The Experts below are selected from a list of 196521 Experts worldwide ranked by ideXlab platform
Issha Kayo - One of the best experts on this subject based on the ideXlab platform.
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non gaussian tails of cosmological density distribution function from dark halo approach
Monthly Notices of the Royal Astronomical Society, 2003Co-Authors: Atsushi Taruya, Takashi Hamana, Issha KayoAbstract:We present a simple model based on the dark halo approach which provides a useful way to understand key points that determine the shape of the non-Gaussian tails of the dark matter one-point probability distribution function (PDF). In particular, using scale-free models with a Power-law profile of dark haloes, we derive a simple analytic expression for the one-point PDF. It is found that the shape of the PDF changes at a characteristic value of δ*, which is defined by the smoothed density of a halo with characteristic mass M* at the epoch. In cold dark matter models with top-hat smoothing filters, the characteristic smoothed density at the present time typically takes the value δ*≫ 1 for a small smoothing scale Rth∼ 1 h−1 Mpc and conversely δ*≪ 1 for a large smoothing scale Rth > 10 h−1 Mpc. In the range δ/δ* 1 basically follow the steep exponential tails of the halo mass function, which exhibit a strong sensitivity on both the outer slope of the halo profile and the Initial Power spectrum. Based on these results, a discussion on the PDF of galaxy distribution and application to weak lensing statistics are also presented.
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non gaussian tails of cosmological density distribution function from dark halo approach
arXiv: Astrophysics, 2002Co-Authors: Atsushi Taruya, Takashi Hamana, Issha KayoAbstract:We present a simple model based on the dark halo approach which provides a useful way to understand key points determining the shape of the non-Gaussian tails of the dark matter one-point probability distribution function(PDF). In particular, using the scale-free models with Power-law profile of dark halos, we derive a simple analytic expression for the one-point PDF. It is found that the shape of the PDF changes at the characteristic value of $\delta_*$ which is defined by the smoothed density of a halo with the characteristic mass $M_*$ at the epoch. In cold dark matter models with top-hat smoothing filters, the characteristic smoothed density at present time typically takes the value $\delta_*\gg 1$ for a small smoothing scale $\rth\sim 1$Mpc$/h$ and conversely $\delta_*\ll 1$ for a large smoothing scale $\rth > 10$Mpc$/h$. On the range $\delta/\delta_* 1$ basically follow the steep exponential tails of the halo mass function, which exhibit a strong sensitivity to both the outer slope of the halo profile and the Initial Power spectrum. Based on these results, the discussion on the PDF of galaxy distribution and the application to the weak lensing statistics are also presented.
J Frieman - One of the best experts on this subject based on the ideXlab platform.
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loop corrections in nonlinear cosmological perturbation theory ii two point statistics and self similarity
The Astrophysical Journal, 1996Co-Authors: Roman Scoccimarro, J FriemanAbstract:We calculate the lowest order nonlinear contributions to the Power spectrum, two-point correlation function, and smoothed variance of the density field, for Gaussian Initial conditions and scale-free Initial Power spectra, P(k) ~ kn. These results extend and, in some cases, correct previous work in the literature on cosmological perturbation theory. Comparing with the scaling behavior observed in N-body simulations, we find that the validity of nonlinear perturbation theory depends strongly on the spectral index n. For n < −1, we find excellent agreement over scales where the variance σ2(R) 10; however, for n ≥ −1, perturbation theory predicts deviations from self-similar scaling (which increase with n) not seen in numerical simulations. This anomalous scaling suggests that the principal assumption underlying cosmological perturbation theory, namely, that large-scale fields can be described perturbatively even when fluctuations are highly nonlinear on small scales, breaks down beyond leading order for spectral indices n ≥ −1. For n < −1, the Power spectrum, variance, and correlation function in the scaling regime can be calculated using dimensional regularization.
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loop corrections in non linear cosmological perturbation theory ii two point statistics and self similarity
arXiv: Astrophysics, 1996Co-Authors: Roman Scoccimarro, J FriemanAbstract:We calculate the lowest-order non-linear contributions to the Power spectrum, two-point correlation function, and smoothed variance of the density field, for Gaussian Initial conditions and scale-free Initial Power spectra, $P(k) \sim k^n$. These results extend and in some cases correct previous work in the literature on cosmological perturbation theory. Comparing with the scaling behavior observed in N-body simulations, we find that the validity of non-linear perturbation theory depends strongly on the spectral index $n$. For $n<-1$, we find excellent agreement over scales where the variance $\sigma^2(R) \la 10$; however, for $n \geq -1$, perturbation theory predicts deviations from self-similar scaling (which increase with $n$) not seen in numerical simulations. This anomalous scaling suggests that the principal assumption underlying cosmological perturbation theory, that large-scale fields can be described perturbatively even when fluctuations are highly non-linear on small scales, breaks down beyond leading order for spectral indices $n \geq -1$. For $n < -1$, the Power spectrum, variance, and correlation function in the scaling regime can be calculated using dimensional regularization.
Naoki Yoshida - One of the best experts on this subject based on the ideXlab platform.
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the mass function of dark matter haloes
Monthly Notices of the Royal Astronomical Society, 2001Co-Authors: Adrian Jenkins, C S Frenk, Simon D M White, J M Colberg, Shaun Cole, August E Evrard, H M P Couchman, Naoki YoshidaAbstract:We combine data from a number of N-body simulations to predict the abundance of dark haloes in cold dark matter (CDM) universes over more than four orders of magnitude in mass. A comparison of different simulations suggests that the dominant uncertainty in our results is systematic and is smaller than 10–30 per cent at all masses, depending on the halo definition used. In particular, our 'Hubble volume' simulations of τCDM and ΛCDM cosmologies allow the abundance of massive clusters to be predicted with uncertainties well below those expected in all currently planned observational surveys. We show that for a range of CDM cosmologies and for a suitable halo definition, the simulated mass function is almost independent of epoch, of cosmological parameters and of the Initial Power spectrum when expressed in appropriate variables. This universality is of exactly the kind predicted by the familiar Press–Schechter model, although this model predicts a mass function shape that differs from our numerical results, overestimating the abundance of 'typical' haloes and underestimating that of massive systems.
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mass function of dark matter halos
arXiv: Astrophysics, 2000Co-Authors: Adrian Jenkins, C S Frenk, Simon D M White, J M Colberg, Shaun Cole, August E Evrard, H M P Couchman, Naoki YoshidaAbstract:We combine data from a number of N-body simulations to predict the abundance of dark halos in Cold Dark Matter universes over more than 4 orders of magnitude in mass. A comparison of different simulations suggests that the dominant uncertainty in our results is systematic and is smaller than 10--30% at all masses, depending on the halo definition used. In particular, our ``Hubble Volume'' simulations of \tcdm and \lcdm cosmologies allow the abundance of massive clusters to be predicted with uncertainties well below those expected in all currently planned observational surveys. We show that for a range of CDM cosmologies and for a suitable halo definition, the simulated mass function is almost independent of epoch, of cosmological parameters, and of Initial Power spectrum when expressed in appropriate variables. This universality is of exactly the kind predicted by the familiar Press-Schechter model, although this model predicts a mass function shape which differs from our numerical results, overestimating the abundance of ``typical'' halos and underestimating that of massive systems.
Jorge Cortes - One of the best experts on this subject based on the ideXlab platform.
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Initialization free distributed coordination for economic dispatch under varying loads and generator commitment
Automatica, 2016Co-Authors: Ashish Cherukuri, Jorge CortesAbstract:This paper considers the economic dispatch problem for a network of Power generating units communicating over a strongly connected, weight-balanced digraph. The collective aim is to meet a Power demand while respecting individual generator constraints and minimizing the total generation cost. In Power networks, this problem is also referred to as tertiary control. We design a distributed coordination algorithm consisting of two interconnected dynamical systems. One block uses dynamic average consensus to estimate the evolving mismatch in load satisfaction given the generation levels of the units. The other block adjusts the generation levels based on the optimization objective and the estimate of the load mismatch. Our convergence analysis shows that the resulting strategy provably converges to the solution of the dispatch problem starting from any Initial Power allocation, and therefore does not require any specific procedure for Initialization. We also characterize the algorithm robustness properties against the addition and deletion of units (capturing scenarios with intermittent Power generation) and its ability to track time-varying loads. Our technical approach employs a novel refinement of the LaSalle Invariance Principle for differential inclusions, that we also establish and is of independent interest. Several simulations illustrate our results.
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Initialization free distributed coordination for economic dispatch under varying loads and generator commitment
arXiv: Optimization and Control, 2014Co-Authors: Ashish Cherukuri, Jorge CortesAbstract:This paper considers the economic dispatch problem for a network of Power generating units communicating over a strongly connected, weight-balanced digraph. The collective aim is to meet a Power demand while respecting individual generator constraints and minimizing the total generation cost. We design a distributed coordination algorithm consisting of two interconnected dynamical systems. One block uses dynamic average consensus to estimate the evolving mismatch in load satisfaction given the generation levels of the units. The other block adjusts the generation levels based on the optimization objective and the estimate of the load mismatch. Our convergence analysis shows that the resulting strategy provably converges to the solution of the dispatch problem starting from any Initial Power allocation, and therefore does not require any specific procedure for Initialization. We also characterize the algorithm robustness properties against the addition and deletion of units (capturing scenarios with intermittent Power generation) and its ability to track time-varying loads. Our technical approach employs a novel refinement of the LaSalle Invariance Principle for differential inclusions, that we also establish and is of independent interest. Several simulations illustrate our results.
Mark Vogelsberger - One of the best experts on this subject based on the ideXlab platform.
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scattering damping and acoustic oscillations simulating the structure of dark matter halos with relativistic force carriers
Physical Review D, 2014Co-Authors: Matthew R Buckley, Jesus Zavala, Francisyan Cyrracine, Kris Sigurdson, Mark VogelsbergerAbstract:We demonstrate that self-interacting dark matter models with interactions mediated by light particles can have significant deviations in the matter Power spectrum and detailed structure of galactic halos when compared to a standard cold dark matter scenario. While these deviations can take the form of suppression of small-scale structure that are in some ways similar to that of warm dark matter, the self-interacting models have a much wider range of possible phenomenology. A long-range force in the dark matter can introduce multiple scales to the Initial Power spectrum, in the form of dark acoustic oscillations and an exponential cutoff in the Power spectrum. Using simulations we show that the impact of these scales can remain observationally relevant up to the present day. Furthermore, the self-interaction can continue to modify the small-scale structure of the dark matter halos, reducing their central densities and creating a dark matter core. The resulting phenomenology is unique to these type of models.