Tootfinder

Very quick overview of recent #cosmology data that is calling into question our fundamental understanding of our universe.
Including one I have always found interesting, whether some basic scientific "laws" are the same everywhere in the universe and over time.

Astronomers Use a Neutron Star Merger to Measure Cosmic Expansion - Universe Today
Astronomers Use a Neutron Star Merger to Measure Cosmic Expansion - Universe Today https://www.universetoday.com/articles/astronomers-use-a-neutron-star-…

CoComelon parent Moonbug is experimenting with AI; its "Studio AI Bible" notes "we can only own (copyright) what a human has created" so human input is needed (Jason Koebler/404 Media)
https://www.404media.co/cocomelons-studio-t…

Cocomelon's Studio Tells Its Artists to Start Experimenting With AI
Moonbug Entertainment, which makes Cocomelon, Blippi, and other popular content for children, says it will begin using AI but will always have a 'human in the loop.

RE: https://infosec.exchange/@david_chisnall/117066183348062085
This remind me of a similar problem with stock photo companies (I used to work for them) where they actually didn't guarantee the photos on the site were not stolen. They did a bes…

The local galaxy distribution does not violate the #CosmologicalPrinciple: https://arxiv.org/abs/2607.01172 -> thread https://bsky.app/profile/seshnadathur.bsky.social/post/3mpqaru6xg223 - that's vs. some paper hidden behind a paywall and thus irrelevant anyway, but if you must know https://www.cref.it/en/news-en/anisotropic-structures-identified-on-a-cosmic-scale-new-results-from-desi-data-published-in-nature/ described it.

Integrable models of inflation beyond slow-roll
M. Bianchi, G. Dibitetto, J. F. Morales, V. Zevola
https://arxiv.org/abs/2608.06071 https://arxiv.org/pdf/2608.06071 https://arxiv.org/html/2608.06071
arXiv:2608.06071v1 Announce Type: new
Abstract: We propose a novel analytic approach to the study of multi-component FLRW cosmologies and their perturbations. The dynamics is triggered by a single scalar field with a scalar potential codifying the energy density and pressure of the multi-component fluid. This description unifies standard Big Bang cosmologies, models of inflation and dark energy under a unique framework. The key to integrability is to express the scalar potential in terms of the Hubble function $H(\phi)$ that plays the role of a fake superpotential, turning the dynamics into a first order problem, that may be analytically solved in a suitable time coordinate. In this framework, we propose integrable inflationary models with similar properties to the ones analysed in the literature and compatible with observations. Finally, we study scalar and tensor cosmological perturbations in each model by integrating Mukhanov-Sasaki equations via numerical and (semi-)analytic techniques. This allow us to compute the power spectrum, the spectral indices and the tensor-to-scalar ratio beyond the slow-roll approximation and compare our general results {against} the currently available observations and the theoretical predictions based on the slow-roll approximation.
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The environmental dependence of the circumgalactic medium in a high-resolution cosmological simulation
Georg Herzog, Rajeshwari Dutta, Michele Fumagalli
https://arxiv.org/abs/2609.08654 https://arxiv.org/pdf/2609.08654 https://arxiv.org/html/2609.08654
arXiv:2609.08654v1 Announce Type: new
Abstract: There is increasing evidence from observations that the circumgalactic medium (CGM) of galaxies depends on the large-scale structure in which they are embedded. When probing the CGM in absorption using quasar sightlines, studies find an enhanced sky coverage in the CGM of galaxies in overdensities compared to galaxies in isolation. However, the exact reason for this environmental dependence is still unclear. In this work we aim to model for the first time the influence of the large-scale structure on the cool and warm ($T\sim10^{4-5}$ K) gas phases of the CGM. We use a high-resolution ($m_{gas}\approx 4.5\times 10^4$ M$_{\odot}$, $m_{dm}\approx 2.4\times 10^5$ M$_{\odot}$) cosmological simulation based on the EAGLE model of galaxy formation. We select all galaxies at $z=0$ with stellar mass $M_*>10^8$ M$_\odot$ and split them into galaxies in overdensities (group galaxies) and galaxies in isolation using a Friends-of-Friends algorithm. For these two samples, we investigate how the large-scale structure influences the physical properties of the CGM and the measured covering fractions of the cool and warm gas phases. When the two samples of group and isolated galaxies are matched in stellar mass, halo mass, and we use only central galaxies, we do not find any significant difference in the physical properties of the CGM and the measured covering fractions. However, when satellite galaxies are included, we recover the observational trends in the difference of covering fractions with the environment. The difficulty of recovering the observational trends shows the complexity of capturing the multiphase CGM in simulations. However, since our results concerning the admixture of satellites are independent of the employed subgrid physics, this work shows that central galaxies and satellites need to be disentangled in observational studies to clearly discern the role of the environment on the CGM.
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Cosmology in the Einstein Telescope era: comparing traditional and simulation-based methods for population inference
Giovanni Antinozzi, Guillermo Franco Abell\'an, Davide Sciotti, Matteo Martinelli
https://arxiv.org/abs/2608.04005 https://arxiv.org/pdf/2608.04005 https://arxiv.org/html/2608.04005
arXiv:2608.04005v1 Announce Type: new
Abstract: The next generation of gravitational wave detectors, such as the Einstein Telescope (ET), will observe orders of magnitude more binary black hole mergers than current facilities. Most of these events will lack an electromagnetic counterpart, also known as dark siren events, yet will still enable percent-level cosmological constraints. However, the likelihood traditionally used in Hierarchical Bayesian Inference (HBI) for population-level analyses becomes computationally prohibitive as the size of dark siren catalogues and population parameters grow. In this work we compare HBI against simulation-based inference (SBI) as a scalable alternative for cosmological population inference in the ET era. Studying a proof-of-concept example of a mock ET inference, we build a catalogue of $O(10^4)$ binary black hole events, then perform inference on the Hubble constant $H_0$ and matter density $\Omega_m$ in a flat $\Lambda$CDM cosmology, using both a hierarchical analytical likelihood and Marginal Neural Ratio Estimation (MNRE). We find excellent agreement between the two approaches, with SBI reproducing the HBI posteriors to high accuracy, while requiring orders of magnitude less computation once the simulation and training cost is amortized. We further demonstrate that SBI extends straightforwardly to a joint cosmology-plus-astrophysics analysis, simultaneously constraining $(H_0,\Omega_m)$ together with the parameters of the star formation rate density, at negligible additional cost compared to the significant increase in complexity such an extension would require within the HBI framework. Our results indicate that SBI is a promising and scalable tool for population inference with third-generation GW detectors.
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The Quantum Mechanics of Rare Events: From Quantum Walks to Stochastic Inflation
Daniel Green, Kshitij Gupta, Akhil Premkumar
https://arxiv.org/abs/2608.06319 https://arxiv.org/pdf/2608.06319 https://arxiv.org/html/2608.06319
arXiv:2608.06319v1 Announce Type: new
Abstract: Rare fluctuations in physical systems depend on the detailed microphysics responsible for the fluctuations. In classical statistical systems, the large deviation principle has elucidated the role of semi-classics in describing this regime, and has simultaneously provided a the mathematical foundation of statistical mechanics. Large deviation theory for quantum system is considerably less developed. As all physical systems are fundamentally quantum mechanical, this leaves a major gap in our understanding of rare fluctuations relevant to statistical physics, cosmology, and more. In this paper, we develop the practical aspects of the theory of large deviations relevant for calculating rare events in physical systems from quantum walks to cosmology. We first analyze the case of the anharmonic oscillator coupled to a bath, showing explicitly how the system evolves from dominantly statistical (e.g. thermal) to quantum fluctuations. We then generalize these results, showing that the dominant rare fluctuations minimize the measurement-induced relative entropy. This perspective provides a thermodynamic description of a wide range of open quantum systems. We apply these results to random walks that arise in cosmology through stochastic inflation. We show that the evolution of the density matrix of long wavelength fields on a fixed de Sitter background breaks the KMS symmetry, giving rise to a stationary density matrix that does not respect detailed balance.
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