RAS_WEB

Symmetric Bimetric Cosmology: A Minimal Extension of {Lambda}CDM Ghani Imadouchene arXiv:2511.11929v1 Announce Type: cross Abstract: We construct and analyze a symmetric bimetric cosmological model connecting Anti-de Sitter (AdS) and de Sitter (dS) regimes through a coupled scalar field. Starting from a Lagrangian with Einstein-Hilbert terms for two FLRW metrics and an inter-metric potential, we derive modified Friedmann and Klein-Gordon equations governing their evolution. In the symmetric effective-fluid limit, the model reproduces the main phenomenology of the $Lambda$CDM cosmology with a small dynamical correction proportional to $(1+z)^{-3}$, and naturally satisfies local-gravity constraints through Vainshtein screening. This article outlines the theoretical structure and calibration of the modelRead More →

The Great January Comet of 1910 (C/1910 A1): A Key Opportunity Missed by New Zealand Astronomers John Drummond, Wayne Orchiston, Carolyn Brown, Jonathan Horner arXiv:2511.12831v1 Announce Type: cross Abstract: C/1910 A1 was one of the Great Comets of the twentieth century. Although it was widely observed from the Northern Hemisphere, it was first discovered by observers south of the Equator. The comet arrived just months before the widely anticipated apparition of Comet 1P/Halley and was significantly more spectacular. As a result, the two comets were confused, and many who, in later years, talked about how prominent Comet 1P/Halley was in 1910 were often remembering C/1910Read More →

Automated Algorithmic Discovery for Scientific Computing through LLM-Guided Evolutionary Search: A Case Study in Gravitational-Wave Detection He Wang, Liang Zeng arXiv:2508.03661v3 Announce Type: replace-cross Abstract: Automated algorithm discovery in scientific computing faces fundamental challenges: vast design spaces with expensive evaluations, domain-specific physical constraints requiring expert knowledge, and the necessity for interpretable solutions that scientists can validate and understand. We present the Evo-MCTS (Evolutionary Monte Carlo Tree Search) framework, integrating large language models (LLMs) with tree-structured evolutionary search for interpretable algorithm discovery. Evo-MCTS combines reflective code synthesis leveraging LLM domain knowledge, multi-scale evolutionary operations on structured code representations, and interpretable algorithmic pathways emerging from tree-guided exploration.Read More →

The hard ultraluminous state of NGC 5055 ULX X-1 N. Cruz-Sanchez, E. A. Saavedra, F. A. Fogantini, F. Garc’ia, J. A. Combi arXiv:2511.13686v1 Announce Type: new Abstract: We present the results of the first broadband X-ray analysis of the ultraluminous X-ray source NGC 5055 ULX X-1, combining simultaneous data from XMM$-$Newton and NuSTAR missions, with a combined exposure time of $sim$100 ks across the $0.3-20$ keV energy range. The source exhibits a stable flux across the entire exposure with no detectable pulsations by any instrument on their X-ray light curves, placing pulsed-fraction upper limits of 10% and 32% for XMM$-$Newton and NuSTAR, respectively. The X-rayRead More →

MARTA: The connection between chemical enrichment, feedback, and dust in a Wolf-Rayet galaxy at z${sim}$2 Mirko Curti, Elisa Cataldi, Francesco Belfiore, Bianca Moreschini, Magda Arnaboldi, Martyna Chru’sli’nska, Filippo Mannucci, Alessandro Marconi, Quirino D’Amato, Stefano Carniani, William M. Baker, Annalisa De Cia, Nimisha Kumari, Amirnezam Amiri, Giovanni Cresci, Chiaki Kobayashi, Fergus Cullen, Anna Feltre, Roberto Maiolino, Irene Shivaei arXiv:2509.06622v2 Announce Type: replace Abstract: We present the analysis of the stellar and interstellar medium (ISM) properties of MARTA-4327, a star-forming galaxy at z=2.224 observed by means of deep JWST/NIRSpec spectroscopy in both medium- and high-resolution gratings as part of the “Measuring Abundances at high Redshift with theRead More →

Ginnungagap — a massively parallel cosmological initial conditions generator Sergey Pilipenko, Gustavo Yepes, Stefan Gottl"ober, Steffen Knollmann arXiv:2511.10353v2 Announce Type: replace Abstract: Ginnungagap is a fully parallel (MPI+OpenMP) code designed to generate cosmological initial conditions for simulations involving very large numbers of particles. It operates in several modes, including the creation of initial conditions with either uniform or spatially varying resolution (for “zoom-in” simulations). The initial conditions can be fully random or derived by extending the resolution of existing ones while preserving the large-scale structures. Ginnungagap is open source and modular, consisting of a collection of independent tools that can be used for a varietyRead More →

Inflation without an Inflaton II: observational predictions Marisol Traforetti, Mariam Abdelaziz, Daniele Bertacca, Raul Jimenez, Sabino Matarrese, Angelo Ricciardone arXiv:2511.11808v1 Announce Type: new Abstract: We present a complete computation of the scalar power spectrum in the emph{inflation without inflaton} (IWI) framework, where the inflationary expansion is driven solely by a de~Sitter (dS) background and scalar fluctuations arise as second-order effects sourced by tensor perturbations. By explicitly deriving and numerically integrating the full second-order kernel of the Einstein equations, we obtain a scale-invariant scalar spectrum without invoking a fundamental scalar field. In this framework, the amplitude of the scalar fluctuations is directly linked to the scaleRead More →

A possible correction of the Saha curve for non-equilibrium states L. L. Sales, F. C. Carvalho, H. T. C. M. Souza arXiv:2505.08972v2 Announce Type: replace Abstract: It is widely known that the Saha equation is not suitable for describing plasmas out of thermodynamic equilibrium. The primordial hydrogen recombination plasma is an example of this. In this work, we propose a theoretical modification to the standard Saha curve motivated by Tsallis statistics. In particular, we explore the possibility that a time-dependent $q$-parameter may serve as an effective proxy for the evolving thermodynamic conditions during recombination, especially considering that hydrogen recombination occurs from excited states. Within thisRead More →

LEGA-C stellar populations scaling relations. II: Dissecting mass-complete archaeological trends and their evolution since z~0.7 with LEGA-C and SDSS Anna R. Gallazzi (INAF-Arcetri Astrophysical Observatory), Stefano Zibetti (INAF-Arcetri Astrophysical Observatory), Arjen van der Wel (Sterrenkundig Observatorium Universiteit Gent), Angelos Nersesian (Sterrenkundig Observatorium Universiteit Gent), Yasha Kaushal (University of Pittsburgh), Rachel Bezanson (University of Pittsburgh), Daniele Mattolini (INAF-Arcetri Astrophysical Observatory, Universita’ di Trento), Eric F. Bell (University of Michigan), Laura Scholz-Diaz (INAF-Arcetri Astrophysical Observatory), Joel Leja (Pennsylvania State University), Francesco D’Eugenio (University of Cambridge), Po-Feng Wu (National Taiwan University), Camilla Pacifici (StSCI Baltimore), Michael Maseda (StSCI Baltimore) arXiv:2511.11805v1 Announce Type: new Abstract: With a sample ofRead More →

KDP as a thermal blocking filter – Deep near IR observations with a warm narrow band filter J. K. M. Viuho (Cosmic Dawn Center, Niels Bohr Institute, University of Copenhagen, Jagtvej 155A, DK-2200, Copenhagen N, Denmark, Nordic Optical Telescope, Rambla Jose Ana Fernandez Perez 7, ES-38711 Brena Baja, Spain, Department of Physics and Astronomy, Aarhus University, Munkegade 120, DK-8000 Aarhus C, Denmark), A. A. Djupvik (Nordic Optical Telescope, Rambla Jose Ana Fernandez Perez 7, ES-38711 Brena Baja, Spain, Department of Physics and Astronomy, Aarhus University, Munkegade 120, DK-8000 Aarhus C, Denmark), A. N. S{o}rensen (Cosmic Dawn Center, Niels Bohr Institute, University of Copenhagen, Jagtvej 155A,Read More →

Not all cores are equal: Phase-space origins of dynamical friction, stalling and buoyancy Shashank Dattathri, Frank C. van den Bosch, Uddipan Banik, Martin Weinberg, Priyamvada Natarajan, Zhaozhou Li, Avishai Dekel arXiv:2511.11804v1 Announce Type: new Abstract: Dynamical friction governs the orbital decay of massive perturbers within galaxies and dark matter halos, yet its standard Chandrasekhar formulation fails in systems with cores of (roughly) constant density, where inspiral can halt or even reverse, phenomena known respectively as core stalling and dynamical buoyancy. Although these effects have been observed in simulations, the conditions under which they arise remain unclear. Using high-resolution N-body simulations and analytic insights from kineticRead More →

Rock vapour is opaque: implications for dynamics and observations of lava planets T. Giang Nguyen, Nicolas B. Cowan, Gunnar Montseny Gens, Charles-Edouard Boukare, William Eaton, Karolina Sienko arXiv:2511.11800v1 Announce Type: new Abstract: Extreme instellation on lava planets causes the rocky surface to melt and vaporize. Because the rock vapour composition is intrinsically tied to the mantle, atmospheric characterization of lava planets can hold valuable insight into the interior processes of rocky planets. To help interpret current data and strategize for future observations, we develop the model SonicVapour to simulate the dynamics of chemically complex secondary atmosphere of lava planets. We find that for planets withRead More →

Hydrodynamic instabilities in long-term three-dimensional simulations of neutrino-driven supernovae of 13 red supergiant progenitors Beatrice Giudici, Michael Gabler, Hans-Thomas Janka arXiv:2511.11796v1 Announce Type: new Abstract: We present long-term three-dimensional (3D) simulations of Type-IIP supernovae (SNe) for 13 non-rotating, single-star, red-supergiant (RSG) progenitors with zero-age-main-sequence masses between 12.5 M$_{odot}$ and 27.3 M$_{odot}$. The explosions were modelled with a parametric treatment of neutrino heating to obtain defined energies, ${}^{56}$Ni yields, and neutron-star properties in agreement with previous results. Our 3D SN models were evolved from core bounce until 10 days to study how the large-scale mixing of chemical elements depends on the progenitor structure. Rayleigh-Taylor instabilities (RTIs),Read More →

Gravitational–Electromagnetic Coupling on Kerr Spacetime Fawzi Aly, Dejan Stojkovic arXiv:2511.13642v1 Announce Type: cross Abstract: We extend previous metric-based Schwarzschild studies of gravitational–electromagnetic (GEM) coupling to rotating black holes by working directly in a curvature-based Newman–Penrose/Teukolsky framework on Kerr spacetime. Within a minimally coupled Einstein–Maxwell system, we derive explicit quadratic electromagnetic source terms for the spin-$-2$ Teukolsky equation, providing a foundation for future numerical studies of GEM interactions in the framework of black-hole spectroscopy. Moreover, we give order-of-magnitude arguments showing that GEM quadratic quasinormal modes (QQNMs) can become relevant in a range of charged and magnetized astrophysical scenarios. Finally, we show through a brief dilaton-theory exampleRead More →