分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Velocity dispersion of the massive neutrinos presents a daunting challenge for non-linear cosmological perturbation theory. We consider the neutrino population as a collection of non-linear fluids, each with uniform initial momentum, through an extension of the Time Renormalization Group perturbation theory. Employing recently-developed Fast Fourier Transform techniques, we accelerate our non-linear perturbation theory by more than two orders of magnitude, making it quick enough for practical use. After verifying that the neutrino mode-coupling integrals and power spectra converge, we show that our perturbation theory agrees with N-body neutrino simulations to within $10\%$ for neutrino fractions $\Omega_{\nu,0} h^2 \leq 0.005$ up to wave numbers of $k = 1~h/$Mpc, an accuracy consistent with $\leq 2.5\%$ errors in the neutrino mass determination. Non-linear growth represents a $>10\%$ correction to the neutrino power spectrum even for density fractions as low as $\Omega_{\nu,0} h^2 = 0.001$, demonstrating the limits of linear theory for accurate neutrino power spectrum predictions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Simulation of the cosmic clustering of massive neutrinos is a daunting task, due both to their large velocity dispersion and to their weak clustering power becoming swamped by Poisson shot noise. We present a new approach, the multi-fluid hybrid-neutrino simulation, which partitions the neutrino population into multiple flows, each of which is characterised by its initial momentum and treated as a separate fluid. These fluid flows respond initially linearly to nonlinear perturbations in the cold matter, but slowest flows are later converted to a particle realisation should their clustering power exceed some threshold. After outlining the multi-fluid description of neutrinos, we study the conversion of the individual flows into particles, in order to quantify transient errors, as well as to determine a set of criteria for particle conversion. Assembling our results into a total neutrino power spectrum, we demonstrate that our multi-fluid hybrid-neutrino simulation is convergent to $<3\%$ if conversion happens at $z=19$ and agrees with more expensive simulations in the literature for neutrino fractions as high as $\Omega_\nu h^2 = 0.005$. Moreover, our hybrid-neutrino approach retains fine-grained information about the neutrinos' momentum distribution. However, the momentum resolution is currently limited by free-streaming transients excited by missing information in the neutrino particle initialisation procedure, which restricts the particle conversion to z $\gtrsim 19$ if percent-level resolution is desired.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Patrick Huber
Kate Scholberg
Elizabeth Worcester
Jonathan Asaadi
A. Baha Balantekin
Nathaniel Bowden
Pilar Coloma
Peter B. Denton
André de Gouvêa
Laura Fields
Megan Friend
Steven Gardiner
Carlo Giunti
Julieta Gruszko
Benjamin J. P. Jones
Georgia Karagiorgi
Lisa Kaufman
Joshua R. Klein
Lisa W. Koerner
Yusuke Koshio
摘要： This report summarizes the current status of neutrino physics and the broad and exciting future prospects identified for the Neutrino Frontier as part of the 2021 Snowmass Process.
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