Welcome

• Xavier Luri (ICCUB)

Room: Aula Magna Enric Casassas

How can we help?

• Esther Pallares

Room: Aula Magna Enric Casassas

Contributions of the Department of Electronic and Biomedical Engineering to the ICC

• Jose Maria Gomez Cama

Room: Aula Magna Enric Casassas Since the beginning of the ICC, members of the Department of Electronic and Biomedical Engineering has been collaborating with ICC researchers in different projects. This situation improved when they became members of the ICC starting on 2011. Since then, synergies in different fields have arose. This is a brief summary of the past, present and expected future.

PRyMordial: The first minutes of the universe, computed in seconds

• Anne-Katherine Burns (University of Barcelona)

Room: Aula Magna Enric Casassas In this talk I will discuss PRyMordial: a program dedicated to the computation of observables in the early universe with a focus on the cosmological era of Big Bang Nucleosynthesis (BBN). The code is the first of its kind written in python and offers fast and precise evaluation of both the BBN light-element abundances and the effective number of relativistic degrees of freedom. PRyMordial was created for both state-of-the-art analyses in the Standard Model as well as for general investigation of New Physics present in the early universe. In this talk, I will review the physics implemented in PRyMordial and provide a short guide on how to use the code for applications in the Standard Model and beyond.

Relativistic Navier-Stokes: recent developments

• Yago Bea Besada (Universidad de Barcelona)

Room: Aula Magna Enric Casassas The Navier-Stokes equations are ubiquitous in the physical description of our universe, but their relativistic counterpart, as originally formulated many decades ago, suffer severe issues. Alternative formulations, like the widely used Muller-Israel-Stewart (MIS) theories that successfully describe the quark-gluon plasma, have also been recently found to present limitations. Moreover, weak processes in neutron star mergers are believed to give rise to an effective viscosity, for which MIS descriptions find similar limitations. In recent years, a well-behaved version of relativistic Navier-Stokes has been proposed, for which all these limitations are absent, appearing as a promising alternative. We present recent developments in numerical evolutions of the relativistic Navier-Stokes equations, that we use to provide the first description of experimental data of central heavy-ion collisions measured by ALICE.

SiPM-based Detectors for Future Space Missions... and Beyond

• Daniel Guberman (ICCUB)

Room: Aula Magna Enric Casassas The Instrumentation Division of the Technological Unit hosts a multidisciplinary team of physicists and engineers dedicated to developing advanced detectors for various fields, including particle physics, astrophysics, medical imaging, and chemistry. In recent years, we’ve developed an innovative technology that positions us uniquely to contribute to the early stages of future space missions. In this presentation, I will highlight our current contributions to key experiments such as HERD, APT, and LISA, and discuss exciting future opportunities that may lead to collaborations with other ICCUB groups.

ICCUB Technology Unit: Software & data, science & engineering

• Jordi Portell de Mora (ICCUB)

Room: Aula Magna Enric Casassas The ICCUB Technology Unit is contributing to the software development and data processing of several projects of the Institute. The most important one is Gaia, where we develop data processing pipelines and catalogue validation tools, and research on data mining solutions including cloud computing. Gaia has even led to spin-off projects, related to light pollution or even cybersecurity, and we keep an eye on a possible successor, GaiaNIR. We also participate in other remarkable projects such as PLATO, PhotSat, Virgo, LISA and the Einstein Telescope. In this talk I will present and briefly describe these software engineering and data science activities at the ICCUB.

Solving Einstein's Equations within Holography with Physics Informed Neural Networks

• Pablo Tejerina Perez (Institute of Cosmos Sciences of University of Barcelona (ICCUB))

Room: Aula Magna Enric Casassas Holography (or the gauge/gravity correspondence) refers to the dual description of the same phenomena through two seemingly different theories: quantum field theory in four dimensions ("our world") and gravity in five dimensions. In some regimes, holography gives us a map to solve within one of the descriptions (classical Einstein gravity in 5D Anti-de-Sitter spacetime) something that is very difficult to tackle in the other (some strongly coupled quantum field theory) with our current techniques. This map can be extremely difficult to establish; in our case, it involves solving non-linear equations with inverse nature, something that traditional numerical methods are not able to do. I will present a new approach based on machine learning techniques, where a neural network is trained to solve these equations. Specifically, we use PINNs (Physics-Informed-Neural-Networks), in which the equations are embedded in the neural network structure itself.

The Milky Way as a case study for Galactic Dynamics

• Marcin Semczuk (Institut de Ciències del Cosmos, Universitat de Barcelona)

Room: Aula Magna Enric Casassas The Milky Way is a dynamic system, exhibiting a wealth of complex processes revealed through the unprecedented precision of ESA's Gaia mission. Gaia's stellar data provide a detailed window into the ongoing dynamical evolution of our Galaxy. For instance, the Galactic bar appears to be slowing down in its angular rotation, while the outer disc shows perturbations likely caused by the passage of the Sagittarius dwarf galaxy. These observational findings drive theoretical studies aimed at uncovering the underlying physics and improving our understanding of the Milky Way's structure and evolution. In this talk, I will present recent results from computer simulations of disc galaxies within a cosmological context, demonstrating how these tools help us interpret the intricate dynamics shaping our Galaxy.

Gravitational waves from collapsing domain wall networks in the early universe

• Francisco Torrenti (ICCUB, U. Barcelona)

Room: Aula Magna Enric Casassas Unstable domain wall (DW) networks in the early universe are cosmologically viable and can emit a large amount of gravitational waves (GW), both before and during annihilation. In my talk I will present recent results on the form of the generated GW spectrum, based on lattice simulations of the field dynamics in 3+1-dimensions.

Fundamental Physics from Cosmology and Astrophysics

• Jordi Salvado (University of Barcelona)

Room: Aula Magna Enric Casassas

Black hole perturbations in the large D limit

• Jordi Rafecas Ventosa

Room: Aula Magna Enric Casassas

Myths and challenges behind the formation of the Galactic disc

• Matthew Orkney (ICCUB (Universitat de Barcelona))

Room: Aula Magna Enric Casassas The stars in the local stellar disc of the Milky Way (MW) exhibit a bimodal distribution in the chemistry of their alpha-process elements. This creates two distinct sequences: the high and low-alpha discs. Numerous hypotheses have been proposed to explain the origin of this bimodality, including the ‘two-infall’ model, which suggests two distinct epochs of gas accretion. This model is compatible with the recent discovery of an ancient and massive Galactic merger, the Gaia-Sausage Enceladus (GSE), which could have contributed the metal-poor gas needed to fuel the formation of the low-alpha sequence. In this talk I will analyse the Auriga galaxy simulations, which have been shown to feature GSE-like mergers and chemical distributions comparable to the high and low-alpha discs. I will investigate the various formation scenarios that can form a chemical bimodality, and show that these are not reliant on a MW-like accretion history or GSE-like merger event.

Searching for Stellar Merger Precursors in the Milky Way

• Gerard Garcia Moreno (Universitat de Barcelona)

Room: Aula Magna Enric Casassas The merger of binary systems has been identified as the cause of peculiar class of astrophysical transients discovered within the last three decades. Archival pre-outburst data on the progenitors of these transients showed an interesting fact: all but one were Hertzsprung gap stars undergoing a phase of fast expansion after hydrogen exhaustion in the core of the more massive component. This quick growth likely initiated an increasingly large mass transfer towards a nearby companion, ending in instability and eventual merger of the binary. Because of the short timescale of this phase, such binary configurations in pre-merger stage are rare. Understanding these binary progenitors is crucial for unraveling the mechanisms driving binary evolution and shedding light on the final fate of such systems. In this presentation, I will discuss our current knowledge and hypotheses regarding these systems. Additionally, I will present our efforts to identify mass-transferring binaries within the Milky Way using data from Gaia and WISE, focusing on Hertzsprung gap stars sharing several properties with stellar merger progenitors.

Hadron Spectroscopy and Finite Energy Sum Rules

• Nadine Hammoud (University of Barcelona, Faculty of Physics)

Room: Aula Magna Enric Casassas Hadron spectroscopy plays an important role in understanding the strong interactions, from conventional hadrons to exotic states like hybrids with explicit gluonic components. Finite-Energy Sum Rules (FESR) link low-energy resonance dynamics with high-energy Regge behavior, providing a powerful theoretical framework to study these states. Building upon the JPAC's work on $\pi p \to \pi \,\eta\, p$ and COMPASS data on $\eta\pi$ production, we aim to extend the application of the FESR to this process. Our approach simplifies the $2 \to 3$ scattering process into a tractable $2 \to 2$ reaction $f_2 + \pi \to \pi + \eta$, preserving the essential physics while reducing computational complexity. To support this methodology, we analyze fundamental reactions such as $\eta \eta \to \eta \eta$, $\pi \pi \to \pi \pi$, and $\pi \eta \to \pi \eta$, establishing a foundation for exploring more intricate hadronic systems.

Black Hole Information Paradox in JT Gravity

• Mickael Komendyak (ICCUB)

Room: Aula Magna Enric Casassas

Strong lensing time delays and the Hubble tension

• Frederic Courbin (ICC - Universitat de Barcelona)

Room: Aula Magna Enric Casassas The Hubble parameter, H0, is one of the key parameters of the current cosmological model. But its value measured from the Cosmic Microwave Background in the early (distant) universe, differs from the value measured directly in the late (local) universe. Obviously, as all measurements are done in the same universe, they should be the same: any difference, a.k.a. tension between the early and late universe values may point to cracks in the cosmological model. But is the tension real or is it due to observational effects? I will show how strong gravitational lensing can help address the issue, independently of any other cosmological probe.

Puzzling Puzzles in the Standard Model of Cosmology

• Adrià Gómez Valent (Institut de Ciències del Cosmos, Universitat de Barcelona)

Room: Aula Magna Enric Casassas The standard model of cosmology, known as ΛCDM, successfully explains a wide variety of observations spanning different epochs of cosmic evolution. However, its most abundant components—dark energy and dark matter—still lack a fundamental theoretical explanation. In addition, the past decade has highlighted several tensions between the model and observational data, potentially pointing to new physics. In this talk, I will first summarize the key tensions affecting the ΛCDM model, with a focus on the Hubble and growth tensions. The discussion of the Hubble tension, currently the most statistically significant discrepancy in cosmology, relies heavily on baryon acoustic oscillation (BAO) data, which play a pivotal role in constructing the inverse distance ladder. I will discuss the existing tension between angular (2D) and anisotropic (3D) BAO observations and examine how these datasets point to different late-time solutions to the H₀ tension. Finally, I will comment on the importance of unbiased large-scale structure estimators like σ12 for comparing theoretical predictions and observational data from various surveys. I will also evaluate the current status of several models proposed in the literature to address the H₀ and growth tensions, analyzing their strengths and limitations.

Neural Quantum States in Nuclear Physics

• Javi Rozalén Sarmiento (Universitat de Barcelona)

Room: Aula Magna Enric Casassas The nuclear many-body problem poses a significant computational challenge. The Neural-Network Quantum States (NQS) method, leveraging machine learning, has emerged as a promising approach for nuclear structure and quantum many-body simulations [1-4]. This variational method employs neural networks as flexible wave function ansätze, enabling the representation of complex quantum states. In this talk, I present an overview of the NQS method. I discuss the two principal research lines in the field, namely neural network architectures and energy minimisation, and I mention our contributions to these fields [1, 2, 5]. [1] J. Keeble & A. Rios, Phys. Lett. B 809 (2020) [2] J. Rozalén Sarmiento, J. Keeble & A. Rios, EPJ Plus 139 (2024) [3] C. Wang, T. Naito, J. Li & H. Liang, arXiv 2403.16819 (2024) [4] A. Lovato, C. Adams, G. Carleo & N. Rocco, Phys. Rev. Res. 4 (2022) [5] M. Drissi, J. Keeble, J. Rozalén Sarmiento & A. Rios, Phil. Trans. R. Soc. A 382 (2024)

Young(?) and (Metal-)Rich: The Puzzling RR Lyrae Stars in the Galactic Disk

• Giuliano Iorio (University of Padova)

Room: Aula Magna Enric Casassas RR Lyrae stars are a class of variable stars whose luminosity varies periodically, with periods ranging from 0.2 to 1 day. The shape and properties of their light curves correlate with intrinsic characteristics such as luminosity and metallicity (in astrophysics, "metals" refer to all elements heavier than helium). For this reason, RR Lyrae stars are considered standard candles and have been used for decades to measure distances within the Milky Way and its surroundings. They are among the most studied and well-known variable stars, formed from old (>10 Gyr), metal-poor, and low-mass progenitors. Indeed, they are abundant in the oldest structures of our Galaxy, including the stellar halo, the bulge, and globular clusters. However, it is well-established that metal-rich RR Lyrae stars (with metallicities up to solar values) also exist in the Solar neighbourhood. Recent results from the European satellite Gaia have revealed that these metal-rich RR Lyrae stars are distributed across all the Galactic disk, extending well beyond the Solar vicinity. Their kinematics suggest an association with an intermediate-age Milky Way disk population, with ages estimated between 2 and 8 Gyr. These relatively young ages challenge conventional scenarios for RR Lyrae formation, which posit that such stars should be among the oldest in our Galaxy or even too old to exist at higher metallicities. Resolving this conundrum requires exploring alternative formation channels for RR Lyrae stars. One promising alternative formation channel involves mass transfer in binary systems (i.e., systems of two stars gravitationally bound to one another). My primary research focus at the ICCUB is to investigate this alternative formation channel using binary evolution simulations. In this talk, I will present the current state of knowledge on this intriguing problem, share my efforts to address it, and highlight its importance in the broader context of our understanding of the Milky Way and the theories of stellar and binary evolution.

Turning Dissipation into a Resource: Harnessing Collective Radiance in Atom Arrays

• Maria Moreno Cardoner

Room: Aula Magna Enric Casassas Achieving efficient and controlled interactions between light and atoms, or other quantum emitters, is essential for quantum optics and certain quantum technologies. A key challenge in these systems is photon loss —caused by re-scattering into unwanted directions— which fundamentally limits performance. In typical experiments with dilute atomic clouds, atoms are often assumed to emit light independently. However, this assumption breaks down when atoms are separated by distances smaller than the wavelength of light, a regime now accessible with state-of-the-art trapping techniques. In this scenario, atoms couple to a common radiation field, leading to dipole-dipole interactions and collective spontaneous emission. As a result, atomic ensembles can decay at rates significantly faster (superradiance) or slower (subradiance) than a single atom. In this talk, we will explore how these collective dissipation effects can be turned into a resource in quantum applications, as for instance, enhancing the efficiency of single-photon storage and retrieval.

Unveiling the shapes of the atomic nucleus

• Dorian Frycz (University of Barcelona)

Room: Aula Magna Enric Casassas The intricate nature of nucleon-nucleon interactions within the atomic nucleus gives rise to a rich array of collective phenomena, including the emergence of permanently deformed shapes in the nucleus' intrinsic frame of reference$^{[1]}$. While spherical shapes are favored near magic numbers, most nuclei exhibit some degree of deformation, and many display shape coexistence within a narrow energy window of a few MeV. Understanding these phenomena is crucial for refining nuclear interaction models, which have significant implications for nucleosynthesis, astronomical r- and s-processes, and neutrino(less) double beta decay$^{[2]}$. Nuclear spectra, characterized by rotational bands and vibrational states, provide key insights into these deformations. Careful analysis of energy levels and electromagnetic transitions reveals the vast landscape of nuclear shapes. Recent advances have also established connections between high- and low-energy physics, as data from the Large Hadron Collider now offer new ways to probe nuclear deformation. In particular, detailed studies of the quark-gluon plasma produced in heavy-ion collisions provide novel insights into the shape and structure of nuclei under extreme conditions$^{[3]}$. Finally, I will discuss the challenges in accurately describing nuclear deformations, focusing on particularly intriguing cases of shape coexistence$^{[4]}$. A key open question is the robustness of these nuclear shapes, as the parameters defining them often exhibit significant fluctuations, leading to mixing between different configurations. [1] P. E. Garrett, M. Zielińska, and E. Clément, Prog. Part. Nucl. Phys. 124, 103931 (2022). [2] Rodríguez, T. R., and Martínez-Pinedo, G. (2010), Phys. Rev. Lett. 105, 252503 (2010) [3] STAR Collaboration, Nature 635, 67-72 (2024). [4] D. Frycz, J. Menéndez, A. Rios, B. Bally, T. R. Rodríguez, and A. M. Romero, Phys. Rev. C 110, 054326 (2024).

Improving Statistical Analyses in Particle Physics Phenomenology

• Bernat Capdevila (ICCUB)

Room: Aula Magna Enric Casassas

Multi-strange baryon spectroscopy in charm decays at LHCb

• Lukas Calefice (Universitat de Barcelona/ICCUB)

Room: Aula Magna Enric Casassas The study of excitation spectra of hadrons is a crucial experimental tool to understand the binding mechanism of quarks in the strong interaction. While big advances have been made in recent years in the study of heavy-flavour hadrons containing a charm (c) or beauty (b) quark, the field of multi-strange (s) baryons, especially $\Xi^{0,−}$ (ssu, ssd) and $\Omega^−$ (sss), is largely unexplored. To date, only a limited amount of states (10 for $\Xi^{0,−}$ and 4 for $\Omega^−$) are known, most of them seen with very low statistics in small fixed-target experiments in the 1980s but never experimentally confirmed. The vast LHCb dataset of charm hadrons such as the $\Omega^0_c$ baryon offers a rare opportunity to search for missing states in the excitation spectra of strange baryons by looking at decays of the $\Omega^0_c$ baryon such as $\Omega^0_c → \Xi^− \pi^+ K^− \pi^+$. I will discuss some ideas and preliminary results on how a search at LHCb can be performed.

Understanding astronomical catalogues: Gaia and its selection function

• Alfred Castro-Ginard (Universitat de Barcelona)

Room: Aula Magna Enric Casassas Gaia has provided the largest star map in history, but it has only detected the brightest 2% of our Galaxy's stars. Failing to account for this limitation can lead to inaccurate conclusions about the processes that have shaped our Galaxy. In this talk, I will discuss statistical methods to estimate Gaia's completeness and how these can influence the scientific conclusions about the Milky Way.