10,692 research outputs found
Running cosmological constant with observational tests
We investigate the running cosmological constant model with dark energy
linearly proportional to the Hubble parameter, , in which the CDM limit is recovered by taking .
We derive the linear perturbation equations of gravity under the
Friedmann-Lema\"itre-Robertson-Walker cosmology, and show the power spectra of
the CMB temperature and matter density distribution. By using the Markov chain
Monte Carlo method, we fit the model to the current observational data and find
that and for coupled to matter and radiation-matter, respectively,
along with constraints on other cosmological parameters.Comment: 12 pages, 5 figures, version accepted by PL
Matter Power Spectra in Viable Gravity Models with Massive Neutrinos
We investigate the matter power spectra in the power law and exponential
types of viable theories along with massive neutrinos. The enhancement
of the matter power spectrum is found to be a generic feature in these models.
In particular, we show that in the former type, such as the Starobinsky model,
the spectrum is magnified much larger than the latter one, such as the
exponential model. A greater scale of the total neutrino mass, , is allowed in the viable models than that in the CDM
one. We obtain the constraints on the neutrino masses by using the CosmoMC
package with the modified MGCAMB. Explicitly, we get $\Sigma m_{\nu} < 0.451 \
(0.214)\ \mathrm{eV}\Lambda\Sigma m_{\nu} < 0.200\
\mathrm{eV}N_{\mathrm{eff}}\Sigma m_{\nu}N_{\mathrm{eff}} = 3.78^{+0.64}_{-0.84} (3.47^{+0.74}_{-0.60})\Sigma m_{\nu} = 0.533^{+0.254}_{-0.411}< 0.386) \ \mathrm{eV}$ at 95%
C.L. in the Starobinsky (exponential) model.Comment: 15 pages, 5 figures, updated version accepted by PL
Probing gravitational non-minimal coupling with dark energy surveys
We investigate observational constraints on a specific one-parameter
extension to the minimal quintessence model, where the quintessence field
acquires a quadratic coupling to the scalar curvature through a coupling
constant . The value of is highly suppressed in typical tracker
models if the late-time cosmic acceleration is driven at some field values near
the Planck scale. We test in a second class of models in which the field
value today becomes a free model parameter. We use the combined data from
type-Ia supernovae, cosmic microwave background, baryon acoustic oscillations
and matter power spectrum, to weak lensing measurements and find a best-fit
value where is excluded outside the 95 per cent
confidence region. The effective gravitational constant subject
to the hint of a non-zero is constrained to at the same confidence level on cosmological scales, and can be narrowed
down to when combining with Solar
System tests.Comment: Context extended, figures and references added, title changed to
match with accepted version for publicatio
- …