12,694 research outputs found
Constraints on inflation revisited: An analysis including the latest local measurement of the Hubble constant
We revisit the constraints on inflation models by using the current
cosmological observations involving the latest local measurement of the Hubble
constant ( km s Mpc). We constrain the
primordial power spectra of both scalar and tensor perturbations with the
observational data including the Planck 2015 CMB full data, the BICEP2 and Keck
Array CMB B-mode data, the BAO data, and the direct measurement of . In
order to relieve the tension between the local determination of the Hubble
constant and the other astrophysical observations, we consider the additional
parameter in the cosmological model. We find that, for the
CDM++ model, the scale invariance is only excluded at
the 3.3 level, and is favored at the 1.6
level. Comparing the obtained 1 and 2 contours of
with the theoretical predictions of selected inflation models, we find that
both the convex and concave potentials are favored at 2 level, the
natural inflation model is excluded at more than 2 level, the
Starobinsky inflation model is only favored at around 2 level,
and the spontaneously broken SUSY inflation model is now the most favored
model.Comment: 10 pages, 6 figure
Constraining dark energy with Hubble parameter measurements: an analysis including future redshift-drift observations
Dark energy affects the Hubble expansion rate (namely, the expansion history)
by an integral over . However, the usual observables are the
luminosity distances or the angular diameter distances, which measure the
distance-redshift relation. Actually, dark energy affects the distances (and
the growth factor) by a further integration over functions of . Thus, the
direct measurements of the Hubble parameter at different redshifts are
of great importance for constraining the properties of dark energy. In this
paper, we show how the typical dark energy models, for example, the
CDM, CDM, CPL, and holographic dark energy (HDE) models, can be
constrained by the current direct measurements of (31 data in total,
covering the redshift range of ). In fact, the future
redshift-drift observations (also referred to as the Sandage-Loeb test) can
also directly measure at higher redshifts, covering the range of . We thus discuss what role the redshift-drift observations can play in
constraining dark energy with the Hubble parameter measurements. We show that
the constraints on dark energy can be improved greatly with the data
from only a 10-year observation of redshift drift.Comment: 20 pages, 5 figures; final version published in EPJ
Manipulating thermal conductivity through substrate coupling
We report a new approach to the thermal conductivity manipulation --
substrate coupling. Generally, the phonon scattering with substrates can
decrease the thermal conductivity, as observed in recent experiments. However,
we find that at certain regions, the coupling to substrates can increase the
thermal conductivity due to a reduction of anharmonic phonon scattering induced
by shift of the phonon band to the low wave vector. In this way, the thermal
conductivity can be efficiently manipulated via coupling to different
substrates, without changing or destroying the material structures. This idea
is demonstrated by calculating the thermal conductivity of modified
double-walled carbon nanotubes and also by the ice nanotubes coupled within
carbon nanotubes.Comment: 5 figure
Confronting brane inflation with Planck and pre-Planck data
In this paper, we compare brane inflation models with the Planck data and the
pre-Planck data (which combines WMAP, ACT, SPT, BAO and H0 data). The Planck
data prefer a spectral index less than unity at more than 5\sigma confidence
level, and a running of the spectral index at around 2\sigma confidence level.
We find that the KKLMMT model can survive at the level of 2\sigma only if the
parameter (the conformal coupling between the Hubble parameter and the
inflaton) is less than , which indicates a certain level
of fine-tuning. The IR DBI model can provide a slightly larger negative running
of spectral index and red tilt, but in order to be consistent with the
non-Gaussianity constraints from Planck, its parameter also needs fine-tuning
at some level.Comment: 10 pages, 8 figure
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