62 research outputs found
Primordial Non-Gaussianity from LAMOST Surveys
The primordial non-Gaussianity (PNG) in matter density perturbation is a very
powerful probe of the physics of the very early Universe. The local PNG can
induce a distinct scale-dependent bias on the large scale structure
distribution of galaxies and quasars, which could be used for constraining it.
We study the detection limits on PNG from the surveys of the LAMOST telescope.
The cases of the main galaxy survey, the luminous red galaxy (LRG) survey, and
the quasar survey of different magnitude limits are considered. We find that
the MAIN1 sample (i.e. the main galaxy survey with one magnitude deeper than
the SDSS main galaxy survey, or r<18.8) could only provide very weak constraint
on PNG. For the MAIN2 sample (r<19.8) and the LRG survey, the 2\sigma (95.5%)
limit on the PNG parameter f_{NL} are |f_{NL}|<145 and |f_{NL}|<114
respectively, comparable to the current limit from cosmic microwave background
(CMB) data. The quasar survey could provide much more stringent constraint, and
we find that the 2\sigma limit for |f_{NL}| is between 50 and 103, depending on
the magnitude limit of the survey. With Planck-like priors on cosmological
parameters, the quasar survey with g<21.65 would improve the constraints to
|f_{NL}|<43 (2\sigma). We also discuss the possibility of further tightening
the constraint by using the relative bias method proposed by Seljak(2008).Comment: 8 pages, 2 figures, RAA accepte
Cosmological Implications of 5-dimensional Brans-Dicke Theory
The five dimensional Brans-Dicke theory naturally provides two scalar fields
by the Killing reduction mechanism. These two scalar fields could account for
the accelerated expansion of the universe. We test this model and constrain its
parameter by using the type Ia supernova (SN Ia) data. We find that the best
fit value of the 5-dimensional Brans-Dicke coupling contant is .
This result is also consistent with other observations such as the baryon
acoustic oscillation (BAO).Comment: 5 pages, 4 figures, PLB accepte
The consistency test on the cosmic evolution
We propose a new and robust method to test the consistency of the cosmic
evolution given by a cosmological model. It is realized by comparing the
combined quantity r_d^CMB/D_V^SN, which is derived from the comoving sound
horizon r_d from cosmic microwave background (CMB) measurements and the
effective distance D_V derived from low-redshift Type-Ia supernovae (SNe Ia)
data, with direct and independent r_d/D_V obtained by baryon acoustic
oscillation (BAO) measurements at median redshifts. We apply this test method
for the Lambda-CDM and wCDM models, and investigate the consistency of the
derived value of r_d/D_V from Planck 2015 and the SN Ia data sets of Union2.1
and JLA (z<1.5), and the r_d/D_V directly given by BAO data from
six-degree-field galaxy survey (6dFGS), Sloan Digital Sky Survey Data Release 7
Main Galaxy Survey (SDSS-DR7 MGS), DR11 of SDSS-III, WiggleZ and Ly-alpha
forecast surveys from Baryon Oscillation Spectroscopic Data (BOSS) DR-11 over
0.1<z<2.36. We find that r_d^CMB/D_V^SN for both non-flat Lambda-CDM and flat
wCDM models with Union2.1 and JLA data are well consistent with the BAO and CMB
measurements within 1-sigma CL. Future surveys will further tight up the
constraints significantly, and provide stronger test on the consistency.Comment: 11 pages, 5 figures, 4 tables. Version accepted by PR
Cosmological Constraints on Invisible Decay of Dark Matter
The cold dark matter may be in a meta-stable state and decays to other
particles with a very long lifetime. If the decaying products of the dark
matter are weakly interacting, e.g. neutrinos, then it would have little impact
on astrophysical processes and is therefore difficult to observe. However, such
a decay would affect the expansion history of the Universe because of the
change of the equation of state. We utilize a high-quality type Ia supernovae
(SN Ia) data set selected from several resent observations and the position of
the first peak of the Cosmic Microwave Background (CMB) angular spectrum given
by the WMAP three-year data to constrain the dark matter decay-to-neutrino rate
, where is the fraction of the rest mass
which gets converted to neutrinos, and is the decay width. We
find that Gyr at 95.5% confidence level
Two Component Model of Dark Energy
We consider the possibility that the dark energy is made up of two or more
independent components, each having a different equation of state. We fit the
model with supernova and gamma-ray burst (GRB) data from resent observations,
and use the Markov Chain Monte Carlo (MCMC) technique to estimate the allowed
parameter regions. We also use various model selection criteria to compare the
two component model with the LCDM, one component dark energy model with static
or variable w(XCDM), and with other multi-component models. We find that the
two component models can give reasonably good fit to the current data. For some
data sets, and depending somewhat on the model selection criteria, the two
component model can give better fit to the data than XCDM with static w and
XCDM with variable w parameterized by w = w_0 + w_az/(1+z).Comment: 10 pages, 8 figures, 3 tables; Version accepted by PR
Implications of the Stellar Mass Density of High- Massive Galaxies from JWST on Warm Dark Matter
A significant excess of the stellar mass density at high redshift has been
discovered from the early data release of James Webb Space Telescope
(), and it may require a high star formation efficiency. However,
this will lead to large number density of ionizing photons in the epoch of
reionization (EoR), so that the reionization history will be changed, which can
arise tension with the current EoR observations. Warm dark matter (WDM), via
the free streaming effect, can suppress the formation of small-scale structure
as well as low-mass galaxies. This provides an effective way to decrease the
ionizing photons when considering a large star formation efficiency in high-
massive galaxies without altering the cosmic reionization history. On the other
hand, the constraints on the properties of warm dark matter can be derived from
the observations. In this work, we study WDM as a possible solution
to reconcile the stellar mass density of high- massive galaxies
and reionization history. We find that, the high- comoving
cumulative stellar mass density alone has no significant preference for either
CDM or WDM model. But using the observational data of other stellar mass
density measurements and reionization history, we obtain that the WDM particle
mass with keV and star formation
efficiency parameter in 2 confidence level can match
both the high- comoving cumulative stellar mass density and the
reionization history.Comment: 11 pages, 4 figures. Accepted for publication in RA
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