NEHOP 2026 - New Horizons on Primordial Black Hole Physics

15 Jun 2026, 08:30 → 19 Jun 2026, 17:00 Europe/Zurich

4/3-006 - TH Conference Room (CERN)

Antonio Walter Riotto (Universite de Geneve (CH)), Francesca Calore (Unite Reseaux du CNRS (FR)), Gabriele Franciolini, Hyun Min Lee (CAU - Chung-Ang University (KR)), Ki-Young Choi (Sungkyunkwan University (KR)), Matteo Braglia (New York University), Pasquale Serpico (LAPTh - CNRS & Univ. Savoie (FR)), Seong Chan Park (Yonsei University), Silvia Gasparotto, Valerie Domcke (CERN)

After three very successful editions in Naples, Edinburgh and Brussells, we are excited to organize the fourth New Horizons in Primordial Black Hole Physics (NEHOP'26) workshop at CERN. This will be supported by the CERN TH institute program and the CERN-CKC collaboration.

Registrations and abstract submissions are open until 30 April 2026. 

Invited speakers:

• C. Byrnes (Sussex U.)
• S. Delos (Carnegie Inst. Observ.)
• G. Dvali (Munich U., ASC and Munich, Max Planck Inst.)
• J. Gong (Ewha Womans University)
• Y. Gouttenoire (U. Mainz)
• K. Kohri (NAOJ)
• B. Liu (Heidelberg U.)
• P. Mroz (U. of Warsaw)
• S. Profumo (UC, Santa Cruz)
• W. Qin (NYU)
• A. Romero-Rodriguez (Annecy LAPP)
• S. Trifinopoulos (CERN)
• C. Yoo (Nagoya U.)

 

NOTE: on previous occasions, several participants received phishing messages offering to book accommodation for the event (from e.g. conventionsaccommodation, g-travelexperts, etc.). We do not send such messages and participants need to make their own arrangements for their accommodation (either at the CERN hostel or hotels nearby).

Info for the registered participants:
 - Please note that in order to obtain your CERN access card to enter the site, details and a link to obtain an access card will be sent to you before the workshop.

Monday 15 June

08:30 → 09:00 Registration

09:00 → 09:15 Welcome from the organizers / practical information

09:15 → 10:45 Invited Talks

09:15 The Physics of Planck-ton

Primordial black holes, if produced in the early Universe, may not evaporate completely but instead leave behind stable or long-lived Planck-mass remnants, or "Planck-tons". I review theoretical arguments for such relics from quantum gravity frameworks, including generalized uncertainty principles, loop quantum gravity, and string-theoretic corrections, which suggest a breakdown of semiclassical evaporation near the Planck scale. I discuss the resulting relic abundance and show that even a tiny initial PBH fraction can account for the observed dark matter, with relics behaving as ultra-cold, collisionless matter today. I outline possible detection avenues, including high-frequency gravitational waves from evaporation and mergers, electromagnetic signatures of charged relics, and direct mechanical probes. I argue that Planck-scale relics provide a testable link between quantum gravity, early-Universe cosmology, and dark matter.

Speaker: Stefano Profumo

10:00 Black hole memory burden effect

We discuss the Memory Burden Effect in black holes and its observational implications. The essence of this universal phenomenon is that the information load carried by a black hole influences its macroscopic dynamics. This influence is quantified by a new macroscopic characteristics of a black hole in form of the memory burden parameter which measures the ``weight" of its information load. In particular, the memory burden tends to stabilize the host black hole against the Hawking decay. It also affects the dynamics of black holes's classical perturbations. We discuss implications for PBH dark matter as well as for mergers of astrophysical black holes and observable imprints in the spectrum of gravitational waves.

Speaker: Gia Dvali

10:45 → 11:30 Coffee-break

11:30 → 12:30 Contributed talks

11:30 Microscopic primordial black holes as macroscopic dark matter from large extra dimensions

We study the coupled cosmological evolution of primordial black holes (PBHs) and radiation in the Arkani-Hamed-Dimopoulos-Dvali (ADD) framework with $n$ large extra dimensions and a fundamental gravity scale $M_\star$ at the TeV scale. For PBHs with horizon radius smaller than the compactification scale, the higher-dimensional geometry implies a larger horizon size at fixed mass and therefore a suppressed Hawking temperature. As a result, radiation accretion can overcome evaporation in the early Universe and drive a ``runaway'' phase of rapid mass growth. By numerically solving the coupled mass and energy-density evolution equations, we show that for $n \geq 2$ initially microscopic PBHs with initial mass $M_i \gtrsim 10^{12}\,$g can grow by many orders of magnitude and potentially reach macroscopic, even solar-mass, scales by matter-radiation equality. We determine the critical initial abundance $\beta_{\rm crit}$ required for PBHs to account for the observed dark matter density and find that extra dimensions dramatically lower this threshold, allowing viable scenarios with $\beta_{\rm crit}\sim 10^{-44}$. This identifies a previously unexplored region of parameter space in which the dark matter abundance is achieved through dynamical mass growth rather than large initial collapse fractions.

Speaker: Giuseppe Filiberto Vitale

11:45 Hawking radiation as a probe of physics beyond theStandard Model

Hawking radiation from primordial black holes provides a unique link between particle physics and black hole physics. In this work, we investigate the phenomenology of black hole evaporation, focusing on photon and neutrino signals produced through secondary emission processes. Particular attention is given to potential signatures arising in Beyond Standard Model scenarios, such as supersymmetric extensions. Using Monte Carlo simulations, we assess whether these effects lead to observable features, providing an astrophysical probe of new physics complementary to current collider searches.

Speaker: Paola Simone

12:00 Primordial Black Holes as Dark Sector Factories

The Hawking radiation of photons from primordial black holes can be detected in future gamma-ray telescopes if PBHs constitute even a small fraction of dark matter. PBHs can likewise radiate new particles, which is particularly interesting when these particles are largely secluded from the Standard Model sector and would otherwise be difficult to access. In this talk, I will describe how such dark sector particles can be probed through the spectrum of Hawking radiation.

Speaker: Jae Hyeok Chang (Seoul National University)

12:15 Neural Hawking Operator

Primordial black holes (PBHs) have been emitting particles through Hawking radiation since the early universe, and the resulting spectra encode the imprint of their mass distribution. Because realistic PBH formation naturally yields extended mass functions, we develop a learned mapping between the mass function and the photon spectrum in both directions. The conventional forward chain is slow, multi-stage, and non-differentiable, while the corresponding inverse problem is ill-posed. These limitation motivate neural operator learning, which maps between infinite-dimensional function spaces and provides a fast, differentiable, unified framework for both directions. We introduce the Neural Hawking Operator, providing a practical foundation for systematic phenomenology of extended PBH mass functions.

Speaker: yeji park (IBS-CTPU-PTC)

14:00 → 15:30 Invited Talks

14:00 Overview of observational constraints on PBHs

I am going to provide a comprehensive overview of
observational constraints on primordial black holes. If time permits,
I will discuss the following hot topics; PBHs as seeds of SMBHs, the BBN
bound, MeV gamma-rays, formations in the early matter-dominated era,
cosmological accretions, hot spot formations, and the Poltergeist
mechanism.

Speaker: Kazunori Kohri

14:45 [TBA]

Speaker: Jinn-Ouk Gong (Asia Pacific Centerfor Theoretical Physics)

15:30 → 16:15 Coffee-break

16:15 → 17:15 Contributed talks

16:15 Non-Linear Dynamics and Primordial Black Hole Formation During Kination

The early universe may have experienced a kination epoch - a phase where a scalar field's kinetic energy dominates the expansion. In this talk, I will outline how scalar-field inhomogeneities during this era can trigger strong non-linear dynamics, and how these can collapse to form primordial black holes(PBHs). Based on numerical relativity simulations, I will show the conditions under which super-horizon perturbations grow non-perturbatively and the critical initial conditions for PBH formation. I will discuss how a non-standard background like kination opens new pathways for PBH formation and the cosmological implications.

Speaker: Cheng Cheng (Center for Physical Sciences and Technology (FTMC))

16:30 Primordial black hole formation in scalar field cosmologies

In this talk, I will discuss how primordial black holes can form in non-standard stages of the early Universe dominated by scalar fields. I will focus on three representative scenarios: slow reheating with a quadratic potential, a quartic scalar field, and a massless scalar field.

The main goal is to understand when scalar fields can be effectively described as perfect fluids during gravitational collapse, and when this analogy breaks down. I will show that while a quartic scalar field behaves very similarly to a radiation fluid even in the nonlinear regime, the massless scalar field exhibits a different type of critical behavior, including log-periodic oscillations associated with discrete self-similarity.

Overall, the talk will highlight how primordial black hole formation can be used as a probe of the microphysics of scalar fields in the early Universe.

Speaker: Luis Padilla (Rikkyo University)

16:45 Cosmological long-wavelength solutions in non-adiabatic multi-fluid systems

We develop a formulation of nonlinear cosmological perturbations on superhorizon scales in multi-fluid systems. It is based on the Arnowitt–Deser–Misner formalism combined with a spatial gradient expansion, characterized by a small parameter $\epsilon \equiv k/(a^{(b)}H)$, where $a(t)$ is the scale factor of the flat Friedmann-Lemaître-Robertson-Walker spacetime, ${}^{(b)}H(t)$ is the corresponding Hubble parameter, and $k$ is the comoving wavenumber. Within this framework, we explicitly construct nonlinear long-wavelength solutions for cosmological perturbations. Since multi-fluid systems are inherently non-adiabatic, these solutions admit both adiabatic and entropy modes even at nonlinear leading order in the expansion. We define adiabatic and entropy perturbations, while face non uniqueness in defining pure entropy perturbations. Using the possible variations of pure entropy initial conditions, we analyze the time evolution of physical quantities, such as the curvature perturbation and density perturbation, in the geodesic slice for two-fluid systems.

Speaker: HAYAMI IIZUKA (Rikkyo University)

17:00 Trichotomy of PBH initial conditions

We show that the threshold to form a black hole, in an asymptotically flat and radiation-dominated Friedman-Robertson-Walker (FRW) Universe, is not solely (mainly) determined by the behaviour of the compaction function at its extrema, as earlier thought, but also by the Ricci scalar of the spatial geometry at smaller (but super-horizon) scales, which we call "the core". We introduce three classes of initial conditions characterised by an open (O), closed (C), or flat (F) FRW core surrounded by a shell with higher three-dimensional curvature. In the C case, the core helps the collapse so that the black hole formation threshold is the lowest among all cases. Type-II black holes might only be generated by Type-O or F (each of those with different thresholds, with O being the highest) or by a Type-C with a negligible Ricci scalar at the centre, which we call an effective F core.

Speaker: Laia Montellà (ICCUB)

18:00 → 20:00 Welcome reception

Tuesday 16 June

09:15 → 10:45 Invited Talks

09:15 Microlensing Searches for Primordial Black Holes

The field of gravitational microlensing has been closely linked, since its inception, to the search for compact objects (including primordial black holes) as candidates for dark matter. The seminal idea by Bohdan Paczyński to use microlensing as a probe of dark matter launched a field that continues to deliver cutting-edge scientific results.

Microlensing is particularly sensitive to primordial black holes across a wide mass range, from objects with masses comparable to that of the Moon up to thousands of solar masses.

In this talk, I will review the current status of microlensing experiments, focusing on the latest results from OGLE and Subaru Hyper Suprime-Cam, and discuss their implications for primordial black holes as dark matter.

Speaker: Przemek Mróz

10:00 Effects of primordial black holes on early star formation

Primordial black holes (PBHs) have long been considered a promising candidate for or an important component of dark matter. Recent gravitational wave observations of binary black hole (BH) mergers and discoveries at the high-redshift Universe made by JWST have triggered renewed interest in PBHs in the stellar-mass ($\sim10-100\ \rm M_\odot$) and supermassive regimes ($\sim 10^6 − 10^{11}\rm\ M_\odot$). We use cosmological simulations and semi-analytical models to explore the effects of PBHs on early star formation, focusing on two mechanisms: acceleration of structure formation from isocurvature perturbations and (thermal) feedback from BH accretion. Although stellar-mass PBHs do affect the properties of first star-forming halos, the standard picture of first star formation is not changed (for PBH abundances allowed by existing observational constraints), and their global impact on cosmic star formation history is likely minor, as the thermal feedback from PBHs increases the halo mass threshold for star formation, compensating for the enhanced halo abundance. On the other hand, supermassive PBHs may play more important roles as seeds of massive structures, which can explain the apparent overabundance of massive galaxies and overmassive BHs in recent JWST observations. In particular, the special source Abell 2744-QSO1, with an extremely high BH-to-stellar mass ratio and no metal detections, is difficult to reproduce with standard galaxy evolution models in LCDM, but can be naturally explained as a PBH-seeded halo in the early phase dominated by BH feedback. We also find that the UV radiation from PBHs can potentially trigger the formation of direct-collapse BHs, leading to supermassive BH binaries.

Speaker: Dr Boyuan Liu (Center for Astronomy of Heidelberg University)

10:45 → 11:30 Coffee-break

11:30 → 12:30 Contributed talks

11:30 Gravitational Lensing of Fast Radio Bursts as a Probe of Primordial Black Holes Abundance: a forecast for radio telescopes

The Fast Radio Bursts (FRBs) are some of the most intriguing radio phenomena measured in radio astronomy \cite{lorimer}. These energetic bursts have extremely high radio luminosities, corresponding to $\sim 10^{36} \,–\, 10^{44}$ $\mathrm{erg \,s}^{-1}$, which is not far from gamma ray bursts. Since their discovery in 2007, several investigations have been proposed to model their sources and also to use their data for astrophysical and cosmological constraints. Among such efforts, we highlight lensing effects in the propagation of the FRBs, which could be used to constrain Primordial Black Holes (PBHs) \cite{munoz, chime}. These black holes would be produced in the earliest stages of the Universe and could have masses below $1\mathrm{M_{\odot}}$ \cite{carr}. There are several surveys constraining the possible values of mass and fraction of these black holes, and among these proposals lies the lensing effects of FRBs. In this work, we briefly review some generalities about lensing effects for point sources, and we present a forecast for LOFAR, FAST, and BINGO telescopes. These radio telescopes may characterize several FRBs in the coming years. LOFAR and FAST are operating radio telescopes and are expected to be upgraded in the next few years. BINGO \cite{bingo} is a radio telescope under construction in Brazil that may be promising to detect FRBs. The forecast is based on the design features of each of these radio telescopes, and also on the current dataset of 131 confirmed FRB signals, reported by different surveys. Our forecast suggests that LOFAR would be suitable to characterize $f_{\mathrm{PBH}} \sim 16\%$ for lenses around $1\mathrm{M_{\odot}}$, while FAST and BINGO yields to $f_{\mathrm{PBH}} \sim 39\%$ for lenses with $10^{1}\,\mathrm{M_{\odot}}$ and $10^{-1}\,\mathrm{M_{\odot}}$, respectively.

Speaker: Prof. João Rafael Lucio dos Santos (UFCG, Leibniz University and University of Heidelberg)

11:45 Probing Galactic dark matter objects from the heating of exoplanetary systems

We explore the gravitational heating of exoplanetary systems by dark matter substructures of different kinds (primordial black holes -- PBHs, ultra-compact -- UCMHs, or classical subhalos). In this context, the scales of the dark objects probed are of the same order as the orbital radii of planets of interest. Distant exoplanets are quite sensitive to heating processes because less bound to their stars, and a typical signature of the presence of Galactic dark objects would be multi-planets systems with increasing inclination with increasing planetary distance to the stars, up to full ejection of the most distant ones. This allows us to set new upper bounds on the abundance of PBHs and UMCHs in the mass range $10-10^8$M$_\odot$, translating into bounds on the amplitude of the primordial power spectrum in the wavenumber range $10-1000$Mpc$^{-1}$.

Speaker: Théo Paré (LUPM)

12:00 Can Torques Save Primordial Black Hole Spikes?

Density spikes are steep enhancements in the dark matter (DM) distribution that arise from gravitational infall onto a central compact object. In the standard scenario where DM consists of particles, such spikes may form around a sub-dominant population of massive primordial black holes (PBHs), potentially leading to large enhancements of the DM density in their vicinity.

The situation can be qualitatively different if, instead, the bulk of the DM is also composed of PBHs, which are viable alternative candidates to particle DM and can constitute the entirety of it if, for example, they have masses around $M \sim 10^{17}-10^{23}\,\mathrm{g}$. In this scenario, lighter PBHs may avoid capture only if they develop enough angular momentum as a consequence of the torques exerted by both small-scale and large-scale fluctuations.

We investigate the mechanisms and initial conditions—such as the mass and initial separation from a central heavy PBH ($M \sim M_\odot$)—that enable lighter PBHs ($M \sim 10^{18}$–$10^{28},\mathrm{g}$) within such spikes to develop long-lived density enhancements. More specifically, we characterize the torque distribution and its evolution, and follow the resulting angular momentum dynamics using a combination of analytical approaches and numerical simulations.

Speaker: Agnese Tolino (IFIC (CSIC-UV))

12:15 Constraining reheating through PBH condensation

Very little is known about the reheating phase after inflation, which is only constrained to end before Big Bang Nucleosynthesis, at a temperature higher than O(1) MeV. We show that this effectively matter dominated phase can be long enough that structures, such as halos, can form, inflaton stars can condense inside the halos and eventually grow to collapse into PBH. By employing PBH constraints we are able to improve constraints on reheating temperature, depending on the scale of inflation, strengthening existing bounds by several orders of magnitude.

Speaker: Francescopaolo Lopez

14:00 → 14:45 Invited Talks

14:00 Dynamics of Primordial Black Hole Formation in a Matter Dominated Universe

In this talk, we will begin by briefly reviewing the research conducted so far on the formation of primordial black holes during the matter-dominated era. Then we introduce more details of the analytical investigation on the formation dynamics, particularly focusing on the effect of inhomogeneity and ellipticity. Finally, we will report recent results obtained from the attempts on numerical investigations of primordial black hole formation in a matter-dominated universe.

Speaker: Chulmoon Yoo

14:45 → 16:00 Contributed talks

14:45 Stochastic inflation on the hilltop and beyond

Stochastic inflation allows us to study large inflationary perturbations that may collapse into primordial black holes. I discuss the spectral decomposition of the perturbation distribution in stochastic inflation near a local maximum of the inflaton potential, relevant for primordial black hole production from inflection point models. I compare the stochastic computation with results from classical $\Delta N$ formalism, illustrating, in particular, the difficulties that arise from trajectories that pass `beyond the hilltop,' into the quantum-dominated regime.

Speaker: Eemeli Tomberg (UCLouvain)

stochhilltop.pdf

15:00 Stochastic scalar-tensor Inflation

In this talk, I will review our recent work and its attempt to extend the scope and predictive power of the stochastic formalism for inflation. After briefly introducing the specificity of our stochastic coarse-graining procedure, I will discuss our formulation of stochastic dynamics in full General Relativity, including all metric and scalar matter degrees of freedom, as well as gradient contributions. I will then present numerical implementations of these stochastic equations within the framework of Numerical Relativity, demonstrating their efficacy in well-understood scenarios and their application to ongoing investigations, relevant for a rigourous understanding of phenomena such as primordial black hole formation.

With this framework fully established, I will show how the formalism can be generalised beyond General Relativity, in particular to scalar–tensor theories of dark energy and multifield scenarios, and potentially beyond.

Speaker: Yoann Launay

15:15 Classical and quantum evolution of inflationary fluctuations

Computing the abundance of primordial black holes from inflation requires dealing with large, non-Gaussian primordial quantum fluctuations. Recently, progress has been made in computing the statistics of such perturbations using classical or semiclassical techniques, like lattice calculations. One may question, however, the reliability of these methods to capture the underlying quantum dynamics. In this work, we address this issue by comparing the three-point correlation function of inflationary perturbations computed either with quantum or classical dynamics. We find that, even when the two are enforced to agree at a specific time during inflation, classical and quantum correlations differ at the end of it, with the difference being exponentially sensitive to the number of e-folds elapsed since the time of agreement. Finally, we assess the validity of classical Green's function methods used to compute the amplitude of inflationary scalar-induced gravitational waves.

Based on work in progress (soon to appear in arXiv) with Guillermo Ballesteros and Jesus Gambin Egea.

Speaker: Alejandro Perez Rodriguez (University of Washington)

15:30 Promises and Pitfalls of Inflation on the Lattice

Large inflationary perturbations are a leading mechanism for primordial black hole (PBH) formation. Lattice simulations have been proposed as a route beyond perturbation theory, but their reliability has not been systematically established. In this talk, we demonstrate that certain implementations can produce significantly incorrect PBH abundances and identify the key sources of these failures. We derive concrete criteria for assessing the viability of lattice simulations and apply them across slow-roll, ultra-slow-roll, and strongly resonant regimes. Finally, we outline improved implementations that bring lattice techniques closer to delivering reliable non-perturbative predictions of large inflationary perturbations.

Based on: arXiv 2605.xxxx by W. Barker, B. Gladwyn and S. Zell

Speaker: Benjamin Charles Gladwyn (University of Oxford (GB))

15:45 Moving barriers in Excursion-Set Theory for PBHs: method, mass functions and quantitative clustering

In the excursion-set formalism, various quantities are derived
from the first-passage time of a random walk describing the density contrast as the coarse-graining scale varies. In the context of Primordial Black Holes (PBHs) formation, I will show that different choices of hypersurfaces for the sampling of the theory affect the nature of the random walk.

Using a synchronous sampling, the random walk becomes a Brownian Motion with moving barrier. I will present quantitative estimates of the mass fraction of PBHs for various power spectra, top-hat, log-normal, both narrow and wide, but also doubly peaked. The effect of cloud-in-cloud as well as the current limitations of the excursion-set approach are discussed.

I will then show, in the context of PBHs clustering at formation, how the excursion-set enables to go beyond pointlike treatments (e.g. Poisson model) by including small scales exclusion effects and removing the contribution of the shot noise at zero separation. Quantitative estimates of clustering will be presented for both narrow, wide or doubly peaked power spectra.

Based on ArXiv:2603.04185 and a forthocoming accompanying article.

Speaker: Baptiste Blachier

16:00 → 16:30 Coffee-Break

16:30 → 17:30 Guided Thematic Discussion

Wednesday 17 June

09:15 → 10:45 Invited Talks

09:15 Updated Upper Limits on the Amplitude of a Scalar-Induced Gravitational-Wave Background Using Data from LIGO–Virgo–KAGRA's O4a Observing Run

The formation of primordial black holes from large-amplitude primordial curvature perturbations is expected to be accompanied by a stochastic background of scalar-induced gravitational waves. In this talk, I will present the latest constraints on the integrated power of the curvature power spectrum peak associated with such a background, derived using data from the O4a observing run of the LIGO–Virgo–KAGRA (LVK) Collaboration.

I will briefly introduce the LVK search for an isotropic stochastic gravitational-wave background, which combines frequentist and Bayesian inference techniques. Although no stochastic background has been detected so far, the absence of a signal allows us to place meaningful constraints on models describing its potential sources. I will therefore discuss the agnostic parametrization adopted to describe the primordial curvature perturbation spectrum and show how the frequentist results of the O4a analysis can be translated into upper limits on the integrated power of the curvature power spectrum peak.

Speaker: Alba Romero Rodríguez

10:00 Charting the Universe with Primordial Black Holes: From Planetary to Supermassive

Primordial black holes (PBHs) offer a particularly rich window onto the early Universe: the same large primordial curvature perturbations that collapse to form PBHs also generate a stochastic background of scalar-induced gravitational waves (SIGWs), while the PBHs themselves can later form binaries and merge, producing gravitational-wave signals in complementary frequency bands. In this talk, I will explore how these signals can be connected across different experiments to probe PBHs over a vast range of masses. I will begin with planetary-mass PBHs, whose formation is associated with micro-Hz SIGWs that could be targeted by future Lunar and Satellite Laser Ranging measurements. I will then turn to sub-solar PBHs, discussing how mergers in ground-based interferometers and a nano-Hz SIGW background observed by pulsar timing arrays (PTAs) can arise from a common primordial origin. Finally, I will switch gears to supermassive PBHs, whose binaries can produce chirping signals in PTAs, but their abundance is strongly constrained by an effective field theory description of the high-redshift Lyman-alpha forest.

Speaker: Sokratis Trifinopoulos (University of Zurich (CH))

10:45 → 11:30 Coffee-Break

11:30 → 12:30 Contributed talks

11:30 Towards Accurate Merger Rates of Early Primordial Black Hole Binaries with an Extended Mass Function

This talk focuses on the dynamics of early primordial black hole binaries with a broad mass distribution. We highlight the subtleties that arise when calculating merger rates for these distributions and propose a framework to account for some of them. While the quest for a definitive rate remains ongoing, we provide critical insights into how mass-function variance impacts theoretical predictions. Finally, we present specific edge cases to demonstrate where current gravitational wave constraints remain robust, where they must be viewed with caution, and where they fail, depending on the underlying mass distribution.

Speaker: Simon Biot (ULB)

11:45 When Tiny Halos Stir Spacetime : Gravitational Waves from Fifth-Force Mergers

Dark matter fermions interacting through an attractive force mediated by a light scalar can form bound structures already in the very early universe. We show that binaries composed of such dark matter halos can generate gravitational wave (GW) signals observable today, even when the individual halos are extremely light. Because the dark Yukawa interaction, which is much stronger than gravity, governs the dynamics of these systems, they can emit sizable GW signals at initially very high frequencies despite their low masses. As the universe expands, these signals are redshifted into frequency bands accessible to current and future GW detectors.

The resulting GW signatures exhibit distinctive features that can differentiate them from conventional astrophysical sources. Remarkably, even if only a small fraction of dark matter participates in such strong self-interactions, the associated GW signals may still be detectable. This opens a new avenue for probing self-interacting dark matter through gravitational wave observations.

Speaker: Xinpeng Wang (Kavli IPMU, University of Tokyo)

12:00 Probing the reheating epoch with induced gravitational waves and connections to PBH scenarios

In the standard formation picture, primordial black holes (PBHs) form in the radiation-dominated early Universe from the collapse of enhanced curvature perturbations. However, the reheating period connecting inflation to the radiation epoch is poorly constrained, as is the inflaton potential below CMB scales. Observational constraints are therefore consistent with the Universe having undergone an early matter-dominated (eMD) epoch driven by ultra-light, evaporating PBHs or oscillons -- long-lived quasi-solitonic objects formed from the fragmentation of the inflaton condensate.
In both cases, the sudden eMD-to-radiation transition strongly enhances scalar-induced gravitational waves (SIGWs) via the Poltergeist mechanism, making SIGWs a powerful probe of this epoch. In this talk we discuss the parallels between the PBH and oscillon scenarios in this context, and then focus on the latter to show how the observational bound on the effective number of relativistic species, $\Delta N_{\text{eff}}$, applied to the induced GW background sets novel constraints on the inflaton potential in regions of parameter space inaccessible to CMB measurements of the scalar power spectrum alone.

Speaker: Jan Tränkle

12:15 Gravitational Waves from Black Hole Reheating

We investigate the scalar-induced gravitational wave (SIGW) signal originating from the evaporation of primordial black holes (PBHs). In the idealized monochromatic mass scenario, a pronounced SIGW signal arises via the so-called poltergeist mechanism, triggered by a sharp transition from matter to radiation domination. However, more realistic extended mass distributions—such as those predicted by the Press–Schechter formalism and peak theory for PBHs formed from the collapse of superhorizon overdensities—smooth this transition.
Using both Press–Schechter and peak theory, we derive the narrowest extended mass function consistent with superhorizon collapse. We show that even in this limiting case, the associated smoothing leads to a significant suppression of the resulting GW signal. This suppression limits the detectability of large parts of the ultra-light PBH parameter space by future GW observatories, while simultaneously relaxing stringent Big Bang nucleosynthesis (BBN) bounds and reopening previously excluded regions.
Our analysis carefully treats the curvature power spectrum cutoff and consistently includes contributions from both adiabatic and isocurvature initial conditions. In particular, we revisit and update the transfer functions and the evolution of adiabatic and isocurvature fluctuations across the radiation-dominated to early matter-dominated transition.
Furthermore, we extend our framework to SIGWs generated during early matter- and radiation-dominated phases, including enhancements of the power spectrum at PBH formation. Separately, we analyze the high-frequency gravitational wave contribution from PBH binaries, accounting for different merger channels, as well as from PBH evaporation.

Speaker: Nicholas Leister

14:00 → 15:00 Invited Talks: TH - Colloquium

14:00 Introducing primordial black holes

While black holes can be the remnants of stellar collapse, some may have formed in the early universe - making them primordial black holes (PBHs). These would form a relic from the early universe, preserving a memory of the initial conditions of the universe at early times and on small scales. PBHs do not require the introduction of new fundamental physics, making them a special dark matter candidate. In this talk, I will outline observational constraints on PBHs and potential routes to a detection, explore their connections to gravitational wave signals and early universe cosmology, and discuss how the evaporation of primordial black holes could produce high-energy particles.

Speaker: Christian Byrnes (University of Sussex)

15:00 → 16:15 Coffee-Break

16:15 → 17:30 Contributed talks

16:15 GrayHawk v2: Wormholes and Numeric Extension

We enlarged the capabilities of the publicly available Mathematica-based tool $\tt GrayHawk$. This second version enlarges the spectrum of metrics that can be considered in two distinct and disjoined directions. First, it allows a fully numeric computation of tortoise coordinates integral, allowing the user to take into account many metrics for which the analytic computation was impractical. Second, it extends the scattering problem to wormhole solutions.

\noindent The pool of pre-loaded metrics is enriched, offering the immediate possibility of testing the new features, and the code modular structure is maintained to facilitate users in easily modifying the code. This implementation proves $\tt GrayHawk$ adaptability and makes it an even more powerful tool for studying black holes, wormholes, Hawking radiation, and other features involving field propagation on curved manifolds.

\noindent The codes described will soon be made publicly available at \href{https://github.com/marcocalza89/GrayHawk}{\faGithub}.

Speaker: Marco Calza (University of Trento)

16:30 Primordial Black Holes in Einstein–Dilaton–Gauss–Bonnet Gravity

Primordial black hole (PBH) formation is a manifestation of critical phenomena in gravitational collapse, where near the threshold the black hole mass exhibits a universal scaling behavior. The Einstein–Dilaton–Gauss–Bonnet (EdGB) gravity is the simplest extension of the Einstein Gravity with the higher curvature by introducing the Gauss-Bonnet term without any ghost states. The scalar–Gauss–Bonnet interaction modifies this critical scaling and can introduce a mass gap, implying the existence of a minimum PBH mass. These modifications directly affect both the collapse threshold and the resulting PBH mass spectrum, with important implications for early-universe cosmology. Currently, we are investigating PBH formation in EdGB gravity through the framework of the generalized Misner–Sharp mass, showing how the curvature–dilaton coupling reshapes the collapse dynamics and leads to systematic departures from
the standard general relativistic picture.

Speaker: Prof. Bum-Hoon Lee (Sogang University)

16:45 Are Hairy Black Holes Primordial?

We study the cosmological implications of stable hairy black hole solutions by spontaneous symmetry breaking (SSB) in Einstein-scalar-Gauss-Bonnet theory. For such solutions and the SSB potential to be consistent with the cosmological history, we find that the compact objects that develop scalar hair might be in the primordial black hole mass range. We estimate the evolution of such PBH in the early Universe, including possible signatures.

Speaker: Suruj Jyoti Das (Institute for Basic Science, CTPU)

17:00 Lukewarm inflation, primordial black holes and gravitational waves

We show that a late period of warm inflation, denoted as lukewarm inflation and sustaining a slowly-varying temperature parametrically below the GUT scale, naturally leads to an enhanced and nearly scale-invariant curvature perturbation power spectrum at small scales. We compute the resulting spectrum of primordial black holes and scalar-induced gravitational waves, which depend on the temperature and duration of the lukewarm inflation period, the strength of the dissipative effects that sustain it and the form of the scalar potential. Interestingly, we show that recent hints for planetary-mass black holes and a stochastic gravitational wave background at nanoHertz frequencies could simultaneously be explained by a lukewarm inflation period at temperatures just above the TeV scale.

Speaker: Joao Rosa (University of Coimbra)

19:00 → 21:00 Reception

Thursday 18 June

09:15 → 10:00 Invited Talks

09:15 Not-quite-primordial black holes

In this talk, I will discuss a new mechanism for the formation of seeds of supermassive black holes at early cosmic epochs. Enhanced density fluctuations with amplitudes that are not large enough to form primordial black holes post-inflation can still lead to collapsed dark matter halos at very early times. For halos forming prior to 1+z ~ 200, the Cosmic Microwave Background (CMB) is energetic enough to suppress the formation of molecular hydrogen, hence preventing cooling and fragmentation, as a consequence of which baryons falling into the potential well of the halo may undergo “direct collapse" into a black hole. I will show using a few illustrative models how this mechanism may account for the abundance of high-redshift black holes inferred from observations by the James Webb Space Telescope while remaining consistent with current limits from CMB spectral distortions. Limits on the primordial power spectrum are also derived by requiring that the universe not reionize too early.

Speaker: Ms Wenzer Qin (New York University)

10:00 → 10:45 Contributed talks

10:00 Large Primordial Fluctuations: Stochastic vs. Classical $\delta N$ approaches

Quantum fluctuations during cosmic inflation inevitably generate inhomogeneities and anisotropies on all observable scales and beyond. The $\delta N$ formalism provides a powerful framework to describe the nonlinear curvature perturbation in terms of fluctuations in the duration of inflation, $N$. In its standard implementation, $\delta N$ is calculated using the classical trajectory to find the number of e-folds of inflation from a given field value to the end of inflation. In contrast, the stochastic $\delta N$ formalism incorporates quantum fluctuations as stochastic noise along the trajectory, enabling a non-perturbative treatment of inflationary dynamics that can be crucial for rare, large fluctuations. In this work, we compare the classical and stochastic approaches to study the statistics of large curvature perturbations when coarse-grained at a given length scale. This is particularly relevant for calculations of primordial black hole formation. Using the numerical code PyFPT, we compute the distribution of curvature perturbations from slow-roll inflation driven by a quadratic potential, and perform a detailed comparison with the classical $\delta N$ formalism, identifying regimes where quantum diffusion significantly impacts the probability distribution of large fluctuations.

Speaker: Parth Bhargava (Institute of Cosmology and Gravitation (ICG), Portsmouth)

10:15 Primordial Black Holes from Coloured Noises

The excursion-set formalism enables us to infer the mass distribution of collapsed objects, such as primordial black holes (PBHs), by the language of stochastic processes. Within the framework, it is investigated how the resulting PBH mass function is affected by a smooth coarse-graining procedure, for which the stochastic noise becomes fully correlated across scales. It is found that these correlated noises result in a mass function of PBHs whose maximum and its neighbourhood are predominantly determined by the probability that the density contrast exceeds a given threshold at each mass scale.

Speaker: Koki Tokeshi

10:30 Scalar field scattering from a Schwarzschild-de Sitter black hole

I will discuss the scattering problem for a massless scalar field in a Schwarzschild-de Sitter black hole background and its possible implications for primordial black holes. A rigorous application of the method of matched asymptotic expansions allows us to solve analytically the low-frequency s-wave dynamics, and connect the scalar’s evolution in the proximity of the black-hole horizon with that on cosmological scales. The scattering coefficients, greybody factors, and Wigner time delay are computed explicitly. We consider both small and large black holes, with black-hole to cosmological horizon radii parametrically small and of order unity, respectively. This extends previous studies confined to the small black-hole regime only. In addition, for small black holes we perform a calculation that remains agnostic about the relative size between the ratio of the geometry’s horizons and the scalar’s frequency in units of the black-hole radius. In this case, we find that they are interchangeable in the greybody factor, which is symmetric under $\omega\leftrightarrow 1/r_c$ (where $\omega$ is the scalar’s frequency and $r_c$ the cosmological horizon radius).
Based on joint work with M. Miranda and A.P. Porfyriadis, arxiv:2511.09168 (to appear in PRD).

Speaker: Marco de Cesare (Scuola Superiore Meridionale)

10:45 → 11:30 Coffee-break

11:30 → 12:30 Contributed talks

11:30 Reviving PBHs: primordial black holes from supercooled phase transitions revisited

Black holes in the asteroid-mass range, $10^{15}$ - $10^{20}$ kg, provide a compelling candidate for dark matter. This window remains largely unconstrained observationally, while the low masses provide an interesting challenge in explaining their possible origin. In this talk, I will discuss a particular formation scenario of such objects, where curvature perturbations responsible for gravitational collapse into black holes are generated by a cosmological first-order phase transition. If the transition is strongly supercooled and slow compared to the Hubble expansion, fluctuations in the bubble nucleation history in different patches of the Universe can produce a large spectrum of curvature perturbations. I will present a covariant formalism that can be adopted to compute the evolution of energy-density fluctuations within a fixed comoving volume. Within this formalism, I will highlight the crucial role of energy flux carried by expanding bubble walls in amplifying curvature perturbations to the level required for black hole formation. Finally, I will identify the transitions for which the population of produced black holes can fully explain the abundance of dark matter observed today.

Speaker: Piotr Toczek (University of Warsaw)

11:45 Thermodynamic limitations for primordial black holes from cosmological phase transitions

Strongly supercooled first-order phase transitions have been proposed as a primordial black hole (PBH) production mechanism, but existing estimates rely on simplified thermodynamics. Reliable PBH predictions require precise nucleation dynamics within realistic, classically conformal extensions of the Standard Model.

In this talk, I employ high-temperature dimensional reduction and one-loop fluctuation determinants to perform a state-of-the-art thermodynamic analysis of classically conformal gauge–Higgs theories and compute the resulting PBH abundance. Accounting for constraints from successful percolation and QCD chiral symmetry breaking, the parameter space where PBHs are viable dark matter candidates is severely limited [1].

[1] M. Kierkla, N. Ramberg, P. Schicho, and D. Schmitt, Theoretical uncertainties for
primordial black holes from cosmological phase transitions, (2025), [2506.15496].

Speaker: Philipp Schicho (University of Geneva)

12:00 Evaporating black holes: how the burden of their memory stabilizes them

The memory burden effect describes how an object's stored information resists its own decay. I will show how this mechanism can halt Hawking evaporation and dynamically stabilize black holes against complete decay. Importantly, the phenomenon is not exclusive to gravity: it can arise in generic quantum many-body systems and renormalizable field theories, underscoring its broader theoretical relevance. I will then discuss the phenomenological consequences, focusing on potential signatures in the early Universe and today. In particular, memory-stabilized black holes can open a new dark-matter window and produce distinctive high-energy cosmic-ray signals, while leaving correlated imprints on the CMB and other cosmological observables. I will conclude with emerging gravitational-wave implications, including the possibility that mergers of black holes probe the underlying information sector through modified ringdown dynamics.

Speaker: Michael Zantedeschi

14:00 → 14:45 Invited Talks

14:00 Structure formation with primordial black holes

Primordial black holes (PBHs) reshape how cosmic structure forms. I will trace how a PBH population's discreteness, dynamics, and formation history each leave their mark. Being discrete and massive, PBHs carry Poisson fluctuations that seed excess small-scale power and accelerate early structure growth. But PBHs also interact gravitationally with one another, and I will present the first cosmological simulations to fully resolve their few-body and relativistic dynamics. For example, many-body encounters give rise to a subcomponent of hot PBHs that suppresses structure up to billion-PBH scales, and these interactions also scramble binary merger times, reshaping the resulting gravitational-wave signal. I then turn to "warm" PBHs carrying a primordial velocity dispersion, for which we have built the first linear perturbation theory uniting discreteness with free streaming. Finally, I show that PBH formation is rarely clean: the same large primordial fluctuations produce a far greater abundance of ultradense minihalos, which can dominate the dark matter even at minuscule PBH fractions and are already constrained by microlensing. Together, these effects sharpen and transform the observational signatures of PBH dark matter.

Speaker: Dr Sten Delos (Carnegie Observatories)

14:45 → 15:45 Contributed talks

14:45 Ultra-fast growth of primordial black holes through radiative absorption

We show that Schwarzschild primordial black holes (PBHs) formed in the radiation-dominated era can grow extremely rapidly through \textit{radiative absorption} governed by the full Stefan--Boltzmann law. Interestingly enough, we find that whenever the temperature of the PBH environment is larger than the PBH horizon temperature, PBHs generically gain mass. In particular, for PBHs masses following the critical collapse mass-scaling law with critical exponent $\gamma_\mathrm{crit}$ close to $0.362$ the radiative absorption mass growth mechanism mentioned above produces a striking effect: PBHs forming with a mass $10^4M_\odot$ during Big Bang Nucleosynthesis (BBN) can reach $\mathcal{O}(10^{9} M_\odot)$ within $2$ days. Interestingly enough, small deviations from values of $\gamma_\mathrm{crit}$ close to $0.362$,
yield a continuous PBH mass spectrum providing us ultimately with a single, Standard-Model–based explanation for the origin of stellar-mass, intermediate-mass, and supermassive black holes (SMBHs), and naturally accounting for the early appearance of SMBHs. Furthermore, due to this ultra-fast mass growth channel, small mass PBHs, thought to have evaporated by now, can survive today, opening thus the mass window for PBH dark matter. The Schwarzschild treatment presented here can be extended to spherically symmetric cosmological black holes, indicating that radiative absorption is a dominant and previously overlooked PBH growth channel in the early Universe.

Speaker: Prof. Theodoros Papanikolaou (University of Patras, Greece)

15:00 Primordial Black Hole Reformation in the Early Universe

I will present the PBH reformation mechanism, wherein light PBHs can recollapse into heavier and more stable PBHs. Given a moderate initial abundance, light PBHs can initiate an early matter-dominated era before evaporating and reheating the radiation plasma. Structure formation is enabled during matter-domination, leading to clouds of PBHs growing and collapsing into heavier PBHs. Compared to the usual formation mechanism during the radiation era, the formation probability of PBHs is greatly increased and does not require any initial clustering. The heavier reformed PBH population could survive to the present day, emitting high energy cosmic rays while producing a coincident gravitational wave background, both potentially detectable by the next generation of experiments.

Speaker: Philip Lu (KIAS)

15:15 Analytic Gravitational Wave Signatures of Dark Matter Spikes around Primordial Black Hole Binaries

Primordial black holes (PBHs) serve as a compelling and natural dark-matter candidate, originating from the nonlinear collapse of overdense regions in the early Universe without requiring extensions to the Standard Model. During their cosmic evolution, PBH binaries are expected to accrete surrounding dark matter, forming extremely dense minihalos or ``spikes.'' These environments exert dynamical friction on the binary, accelerating the orbital inspiral and imprinting distinct dephasing signatures on the emitted gravitational waves (GWs).

In this work, we develop a comprehensive analytic framework to model the inspiral dynamics of PBHs embedded in generic dark-matter spikes. We characterize the dark-matter density profiles using a generalized power-law form, $\rho(r) = \rho_{\rm sp} (r_{\rm sp}/r)^\gamma$, encompassing cuspy, cored, and truncated distributions. To rigorously quantify the environmental impact, we introduce a ``same-frequency'' definition for the phase difference, $\Delta\phi(f) = \phi_{\rm env}(f) - \phi_{\rm vac}(f)$, evaluated at a common instantaneous GW frequency $f$. We analytically demonstrate that dynamical friction introduces a leading-order phase shift that scales as $\Delta\phi(f) \propto f^{-(11-2\gamma)/3}$.

Crucially, our formalism successfully breaks the theoretical degeneracy between environmental effects and vacuum General Relativity parameters. We isolate the specific spike contributions that can be completely absorbed into an effective chirp mass renormalization, $\delta \mathcal{M}_c / \mathcal{M}_c$, from those that generate genuinely frequency-dependent phase distortions. By providing closed and semi-closed expressions for these dephasing observables, our analytic approach establishes a minimal and robust theoretical bridge between PBH dark-matter scenarios and precision GW phase diagnostics, offering a targeted strategy to hunt for dark-matter environments using next-generation GW interferometers.

Speaker: Mr Jingxu Wu (M.V.Lomonosov Moscow State University)

15:30 Towards Precision Measurements of $H_0$ with Multi-band Gravitational Waves

The Hubble parameter, $H_0$, remains a cornerstone of modern cosmology, yet its precise determination continues to be challenged by the persistent tension between early- and late-Universe measurements. In this talk, I investigate the potential of multi-band gravitational-wave (GW) observations to provide an independent and complementary probe of $H_0$ using primordial black holes (PBHs) as astrophysical sources. I present a framework that combines scalar-induced and merger-induced GW signals and discuss prospects for joint observations with the Square Kilometre Array (SKA) and the Einstein Telescope (ET), enabling a multi-band analysis across a broad frequency range. Employing signal-to-noise ratio (SNR) forecasts and Fisher matrix techniques, I show how future GW observations can constrain the PBH mass, $M_{\rm PBH}$, and abundance, $f_{\rm PBH}$, and how the resulting parameter uncertainties propagate to $H_0$. For fractional uncertainties $\delta\theta_i/\theta_i \lesssim 0.1$, where $\theta_i \equiv {M_{\rm PBH}, f_{\rm PBH}}$, we obtain $\delta H_0 \lesssim 2,{\rm km,s^{-1},Mpc^{-1}}$, improving to $\delta H_0 \lesssim \mathcal{O}(0.1),{\rm km,s^{-1},Mpc^{-1}}$ for $\delta\theta_i/\theta_i \lesssim 0.01$. Finally, I demonstrate that these forecasts are largely insensitive to the fiducial value of $H_0$ and exhibit only moderate dependence on the PBH collapse efficiency, highlighting the potential of multi-band GW observations as a cosmic distance ladder-independent avenue for precision cosmology.

Speaker: Dr Mohammed Riajul Haque (Tsung Dao Lee Institute, Shanghai Jiao Tong University)

15:45 → 16:30 Coffee-Break

16:30 → 17:30 Guided Thematic Discussion

Friday 19 June

09:15 → 10:00 Invited Talks

09:15 Gravitational Waves from Primordial Black Hole Reheating

I will present the 13 channels of gravitational wave production which are at play when the universe is reheated from the evaporation of a population of primordial black holes dominating the energy density of the universe

Speaker: Yann GOUTTENOIRE (Institute of Astrophysics of Paris)

10:00 → 11:00 Contributed talks

10:00 Evaporation of Primordial Black Holes in a Thermal Universe: A Thermofield Dynamics Approach

We investigate the impact of a finite temperature environment on the Hawking radiation from black holes (BHs), immersed in a cosmological thermal bath. The emitted particles from BHs interact with the thermal background and thermalize, leading to a modification in the Hawking radiation spectrum. By employing the methods of Thermofield Dynamics (TFD), a real time formalism of thermal quantum field theory, we derive the modified occupation numbers of the Hawking spectrum for asymptotically flat spacetime. These corrections depend on the interplay between the BH temperature and the ambient bath temperature. We apply this formalism in the early universe reheating background scenario arising after inflation and demonstrate that the thermal correction to Hawking spectrum enhances the evaporation rate of primordial black holes (PBHs). As a result, the lifetime of PBH shortens compared to the zero temperature vacuum and leads to interesting cosmological consequences.

Speaker: Jitumani Kalita (Indian Institute of Technology, Guwahati)

10:15 Primordial Black Hole Hotspots Beyond Flat Spacetime

Evaporating primordial black holes heat the surrounding plasma via Hawking radiation, forming localized hotspots whose temperature may far exceed that of the cosmological background. Previous studies of hotspot formation and cooling have treated the subsequent energy transport in flat spacetime, thereby neglecting the expansion of the Universe. We formulate the diffusion equation governing the hotspot evolution in an expanding universe, and clarify the regime in which the formalism is valid. We find that hotspot formation is robust against cosmological expansion, and the critical distance scale where Hubble expansion overtakes diffusion coincides with the decoupling radius introduced in earlier work. However, the cooling stage is substantially modified: the plateau temperature decreases more steeply than in the flat-spacetime treatment, and this scaling cannot be obtained by simply redshifting the flat-spacetime solution because expansion also suppresses diffusive transport. As a consequence, all hotspots disappear within a finite time, as opposed to the flat-spacetime prediction of everlasting hotspots in part of the parameter space.

Speaker: Dr Jong-Hyun Yoon (Chungnam National University)

10:30 Asteroid-mass Primordial Black Holes as Dark Matter from Supersymmetry

We investigate how the formation of primordial black holes (PBHs) in the early Universe can be enhanced by a temporary softening of the equation of state, caused by heavy particles becoming non-relativistic. As a concrete example, we consider the Minimal Supersymmetric Standard Model (MSSM) and compute the resulting equation of state for different realizations of its mass spectrum.
Assuming a broad and nearly flat primordial curvature power spectrum, we derive the corresponding PBH mass functions and compare them with current observational constraints. We find that, for particle masses above $\sim 10^5\mathrm{GeV}$, the PBH abundance is significantly enhanced in the asteroid-mass window, allowing PBHs to account for all of the dark matter while remaining consistent with existing bounds. In contrast, the same setup within the Standard Model is excluded.
For lighter masses, PBH production is shifted to $M \gtrsim 10^{22}\mathrm{g}$, where microlensing constraints strongly limit their contribution to dark matter.

Speaker: Andrea Boccia (Scuola Superiore Meridionale)

10:45 Gravitational Waves and Grand Unified Theories

Stochastic Gravitational Wave Backgrounds (SGWBs) can arise from a variety of cosmological and astrophysical sources. In this work, we explore several well-motivated scenarios within Grand Unified Theories (GUTs) that can generate a SGWB, where an inflationary phase is required to ensure consistency with current observational constraints. The resulting gravitational wave signals can explain the recent PTA results for specific parameter space, and for different parameter space fall within the sensitivity range of future detectors such as the Einstein Telescope (ET) and Laser Interferometer Space Antenna (LISA), offering promising opportunities for probing high-energy physics in the early Universe.

Speaker: Ahmad Elsayed Moursy (Cairo University)

11:00 → 11:30 Coffee-Break

11:30 → 12:30 Guided Thematic Discussion

12:30 → 12:45 Farewell and announcements