale periodicity in the distribution of QSO absorption-line systems
The spatial-temporal distribution of absorption-line systems (ALSs) observed
in QSO spectra within the cosmological redshift interval z = 0.0--4.3 is
investigated on the base of our updated catalog of absorption systems. We
consider so called metallic systems including basically lines of heavy
elements. The sample of the data displays regular variations (with amplitudes ~
15 -- 20%) in the z-distribution of ALSs as well as in the eta-distribution,
where eta is a dimensionless line-of-sight comoving distance, relatively to
smoother dependences. The eta-distribution reveals the periodicity with period
Delta eta = 0.036 +/- 0.002, which corresponds to a spatial characteristic
scale (108 +/- 6) h(-1) Mpc or (alternatively) a temporal interval (350 +/- 20)
h(-1) Myr for the LambdaCDM cosmological model. We discuss a possibility of a
spatial interpretation of the results treating the pattern obtained as a trace
of an order imprinted on the galaxy clustering in the early Universe.Comment: AASTeX, 13 pages, with 9 figures, Accepted for publication in
Astrophysics & Space Scienc
Revisiting Cardassian Model and Cosmic Constraint
In this paper, we revisit the Cardassian model in which the radiation energy
component is included. It is important for early epoch when the radiation
cannot be neglected because the equation of state (EoS) of the effective dark
energy becomes time variable. Therefore, it is not equivalent to the
quintessence model with a constant EoS anymore. This situation was almost
overlooked in the literature. By using the recent released Union2 557 of type
Ia supernovae (SN Ia), the baryon acoustic oscillation (BAO) from Sloan Digital
Sky Survey and the WiggleZ data points, the full information of cosmic
microwave background (CMB) measurement given by the seven-year Wilkinson
Microwave Anisotropy Probe observation, we constrain the Cardassian model via
the Markov Chain Monte Carlo (MCMC) method. A tight constraint is obtained: in regions. The
deviation of Cardassian model from quintessence model is shown in CMB
anisotropic power spectra at high l's parts due to the evolution of EoS. But it
is about the order of 0.1% which cannot be discriminated by current data sets.
The Cardassian model is consistent with current cosmic observational data sets.Comment: 6 pages, 5 figures, match the published versio
Cosmological scaling solutions in generalised Gauss-Bonnet gravity theories
The conditions for the existence and stability of cosmological power-law
scaling solutions are established when the Einstein-Hilbert action is modified
by the inclusion of a function of the Gauss-Bonnet curvature invariant. The
general form of the action that leads to such solutions is determined for the
case where the universe is sourced by a barotropic perfect fluid. It is shown
by employing an equivalence between the Gauss-Bonnet action and a scalar-tensor
theory of gravity that the cosmological field equations can be written as a
plane autonomous system. It is found that stable scaling solutions exist when
the parameters of the model take appropriate values.Comment: 10 pages and 5 figure
Detecting a stochastic background of gravitational radiation: Signal processing strategies and sensitivities
We analyze the signal processing required for the optimal detection of a
stochastic background of gravitational radiation using laser interferometric
detectors. Starting with basic assumptions about the statistical properties of
a stochastic gravity-wave background, we derive expressions for the optimal
filter function and signal-to-noise ratio for the cross-correlation of the
outputs of two gravity-wave detectors. Sensitivity levels required for
detection are then calculated. Issues related to: (i) calculating the
signal-to-noise ratio for arbitrarily large stochastic backgrounds, (ii)
performing the data analysis in the presence of nonstationary detector noise,
(iii) combining data from multiple detector pairs to increase the sensitivity
of a stochastic background search, (iv) correlating the outputs of 4 or more
detectors, and (v) allowing for the possibility of correlated noise in the
outputs of two detectors are discussed. We briefly describe a computer
simulation which mimics the generation and detection of a simulated stochastic
gravity-wave signal in the presence of simulated detector noise. Numerous
graphs and tables of numerical data for the five major interferometers
(LIGO-WA, LIGO-LA, VIRGO, GEO-600, and TAMA-300) are also given. The treatment
given in this paper should be accessible to both theorists involved in data
analysis and experimentalists involved in detector design and data acquisition.Comment: 81 pages, 30 postscript figures, REVTE
Observational constraint on dynamical evolution of dark energy
We use the Constitution supernova, the baryon acoustic oscillation, the
cosmic microwave background, and the Hubble parameter data to analyze the
evolution property of dark energy. We obtain different results when we fit
different baryon acoustic oscillation data combined with the Constitution
supernova data to the Chevallier-Polarski-Linder model. We find that the
difference stems from the different values of . We also fit the
observational data to the model independent piecewise constant parametrization.
Four redshift bins with boundaries at , 0.53, 0.85 and 1.8 were chosen
for the piecewise constant parametrization of the equation of state parameter
of dark energy. We find no significant evidence for evolving .
With the addition of the Hubble parameter, the constraint on the equation of
state parameter at high redshift isimproved by 70%. The marginalization of the
nuisance parameter connected to the supernova distance modulus is discussed.Comment: revtex, 16 pages, 5 figures, V2: published versio
The novel transcriptional regulator SczA mediates protection against Zn2+ stress by activation of the Zn2+-resistance gene czcD in Streptococcus pneumoniae
Maintenance of the intracellular homeostasis of metal ions is important for the virulence of many bacterial pathogens. Here, we demonstrate that the czcD gene of the human pathogen Streptococcus pneumoniae is involved in resistance against Zn2+, and that its transcription is induced by the transition-metal ions Zn2+, Co2+ and Ni2+. Upstream of czcD a gene was identified, encoding a novel TetR family regulator, SczA, that is responsible for the metal ion-dependent activation of czcD expression. Transcriptome analyses revealed that in a sczA mutant expression of czcD, a gene encoding a MerR-family transcriptional regulator and a gene encoding a zinc-containing alcohol dehydrogenase (adhB) were downregulated. Activation of the czcD promoter by SczA is shown to proceed by Zn2+-dependent binding of SczA to a conserved DNA motif. In the absence of Zn2+, SczA binds to a second site in the czcD promoter, thereby fully blocking czcD expression. This is the first example of a metalloregulatory protein belonging to the TetR family that has been described. The presence in S. pneumoniae of the Zn2+-resistance system characterized in this study might reflect the need for adjustment to a fluctuating Zn2+ pool encountered by this pathogen during infection of the human body
Combined constraints on modified Chaplygin gas model from cosmological observed data: Markov Chain Monte Carlo approach
We use the Markov Chain Monte Carlo method to investigate a global
constraints on the modified Chaplygin gas (MCG) model as the unification of
dark matter and dark energy from the latest observational data: the Union2
dataset of type supernovae Ia (SNIa), the observational Hubble data (OHD), the
cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the
cosmic microwave background (CMB) data. In a flat universe, the constraint
results for MCG model are,
()
,
()
,
()
,
()
, and ()
.Comment: 12 pages, 1figur
Time-Varying Dark Energy Constraints From the Latest SN Ia, BAO and SGL
Based on the latest SNe Ia data provided by Hicken et al. (2009) with using
MLCS17 light curve fitter, together with the Baryon Acoustic Oscillation(BAO)
and strong gravitational lenses(SGL), we investigate the constraints on the
dark energy equation-of-state parameter in the flat universe, especially
for the time-varying case . The constraints from SNe data
alone are found to be: (a) as the best-fit
results; (b) for
the two parameters in the time-varying case after marginalizing the parameter
; (c) the likelihood of parameter has a high non-Gaussian
distribution; (d) an extra restriction on is necessary to improve
the constraint of the SNe Ia data on the parameters (, ). A joint
analysis of SNe Ia data and BAO is made to break the degeneracy between and
, and leads to the interesting maximum likelihoods and
. When marginalizing the parameter , the fitting results are
found to be . After
adding the splitting angle statistic of SGL data, a consistent constraint is
obtained and the constraints on time-varying
dark energy are further improved to be , which indicates that the phantom type models are
disfavored.Comment: 24 pages, 9 figures, to be published in JCA
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