Deterministic epidemic models, such as the Susceptible-Infected-Recovered (SIR) model, are immensely useful even if they lack the nuance and complexity of social contacts at the heart of network ...science modeling. Here we present a simple modification of the SIR equations to include the heterogeneity of social connection networks. A typical power-law model of social interactions from network science reproduces the observation that individuals with a high number of contacts, “hubs” or “superspreaders”, can become the primary conduits for transmission. Conversely, once the tail of the distribution is saturated, herd immunity sets in at a smaller overall recovered fraction than in the analogous SIR model. The new dynamical equations suggest that cutting off the tail of the social connection distribution, i.e., stopping superspreaders, is an efficient non-pharmaceutical intervention to slow the spread of a pandemic, such as the Coronavirus Disease 2019 (COVID-19).
Future galaxy surveys hope to realize significantly tighter constraints on various cosmological parameters. The higher number densities achieved by these surveys will allow them to probe the smaller ...scales affected by non-linear clustering. However, in these regimes, the standard power spectrum can extract only a portion of such surveys' cosmological information. In contrast, the alternate statistic
* has the potential to double these surveys' information return, provided one can predict the
* power spectrum for a given cosmology. Thus, in this work we provide a prescription for this power spectrum
(
), finding that the prescription is typically accurate to about 5 per cent for near-concordance cosmologies. This prescription will thus allow us to multiply the information gained from surveys such as
and
.
Context.
Cosmic variance limits the accuracy of cosmological
N
-body simulations, introducing bias in statistics such as the power spectrum, halo mass function, or the cosmic shear.
Aims.
We provide ...new methods to measure and reduce the effect of cosmic variance in existing and new simulations.
Methods.
We ran pairs of simulations using phase-shifted initial conditions with matching amplitudes. We set the initial amplitudes of the Fourier modes to ensure that the average power spectrum of the pair is equal to the cosmic mean power spectrum from linear theory.
Results.
The average power spectrum of a pair of such simulations remains consistent with the estimated nonlinear spectra of the state-of-the-art methods even at late times. We also show that the effect of cosmic variance on any analysis involving a cosmological simulation can be estimated using the complementary pair of the original simulation. To demonstrate the effectiveness of our novel technique, we simulated a complementary pair of the original Millennium run and quantified the degree to which cosmic variance affected its the power spectrum. The average power spectrum of the original and complementary Millennium simulation was able to directly resolve the baryon acoustic oscillation features.
This paper presents an approach to Solar Radiation Management (SRM) using a tethered solar shield at the modified gravitational L1 Lagrange point. Unlike previous proposals, which were constrained by ...the McInnes bound on shield surface density, our proposed configuration with a counterweight toward the Sun circumvents this limitation and potentially reduces the total mass by orders of magnitude. Furthermore, only 1% of the total weight must come from Earth, with ballast from lunar dust or asteroids serving as the remainder. This approach could lead to a significant cost reduction and potentially be more effective than previous space-based SRM strategies.
Abstract
We have searched for the signature of cosmic voids in the cosmic microwave background (CMB), in both the Planck temperature and lensing-convergence maps; voids should give decrements in ...both. We use zobov voids from the Data Release 12 Sloan Digital Sky Survey CMASS galaxy sample. We base our analysis on N-body simulations, to avoid a posteriori bias. For the first time, we detect the signature of voids in CMB lensing: the significance is 3.2σ, close to Λ cold dark matter (ΛCDM) in both amplitude and projected density-profile shape. A temperature dip is also seen, at modest significance (2.3σ), with an amplitude about six times the prediction. This temperature signal is induced mostly by voids with radii between 100 and 150 h
−1 Mpc, while the lensing signal is mostly contributed by smaller voids – as expected; lensing relates directly to density, while integrated Sachs–Wolfe effect (ISW) depends on gravitational potential. The void abundance in observations and simulations agree as well. We also repeated the analysis excluding lower significance voids: no lensing signal is detected with an upper limit of about twice the ΛCDM prediction. But the mean temperature decrement now becomes non-zero at the 3.7σ level (similar to that found by Granett et al.), with an amplitude about 20 times the prediction. However, the observed dependence of temperature on void size is in poor agreement with simulations, whereas the lensing results are consistent with ΛCDM theory. Thus, the overall tension between theory and observations does not favour non-standard theories of gravity, despite the hints of an enhanced amplitude for the ISW effect from voids.
We explore linear redshift distortions in wide-angle surveys from the point of view of symmetries. We show that the redshift-space two-point correlation function can be expanded into tripolar ...spherical harmonics of zero total angular momentum S super(l1l2l3) (x sub(1), x sub(2), x). The coefficients of the expansion B super(l1l2l3) are analogous to the C sub(l) of the angular power spectrum and express the anisotropy of the redshift-space correlation function. Moreover, only a handful of B super(l1l2l3) are nonzero: the resulting formulae reveal a hidden simplicity comparable to the distant observer limit. The B super(l1l2l3) depend on spherical Bessel moments of the power spectrum and f = Omega super(0.6)/b. In the plane-parallel limit, the results of Kaiser and Hamilton are recovered. The general formalism is used to derive useful new expressions. We present a particularly simple trigonometric polynomial expansion, which is arguably the most compact expression of wide-angle redshift distortions. These formulae are suitable for inversion because of the orthogonality of the basis functions. An alternative Legendre polynomial expansion was obtained as well. This can be shown to be equivalent to the results of Szalay and coworkers. The simplicity of the underlying theory will admit similar calculations for higher order statistics as well.
ABSTRACT
We perform an analysis of two-point galaxy clustering and galaxy bias using Subaru Hyper-Suprime Cam (HSC) data taken jointly by the Subaru Strategic Program and the University of Hawaii in ...the Cosmic Evolution Survey (COSMOS) field over an area of 1.8 sq deg. The depth of the data is similar to the ongoing Hawaii Two-0 (H20) optical galaxy survey, thus the results are indicative of future constraints from tenfold area. We measure the angular autopower spectra of the galaxy overdensity in three redshift bins, defined by dropouts from the g, r, and i bands, and compare them to the theoretical expectation from concordance cosmology with linear galaxy bias. We determine the redshift distribution of each bin using a standard template-based photometric redshift method, coupled with a self-organizing map to quantify colour space coverage. We also investigate sources of systematic errors to inform the methodology and requirements for H20. The linear galaxy bias fit results are $b_{\mathrm{gal,g}} = 3.90 \pm 0.33 (\mathrm{stat}) \substack{ +0.64 \\ -0.24 } (\mathrm{sys})$ at redshift z ≃ 3.7, $b_{\mathrm{gal,r}} = 8.44 \pm 0.63 (\mathrm{stat}) \substack{ +1.42 \\ -0.72 } (\mathrm{sys})$ at z ≃ 4.7, and $b_{\mathrm{gal,i}} = 11.94 \pm 2.24 (\mathrm{stat}) \substack{ +1.82 \\ -1.27 } (\mathrm{sys})$ at z ≃ 5.9.
We measure the average temperature decrement on the cosmic microwave background (CMB) produced by voids selected in the Sloan Digital Sky Survey Data Release 7 spectroscopic redshift galaxy catalog, ...spanning redshifts 0 < z < 0.44. We find an imprint amplitude between 2.6 and 2.9 mu K as viewed through a compensated top-hat filter scaled to the radius of each void, we assess the statistical significance of the imprint at ~2sigma, and we make crucial use of N-body simulations to calibrate our analysis. As expected, we find that large voids produce cold spots on the CMB through the integrated Sachs-Wolfe (ISW) effect. However, we also find that small voids in the halo density field produce hot spots, because they reside in contracting, larger-scale overdense regions. This is an important effect to consider when stacking CMB imprints from voids of different radii. We have found that the same filter radius that gives the largest ISW signal in simulations also yields close to the largest detected signal in the observations. However, although it is low in significance, our measured signal has a much higher amplitude than expected from ISW in the concordance LambdaCDM universe. The discrepancy is also at the ~2sigma level. We have demonstrated that our result is robust against the varying of thresholds over a wide range.
The most common statistic used to analyse large-scale structure surveys is the correlation function, or power spectrum. Here, we show how ‘slicing’ the correlation function on local density brings ...sensitivity to interesting non-Gaussian features in the large-scale structure, such as the expansion or contraction of baryon acoustic oscillations (BAOs) according to the local density. The sliced correlation function measures the large-scale flows that smear out the BAO, instead of just correcting them as reconstruction algorithms do. Thus, we expect the sliced correlation function to be useful in constraining the growth factor, and modified gravity theories that involve the local density. Out of the studied cases, we find that the run of the BAO peak location with density is best revealed when slicing on an ∼40 h−1Mpc filtered density. But slicing on an ∼100 h−1 Mpc filtered density may be most useful in distinguishing between underdense and overdense regions, whose BAO peaks are separated by a substantial ∼5 h−1 Mpc at z = 0. We also introduce ‘curtain plots’ showing how local densities drive particle motions towards or away from each other over the course of an N-body simulation.
Abstract
The distribution of matter in the Universe is approximately lognormal, and one can improve this approximation by characterizing the third moment (skewness) of the log density field. Thus, ...using Millennium Simulation phenomenology and building on previous work, we present analytic fits for the mean, variance and skewness of the log density field A, allowing prediction of these moments given a set of cosmological parameter values. We further show that a generalized extreme value (GEV) distribution accurately models A; we submit that this GEV behaviour is the result of strong intrapixel correlations, without which the smoothed distribution would tend towards a Gaussian (by the central limit theorem). Our GEV model (with the predicted values of the first three moments) yields cumulative distribution functions accurate to within 1.7 per cent for near-concordance cosmologies, over a range of redshifts and smoothing scales.
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