40,589 research outputs found
Nonlinear power spectrum in the presence of massive neutrinos: perturbation theory approach, galaxy bias and parameter forecasts
Future or ongoing galaxy redshift surveys can put stringent constraints on
neutrinos masses via the high-precision measurements of galaxy power spectrum,
when combined with cosmic microwave background (CMB) information. In this paper
we develop a method to model galaxy power spectrum in the weakly nonlinear
regime for a mixed dark matter (CDM plus finite-mass neutrinos) model, based on
perturbation theory (PT) whose validity is well tested by simulations for a CDM
model. In doing this we carefully study various aspects of the nonlinear
clustering and then arrive at a useful approximation allowing for a quick
computation of the nonlinear power spectrum as in the CDM case. The nonlinear
galaxy bias is also included in a self-consistent manner within the PT
framework. Thus the use of our PT model can give a more robust understanding of
the measured galaxy power spectrum as well as allow for higher sensitivity to
neutrino masses due to the gain of Fourier modes beyond the linear regime.
Based on the Fisher matrix formalism, we find that BOSS or Stage-III type
survey, when combined with Planck CMB information, gives a precision of total
neutrino mass constraint, sigma(m_nu,tot) 0.1eV, while Stage-IV type survey may
achieve sigma(m_nu,tot) 0.05eV, i.e. more than a 1-sigma detection of neutrino
masses. We also discuss possible systematic errors on dark energy parameters
caused by the neutrino mass uncertainty. The significant correlation between
neutrino mass and dark energy parameters is found, if the information on power
spectrum amplitude is included. More importantly, for Stage-IV type survey, a
best-fit dark energy model may be biased and falsely away from the underlying
true model by more than the 1-sigma statistical errors, if neutrino mass is
ignored in the model fitting.Comment: 33 pages, 11 figure
Measuring the cosmological constant with redshift surveys
It has been proposed that the cosmological constant might be
measured from geometric effects on large-scale structure. A positive vacuum
density leads to correlation-function contours which are squashed in the radial
direction when calculated assuming a matter-dominated model. We show that this
effect will be somewhat harder to detect than previous calculations have
suggested: the squashing factor is likely to be , given realistic
constraints on the matter contribution to . Moreover, the geometrical
distortion risks being confused with the redshift-space distortions caused by
the peculiar velocities associated with the growth of galaxy clustering. These
depend on the density and bias parameters via the combination , and we show that the main practical effect of a geometrical
flattening factor is to simulate gravitational instability with . Nevertheless, with datasets of sufficient size it is
possible to distinguish the two effects; we discuss in detail how this should
be done. New-generation redshift surveys of galaxies and quasars are
potentially capable of detecting a non-zero vacuum density, if it exists at a
cosmologically interesting level.Comment: MNRAS in press. 12 pages LaTeX including Postscript figures. Uses
mn.sty and epsf.st
CMB Lensing Reconstruction in Real Space
We explore the reconstruction of the gravitational lensing field of the
cosmic microwave background in real space showing that very little statistical
information is lost when estimators of short range on the celestial sphere are
used in place of the customary estimators in harmonic space, which are nonlocal
and in principle require a simultaneous analysis of the entire sky without any
cuts or excisions. Because virtually all the information relevant to lensing
reconstruction lies on angular scales close to the resolution scale of the sky
map, the gravitational lensing dilatation and shear fields (which unlike the
deflection field or lensing potential are directly related to the observations
in a local manner) may be reconstructed by means of quadratic combinations
involving only very closely separated pixels. Even though harmonic space
provides a more natural context for understanding lensing reconstruction
theoretically, the real space methods developed here have the virtue of being
faster to implement and are likely to prove useful for analyzing realistic maps
containing a galactic cut and possibly numerous small excisions to exclude
point sources that cannot be reliably subtracted.Comment: 21 pages, 8 figure
Model-Free Multi-Probe Lensing Reconstruction of Cluster Mass Profiles
Lens magnification by galaxy clusters induces characteristic spatial
variations in the number counts of background sources, amplifying their
observed fluxes and expanding the area of sky, the net effect of which, known
as magnification bias, depends on the intrinsic faint-end slope of the source
luminosity function. The bias is strongly negative for red galaxies, dominated
by the geometric area distortion, whereas it is mildly positive for blue
galaxies, enhancing the blue counts toward the cluster center. We generalize
the Bayesian approach of Umetsu et al. for reconstructing projected cluster
mass profiles, by incorporating multiple populations of background sources for
magnification bias measurements and combining them with complementary lens
distortion measurements, effectively breaking the mass-sheet degeneracy and
improving the statistical precision of cluster mass measurements. The approach
can be further extended to include strong-lensing projected mass estimates,
thus allowing for non-parametric absolute mass determinations in both the weak
and strong regimes. We apply this method to our recent CLASH lensing
measurements of MACS J1206.2-0847, and demonstrate how combining multi-probe
lensing constraints can improve the reconstruction of cluster mass profiles.
This method will also be useful for a stacked lensing analysis, combining all
lensing-related effects in the cluster regime, for a definitive determination
of the averaged mass profile.Comment: 13 pages, 2 figures; Typo corrections (Appendix A.2.) to match the
published version in Ap
Energy efficiency of mmWave massive MIMO precoding with low-resolution DACs
With the congestion of the sub-6 GHz spectrum, the interest in massive
multiple-input multiple-output (MIMO) systems operating on millimeter wave
spectrum grows. In order to reduce the power consumption of such massive MIMO
systems, hybrid analog/digital transceivers and application of low-resolution
digital-to-analog/analog-to-digital converters have been recently proposed. In
this work, we investigate the energy efficiency of quantized hybrid
transmitters equipped with a fully/partially-connected phase-shifting network
composed of active/passive phase-shifters and compare it to that of quantized
digital precoders. We introduce a quantized single-user MIMO system model based
on an additive quantization noise approximation considering realistic power
consumption and loss models to evaluate the spectral and energy efficiencies of
the transmit precoding methods. Simulation results show that
partially-connected hybrid precoders can be more energy-efficient compared to
digital precoders, while fully-connected hybrid precoders exhibit poor energy
efficiency in general. Also, the topology of phase-shifting components offers
an energy-spectral efficiency trade-off: active phase-shifters provide higher
data rates, while passive phase-shifters maintain better energy efficiency.Comment: Published in IEEE Journal of Selected Topics in Signal Processin
Algorithmic linear dimension reduction in the l_1 norm for sparse vectors
This paper develops a new method for recovering m-sparse signals that is
simultaneously uniform and quick. We present a reconstruction algorithm whose
run time, O(m log^2(m) log^2(d)), is sublinear in the length d of the signal.
The reconstruction error is within a logarithmic factor (in m) of the optimal
m-term approximation error in l_1. In particular, the algorithm recovers
m-sparse signals perfectly and noisy signals are recovered with polylogarithmic
distortion. Our algorithm makes O(m log^2 (d)) measurements, which is within a
logarithmic factor of optimal. We also present a small-space implementation of
the algorithm. These sketching techniques and the corresponding reconstruction
algorithms provide an algorithmic dimension reduction in the l_1 norm. In
particular, vectors of support m in dimension d can be linearly embedded into
O(m log^2 d) dimensions with polylogarithmic distortion. We can reconstruct a
vector from its low-dimensional sketch in time O(m log^2(m) log^2(d)).
Furthermore, this reconstruction is stable and robust under small
perturbations
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