2,852 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
Utility Maximization for Uplink MU-MIMO: Combining Spectral-Energy Efficiency and Fairness
Driven by green communications, energy efficiency (EE) has become a new
important criterion for designing wireless communication systems. However, high
EE often leads to low spectral efficiency (SE), which spurs the research on
EE-SE tradeoff. In this paper, we focus on how to maximize the utility in
physical layer for an uplink multi-user multiple-input multipleoutput (MU-MIMO)
system, where we will not only consider EE-SE tradeoff in a unified way, but
also ensure user fairness. We first formulate the utility maximization problem,
but it turns out to be non-convex. By exploiting the structure of this problem,
we find a convexization procedure to convert the original nonconvex problem
into an equivalent convex problem, which has the same global optimum with the
original problem. Following the convexization procedure, we present a
centralized algorithm to solve the utility maximization problem, but it
requires the global information of all users. Thus we propose a primal-dual
distributed algorithm which does not need global information and just consumes
a small amount of overhead. Furthermore, we have proved that the distributed
algorithm can converge to the global optimum. Finally, the numerical results
show that our approach can both capture user diversity for EE-SE tradeoff and
ensure user fairness, and they also validate the effectiveness of our
primal-dual distributed algorithm
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