 Award ID(s):
 1813694
 NSFPAR ID:
 10173387
 Date Published:
 Journal Name:
 ArXivorg
 ISSN:
 23318422
 Page Range / eLocation ID:
 1  17
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
More Like this

A bstract The cosmic neutrino background is both a dramatic prediction of the hot Big Bang and a compelling target for current and future observations. The impact of relativistic neutrinos in the early universe has been observed at high significance in a number of cosmological probes. In addition, the nonzero mass of neutrinos alters the growth of structure at late times, and this signature is a target for a number of upcoming surveys. These measurements are sensitive to the physics of the neutrino and could be used to probe physics beyond the standard model in the neutrino sector. We explore an intriguing possibility where light righthanded neutrinos are coupled to all, or a fraction of, the dark matter through a mediator. In a wide range of parameter space, this interaction only becomes important at late times and is uniquely probed by latetime cosmological observables. Due to this coupling, the dark matter and neutrinos behave as a single fluid with a nontrivial sound speed, leading to a suppression of power on small scales. In current and nearterm cosmological surveys, this signature is equivalent to an increase in the sum of the neutrino masses. Given current limits, we show that at most 0.5% of the dark matter could be coupled to neutrinos in this way.more » « less

ABSTRACT Upcoming galaxy surveys will allow us to probe the growth of the cosmic largescale structure with improved sensitivity compared to current missions, and will also map larger areas of the sky. This means that in addition to the increased precision in observations, future surveys will also access the ultralargescale regime, where commonly neglected effects such as lensing, redshiftspace distortions, and relativistic corrections become important for calculating correlation functions of galaxy positions. At the same time, several approximations usually made in these calculations such as the Limber approximation break down at those scales. The need to abandon these approximations and simplifying assumptions at large scales creates severe issues for parameter estimation methods. On the one hand, exact calculations of theoretical angular power spectra become computationally expensive, and the need to perform them thousands of times to reconstruct posterior probability distributions for cosmological parameters makes the approach unfeasible. On the other hand, neglecting relativistic effects and relying on approximations may significantly bias the estimates of cosmological parameters. In this work, we quantify this bias and investigate how an incomplete modelling of various effects on ultralarge scales could lead to false detections of new physics beyond the standard ÎCDM model. Furthermore, we propose a simple debiasing method that allows us to recover true cosmologies without running the full parameter estimation pipeline with exact theoretical calculations. This method can therefore provide a fast way of obtaining accurate values of cosmological parameters and estimates of exact posterior probability distributions from ultralargescale observations.

The hot dense environment of the early universe is known to have produced large numbers of baryons, photons, and neutrinos. These extreme conditions may have also produced other longlived species, including new light particles (such as axions or sterile neutrinos) or gravitational waves. The gravitational effects of any such light relics can be observed through their unique imprint in the cosmic microwave background (CMB), the largescale structure, and the primordial light element abundances, and are important in determining the initial conditions of the universe. We argue that future cosmological observations, in particular improved maps of the CMB on small angular scales, can be orders of magnitude more sensitive for probing the thermal history of the early universe than current experiments. These observations offer a unique and broad discovery space for new physics in the dark sector and beyond, even when its effects would not be visible in terrestrial experiments or in astrophysical environments. A detection of an excess light relic abundance would be a clear indication of new physics and would provide the first direct information about the universe between the times of reheating and neutrino decoupling one second later.more » « less

ABSTRACT Cosmological simulations are an important theoretical pillar for understanding nonlinear structure formation in our Universe and for relating it to observations on large scales. In several papers, we introduce our MillenniumTNG (MTNG) project that provides a comprehensive set of highresolution, largevolume simulations of cosmic structure formation aiming to better understand physical processes on large scales and to help interpret upcoming largescale galaxy surveys. We here focus on the full physics box MTNG740 that computes a volume of $740\, \mathrm{Mpc}^3$ with a baryonic mass resolution of $3.1\times ~10^7\, \mathrm{M_\odot }$ using arepo with 80.6Â billion cells and the IllustrisTNG galaxy formation model. We verify that the galaxy properties produced by MTNG740 are consistent with the TNG simulations, including more recent observations. We focus on galaxy clusters and analyse cluster scaling relations and radial profiles. We show that both are broadly consistent with various observational constraints. We demonstrate that the SZsignal on a deep lightcone is consistent with Planck limits. Finally, we compare MTNG740 clusters with galaxy clusters found in Planck and the SDSS8 RedMaPPer richness catalogue in observational space, finding very good agreement as well. However, simultaneously matching cluster masses, richness, and Comptony requires us to assume that the SZ mass estimates for Planck clusters are underestimated by 0.2Â dex on average. Due to its unprecedented volume for a highresolution hydrodynamical calculation, the MTNG740 simulation offers rich possibilities to study baryons in galaxies, galaxy clusters, and in largescale structure, and in particular their impact on upcoming large cosmological surveys.

Abstract In this work we present : A package dedicated to efficient computations of observables in the Early Universe with the focus on the cosmological era of Big Bang Nucleosynthesis (BBN). The code offers fast and precise evaluation of BBN lightelement abundances together with the effective number of relativistic degrees of freedom, including noninstantaneous decoupling effects. is suitable for stateoftheart analyses in the Standard Model as well as for general investigations into New Physics active during BBN. After reviewing the physics implemented in , we provide a short guide on how to use the code for applications in the Standard Model and beyond. The package is written in Python, but more advanced users can optionally take advantage of the opensource community for Julia. is publicly available on GitHub.