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CosmoVerse@Bilbao 2026

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Descripción

Our understanding of the Universe is at a turning point with the predictions of the standard cosmological model and the observations from different surveys are showing tensions in several key areas. The disagreement is expressed in the value of cosmic expansion as well as in the growth of large-scale structure in the Universe. New cosmological surveys, many of which are European, may expose tension in additional areas of the concordance model. The question of cosmological tensions can be confronted in a number of ways. Firstly, survey data needs to be further analyzed for potential systematic uncertainties or biases. Secondly, there have been numerous advances in approaches to data analysis and statistics, some of which provide less dependence on cosmological models to make cosmological parameter estimates. Lastly, there are a plethora of new proposals from fundamental physics which range from novel neutrino physics to dark energy proposals (and others) which may contribute to a solution to the cosmological tensions problem. These represent the three research themes through which cosmological tensions will either be alleviated or resolved.

CosmoVerse@Bilbao 2026 (15 September – 17 September 2026 & 18 September Management Committee Meeting) is the fourth annual conference in a series of conferences that aim to establish a link between the different research areas in cosmology with the main focus on challenges of tensions in cosmological survey data.

This conference is organized within the COST Action initiative CA21136 – Addressing observational tensions in cosmology with systematics and fundamental physics (CosmoVerse).

The first conference called CosmoVerse@Lisbon 2023 took place between 30 May and 1st June 2023. All of the recorded talks and presentations are public and available here. The second conference called CosmoVerse@Krakow 2024 took place between 9 and 11 July 2024. All of the recorded talks and presentations are available here. The third conference called CosmoVerse@Istanbul 2025 took place between 24 and 26 June 2025. All of the recorded talks and presentations are available here.

The conference is organized together with IFIC (Institut de Physica Corpuscular), EHU QC at Universidad del Pais Vasco, and Basque foundation for Science.

Main topics

  • Observational cosmology and Systematics (cross-correlation of data, systematic effects)
  • Data analysis (astrostatistics; data science in astronomy; Bayesian analysis; machine learning and artificial intelligence)
  • Fundamental Physics (challenge of the cosmological hypothesis, dark energy and modified gravity, neutrino physics, dark energy, and dark matter interaction)

Invited Talks

  • Tessa Baker (Institute of Cosmology and Gravitation, University of Portsmouth, UK)
  • Stefano Casertano (Space Telescope Science Institute, USA)
  • Jens Chluba (Jodrell Bank Centre for Astrophysics, University of Manchester, UK)
  • Willem Elbers (Institute for Computational Cosmology, Durham University, UK)
  • Martina Gerbino (University of Ferrara, Italy)
  • Valeria Pettorino (European Space Agency/ESTEC, The Netherlands)
  • Jesús Torrado (Institute for the Structure of Matter (IEM-CSIC), Spain)

** WARNING: Regarding hotel bookings: conference organizers HAVE NEVER AUTHORISED ANY COMPANY to send any requests regarding accommodation or travel. We strongly advise you NOT TO reply to any emails or calls from such companies and we do not accept any responsibility for adverse consequences should you choose to do so.

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Venue

The conference will take place at the Bilbao Aretoa. The talk will be at the Mitxelena auditorium and the posters will be exhibited at the Chillida and Axular rooms.

Participantes
  • Abhinav Roy
  • Abhrajit Bhattacharjee
  • Abraão Capistrano
  • Adrian Kai En Tee
  • Adrià Gómez-Valent
  • Afonso Ferreira
  • Agnieszka Pollo
  • Aleksandra Kravtsova
  • Alex González-Fuentes
  • Alexandra Turmina Petreca
  • Amel Durakovic
  • Amresh Verma
  • Ander Urio
  • Andrea Mabel Penaherrera Rueda
  • Animesh Sah
  • Antonio Ferreiro
  • Araceli Soler Oficial
  • Archan S Majumdar
  • Asier Alonso-Bardaji
  • Asier Lopez-Eiguren
  • Athanasios Bakopoulos
  • AYAN NANDA
  • Benjamin Sutton
  • Beñat Ibarra-Uriondo
  • Bidisha Samanta
  • Bivudutta Mishra
  • Brahim ASFOUR
  • Burcu Öztürk
  • CARLOS ALBERTO ALMEIDA
  • Carlos G. Boiza
  • Carmelo López Mediavilla
  • Catarina Ferreira
  • Chandra Shekhar Saraf
  • Chaymae Karam
  • Daniel Kessler
  • David Figueruelo
  • David Fonseca Mota
  • David Wiltshire
  • Davide Pedrotti
  • Denitsa Staicova
  • Dong Ha Lee
  • Dr. GOUTAM MANNA
  • Drishti Sharma
  • Eduardo Guendelman
  • Eira Casanovas Marsè
  • Elena Hernández Martínez
  • Eleonora Di Valentino
  • Elliot Scott
  • Elvis Baraković
  • Eneko Aranguren
  • Enrico Specogna
  • Erik Jensko
  • Fotios Anagnostopoulos
  • Francesca Spinnato
  • frederic henry-couannier
  • Gabriel Farrugia
  • Gauri Shankar Hari
  • Germano Nardini
  • Giuseppe Sarracino
  • Gonzalo J. Olmo
  • Goran Djordjevic
  • Guido Risaliti
  • Halil Mutuk
  • Hareesh Thuruthipilly
  • Ismael Ayuso
  • Ismael Ayuso
  • Isra Gashi
  • Ivan Dimitrijevic
  • Ivan Esteban
  • J Alberto Vazquez
  • Jackson Levi Said
  • James Hallam
  • Jana Bogdanoska
  • Javier Ortega del Río
  • Jens Chluba
  • Jess Worsley
  • Jesús Torrado
  • Joanes Lizarraga
  • John Blakeslee
  • Jon Urrestilla
  • Jose Antonio Najera
  • Juan Magaña
  • Julen Estonba Loinaz
  • Kata Karacsonyi
  • Kepa Sousa
  • Kishan Deka
  • Kostas Dialektopoulos
  • Krzysztof Lisiecki
  • Ladghami yahya
  • Laur Järv
  • Leandros Perivolaropoulos
  • Lilia Anguelova
  • Lindita Hamolli
  • Luisa G. Jaime
  • László Árpád Gergely
  • Mahdi Najafi
  • Mahmood Roshan
  • Mali Land-Strykowski
  • Marco Regis
  • Maria Petronikolou
  • Mariam Abdelaziz
  • Mariam Bouhmadi-López
  • Mariam López
  • Mariana Jaber
  • Mariana Jaber
  • Martina Gerbino
  • Maryam Aghaei
  • María Pérez Garrote
  • Massimiliano Romanello
  • Mateusz Rałowski
  • Meet Vyas
  • Merab Gogberashvili
  • Micol Benetti
  • Miguel Angel García-Aspeitia
  • Mikel Artola
  • Mikhail Starzhitsky
  • Mina Ghodsi Yengejeh
  • Mine Gökçen
  • Murat Yılmaz
  • Natascha Riahi
  • Nathaniel Woodcock
  • Nicola Principi Cavaterra
  • Nicolina Rodica Pop
  • Nicolina Rodica Pop
  • Nihan Katirci
  • NURAY BAYAR MULUK
  • Okba Bradji
  • OLEKSANDR (Alexander) Zhuk
  • Olga Mena
  • Oliver Oayda
  • Ozgur Akarsu
  • Pablo Marcel Cucurullo Pache
  • Paloma Morilla
  • Pawel Bielewicz
  • Pawel Siegmund
  • Pilar Ruiz-Lapuente
  • Praveen Kumar Dhankar
  • Prince Kumar
  • Rafid H. Dejrah
  • Rahul Shah
  • Rasa Cereskaite
  • Rebecca Briffa
  • Redouane OUARDI
  • Remo Garattini
  • Richad Stiskalek
  • Richard Anderson
  • Roberto Vinhaes Maluf
  • Ruth Lazkoz
  • Saboura Zamani
  • Salvatore Capozziello
  • Samuel Pinto
  • Santosh Lohakare
  • Sara F. Uria
  • Saule Shomshekova
  • Simone D'Onofrio
  • Sonali Borah
  • Sonej Alam
  • Spyros Basilakos
  • Stefano Casertano
  • stephan walrand
  • Stylianos (Stelios) Papadopoulos
  • Sujatha Ramakrishnan
  • Sulona Kandhai
  • Surajit Kalita
  • Tania Robens
  • Tanja Petrushevska
  • Tassia Ferreira
  • Tessa Baker
  • Tiziano Schiavone
  • Trisha Khan
  • Trupti Patil
  • Upala Mukhopadhyay
  • Valeria Pettorino
  • Veaceslav Albu
  • Vedad Pasic
  • Vincenzo Salzano
  • Vineshree Pillay
  • Vineshree Pillay
  • Vitor da Fonseca
  • Viviane Alfradique
  • Willem Elbers
  • Yahya Mohammadi
  • Yo Toda
  • Yosef Verbin
  • Yoshiyuki Watabiki
  • Young-Wook Lee
  • Zahra Davari Dolatabadi
  • ZAKARIA AHAL
  • Özgür Toprak Şahin
Contact
  • martes, 15 septiembre
    • 8:15 → 9:00
      Registration 45m
    • 9:00 → 12:40
      Morning Session (Tuesday)
      • 9:00
        Opening Talks 10m
      • 9:10
        Overview of the ESA Euclid mission 40m

        TBA

        Ponente: Valeria Pettorino (ESA ESTEC)
        cosmoverse2026_Pettorino_13Sept.pdf
      • 9:50
        Evidence of deviations from LCDM from a new Hubble Diagram of Quasars 25m

        I present new cosmological fits to a Hubble diagram built from supernovae and a homogeneous quasar sample spanning a redshift interval z = 0.7--3.5. The quasar distances are derived from the non-linear relation between X-ray and UV luminosities, and the sample is selected to minimize dust reddening, gas obscuration, host-galaxy contamination, and selection biases as described in the companion paper. This provides high-quality constraints in a redshift range otherwise poorly covered by Type~Ia supernovae. The main results are: (1) the combined Hubble diagram shows strong (> 4 σ) tension with the standard flat ΛCDM model at z ≥ 1.5; (2) in the overlap region, the quasar and supernova Hubble diagrams are fully consistent, supporting a common distance scale; (3) allowing for an evolving dark-energy equation of state yields a significantly better fit, with w_0 and w_a values compatible with those favored by recent DESI results; (4) our quasar Hubble diagram and cosmological constraints agree closely with an independent analysis based on ~6,000 quasars standardized via variability distances (Dutra et al.~2026). The convergence of two independent quasar methods strengthens the case that the deviation from flat lcdm at high redshift is not driven by sample-specific systematics.

        Ponente: Guido Risaliti (Università di Firenze)
        2 Guido Risaliti.pdf
      • 10:15
        CORN - Chronometers Of Relic Nature: Estimate of the expansion rate of the Universe using compact relic galaxies 25m

        The persistent discrepancy between the locally measured Hubble constant, derived from Cepheids and Type Ia supernovae, and the value inferred from the cosmic microwave background underscores the need for independent cosmological probes. Cosmic chronometers provide a direct, model-independent measurement of the expansion history, but their accuracy is currently limited by systematic uncertainties in stellar population modelling, particularly when the full red and quiescent population is used.
        I propose an alternative chronometer strategy based on relic galaxies: the oldest, most compact, and most dynamically evolved systems at a given epoch. These galaxies are expected to host uniformly old, rapidly formed stellar populations with minimal subsequent mass growth, making them closer to ideal single-burst populations. By focusing on this population, we can reduce uncertainties associated with composite star formation histories and mitigate biases arising from late-time rejuvenation.
        In this work I use the largest catalogue of relics, to construct a cleaner differential age–redshift relation. Particular emphasis will be placed on assessing the limitations of current single stellar population models, including metallicity, initial mass function, and alpha-enrichment. By quantifying how these ingredients affect absolute and differential age estimates, we aim to establish a more robust systematic floor for the chronometer method. A relic-based approach has the potential to tighten stellar age constraints at fixed redshift, refine the expansion history measurement, and provide an independent perspective on the Hubble tension.

        Ponente: Krzysztof Lisiecki (National Centre for Nuclear Reserach, Poland)
        3. Krzysztof Lisiecki.pdf
      • 10:40
        Coffee Break 30m
      • 11:10
        Is the Hubble tension a mystery of the small-scale Universe? 40m
        Ponente: Jens Chluba (University of Manchester)
        1. Jens.pdf
      • 11:50
        New Constraints on the Varying Electron Mass Solution to the Hubble Tension 25m

        Despite its remarkable success, the standard cosmological model, $\Lambda$CDM, faces several serious challenges. Among them, the “Hubble tension”—the discrepancy between the value of the Hubble constant inferred from observations of the early Universe and that obtained directly from local measurements—is one of the most important problems in modern cosmology. As a possible solution to this tension, models in which the electron mass varies with time around the epoch of recombination have been proposed.

        In this talk, I will provide an overview of how a time-varying electron mass modifies the recombination history and affects the sound-horizon scale, thereby potentially alleviating the Hubble tension. I will then present the observational constraint $\frac{m_e}{m_{e,0}} = 1.0101 \pm 0.0046$, obtained using the Markov Chain Monte Carlo code COBAYA from a combined analysis of the latest cosmic microwave background data from Planck, baryon acoustic oscillation data from DESI, and Type Ia supernova data from Pantheon+. Finally, I will discuss the physical implications of this result.

        Ponente: Yo Toda (Kochi University of Technology)
        2. Yo Toda.pdf
      • 12:15
        AMICO galaxy clusters in KiDS-1000: cosmological constraints from the two-point correlation function 25m

        We study the clustering of an optically identified galaxy cluster catalogue from the fourth data release of the Kilo Degree Survey (KiDS-1000). The photometric sample was identified by the Adaptive Matched Identifier of Clustered Objects (AMICO) algorithm and consists of 9049 clusters with $S/N\geq3.5$, in redshift range $0.1\leq z<0.8$, spread over an effective area of 838.78 deg$^2$. They are selected according to their observed intrinsic richness, with thresholds of $\lambda_\mathrm{ob}^*\geq 20-25-30$ within $0.10\leq z<0.30$, $0.30\leq z<0.45$ and $0.45\leq z<0.80$, respectively. We measure the multipoles of the two-point correlation function over a variable range of scales from 5 Mpc $h^{-1}$ to 150 Mpc $h^{-1}$. We model the clustering signal in the context of the $\Lambda$-Cold Dark Matter cosmology, accounting for the main observational systematics, such as geometric and redshift-space distortions, and photo-$z$ uncertainties. The effective bias of the cluster sample is estimated via a mass-richness scaling relation, calibrated in a previous work through a joint modeling of weak gravitational lensing and cluster abundance measurements. For the Markov Chain Monte Carlo (MCMC) analysis, we adopt Gaussian priors on the parameters of the mass-richness relation, and broad, uniform priors to derive cosmological constraints on the matter density parameter, the power spectrum amplitude and the structure growth parameter, $S_8\equiv\sigma_8 \sqrt{\Omega_\mathrm{m}/0.3}$. Specifically, we find $\Omega_\mathrm{m}=0.25^{+0.02}_{-0.02}$, $\sigma_8=0.89^{+0.11}_{-0.11}$ and $S_8=0.81^{+0.08}_{-0.08}$, representing an improvement over both the 2D and 3D clustering analyses performed on the previous KiDS data release. These results are also in $1\sigma$ agreement with the KiDS-1000 number counts constraints derived from the same catalogue, as well as with external early- and late-Universe data sets. Our work strengthens the cluster clustering as a competitive and complementary probe, to be included in the final KiDS-Legacy cluster cosmological analysis, and for other ongoing and future photometric redshift surveys.

        Ponente: Massimiliano Romanello (University of Bologna)
        3. Massimiliano Romanello.pdf
    • 12:40 → 14:10
      Lunch 1h 30m
    • 14:10 → 17:30
      Afternoon Session (Tuesday)
      • 14:10
        The Distance Network: a unified analysis of local H0 measurements 40m

        The Distance Network provides a unified, statistically rigorous framework for a robust combined statistical analysis of a broad variety of local measurements of the Hubble constant. This approach provides full error propagation, accounting for commonalities between measurements, and statistical tests to identify possible outliers. We obtain an improved determination of the Hubble constant, with a baseline value of 73.50+/-0.81 km/s/Mpc, over 7 sigma from current Lambda-CDM based estimates. We test many variants that include, exclude, or modify various methods; all yield values between 72.5 and 74.0 km/s/Mpc. The algorithm and data are publically available and allow the inclusion of future measurements in this framework.

        Ponente: Stefano Casertano (Space Telescope Science Institute)
      • 14:50
        Convergence in the value of H0 from Type Ia Supernovae 25m

        Convergence in the value of H0 from Type Ia Supernovae

        In this talk, I will review new findings that point towards a
        concordant value of the Hubble constant (H0) from data based in
        the SH0ES collaboration and the Chicago--Carnegie Supernova Project
        using the ''SNe Ia twins method'' and using, as well, the common
        ''SNe Ia light curve method''.
        There has been usually a discrepancy in the H0 value given by the
        two collaborations. Here we show that such disagreement should not exist.
        I will present the advancement to convergence in the value of H0 and
        the improvements being made in the field.

        Ponente: Prof. PIlar Ruiz-Lapuente (Instituto de Física Fundamental (CSIC) and ICCUB)
      • 15:15
        Coffee Break 30m
      • 15:45
        Beyond LCDM with future surveys: Rubin LSST, SKAO and Simons Observatory 25m

        Recent results from the Dark Energy Spectroscopic Instrument has shifted our understanding about dark energy, preferring about 2-3 sigma evidence for evolving dark energy. The phantom crossing of the dark energy equation of state has motivated the search of new cosmological models. In this talk, I will discuss how combinations of data from Rubin Observatory LSST, Simons Observatory and SKAO can assist in better understanding the nature of dark energy and solutions to cosmological tensions. I will present forecasts on Rapid Transition Dark Energy and Early Dark Energy models, and discuss the challenges and systematics in different datasets. Specifically, I will present which combinations to datasets generate best constraints on extended models.

        Ponente: Dr. Chandra Shekhar Saraf (Korea Astronomy and Space Science Institute)
        1. Chandra Shekhar Saraf.pdf
      • 16:10
        Wising up to CatWISE: using simulation-based inference to measure the cosmic dipole 25m

        We apply Simulation-Based Inference ('SBI') to the cosmic dipole problem for the first time, measuring the distribution of quasar counts over the sky in the infrared CatWISE2020 sample. Our SBI-based approach alleviates systematic effects arising from the WISE instrument itself and enables direct inference of the sample's dipole. We find a dipole that is twice as large as the CMB expectation but more seriously misaligned with the CMB direction (≈3σ), adding further evidence to the persistent 'dipole tension'. This remains a serious challenge for ΛCDM. However, our result highlights the power of SBI at machine-inferring a likelihood function in the presence of difficult systematics, which will make it a natural choice for robust inference with new datasets. For example, in the radio regime, the Rapid ASKAP Continuum Survey contains a wealth of unexplored information but has possible systematics that must be understood before measuring the dipole. SBI will be a natural technique to disentangle the signal from the systematic, shedding new light on the dipole tension.

        Ponente: Oliver Oayda (The University of Sydney)
        2. Oliver Oayda.pdf
      • 16:35
        Simulation-based tension quantification of the cosmic dipole anomaly 25m

        The cosmic dipole observed in the matter distribution of galaxy surveys consistently disagrees with the kinematic expectation set by the cosmic microwave background, posing a serious challenge to the Cosmological Principle and the standard model of cosmology. However, the fidelity of the dipoles we infer rests on our understanding of the systematics present in the surveys. For many systematics, their analytical effect on the source counts is unknown, rendering the likelihood function intractable. We demonstrate that Simulation-Based Inference (SBI) is an effective tool for quantifying tensions between cosmic dipole data sets, enabling inference when likelihoods are intractable. Here, we apply neural-ratio estimation to the cosmic dipole for the first time, recovering tensions between Planck, NVSS, RACS, and CatWISE under different treatments of systematics. Our SBI architecture provides a robust machinery for future dipole analyses with LSST, Euclid, and the SKA, where it will be essential to model complex observational systematics.

        Ponente: Sr. Mali Land-Strykowski (UNIVERSITY OF SYDNEY)
        3. Mali Land-Strykowski.pptx
      • 17:00
        Role of large-scale structures in cosmological evolution with multi-messenger signatures 25m

        Recent observations have revealed the presence of cosmic structures at even very large scales in the Universe. This, along with cosmological tensions, motivates re-examination of the standard paradigm of the concordance model based on assumptions of homogeneous matter distribution at various cosmological scales. The observed large-scale matter inhomogeneities may possibly impact the background Hubble evolution through their backreaction on the cosmological metric. We compute the effects of backreaction through the Buchert formalism for averaging on spatial hypersurfaces, employing various physically motivated ansatzes for multiple-domain cosmic inhomogeneities. The resulting altered Hubble evolution, when confronted with data from various recent observations, leads to tight constraints on the backreaction models. Remarkably, our analysis predicts interesting signatures on various kinds of astronomical signals, such as the, (a) red-shift drift, (b) 21-cm brightness temperature, and (c) amplitude of gravitational waves from compact binaries. Moreover, we show how the Hubble tension gets alleviated through the obtained best-fit parameters of our backreaction models.

        References:
        [1] Effect of inhomogeneities on the propagation of gravitational waves from binaries of compact objects, S. S. Pandey, A. Sarkar, A. Ali, A. S. Majumdar, JCAP 06, 021 (2022).
        [2] Global 21-cm brightness temperature in viscous dark energy models, A. Halder, S. S. Pandey, A. S. Majumdar, JCAP 10, 049 (2022).
        [3] Viscous attenuation of gravitational waves propagating through an inhomogeneous background, S. S. Pandey, A. Sarkar, A. Ali, A. S. Majumdar, Eur. Phys. J. C 83, 435 (2023).
        [4] Future deceleration due to backreaction in a Universe with multiple inhomogeneous domains, A. Halder, S. S. Pandey, A. S. Majumdar, JCAP 08, 064 (2023).
        [5] Analyzing the 21-cm signal brightness temperature in the Universe with inhomogeneities, S. S. Pandey, A. Halder, A. S. Majumdar, Phys. Rev. D 110, 043531 (2024).
        [6] Constraining the Hubble parameter with the 21-cm brightness temperature signal in a universe with inhomogeneities, S. Mukherjee, S. S. Pandey, A. S. Majumdar, Phys. Rev. D 112, 063520 (2025).
        [7] Optical depth to reionization in a Universe with multiple inhomogeneous domains, S. S. Pandey, Ruchika, S. Mukherjee, A. S. Majumdar, arXiv: 2604.13718 [astro-ph.CO].

        Ponente: Prof. Archan S Majumdar (S. N. Bose National Centre for Basic Sciences)
        archan_cosmoverse_bilbao_sep26.ppt
    • 18:00 → 19:30
      Welcome drinks & Poster session
  • miércoles, 16 septiembre
    • 9:00 → 12:30
      Morning Session (Wednesday)
      • 9:00
        H0 (+other things) from GW Sirens 40m
        Ponente: Tessa Baker (University of Portsmouth)
      • 9:40
        Geometric Constraints on the Pre-Recombination Expansion History from the Hubble Tension 25m

        I perform a model-independent reconstruction of the background pre-recombination expansion history of the Universe. I find that purely early-time resolutions to the Hubble tension, satisfying the geometric CMB constraints, exist at the background level. This class of solutions requires a smooth transition around matter-radiation equality, characterized by a ≃15% expansion rate enhancement prior to recombination. This result serves as a blueprint for future model-building approaches, providing a background stress-test for Hubble tension proposals.

        Ponente: Davide Pedrotti (TIFPA-INFN, Università di Trento)
      • 10:05
        Revisiting the Hubble Constant with FRBs: Evidence for Redshift Evolution 25m

        Fast Radio Bursts (FRBs) are millisecond radio transients with high dispersion measures, making them powerful tracers of ionized matter across cosmological distances. In this talk, I will present two complementary approaches, Bayesian analysis and machine learning, applied to a set of localized FRBs to rigorously test the consistency of the $\Lambda$CDM model at late cosmic epoch. Our results reveal a redshift evolution of the Hubble constant, a behavior that stands in contradiction to the core postulate standard cosmology. I will further show that this discrepancy can be resolved for alternate cosmological models. These findings suggest a fundamental inadequacy in the standard cosmological framework and necessitate a deeper revision of the theoretical underpinnings of cosmology to resolve the Hubble tension.

        Ponente: Dr. Surajit Kalita (University of Warsaw)
      • 10:30
        Coffee Break 30m
      • 11:00
        Cobaya development updates 40m
        Ponente: Jesus Torrado (Instituto de Estructura de la Materia (IEM-CSIC))
      • 11:40
        Systematic uncertainties in optimal de-lensing of CMB B modes with cross-correlation of CMB and galaxy survey 25m

        In the era of high-precision Cosmic Microwave Background (CMB) anisotropy measurements, detection of primordial gravitational waves (PGWs) will be one of the main goals of current CMB experiments. Detection of a divergence-free (B-mode) component in CMB polarisation will provide direct evidence of inflationary PGWs in the early universe. However, weak gravitational lensing of CMB photons due to intervening mass distributions of the Universe distorts the primordial polarisation patterns, introducing an additional lensing-induced B-mode signal. Removing these lensing-induced B-modes is essential for improving constraints on the amplitude of PGWs. In this work, we test a tomographic delensing method on simulations of the Rubin Observatory LSST galaxy catalogue and Simons Observatory (SO) CMB maps. A significant improvement in delensing efficiency is achieved by using a multi-tracer approach, where we split the galaxy dataset into tomographic redshift bins. However, uncertainties in photometric redshift measurements pose a problem for optimal weighting of the tracers. We explore the impact of photometric redshift errors with realistic simulations and build a pipeline to propagate these uncertainties to constraints on the amplitude of primordial gravitational waves. Additionally, we explore constraints on the galaxy bias,b(z), and the amplitude of matter fluctuations parameter,σ8, through tomographic cross-correlations using realistic simulations of photometric measurements from LSST 10-year datasets.

        Ponente: Kishan Deka
      • 12:05
        Constraining primordial gravitational wave amplitude and de-lensing of CMB maps - influence of Galactic foregrounds 25m

        Detecting primordial gravitational waves (PGWs) is one of the main goals for upcoming Cosmic Microwave Background (CMB) experiments. Achieving this objective requires precise removal of the CMB gravitational lensing signal from polarisation maps -- so-called de-lensing -- as well as cleaning the maps from diffuse Galactic foregrounds. In this talk, I will present studies on influence of the Galactic emission on the reconstruction of the CMB lensing potential and de-lensing of the divergence-free component of CMB polarization maps. Using realistic foreground models of varying complexity, we test the sensitivity of constraints on the primordial gravitational wave amplitude and the $\sigma_8$ parameter to residual Galactic contamination and its interplay with de-lensing. Our results highlight that precise modelling and removal of Galactic emission will be crucial for reliably estimating the amplitude and $\sigma_8$ parameter in next-generation CMB experiments.

        Ponente: Pawel Bielewicz (National Centre for Nuclear Research)
    • 12:30 → 12:35
      Conference Photo
    • 12:35 → 14:00
      Lunch 1h 25m
    • 14:00 → 17:25
      Afternoon Session (Wednesday)
      • 14:00
        Reconstructing the Type Ia Supernova Absolute Magnitude with Two-Probe Physics-Informed Neural Networks 25m

        We apply two variants of Physics-Informed Neural Networks (PINNs) to reconstruct the Type Ia supernova absolute magnitude M_B(z) from joint BAO and supernova data under four cosmological models (\LambdaCDM, CPL, GEDE, \Lambda_sCDM) and two DESI DR2 fiducial sets. A heteroscedastic single-network method tested across four constraint configurations establishes that the Etherington distance duality relation is more fundamental constraint than cosmological model priors, with DDR violations of 30--52 mmag under physical constraints versus 85--2330 mmag without. Under full constraints all models recover M_B \approx -19.3 mag with biases below 0.05 mag. A Fisher information-weighted two-network variant trains independent networks on BAO and SN data, providing clean probe separation and finding no significant M_B evolution in z \in [0.3, 1.5]. The heteroscedastic method identifies a persistent 2-3\sigma residual at z \sim 0.4-0.5 that is consistent across all four models and both fiducials; the Fisher method finds no significant pointwise deviation in z\in[0.3,1.5] but shows a systematic separation of redshift-binned M_B distributions consistent with the same underlying tension. While the origin of this feature remains ambiguous, its model-independence and cross-method consistency warrant further investigation with forthcoming data.

        Ponente: Denitsa Staicova (Institute for Nuclear Research and Nuclear Energy)
      • 14:25
        Defocusing dark energy: Raychaudhuri diagnostics beyond $w<-1/3$ and the phantom divide 25m

        In general relativity, cosmic acceleration is a statement about geometry---the timelike defocusing of the comoving congruence---and the field equations source it with mass--energy combinations, not with any equation-of-state ratio. Evolving dark energy is now back at the center of cosmology, and several scenarios under active discussion---sign-switching $\Lambda_{\rm s}$CDM and AdS-to-dS transitions, which simultaneously ease the $H_0$ and $S_8$ tensions and restore $\sum m_\nu$ to physical values, as well as modified-gravity backgrounds recast in GR-like form---feature an effective dark-energy density that is negative in the past and crosses zero at some redshift $z_\dagger$. Our standard language quietly assumes this never happens: $w_{\rm de}<-1/3$ signals repulsion only while $\rho_{\rm de}>0$ and the inequality reverses on the negative branch; the phantom divide $w_{\rm de}=-1$ stops separating anything once the density changes sign; at $\rho_{\rm de}=0$ the ratio $w_{\rm de}$ does not exist, though nothing physical is singular there; and sign-preserving parametrizations such as $w_0$--$w_a$ cannot represent the crossing at all. In this talk, based on arXiv:2607.18008, we ask what defines dark energy when $w$ cannot, and answer with the two combinations the field equations actually use: the active gravitational mass density $\mathcal{M}=\rho+3p$, which drives Raychaudhuri defocusing, and the inertial mass density $\mathcal{I}=\rho+p$, whose zero---the null energy condition (NEC) boundary---replaces the phantom divide as the regular separator. Sharp results follow: any smooth sign switch is phantom-like and repulsive at the crossing, with the total NEC intact; the pole in $w_{\rm de}$ is purely kinematic, with universal residue $n(1+z_\dagger)/3$, so $w_{\rm de}=-1$ is never attained and the two sides of the divide connect only through the pole; repulsion begins strictly before the switch, at $z_{\rm rep}>z_\dagger$; an exact window in $\rho_{\rm de}'(z_\dagger)$ permits acceleration at the crossing itself; and the deceleration parameter admits exactly one or three sign-changing zeros. An analytic $\Lambda_{\rm s}$CDM profile, exponential infrared $f(T)$ gravity, and the minimal phantom brane realize the pattern. The practical moral for reconstructions: across $\rho_{\rm de}=0$ the regular targets are $(\rho_{\rm de},p_{\rm de},\mathcal{I}_{\rm de},\mathcal{M}_{\rm de})$---kinematic totals need no dark-sector split---and parametrizations should be allowed to change sign.

        Ponente: Ozgur Akarsu (Istanbul Technical University (ITU))
      • 14:50
        Addressing the DESI DR2 Phantom-Crossing Anomaly and Enhanced $H_0$ Tension with Reconstructed Scalar-Tensor Gravity 25m

        Recent cosmological data, including DESI DR2, highlight significant tensions within the $\Lambda$CDM paradigm. When analyzed in the context of General Relativity (GR), the latest DESI data favor a dynamical dark energy (DDE) equation of state, $w(z)$, that crosses the phantom divide line $w=-1$. However, this framework prefers a lower Hubble constant, $H_0$, than Planck 2018, thereby worsening the tension with local measurements. This phantom crossing is a key feature that cannot be achieved by minimally coupled scalar fields (quintessence) within GR. This suggests the need for a new degree of freedom that can simultaneously: (A) increase the best-fit value of $H_0$ in the context of the DESI DR2 data, and (B) allow the crossing of the $w=-1$ line within a new theoretical approach. In this talk I will demonstrate that both of these goals may be achieved in the context of Modified Gravity (MG), and in particular, Scalar-Tensor (ST) theories, where phantom crossing is a natural and viable feature.

        Ponente: Prof. Leandros Perivolaropoulos
      • 15:15
        Coffee Break 30m
      • 15:45
        Safe Phantom Divide Crossing from Unscreened Non-Minimal Coupling to Gravity 25m

        Recent hints of dynamical dark energy, including a possible crossing of the phantom divide inferred from the latest cosmological data, have motivated the search for viable theoretical explanations. Scalar fields non-minimally coupled to gravity with a coupling of the form $F(\varphi)=1+\alpha\varphi^2$ are physically motivated and have emerged as promising candidates, providing a significantly improved fit to the data compared to $\Lambda$CDM and even outperforming the $w_0w_a$CDM parametrization. However, in the absence of a screening mechanism, the regions of parameter space examined exhaustively so far in the literature (with $\alpha<0$) violate stringent local constraints on the strength and time variation of gravity and enhance the amplitude of matter fluctuations at low redshifts and cosmological scales, in tension with galaxy clustering and weak-lensing observations, thereby compromising the actual viability of these solutions. In this work, we investigate a largely unexplored region of parameter space (with $\alpha>0$) that realizes a crossing of the phantom divide while remaining consistent with Cassini–Huygens bounds and the most recent (and tightest) Lunar Laser Ranging measurements, without introducing higher-derivative terms in the action. This setup, which admittedly is subject to some degree of fine-tuning, fully respects the BBN constraints and leads only to mildly larger values of the effective gravitational coupling in the past, peaking at the onset of dark energy domination at approximately 0.5\% above Newton's constant. We review the background and linear perturbation dynamics of the model, deriving illustrative analytical results that provide physical insight into its behavior, and update the constraints on the model using the latest cosmological data, including the DES-Dovekie supernova sample. We perform for the first time a full-fledged Monte Carlo analysis with $\alpha>0$, studying also the impact of the variation of $G$ on the supernovae likelihood, and compare the results obtained with $\alpha<0$.

        Ponente: Dr. Adrià Gómez-Valent (Institut de Ciències del Cosmos, Universitat de Barcelona)
      • 16:10
        Pseudo-scalar dark energy and cosmic birefringence 25m

        A cosmological pseudo-scalar field provides a compelling realization of dynamical
        dark energy (DE). If its coupling to photons is non-negligible, the cosmic microwave background acquires a rotation of its polarization plane, known as cosmic birefringence. We discuss pseudo-scalar models that can simultaneously account for the recent hints of evolution in the equation of state of DE and of the presence of cosmic birefringence.

        Ponente: Marco Regis (University of Torino and INFN)
      • 16:35
        The Universal Rotation Curve of disk galaxies: probing dark matter and the local expansion rate 25m

        The Universal Rotation Curve provides a powerful empirical framework to investigate the distribution of luminous and dark matter in disk galaxies. By adopting normalized radial and velocity coordinates, we investigate the emergence of universal kinematic properties across galaxies with different masses and luminosities. The resulting co-added rotation curves will be analyzed through different dark matter mass models to constrain the halo density profiles. Finally, we discuss the use of the radial Tully–Fisher relation to obtain an independent estimate of the Hubble constant in the local Universe. This work represents a first step toward a unified analysis of galaxy rotation curves and their cosmological applications.

        Ponente: Tiziano Schiavone (SISSA, Trieste)
      • 17:00
        Probing dark energy evolution with Quaia quasars through the integrated Sachs-Wolfe effect 25m

        The Integrated Sachs--Wolfe (ISW) effect probes the late-time evolution of gravitational potentials and provides a complementary test of the nature of dark energy. We investigate whether the redshift evolution of the ISW effect can provide new constraints on the time evolution of dark energy. We consider theoretical predictions for the standard ΛCDM cosmology and alternative w0waCDM models favoured by recent DESI BAO and DES Y6 constraints. We perform a tomographic cross-correlation analysis of the Quaia quasar catalogue and \textit{Planck} CMB temperature maps to measure the ISW signal over a broad redshift range, spanning about (10h−1 Gpc)3 comoving volume. We assess the robustness of the inferred ISW amplitude against variations in sky coverage, multipole range, and tomographic binning. We detect the ISW effect at a significance of 2.8σ, corresponding to an amplitude of AISW≃1.69±0.61 relative to the Planck ΛCDM prediction. The inferred signal remains stable against various analysis choices, including various CMB maps (SMICA, NILC, SEVEM), different choices of ℓmax and the number of multipole bins, and an alternative quasar bias model. The measured ISW amplitude is moderately stronger than predicted by the fiducial ΛCDM cosmology, and the alternative w0waCDM models do not account for this discrepancy. Future tomographic ISW measurements with improved quasar catalogues from Gaia and forthcoming wide-area galaxy surveys such as Euclid and DESI will help clarify the origin of this difference.

        Ponente: Mina Ghodsi Yengejeh (Konkoly Observatory)
    • 20:00 → 22:30
      Conference Dinner
  • jueves, 17 septiembre
    • 9:00 → 12:30
      Morning Session (Thursday)
      • 9:00
        TBA 40m
        Ponente: Willem Elbers (Institute for Computational Cosmology, Durham University)
      • 9:40
        Augmenting Galaxy Catalogues in FLAMINGO using Machine Learning 25m

        Robust hydrodynamic simulations are necessary for placing strong constraints on cosmological parameters through the analysis pipelines of observations of statistics such as galaxy clustering. However, for these purposes, the simulations need both large box size and high resolution, which is computationally prohibitive. In this work we use the connection between galaxies and their host dark matter halos to populate dark-matter-only simulations, using data from the FLAMINGO simulations suite. We employ the Extremely Randomized Trees algorithm to model the connection between the mass profile, history and environment of dark matter halos and the probability distribution of the stellar mass of the galaxy contained in the halo. However, we also demonstrate that dark matter properties which probe the centre of the dark matter profile are highly predictive when applied to data from hydrodynamic simulations but are also sensitive to the baryonic feedback missing from dark-matter-only simulations. We use a Gaussian Processes emulator that simultaneously optimises the hyperparameters of our model and selects for the dark matter features which are predictive of the stellar mass while being insensitive to the differences between the hydrodynamic and dark-matter-only simulations. Using this combination of features, we produce novel catalogues from large box dark-matter-only simulations in FLAMINGO. Our catalogue from the FLAMINGO-10k simulation reproduces the galaxy stellar mass function in the hydrodynamic simulations to within 0.1 dex in the range of stellar masses to which the FLAMINGO stellar mass function was calibrated. We also reproduce the mean and scatter of the stellar mass-halo mass relation to within 0.2 dex over a large range of halo masses. Furthermore we find agreement in the two-point correlation function within several stellar mass ranges to match to within 0.1 dex over a large range of length scales.

        Ponente: Elliot Scott (Newcastle University)
      • 10:05
        Dynamical dark energy from exponential f(R) gravity: cosmological tensions and neutrino mass after DESI DR2 25m

        The latest DESI DR2 BAO data favor a dynamical dark energy equation of state, reviving the question of whether late-time modifications of gravity can ease the tensions of the standard model. We test a generalized exponential $f(R)$ model with massive neutrinos, which produces an effective dynamical dark energy at low redshift while recovering $\Lambda$CDM at early times. Through a Bayesian MCMC analysis combining cosmic chronometers, DESI DR2 BAO, the CMB acoustic scale, and Pantheon+ supernovae, we constrain the model jointly with the total neutrino mass and compare it with $\Lambda$CDM and w0waCDM. The exponential $f(R)$ model is statistically favored over $\Lambda$CDM, partially alleviates the Hubble tension, and mildly relaxes the cosmological neutrino mass bound, while retaining the theoretical foundation that the phenomenological CPL parameterization lacks. These results show how the interplay between modified gravity and neutrino physics offers a viable route to addressing cosmological tensions.

        Ponente: Simone D'Onofrio (ICE - CSIC)
      • 10:30
        Coffee Break 30m
      • 11:00
        TBA 40m
        Ponente: Martina Gerbino (INFN Ferrara)
      • 11:40
        Multifield cosmology with higher curvature terms 25m

        Effective actions with higher curvature terms can have cosmological solutions exhibiting a transient phantom regime. I will discuss a generalization of multifield cosmology in the presence of a higher curvature term, namely the Gauss-Bonnet term. I will show that in this context there are novel features of the so called rapid turn regime, in which multifield models of cosmic acceleration (i.e. of inflation or dark energy) are phenomenologically distinct from single-scalar ones.

        Ponente: Lilia Anguelova (INRNE, Bulgarian Academy of Sciences)
      • 12:05
        Timescape versus ΛCDM — precision tests of emerging spatial curvature 25m

        The timescape cosmology returns to first principles, to explain apparent cosmic acceleration in the statistical regime of general relativity. As inhomogeneities in density and expansion grow, they back react on the average cosmic expansion, which differs from conventional FLRW models. Crucially, dynamical spatial curvature arises as time-varying gradients of the kinetic energy of expansion, depending directly on the volume fraction of cosmic voids.

        The timescape expansion history is close to ΛCDM, but with differences at a precision which we are now finally probing. Whereas ΛCDM is increasingly challenged, independent observational tests now favour timescape. In particular, the recent DESI evidence for "evolving dark energy" gives a dark energy "equation of state" w(z) consistent with timescape's non-FLRW evolution, as predicted in 2009. Projections made in 2014 for the Euclid mission showed that Euclid will distinguish FLRW expansion histories from those with emerging spatial curvature, including timescape, by the definitive Clarkson-Bassett-Lu (CBL) test. The CBL test consists of two parts: the first part requiring over 1000 precise type Ia supernova luminosity distance measurements was completed in our recent analysis of the Pantheon+ data, finding very strong Bayesian evidence (ln B > 5) in favour of timescape over ΛCDM. Furthermore, even restricting the sample to redshifts beyond any conventional scale of statistical homogeneity, z > 0.075, timescape is preferred over ΛCDM with ln B > 1. This was confirmed independently by the DES survey.

        The second part of the CBL test involving Euclid BAOs over a redshift range, 0.7 < z < 2.0, requires geometric new tools. Since the ratio of dark matter to baryonic matter must be recalibrated for timescape, this requires that we revisit cosmological perturbation theory. Our team has now developed a framework for analysing the growth of perturbations on generic averaged backgrounds, without assuming an exact global ΛCDM evolution, but only causality on the subhorizon scales on which matter and geometry are directly coupled.

        In this talk I will outline results to date, and discuss the remaining challenges to test a fundamentally new paradigm for cosmology with the same precision as ΛCDM by 2030.

        Ponente: Prof. David Wiltshire
    • 12:30 → 12:35
      Best Poster Award
    • 12:35 → 14:00
      Lunch 1h 25m
    • 14:00 → 17:25
      Afternoon Session (Thursday)
      • 14:00
        Can a slime mould help us with cosmological tensions? 25m

        Modern cosmology is confronted with persistent observational tensions that challenge the standard cosmological model. While most proposed solutions rely on extending existing theoretical frameworks, we are developing an alternative, model-independent approach inspired by the collective dynamics of biological systems. We present the motivation, methodology, and current status of a proof-of-concept project aimed at investigating whether a slime-mould-inspired algorithm can extract cosmological information directly from the large-scale distribution of matter without assuming a specific theory of gravity. The ongoing work focuses on transforming this algorithm from an interpolation tool into a predictive framework through systematic calibration against numerical cosmological simulations, followed by its application to observational data. We will discuss the planned validation strategy, including tests of its ability to reproduce cosmic structures, generate realistic mock observations, and infer statistically robust information about the underlying cosmological model. By introducing this research programme and its first developments, we aim to open a novel avenue for model-independent studies of gravity and the origin of current cosmological tensions.

        Ponente: Prof. Vincenzo Salzano
      • 14:25
        The inertial mass density : Cosmology, Post-Newtonian Physics, and Galactic Kinematics 25m

        The persistent  tension and the improved supernova–BAO consistency under dynamical dark energy after DESI DR2 motivate rethinking how dark energy evolution is parametrized. We formulate it directly through the inertial mass density (IMD), $\rho+p$IMD, and show that an IMD evolving from a negative to an equal positive constant toward z->0 can induce a past sign change in  itself, with background constraints from SimpleMC and a full perturbative analysis using CAMB and COBAYA underway. We then turn to the face that cosmology leaves dormant — the genuinely inertial role of IMD — in self-gravitating systems, where at first post-Newtonian order the IMD acquires pressure and gravitational-self-energy contributions whose rescaling by two parameters breaks the strong equivalence principle. The resulting local effects, a Nordtvedt effect and a non-conservation of momentum, are small enough to pass tight Solar-System and pulsar-timing tests, yet the same corrections accumulate on large scales and reshape galactic kinematics as an alternative to dark matter. In short, we present IMD as a single, fundamental variable connecting the dark sector across scales.

        Ponente: Nihan Katirci (Dogus University)
      • 14:50
        Beyond j=1: Observational Constraints on Almost-ΛCDM Cosmologies 25m

        The cosmographic condition $j(z)=1$ provides the kinematical signature of the spatially flat $\Lambda$CDM model independently of any specific dark-energy or modified-gravity theory. We investigate the extent to which current observations permit departures from this condition by considering three phenomenological ``almost-$\Lambda$CDM'' cosmographic closures in which the cosmic jerk differs slightly from unity through a small deformation parameter $\epsilon$. The models are constrained using Markov Chain Monte Carlo analyses of recent DESI baryon acoustic oscillation measurements together with compressed Planck cosmic microwave background likelihoods and the Union3, Pantheon+, and DESY5 Type Ia supernova compilations.

        Unlike conventional analyses that infer the expansion history after imposing an explicit parameterization of the dark-energy equation of state, our cosmographic framework reconstructs the expansion history directly from observations, with the effective dark-energy equation of state emerging as a derived quantity rather than an assumed one. We find that all three cosmographic closures are confined by current observations to a remarkably small neighbourhood of the $\Lambda$CDM cosmographic fixed point, with the inclusion of Planck data driving the preferred evolution toward $j_0\simeq1$ and $w_{\rm DE,0}\simeq-1$. Despite their distinct kinematical constructions, the reconstructed dark-energy evolution consistently exhibits a smooth freezing behaviour that remains close to $w=-1$ without crossing the phantom divide.

        Model comparison using the Akaike and Bayesian information criteria shows that the almost-$\Lambda$CDM cosmographic models remain statistically competitive with standard dark-energy parameterizations while relying on fewer assumptions regarding the functional form of $w(z)$. Our analysis demonstrates that current observations constrain the cosmic expansion history more robustly than the detailed evolution of the dark-energy equation of state, which remains sensitive to the reconstruction methodology employed. These results highlight the importance of model-independent cosmographic approaches for interpreting current evidence for dynamical dark energy and provide a natural framework for future studies of cosmological perturbations and structure formation.

        Ponente: Sra. Jess Worsley (1Department of Mathematics and Applied Mathematics, University of Cape Town, 7 University Ave N, 7700, South Africa.)
      • 15:15
        Coffee Break 30m
      • 15:45
        Investigating Expansion-History Mismatch with Diverse Dark Energy Parametrization Frameworks 25m

        The $\Lambda$CDM model successfully explains a wide range of cosmological observations; however, persistent discrepancies most notably the $H_0$ tension between early and late time measurements challenge its completeness. No proposed extension has yet resolved this tension while retaining the overall success of $\Lambda$CDM. We have investigated whether the $H_0$ tension can be associated with a specific epoch in the cosmic expansion history and identify the redshift range most relevant for understanding its origin. In addition to the cosmological constant, we have considered three phenomenological models based on general parametrizations of key quantities governing cosmic expansion: the dark energy (DE) equation of state, the DE pressure density, and the scale factor. Using early time Planck data and late time Pantheon+ (with and without SH0ES calibration) and DESI measurements, we have constrained model parameters and examined the evolution of the Hubble parameter H(z). We have found that $\Lambda$CDM exhibits discrepancies across all redshifts, whereas the other models show them mainly at low redshifts. Further analysis at low redshifts reveals significantly larger deviations in $H(z)$ at $z$=0.51 and 0.706 compared to other ranges. We have also found that the pressure density parametrization alleviates the $H_0$ tension, reducing it to $\sim 2.7\sigma$, while the other models do not provide significant improvements.

        Ponente: Dr. Upala Mukhopadhyay (University of Luxembourg)
      • 16:10
        Connecting Early Dark Energy to Late Dark Energy by the Diluting Matter Potential 25m

        In this work we study a scale invariant gravity theory containing two scalar fields, dust particles and a measure defined from degrees of freedom independent of the metric. The integration of the degrees of freedom that define the measure spontaneously break the scale symmetry, leaving us in the Einstein frame with an effective potential that is dependent on the density of the particles. The potential contains three flat regions, one for inflation, another for early dark energy and the third for late dark energy. At a certain point, as the matter dilutes, tunneling from the early dark energy to the late dark energy can start efficiently.
        This mechanism naturally alleviated the observed Hubble tension by modifying the sound horizon prior to recombination while preserving late-time cosmology. Moreover, the model predictions are consistent with observations from the reduced CMB, BAO, and local measurement of $H_0$, providing a coherent and unified description of the universe. In this context, the Bayesian analysis of these datasets confirms the viability of our scenario, with the best-fit parameters indicating an early dark energy fraction of $f_{\rm NEDE}\approx 0.3$ at a redshift
        of $z^{\prime}=5000$. This preliminary estimate, obtained
        using the reduced CMB dataset, is expected to be tightened
        once the full CMB likelihood is considered.

        Ponente: Eduardo Guendelman (Ben Gurion University)
      • 16:35
        An Agnostic Exploration of Novel Equation Structures for Dynamical Dark Energy 25m

        Cosmological tensions between early- and late-Universe probes, most notably the Hubble tension in $H_0$ have intensified scrutiny of the ΛCDM paradigm and motivated flexible dark-energy scenarios beyond a cosmological constant. A persistent obstacle is that the functional form of the dark-energy equation of state $w(a)$ is usually chosen by hand (e.g.wCDM or CPL), so potentially viable models may never be tested.

        We present an automated pipeline that searches a large combinatorial space of dynamical dark-energy parametrisations using a mask-based genetic algorithm coupled to the CLASS Boltzmann code. Each candidate is a sum of coefficient–shape terms $w(a)=\sum c_i f_j(a)$, the genetic algorithm selects which terms are active, while coefficients are constrained with datasets via Cobaya (with optional neural-network acceleration through CLiENT). Fitness is driven by $\chi^2$, enabling evolutionary discovery of competitive $w(a)$ structures without fixing a single parametric ansatz a priori.

        This approach sits at the intersection of data-analysis and fundamental-physics themes: it uses evolutionary optimisation and likelihood-driven model search to explore dark-energy phenomenology that may help interpret, and ultimately alleviate, tensions with the concordance model. We discuss validation against standard baselines (including CPL), the best-performing symbolic forms found so far, and the path toward multi-probe analyses (CMB, BAO/DESI) needed to assess tension relief robustly.

        Ponente: Dr. Rebecca Briffa (University of Malta)
      • 17:00
        Primordial Black Holes as Cosmic Expansion Accelerators 25m

        In this seminar, I will present a novel mechanism for cosmic acceleration driven by primordial black holes with effective repulsive behavior. Using a new Swiss Cheese cosmological framework, I will discuss four black hole spacetimes—Hayward, Bardeen, Dymnikova, and de Sitter-Schwarzschild—to show that this acceleration emerges naturally from the geometry itself. The results suggest that ultra-light PBHs could drive inflation without requiring an inflaton, while PBHs with masses $m \sim 10^{12}\mathrm{g}$ and abundances $0.107 < \Omega^\mathrm{eq}_\mathrm{PBH}< 0.5$, slightly before matter-radiation equality, can produce a substantial amount of early dark energy, helping to alleviate the Hubble tension.

        Ponente: Konstantinos Dialektopoulos (University of Malta)
    • 20:00 → 21:30
      Public Talk
  • viernes, 18 septiembre
    • 9:30 → 12:30
      MC Meeting
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