Welcome Room: Aula Magna Enric Casassas

The trichotomy of Primordial Black Holes initial conditions

• Laia Montellà (ICCUB)

Room: Aula Magna Enric Casassas In this talk, I will show that the formation of primordial black holes, in an asymptotically flat and radiation dominated Friedman-Robertson-Walker (FRW) Universe, is not mainly determined by the behaviour of the smoothed linear over-density at its maximum, as earlier thought, but also by the three-dimensional curvature at smaller (but super-horizon) scales, which is called “the core”. I will present three classes of initial condition characterised by an open, closed or flat FRW core. I will motivate the use of the three-dimensional curvature as the key parameter to determine the threshold of PBH formation.

Nuclear equation of state: from the Lab to the Stars

• Xavier Roca Maza (University of Barcelona and University of Milan)

Room: Aula Magna Enric Casassas The nuclear equation of state (EoS) at zero temperature (T) can be expressed as the energy (E) per particle (A) or pressure (P=–∂E/∂V for A=constant) of an uniform system of neutrons and protons in their ground state. This ideal system is of particular interest for different reasons: i) Coulomb and finite-size effects are avoided (by construction) making comparisons among different models easier; ii) sound methods exist to solve the nuclear many-body problem in this limit; iii) neutrons and protons away from the surface of the nucleus approximately behave as those of the uniform system (saturation density); or iv) neutron star outer core is thought to be made of neutrons and few protons in β–equilibrium with electrons and muons; among others. The properties of this ideal system can be studied from laboratory data and inferred from Neutron Star observations only via nuclear models. Most nuclear models are based on two pillars: the Hamiltonian and a sound many-body method. While accurate and systematically improvable many-body methods exist, this is not exactly the case of the nuclear effective Hamiltonian that has not been fully characterised yet. In this short introductory presentation I will focus on some selected examples that allow us to learn about the nuclear EoS from experiments and observations.

Late Reheating scenarios: How low can we really go?

• Pau Carles Llorca (Institut de Ciències del Cosmos (ICCUB))

Room: Aula Magna Enric Casassas Modern, ground and space based observatories have provided us with a wide range of observations from different epochs of the Universe. Despite these efforts, the Universe before Big Bang Nucleosynthesis (BBN) remains obscure to us. Then, the measurements of the primordial abundances of light elements are key when exploring theories for the early Universe. In this talk, I will discuss the phenomenology of reheating scenarios around neutrino decoupling and the formation of primordial elements. In such cases, we parametrize the reheating with a new particle called $X$ that is set to decay just before the start of BBN. The presence and posterior decay of such particle modifies the expansion history of the Universe as well as the neutrino thermalization, up until the freeze-out of the weak rates. I will explain what is our approach to these scenarios and why previous constraints on reheating temperatures are sometimes not as robust as we think. In the end, I will also mention the next steps to make the most general and consistent bounds on the reheating temperature.

A fast code for the evolution of tidally limited star clusters and their binary black hole mergers

• Fotios Fronimos Pouliasis (ICCUB)

Room: Aula Magna Enric Casassas Star clusters play a key role in shaping the population of compact-object binaries observed through gravitational waves, but modeling their long-term evolution across a wide range of initial conditions remains computationally challenging. Fast and physically motivated models are therefore essential. I will present an updated version of the clusterBHBdynamics code, a rapid framework for evolving star clusters containing stars and stellar-mass black holes. The new version improves the treatment of tidal mass loss, incorporates the effects of metallicity and stellar mass function variations, and introduces a revised gravitational-wave module. In particular, it includes prescriptions for gravitational-wave captures during dynamical interactions and for inspirals triggered by eccentricity growth between encounters. The model is calibrated against a large set of Cluster Monte Carlo and direct $N$-body simulations spanning a broad range of cluster masses, sizes, metallicities, and Galactic environments. With the calibrated parameters, the code reproduces the global evolution of clusters and their black hole populations to within ~15%, and predicts binary black hole merger rates consistent with numerical simulations at the ~20% level. Owing to its sub-second runtime per cluster, clusterBHBdynamics enables efficient exploration of star cluster populations and their contribution to gravitational-wave sources.

From Jets to Wakes: Hydrodynamic Response of the Quark–Gluon Plasma

• Jorge Casalderrey Solana (ICCUB)

Room: Aula Magna Enric Casassas When strongly interacting matter is heated to extraordinarily high temperatures, it undergoes a transition to the quark–gluon plasma, a state of matter that behaves as an almost perfect fluid, characterized by a remarkably small shear viscosity to entropy density ratio. Understanding how this collective behavior emerges from the underlying microscopic dynamics is a central goal of heavy-ion physics. Such matter is routinely created in heavy-ion collisions at RHIC and the LHC, where energetic jets provide microscopic probes of the medium. While jets are strongly modified by their interaction with the plasma, they also deposit energy and momentum, inducing a medium response that manifests itself as modifications of the collective flow, analogous to the patterns generated by objects moving through an ordinary liquid. In this talk, I will discuss how these jet-induced flow effects appear in experimental measurements and how they can be used to gain new insight into the collective dynamics of deconfined QCD matter.

The PhotSat mission: Ultraviolet and visible all-sky monitoring with a CubeSat

• Josep Manel Carrasco Martínez (Institut d'Estudis Espacials de Catalunya)

Room: Aula Magna Enric Casassas PhotSat is the first astrophysical satellite developed from design to operations by the Institute of Space Studies of Catalonia (IEEC) and the Catalan industrial ecosystem. The main scientific goal of the mission is to obtain a full sky photometric monitoring of the approximately 40 million brighter astrophysical sources down to magnitude 15, performing studies of transients, exoplanets, solar system bodies, stars, galaxies, etc. By using a cubesat platform in low-Earth orbit, PhotSat will be able to access both the optical and ultraviolet ranges using two independent telescopes. Thanks to their wide field of view (8 degrees) the mission will be able to revisit each sky position with a cadence of only 2-3 days during the design lifetime of 2-3 years. PhotSat will provide dense light curves for all bright sources in the sky, simultaneously in three different passbands (one in the ultraviolet and two in the optical) using CMOS detectors. The PhotSat consortium is composed of several institutes, universities and industries in the Catalan ecosystem. In this sense, PhotSat is also helping to establish new collaborations and develop the joint capability of executing science experiments from their initial stages, including preliminary design, construction, launch, and operations; using off-the-shelf NewSpace technologies.

Neutron Star Glitches in Dipolar Supersolids

• Héctor Briongos-Merino (University of Barcelona)

Room: Aula Magna Enric Casassas Glitches in neutron stars are sudden increases in their rotational frequency and are believed to originate from the stochastic unpinning of quantized vortices stored in their interior [1]. While previous studies explored this mechanism using externally imposed pinning potentials [2], dipolar atoms in the supersolid phase offer a distinct advantage: their intrinsic density modulation naturally provide the required pinning forces required for vortex trapping [3]. In this talk, I will employ dipolar supersolids as platform to explore vortex dynamics related to a glitch signal. By tuning the strength of the isotropic interaction, we investigate more accurately the dynamics of vortices across different phases ( e.g. uniform-modulated superfluid), mimicking different radial depths of the star. [1] A. Melatos et al 2008 ApJ 672 1103 (2008) [2] Mon. Not. R. Astron. Soc. 415, 1611–1630 (2011) [3] Phys. Rev. Lett. 131, 223401 (2023)

Estimating the Rates of Stellar Mergers in the Milky Way from Astrophysical Transients

• Grace Katusiime (ICCUB)

Room: Aula Magna Enric Casassas Luminous Red Novae (LRNe) are astrophysical transients thought to arise from stellar mergers, offering an important insight into the final stages of binary evolution. To date, only four Galactic LRNe have been identified, with the most recent detected in 2008, making it difficult to constrain their intrinsic rate in the Milky Way. In this PhD project, I investigate how detections from current time-domain surveys can be used to estimate the Galactic stellar merger rate by simulating the detectability of LRNe. I develop an injection-and-recovery simulation framework in which synthetic LRNe light curves are generated using templates of known Galactic LRNe (V4332 Sgr, V838 Mon, and V1309 Sco) and placed at random locations throughout the Milky Way, assuming they trace the stellar mass distribution of the disk and bulge. These simulated events are scaled for distance and interstellar extinction using three-dimensional dust maps and are then sampled through the actual cadence and sensitivity of the Zwicky Transient Facility (ZTF). By quantifying the fraction of injected LRNe that would be recovered by ZTF, I determine the detection efficiency for different types of Galactic stellar mergers. I will discuss the main challenges of this approach and present current progress, including searches for candidate events in real-time alert streams.

Inflation without an inflaton

• Marisol Traforetti (ICCUB)

Room: Aula Magna Enric Casassas The inflationary paradigm successfully explains the observed large-scale homogeneity and isotropy of the Universe, while also providing a mechanism for generating the seeds necessary for the formation of cosmic structures. In the simplest models, the nearly scale-invariant and almost Gaussian primordial perturbations arise from the amplification of quantum vacuum fluctuations of the scalar inflaton field, whose microphysical origin and the structure of its potential remain unknown. Motivated by the search for a model-independent description of inflationary dynamics, I will discuss a novel scenario in which inflation is produced without relying on a scalar field. In the ‘inflation without inflaton’ framework, the inflationary expansion is driven by a de Sitter background and scalar fluctuations arise as second-order effects from tensor metric perturbations (i.e. gravitational waves). I will outline the theoretical framework, present the prediction for the scalar power spectrum and discuss the new advances in the study of its intrinsic primordial non-Gaussianity.

Quantum science with cold atoms at ICCUB

• Antonio Rubio-Abadal (UB, ICCUB)

Room: Aula Magna Enric Casassas Cold neutral atoms constitute a highly controllable platform for studying complex quantum phenomena as well as for developing quantum technology. Some examples of their applications include atomic clocks, quantum computation and simulation, and the testing of fundamental physics. In recent years, the detection and manipulation of atoms at the individual level have pushed forward many directions in the field. A major example can be found in quantum-gas microscopes, which enable the direct characterization of strongly correlated quantum many-body systems. In this talk, I will begin by giving an introduction to the field of cold atoms, discussing concepts like laser cooling and optical trapping. I will then focus on their use as quantum simulators, based on some of my previous experimental research works. In the final part of the talk, I will present the first steps toward establishing the first cold-atom experiment at the Universitat de Barcelona.

The Nuclear Bridge to New Physics: Theoretical challenges in $0\nu\beta\beta$

• Daniel Castillo Garcia (University of Barcelona/ICCUB)

Room: Aula Magna Enric Casassas The exploration of physics Beyond the Standard Model within nuclear physics is closely tied to the investigation of rare electroweak transitions. The most promising process correspond to the neutrinoless double-beta decay ($0\nu\beta\beta$) which is a transition in nuclei where two neutrons simultaneously transform into two protons, accompanied by the emission of only two electrons [1]. This second-order decay, if observed, would prove that neutrinos are Majorana particles (their own antiparticles), shed light on the existence of massive neutrinos, and help explain the predominance of matter over antimatter in the universe. Understanding this kind of process would unveil important features on neutrino physics, astrophysics and cosmology. The half-lives depend on the square of the nuclear matrix elements (NMEs), which must be computed since $0\nu\beta\beta$ has not been observed yet. In this talk, I will present the framework used to compute NMEs and discuss their crucial role in the search for $0\nu\beta\beta$. I will then address higher-order corrections to the NMEs within the nuclear shell model (NSM) and the quasiparticle random-phase approximation (QRPA) frameworks [2]. These calculations aim to reduce the theoretical uncertainties associated with NMEs. Finally, I will briefly present new predictions for two-neutrino double-beta ($2\nu\beta\beta$) transition half-lives, from the $0^+$ ground state to the first $0^+$ excited state, and discuss their connection to $0\nu\beta\beta$ decay. These results incorporate novel higher-order contributions at the NME level [3,4]. M. Agostini *et al.* Rev. Mod. Phys. **95**, 025002 (2023) L. Jokiniemi, D. Castillo, P. Soriano, J. Menéndez, Phys. Lett. B **860**, 139181 (2025). D. Castillo, D. Frycz, B. Benavente, J. Menéndez, arXiv:2507.21868 S. el Morabit *et al.* JHEP **06**, 082 (2025)

Radial-dependence model of simulated Solar Energetic Electrons

• Roger Prat (Universitat de Barcelona)

Room: Aula Magna Enric Casassas Solar activity, such as flares and Coronal Mass Ejections (CMEs), can accelerate protons, electrons and ions up to relativistic speeds causing Solar Energetic Particle (SEP) Events. These events can have a big role in the amount of radiation received by a spacecraft, astronaut missions or even high altitude flights. They can even afect Earth’s navigation systems or cause communication blackouts when a SEP event is strong enough to produce a Ground Level Enhancement (GLE). The effect of SEP events thoughout the whole heliosphere is just being unveiled by the Solar Orbiter (SolO) and Parker Solar Probe (PSP) missions, but is far from being well characterized. Using state-of-the-art models (PARADISE and EUHFORIA) we simulated the transport of electrons in the interplanetary medium to obtain radial distance dependences of their intensities and fluences. In this brief and introductory presentation I will explain some of the physics underlying the transport of electrons in the inner heliosphere as well as discuss some of our findings.

Dark Matter in a Left-Right Symmetric Model

• keyun wu (ICCUB)

Room: Aula Magna Enric Casassas We investigate dark matter phenomenology in a left-right symmetric model based on an (SU(3)_c \times SU(2)_L \times SU(2)R \times U(1){B-L}) gauge theory with a softly broken parity symmetry. The model naturally contains light neutral fermion and scalar states that serve as viable dark matter candidates, with masses ranging down to the GeV scale. The interactions of dark matter are predominantly governed by couplings to left- or right-handed neutrinos, leading to distinct phenomenological features. We analyze the relic abundance, relevant constraints, and detection prospects of these dark matter candidates using several representative benchmark parameter sets, and identify viable regions of parameter space consistent with current experimental bounds.

Gravitational signals from symmetry breaking

• Miguel Vanvlasselaer (ICCUB)

Room: Aula Magna Enric Casassas Symmetries, and their breaking, are a cornerstone of our understanding of particle physics. Consequently they have been probed intensively at colliders. However, if the breaking of a symmetry occurs at scales much larger than the energy reached in colliders, then it remains elusive. In this talk I will present an alternative method to study the breaking of particle physics symmetry by exploiting the gravitational wave remnants from the very early universe. In fact, the phase transitions breaking a symmetry can typically proceed via two distinct channels: a sharp and discontinuous first order transition or a smoother cross-over. The firts case generates gravitational wave via the expansion of the nucleated bubbles while the second case produce gravitational wave via the formation of topological defects like cosmic strings or domain walls.

Instrumentation activities of the ICCUB Tehcnology Unit

• David Gascon Fora (ICCUB. Universitat de Barcelona)

Room: Aula Magna Enric Casassas The Technological Unit of the ICCUB is currently providing several groups of ICCUB with services, such as instrumentation and software development, in order to support their contributions to international collaborations. Many developments on instrumentation are related to photosensor, microelectronics and space technology with key contributions in international projects such as LHCb, CTA, HERD, LISA, ARIEL and other space projects. Furthermore, this technology is also being applied in medical imaging and other fields in cooperation with academic and industrial partners.

ICCUB Advanced Technology Unit (software & data division): present, future and synergies of the Gaia catalogue

• Jordi Portell de Mora (ICCUB)

Room: Aula Magna Enric Casassas The ICCUB Advanced Technology Unit (ATU) is contributing to the software development and data processing of several projects of the Institute, including PLATO, PhotSat, LISA, and especially Gaia, as well as its proposed successor (GaiaNIR). In the first part of this talk, I will do the usual recap of software & data activities being carried out by the ATU team. Afterwards, I will focus on the current status of Gaia, for which we are intensively working on its fourth data release (planned for December this year). As an appetizer of its contents, publication approach and envisaged tools for the community, and to showcase its possible synergies, I will present one of our recent developments - the GJDR3Plus catalogue, joining Gaia DR3 and J-PLUS DR3 data into a single, convenient table downloadable as Parquet files. This synergetic catalogue provides astrometry and exquisite multi-band photometry for galactic and extra-galactic sources. An experimental on-line service with notebooks and a fast database is also available, the capabilities of which will be shown in this talk.

Science with CTAO/LST: Current and Expected Results

• Pol Bordas (ICCUB)

Room: Aula Magna Enric Casassas The Large-Sized Telescope prototype (LST-1) is the first and the larger of a new generation of instruments that will form the Cherenkov Telescope Array Observatory (CTAO) in the island of La Palma (CTAO-North). CTAO is designed to explore, with unprecedented sensitivity, angular resolution, field of view, and energy coverage, the Universe at very-high-energy gamma rays. Since beginning its observations, LST-1 has been studying the northern sky in an energy range between about a few tens of GeV up to a few TeV. Thanks to its high sensitivity and its ability to quickly point toward flaring targets, LST-1 is particularly well suited to detect and follow up on rapidly changing cosmic sources. In this Winter Meeting contribution, I will present the first scientific results obtained with LST-1 as well as the expectations for the full LST northern array (involving a total of 4 LST telescopes in La Palma), that will become the most sensitive instrument of its class along 2026 regarding new discoveries in the very-high-energy gamma-ray sky.

Chronicles of regular black holes: the higher-curvature saga

• Ángel Jesús Murcia Gil (ICCUB)

Room: Aula Magna Enric Casassas As shown by Hawking and Penrose, black holes in general relativity are doomed to contain a singularity in their interior, where even the notion of space-time breaks down. This is no longer the case for regular black holes, for which no singularities appear. In this talk, I will explain how regular black holes arise naturally as exact solutions of theories of gravity including an infinite tower of higher-curvature corrections. I will also discuss how these regular black holes are formed through dynamical collapse of matter.

From molecular clouds to stellar associations

• Núria Miret Roig (Universitat de Barcelona)

Room: Aula Magna Enric Casassas Understanding how molecular clouds collapse and disperse to form stars and planets is a key question in astronomy. In this talk, I will review several complementary lines of research aimed at uncovering the origin of young star clusters and OB associations in the solar neighborhood. I will discuss how the large number of substellar objects–brown dwarfs and free-floating planets–recently detected in nearby star-forming regions can constrain the formation of these objects. I will also present how the spatial distribution, kinematics, and ages of OB associations trace the propagation of star formation and the dispersal of their parent molecular clouds.

Rethinking Resonance Detectability during Binary Neutron Star Inspiral: Accurate Mismatch Computations for Low-lying Dynamical Tides

• Alberto Revilla (Institut de Ciències del Cosmos Universitat de Barcelona (ICCUB))

Room: Aula Magna Enric Casassas Tidal forces excite oscillatory modes of a neutron star in a binary system as the inspiral sweeps through the mode's resonant frequency. The excitation of the oscillatory modes imprints frequency-dependent signatures on the emitted gravitational waveform. These manifest as a sudden phase change in the waveform and an advance in the merger time of up to a millisecond or so. In this talk we quantify when such resonant effects become observable by current and next-generation gravitational wave observatories. We compare waveforms with and without a resonance to assess the detectability of these effects, and explore the possibility of identifying resonant signatures from previously observed binary neutron star events.

Unveiling the earliest stages of massive star formation through interferometric radio observations

• Josep Maria Masqué (ICCUB)

Room: Aula Magna Enric Casassas The formation of stars with masses greater than 8 times the mass of the Sun still remains unclear. Recently born massive stars are deeply embedded in the most crowded and densest regions of the interstellar medium of galaxies; thus, they are highly obscured to optical and even infrared wavelengths. Therefore, interferometric radio observations are crucial to shedding light on the formation mechanism of massive stars. In this talk I will summarize the results of the analysis of the radio emission from massive star-forming regions observed with high angular resolution, aiming to probe the closest vicinity of massive stars at their earliest stages (i.e., down to Solar System scales). At these scales, essential elements associated with the evolution of protostars like putative disks, companions, ionized inflows or jets can be explored. I will focus on the emblematic example IRAS 18162-2048: an extremely young 20 Msun star that powers the longest and fastest protostellar radio jet known in our Galaxy. We conducted a multi-epoch study of the radio emission originating at the heart of this jet inferring processes that might occur at a few tens of AU, making this IRAS 18162-2048 one of the best case studies on the mechanism of mass growth in massive stars during their earliest stages.

Lepton Flavour Universality tests with b-baryon decays at the LHCb experiment

• Albert López Huertas (Universitat de Barcelona)

Room: Aula Magna Enric Casassas Rare $b\to s \ell\ell$ transitions are strongly suppressed in the Standard Model (SM), making them sensitive to physics beyond the SM. Leptons from the different families have the same coupling to electroweak bosons in the SM, symmetry that is known as Lepton Flavour Universality (LFU). Precise measurements of LFU ratios in $b\to s \ell\ell$ decays provide, then, a very powerful null test of the SM. $R_{pK}$ was the first LFU test involving b-baryons published by LHCb, which studies the decay $\mathit{\Lambda}_b^0\to pK^–\ell^+\ell^−$ using Run 1 and 2016 data and yielded a compatible result with the SM within 1 standard deviation significance, as well as the first observation of the $\mathit{\Lambda}_b^0 \to pK^–e^+e^–$ decay. The new $R_{pK}$ analysis includes full dataset (adds 2017-18 data), a full re-optimisation of the selection after the observation of the electronic decay, with particular focus on the MVA and particle identification requirements. Additionally, the measurement splitted in low and central $q^2$ regions will be provided. The preliminary results show a clear improvement of the statistical uncertainty (16% to 9.5%) with a better control of the backgrounds.

Cosmological simulations of the Local Group as a test of the Cold Dark Matter Model

• Adrián Santander Garrote (ICCUB)

Room: Aula Magna Enric Casassas The standard model of cosmology is the best cosmological model that explains the nature and evolution of the Universe. Over the last decades, cosmological computer simulations have proven to be a very useful tool to test cosmological models such CDM and our Local Group is the perfect laboratory to confront these results with high precision observations. In this work, we performed cosmological simulations of the Local Group using the public program Gadget and our own initial conditions created from specific primordial overdensity fields. The main goal is to obtain specific initial conditions that fit the recent 6-D phase-space observations of our Local Group (including distances and proper motions), and to study the dynamical history of the principal galaxies to test they arise from the growing mode in CDM.