55 research outputs found
Exploring the potentiality of standard sirens to probe cosmic opacity at high redshifts
In this work, using the Gaussian process, we explore the potentiality of
future gravitational wave (GW) measurements to probe cosmic opacity at high
redshifts through comparing its opacity-free luminosity distance (LD) with the
opacity-dependent one from the combination of Type Ia supernovae (SNIa) and
gamma-ray bursts (GRBs). The GW data, SNIa and GRB data are simulated from the
measurements of the future Einstein Telescope, the actual Pantheon compilation
and the latest observation of GRBs compiled by L. Amati {\it et al},
respectively. A nonparametric method is proposed to probe the spatial
homogeneity of cosmic transparency at high redshift by comparing the LD
reconstructed from the GW data with
that reconstructed from the Pantheon and GRB data. In addition, the cosmic
opacity is tested by using the parametrization for the optical depth, and the
results show that the constraints on cosmic opacity are more stringent than the
previous ones. It shows that the future GW measurements may be used as an
important tool to probe the cosmic opacity in the high redshift region.Comment: 21pages, 3 figures accepted by EPJC. arXiv admin note: text overlap
with arXiv:1912.0232
Testing the FLRW metric with the Hubble and transversal BAO measurements
The cosmological principle is one of the fundamental assumptions of the
standard model of Cosmology (SCM), and it allow us to describe cosmic distances
and clocks by using the Friedmann-Lema\rm{\hat{{\i}}}tre-Roberton-Walker
(FLRW) metric. Thus, it is essential to test the FLRW metric with cosmological
observations to verify the validity of the SCM. In this work, we perform tests
of the FLRW metric by comparing the observational comoving angles between the
Hubble and angular Baryon Acoustic Oscillation (BAO) measurements. The
Gaussian process is employed to reconstruct the Hubble measurements and
the angular diameter distance (ADD) from the transversal BAO data. A
non-parametric method is adopted to probe the possible deviations from the FLRW
metric at any redshift by comparing the comoving distances from the
reconstructed Hubble measurements with the ADD reconstructed from the
transversal BAO data. Then, we propose two types of parameterizations for the
deviations from the FLRW metric, and test the FLRW metric by using the priors
of specific sound horizon scales. To avoid the bias caused by the prior of a
specific sound horizon scale, we perform the consistency test with a flat prior
of the sound horizon scale. We find that there a concordance between the FLRW
metric and the observational data by using parametric and non-parametric
methods, and the parameterizations can be employed to test the FLRW metric in a
new way independent of the sound horizon scale.Comment: Submitted to PRD and received comments from referee
A parametrization for the growth index of linear matter perturbations
We propose a parametrization for the growth index of the linear matter
perturbations, . The growth factor of
the perturbations parameterized as is analyzed for both the
CDM model and the DGP model with our proposed form for . We find
that is negative for the CDM model but is positive for the DGP
model. Thus it provides another signature to discriminate them. We demonstrate
that with taking our proposed form approximates
the growth factor very well both at low and high redshfits for both kinds of
models. In fact, the error is below 0.03% for the CDM model and 0.18%
for the DGP model for all redshifts when . Therefore, our
parametrization may be robustly used to constrain the growth index of different
models with the observational data which include points for redshifts ranging
from 0.15 to 3.8, thus providing discriminative signatures for different
models.Comment: 14 pages, 6 figures; Added reference
The growth of linear perturbations in the DGP model
We study the linear growth of matter perturbations in the DGP model with the
growth index as a function of redshift. At the linear approximation:
, we find that, for
, takes the value from 0.658 to 0.671,
and ranges from 0.035 to 0.042. With three low redshift
observational data of the growth factor, we obtain the observational
constraints on and for the and DGP models
and find that the observations favor the model but at the
confidence level both the and DGP models are consistent
with the observations.Comment: 12 pages, 4 figuers, to appear in PL
The growth factor of matter perturbations in an f(R) gravity
The growth of matter perturbations in the model proposed by
Starobinsky is studied in this paper. Three different parametric forms of the
growth index are considered respectively and constraints on the model are
obtained at both the and confidence levels, by using the
current observational data for the growth factor. It is found, for all the
three parametric forms of the growth index examined, that the Starobinsky model
is consistent with the observations only at the confidence level.Comment: 15 pages, 5 figure
Development of a real-time simulator of the radio frequency system for the XFEL toinvestigate the stability of the digital field-controller
An dem Beschleuniger XFEL bei DESY werden neunzellige supraleitende Beschleunigungsresonatoren
benutzt werden. Ein derartiger Beschleunigungsresonator hat einen
Beschleunigungsmode und Störungsmoden. Das elektromagnetische Feld im Beschleunigungsresonator
wird mit einer speziellen Feldregelungselektronik gesteuert. Zur Untersuchung
der Stabilität der Feldregelung werden zwei Simulationsmodelle eines Beschleunigungsresonators
entwickelt. Das ein Modell simuliert den Beschleunigungsmode
jedoch ohne Störungsmode, das andere berücksichtigt insbesondere den hauptsächlichen
Störungsmode. Um schnelle realitätsnahe Ergebnisse zu erhalten, wird ein Echtzeitsimulator
für einen Beschleunigungsresonator in einem FPGA entwickelt. Mit dem Echtzeitsimulator
wird untersucht, wie der Störungsmode auf die Stabilität der Feldregelung
wirkt.Nine-cell superconducting acceleration cavities will be used in the accelarator XFEL at
DESY. This type of cavity can operate in either acceleration or disturbance modes. And
a field controller is used to regulate the accelerating field. To investigate the stabillity
of the field-controller, two simulation models were developed. One was designed only
with the acceleration mode but no disturbance mode, the other was designed including
the main disturbance mode. To get quick and realistic results, a real-time simulator for
the cavity was developed and implemented in an FPGA. With this simulator it can be
further investigated, how the interference mode affects the stablity of the field-controller
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