TAsP Meeting 2026

28 Jan 2026, 13:45 → 30 Jan 2026, 12:45 Europe/Rome

FILIPPO SALA (Università di Bologna and INFN), Michele Lucente (Bologna University), Silvia Pascoli (University of Bologna), Fiorenza Donato (Istituto Nazionale di Fisica Nucleare)

The second meeting of the INFN "Iniziativa Specifica" TAsP, Theoretical Astroparticle Physics, has the main purpose to foster knowledge and scientific collaborations among its members. All people participating in TAsP, and especially younger ones, are warmly invited to present their researches and new ideas that can stimulate interest and interactions within TAsP. 

The meeting will be hosted by the Department of Physics and Astronomy of the University of Bologna and INFN Bologna from January 28 (afternoon) to January 30 (morning). There is no registration fee. Registration deadline January 8.

The meeting will feature the following selected review talks on current hot topics in astroparticle physics

• Eligio Lisi (INFN Bari): Status of neutrino oscillations and impact of JUNO results
• Enrico Morgante (Università di Trieste and INFN Trieste): News on particle cosmology
• Marco Taoso (INFN Torino): Multiwavelength probes of dark matter
• Edoardo Vitagliano (Università di Padova and INFN Padova): BSM probes with stars

In addition, a call for abstracts for plenary talks (8 + 4 minutes) is open. PhD students and postdocs are especially invited to submit an abstract.

The coffee breaks and the lunch break of Thursday 29 are offered. On Thursday 29 we will have a group dinner at Cantina Bentivoglio (Via Mascarella 4/b), where each participant will pay their part and get a receipt for it.

 

 

 

 

 

 

 

 

 

Wednesday 28 January

13:45 → 14:15 Registration

14:15 → 14:30 Welcome and introduction

information.pdf

TAsP_Bologna.pdf

14:30 → 17:30 Afternoon 1

14:30 Status of neutrino oscillations and impact of JUNO results

Speaker: Eligio Lisi (Istituto Nazionale di Fisica Nucleare)

Lisi_TASP_Bologna_2026_reduced.pdf

15:00 New anomalies in the neutrino sector and physics BSM

The question of the anomalies in the neutrino sector is gaining increasing interest. Together with the longstanding short-baseline anomalies, new anomalous results are emerging and consolidating at long baselines. This is the case of the tension observed between NOvA and T2K, which persists since 2020. We will discuss the possible role of new matter effects BSM as a possible explanation of this finding and highlight new perspectives in this field.

Speaker: Antonio Palazzo (Istituto Nazionale di Fisica Nucleare)

TASP_BOLOGNA_2025_palazzo_vdef.pdf

15:12 A strike of luck: the KM3NeT neutrino produced by evaporating burdened PBH.

Primordial black holes (PBHs) may constitute part of all the Dark Matter, and as they evaporate they should emit an all particle spectrum, including neutrinos. The recently suggested theoretical framework of "memory burden" would allow the survival until today of PBHs with masses low enough to evaporate into particles of energy at the PeV and above.
In this talk we explore the scenario in which the ultra-high-energy neutrino event recently detected by KM3NeT could have originated from an evaporating PBH. Using the IceCube data, we place constraints on the combined parameter space of PBH masses and memory burden effects, by systematically scanning the parameter space of burdened PBHs.
We predict the occurrence rate of events similar to the KM3NeT ones under current constraints on PBH dark matter fraction.
Future neutrino telescopes such as IceCube-Gen2 and GRAND will provide crucial tests of these scenarios, with the potential to probe
highly suppressed evaporation regimes and light PBH masses.

Speaker: Andrea Boccia (Scuola Superiore Meridionale)

TaSP26.pdf

15:24 Antiprotons and antideuterons from Primordial Black Holes

In this talk, we present our recent work on cosmic antiproton and antideuteron signatures from primordial black holes (PBHs).
Light PBHs may have formed in the early Universe and could contribute to the dark matter content of our Galaxy. Their Hawking evaporation can lead to the production of antinuclei, which propagate through the Galaxy and reach Earth as cosmic rays with fluxes peaking at GeV energies. We revisit the expected antiproton and antideuteron signals from PBH evaporation, assuming a lognormal PBH mass distribution, state-of-the-art cosmic-ray propagation models, and an improved coalescence framework for antideuteron formation, whose most recent developments will be discussed in more detail in this talk.
Our predictions are compared with AMS-02 measurements of the antiproton flux. We find that AMS-02 data place stringent constraints on the Galactic PBH density, with bounds that depend sensitively on the parameters of the lognormal mass distribution and are comparable to, or slightly stronger than, those derived from other messengers.
Finally, we discuss the prospects for future detection of antideuterons. Given the AMS-02 antiproton limits, we predict that any future observation of cosmic antideuterons by AMS-02 or GAPS would constitute a clear signal of new physics, only part of which could, however, be explained by PBH evaporation.

Speaker: Lorenzo Stefanuto (Istituto Nazionale di Fisica Nucleare)

TAsP26.pdf

15:36 Coffee break

16:06 ALP production from light primordial black holes: The role of superradiance

Light Primordial Black Holes (LPBHs) with masses in the range
$10\mathrm{g} \leq M_{\rm BH} \leq 10^{9}\mathrm{g}$, although they evaporate before Big Bang Nucleosynthesis, can play a significant role in the production of both Dark Matter and Dark Radiation. In particular, LPBHs can evaporate into light axions or axion-like particles (ALPs) with masses $m_a \lesssim \mathrm{MeV}$, contributing to the effective number of neutrino species, $\Delta N_{\rm eff}$. Additionally, heavy scalar particles known as moduli, predicted by String Theory, can be produced both via Hawking evaporation and through amplification by a mechanism called Superradiance Instability in the case of spinning PBHs. These moduli can subsequently decay into ALPs, further amplifying their abundance. In this work, we calculate the number density of ALPs in the presence of moduli enhanced by Superradiance for Kerr PBHs. Using current limits on $\Delta N_{\rm eff}$ from Planck satellite observations, we derive updated constraints on this scenario.

Speaker: Marco Manno (Istituto Nazionale di Fisica Nucleare)

TAsP26_Manno.pdf

16:18 Magnetic Monopole Constraints from Extragalactic Magnetic Fields and TeV Blazars

Magnetic monopoles arise in many beyond Standard Model scenarios, restore the symmetry of Maxwell's equations, and explain the quantization of electric charge. In this work, we explore monopole-induced oscillations of the intergalactic magnetic field (IGMF). We show that these oscillations lead to a collimating effect on the trajectories of electrically charged particles, reducing the usual deflection by the magnetic field. This collimation effect impacts the deflection within the electromagnetic cascades of TeV blazars and leads to a decrease in the angular size of secondary GeV halos. Therefore, the non-observation of the secondary GeV halo translates into bounds on the magnetic monopole abundance. The bounds on the magnetic monopole flux obtained in this work from the blazar 1sES 0229+200, depending on the IGMF strength, can be as strong as $F \lesssim 10^{-22}\, \text{cm}^{-2}\, \text{s}^{-1}\, \text{sr}^{-1}$ for low-mass monopoles $m \lesssim 10^8\, \text{GeV}$, which are stronger than existing laboratory and astrophysical bounds. The bound becomes subdominant to current constraints if the present-day IGMF value is larger than $B \gtrsim 10^{-12}$ G. At the same time, in the case of non-zero monopole abundance, the IGMF lower bound from TeV observations itself should be revised, resulting in a stronger lower bound at higher monopole number densities.

Speaker: Mariia Khelashvili (SISSA)

TAsP_Khelashvili.pdf

16:30 Cosmic-ray cooling by dark matter in astrophysical jets

Astrophysical jets from powerful active galactic nuclei (AGN) have recently been proposed as promising probes of dark matter (DM) in the sub-GeV mass range. AGN launch relativistic jets that accelerate cosmic rays (CRs) to very high energies, which can then interact with their surroundings and produce multiwavelength (MW) emission spanning from radio frequencies to TeV $\gamma$-rays. If DM consists of light particles, their interactions with CRs could lead to an additional cooling mechanism that modifies the expected MW emission.
In this talk, I will analyse the MW spectrum of Markarian 421, a well-studied AGN, using a multizone leptonic jet model that includes the interactions between CR electrons and DM particles. In particular, I will describe the previously neglected uncertainties in the astrophysical jet dynamics, which are crucial for deriving robust constraints on DM-CR interactions. Hence, I will use the MW data from Markarian 421 to place constraints on the DM-induced CR cooling through a simultaneous fit of the jet parameters and the DM-electron interactions.

Speaker: Marco Chianese (Università degli Studi di Napoli Federico II)

TAsP26_Chianese.pdf

16:42 Neutrino signals from Dark Matter scatterings around blazars

Neutrinos from blazars can originate from inelastic scatterings between the protons within their jets and sub-GeV dark matter (DM) around them. I will show how this mechanism can potentially account for both the IceCube detections of neutrinos from the blazar TXS 0506+056, that are otherwise challenging for astrophysical models of its jet, and also saturate the measured diffuse astrophysical neutrino flux at high energies
The same DM-proton interactions will also induce an upscattered DM flux, which could yield measurable nuclear recoil signals at neutrino detectors, such as Super-K, JUNO and DUNE. I will show that searches for such DM component leave room for a variety of DM models to explain observations of IceCube high-energy neutrinos, and will provide future tests of this hypothesis

Speaker: Jacopo Nava (Istituto Nazionale di Fisica Nucleare)

Nava_TaspMeeting_2026.pdf

16:54 Discussion

Thursday 29 January

09:30 → 12:30 Morning 2

09:30 Multiwavelength probes of dark matter

Speaker: Marco Taoso (Istituto Nazionale di Fisica Nucleare)

MTaoso_TaspBo.pdf

10:00 The Galactic Centre Excess via leptophilic dark matter in U(1)Li-Lj models

The particle nature of dark matter remains one of the most important open questions in physics. An intriguing clue is the γ-ray excess observed by Fermi-LAT toward the Galactic Center, whose spectrum resembles the expected signal from annihilating weakly interacting massive particles. However, many conventional dark matter models are now strongly constrained by direct detection and collider experiments. In this talk, I will explore a class of anomaly-free extensions of the Standard Model based on gauged lepton-number differences, $U(1)_{L_i​−L_j}​​$, as well as $U(1)_{B−L}$​. I will show how these models can simultaneously account for the Galactic Center excess, satisfy the relic abundance requirement, and remain consistent with laboratory constraints. Particular attention will be given to the $L_\mu−L_e$​ model, which not only provides a good fit to the data but also connects naturally with the long-standing $(g−2)_{\mu,e}$​ anomalies.

Speaker: Jordan Koechler (Istituto Nazionale di Fisica Nucleare)

2025_Li-Lj_short.pdf

10:12 Searching for ALP DM decay across the electromagnetic spectrum

In this talk I will review two different works that search for axion-like particles (ALPs) decay into two photons. Assuming dark matter (DM) to be in the form of ALPs, we study prospects to detect ALPs with the upcoming near-infrared telescope SPHEREx taking into account signals from the DM halos of dwarf spheroidal galaxies, the Large Magellanic Cloud and the Milky Way. In addition, we show the analysis of real x-ray data taken by eROSITA from the Large Magellanic Cloud, searching for the same signal. All together we show prospects on the axion-photon coupling in the 0.5-3 eV ALP mass range, and exclusion limits on the 2-18 keV mass range.

Speaker: Jorge Terol Calvo (Istituto Nazionale di Fisica Nucleare)

TaspMeeting-1.pdf

10:24 Self-Consistency in Dark Matter Capture by Celestial Objects

Dark matter capture by celestial objects is a powerful method to detect dark matter indirectly. We evaluate conditions on the dark matter annihilation cross section to achieve the commonly assumed situation, capture-annihilation equilibrium, and check its consistency with being thermal relic dark matter, unitarity bounds, and cosmological bounds. We also consider dark matter particles that annihilate to mediators, which subsequently decay to detectable particles after escaping from the celestial body. We then examine requirements on a mediator mass and coupling for this scenario to be viable. Lastly, we quantify the strength of dark matter self-interactions in this scenario and compare it to current bounds from astrophysics.

Speaker: Takuya Okawa (SISSA)

2026_TAsP_Okawa.pdf

10:36 Coffee break

11:06 Extragalactic non-thermal emission

In this work, we use low-frequency radio maps to constrain the diffusion properties of cosmic-ray electrons in external galaxies, demonstrating that these data provide a powerful handle on the diffusion coefficient and its spatial and energy dependence. A central novelty of our previous studies is the implementation of fully realistic galactic geometries and proper line-of-sight integration, which we incorporated by modifying and extending existing propagation computational frameworks such as DRAGON and Hermes. This allowed us to construct the first spatially resolved synchrotron templates for the LMC based on 3D source distributions, magnetic-field modeling, and correct galactic-plane geometries. These developments showed that accurate modeling cannot rely on simplified radial or Milky-Way-optimized treatments, but instead requires galaxy-specific geometries, rotations, and observational projections. Extending these techniques to additional systems such as M31 will enable a new generation of robust, physically motivated astro-physical background models, which will be crucial for deriving competitive and unbiased dark matter limits in the near future.

Speaker: Javier Israel Reynoso Cordova (Istituto Nazionale di Fisica Nucleare)

TASP meeting.pdf

11:18 Addressing the Impact of Solar Modulation Systematic Uncertainties on Cosmic-Ray Propagation Models

While remarkable progress has been made to understand the propagation of cosmic rays, a variety of astrophysical uncertainties persists. At energies below about 50 GeV, the cosmic-ray flux is significantly modulated by solar activity, a process that is not precisely understood. Using the recently published AMS-02 data for the time-dependent cosmic-ray fluxes, we study the effects of solar modulation using force-field and extended force-field models and derive improved cosmic-ray propagation models. We find that simple solar modulation models are likely to underestimate the complexity of comic-ray propagation in the solar system and present limitations in describing the time-dependent fluxes consistently.

Speaker: Isabelle John (University of Turin & INFN Turin)

TAsP_Bologna_2026.pdf

11:30 Wallions: Ultralight Dark Matter from the Boundaries of Field Space

I will present a new framework for generating ultralight dark matter based on a scalar field that experiences boundaries in field space. Such boundaries give rise to wallions, excitations whose masses are exponentially suppressed yet radiatively stable. After introducing the basic setup, I will discuss how wallions behave in the early universe, how these boundaries can form dynamically, and which cosmological or laboratory probes could be sensitive to them.

Speaker: Mathias Becker (University of Padova)

Bologna26_MB.pdf

11:42 Topological Portals to the Dark Sector

I will present the construction and phenomenology of novel portals between the Standard Model and dark sectors, arising from topological operators in chiral perturbation theory. The first example is based on a mixed Wess–Zumino–Witten term that uniquely connects three QCD pions to two dark pions, leading to a consistent framework for light thermal inelastic dark matter with suppressed direct and indirect detection, but distinctive collider signatures. The second example is a minimal model in which gauging the topological Skyrme current naturally links a QCD-like dark sector to the Standard Model, allowing a semi-annihilation process that sets the relic abundance. The purely p-wave nature of these interactions ensures compatibility with existing constraints while offering discovery prospects at colliders and beam-dump experiments.

Speaker: Nudzeim Selimovic (INFN Padova)

TAsP26_Selimovic.pdf

11:54 Seasons of Dark Matter Freeze-In Shaped by the Weather of the Early Universe

Quantifying the imprints of freeze-in dark matter (DM) on cosmological structures requires the knowledge of its phase-space momentum distribution. We investigate how different cosmological histories before nucleosynthesis, what we refer to as “weather” of that epoch, give rise to distinct “seasons” in the DM momentum distribution that govern its warmness. Studying decay-driven production across diverse cosmological scenarios, we map how these conditions shape DM phase-space properties. Our study quantifies how the early universe composition plays a key role in determining the mass bound on freeze-in DM.

Speaker: Tommaso Sassi (INFN Sezione di Firenze, Università degli Studi di Firenze)

TAaP_talk_Sassi.pdf

12:06 Discussion

12:30 → 14:15 Buffet lunch break

14:15 → 17:45 Afternoon 2

14:15 Referees report

Speakers: Daniele Montanino (Istituto Nazionale di Fisica Nucleare), Martina Gerbino (Istituto Nazionale di Fisica Nucleare)

Report from referees (1).pdf

14:30 BSM probes with stars

Speaker: Edoardo Vitagliano (Istituto Nazionale di Fisica Nucleare)

talk_bologna2026.pdf

15:00 When boson stars collapse bubbles can nucleate

In this talk we will discuss a new classical mechanism for bubble nucleation which relies on collapsing boson stars with attractive self-interactions. The phenomena can occur provided dense boson stars are formed in the false vacuum. As the boson star collapse the field value inside the stars core gets significantly enhanced and can classically roll over the potential barrier. Hence the star explodes as true vacuum bubbles and induce a cosmological phase transition. This mechanism reveals the possibility that vacua which are stable against quantum tunneling may be susceptible to astrophysical processes.

Speaker: Nicklas Ramberg (Istituto Nazionale di Fisica Nucleare)

Classical Bubbles from Star Collapse.pdf

15:12 Detecting the QCD axion with the next galactic supernova

The axion is one of the best-motivated candidates for new physics, as it could solve current puzzles such as the Strong CP Problem or the nature of Dark Matter. An especially appealing possibility for its detection comes from astrophysical sources; hot and dense environments, such as Supernovae or Neutron Star mergers, are efficient factories of axions, which can then be converted into photons in the magnetic field around these sources. The resulting electromagnetic radiation could serve as a smoking gun for axion detection. In this talk, we will explore the possibility of detecting the QCD axion with the next ga

Speaker: Ángel Gil Muyor (Università degli studi di Padova)

Bologna.pdf

15:24 Detecting light axions from supernovae in nearby galaxies

Axion-like particles (ALPs) coupled to nucleons can be efficiently produced in core-collapse supernovae (SNe) and then, if they couple to photons, convert into gamma rays in cosmic magnetic fields, generating short gamma-ray bursts. Though ALPs from a Galactic SN would induce an intense and easily detectable gamma-ray signal, such events are exceedingly rare. In contrast, a few SNe per year are expected in nearby galaxies within $\sim \mathcal{O}(10)$ Mpc, where strong magnetic fields can enable more efficient ALP–photon conversions than in the Milky Way, offering a promising extragalactic target.
This circumstance motivates full-sky gamma-ray monitoring, ideally combined with deci-hertz gravitational-wave detectors to enable time-triggered searches from nearby galaxies. We show that, under realistic conditions, a decade of coverage could reach sensitivities to ALP-photon coupling $g_{a\gamma} \gtrsim 10^{-16}~{\rm GeV}^{-1}$ for ALP masses $m_a \lesssim 10^{-9}$ eV and assuming an ALP-nucleon coupling close to SN 1987A cooling bound. This sensitivity would allow one to probe a large, currently-unexplored region of the parameter space below the longstanding SN 1987A bound.

Speaker: Francesca Lecce (Istituto Nazionale di Fisica Nucleare)

Nearby galaxies Lecce.pdf

15:36 Coffee break

16:06 Light scalars from cold isolated neutron stars

Scalars sporting a coupling to nucleons with masses $m_\phi$<1 MeV might be copiously produced in cold isolated neutron stars (NSs). Despite NSs can be only used as probes complementary to the classic supernova (SN) 1987A cooling bound in the case of axions, I will discuss how the shallow temperature dependence of the scalar emissivity leads to a huge enhancement in the effect of scalars on the cooling process of NSs. The absence of any evidence of exotic energy losses allowed us to introduce the most stringent constraint on the scalar-nucleon coupling, superseding all existing limits across six orders of magnitude in the scalar mass. These arguments also lead to the most stringent bounds on the strength of fifth forces acting on micro- to picometer length scales.

Speaker: Alessandro Lella (Istituto Nazionale di Fisica Nucleare)

2026_TAsPMeeting_Bologna_Lella.pdf

16:18 Constraining reheating through PBH production and inflatonovae explosions

Very little is known about the reheating phase after inflation, which is only constrained to finish before BBN, at a temperature higher than O(1) MeV. We show that this effective matter domination can be long enough that structures can form, inflaton star 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 of several orders of magnitude. We then consider a concrete scenario of perturbative reheating, with inflatons decaying into fermions. We show that the loop induced inflaton self-interactions can trigger a Bosenova-like explosion of inflaton stars.

Speaker: Francescopaolo Lopez (SISSA, Istituto Nazionale di Fisica Nucleare)

Pbh condensation def.pdf

16:30 Axion Quality: Challenges and Pathways to Improvement

In this talk I begin by introducing the axion solution to the strong CP problem and the associated axion‑quality puzzle, namely the challenge of protecting the Peccei–Quinn (PQ) symmetry from dangerous explicit breaking. I then present a Pati–Salam–based model where an accidental high‑quality PQ symmetry emerges from the interplay of vertical and horizontal gauge symmetries. The setup predicts light anomalons whose interactions and early‑universe production provide a potential low‑energy probe of the dynamics protecting axion quality.

Speaker: Federico Mescia (Istituto Nazionale di Fisica Nucleare)

Mescia_prin.pdf

16:42 The Standard Model partial unification scale as a guide to new physics model building

In the Standard Model, partial unification of the non-Abelian running gauge couplings is achieved at the scale μ_32^SM≈2.8×10^16 GeV. Elaborating on this fact, we discuss a simple general parametrization for the new physics corrections leading to full unification at some scale M_X​. We show that for any new physics model such that the corrections to the non-Abelian couplings are equal (or nearly so), M_X​ is equal (or close to) the partial unification scale; the latter scales could be disentangled only if the corrections to the non-Abelian couplings are significantly different. We explore how the parametrization works for some relevant models with new physics below M_X​ (as low energy supersymmetry, split supersymmetry, etc), as well as for models with new physics above M_X​ (as string inspired relations and non-renormalizable kinetic terms).
The material is based on arXiv:2510.21420 [hep-ph]

Speaker: Isabella Masina (Istituto Nazionale di Fisica Nucleare)

Masina-TaspBo-26.pdf

Masina-TaspBo-26.pptx

16:54 Discussion

20:00 → 22:30 Dinner at Cantina Bentivoglio

You will be able to pay by card and get a receipt.

Friday 30 January

09:30 → 12:30 Morning 3

09:30 News on particle cosmology

This talk will focus on axions and axion-like particles. I will discuss recent attempts to enlarge the relevant parameter space of axions, and the cosmological and experimental consequences of these models.

Speaker: Enrico Morgante (Università di Trieste & INFN)

2601_TAsP_Morgante.pdf

10:00 Looking for new physics with CMB and 21 cm data

Future cosmological data will improve the constraining power on new physics.
On the one hand, forthcoming CMB data from both ground-based and space-based experiments will allow to get closer to the cosmic variance limit. On the other hand, a completely new window will be opened by the forthcoming facilities that will explore the redshifted 21 cm signal from the Cosmic Dawn.
I will present recent analyses related to both channels and based on WIMP and primordial black hole dark matter as a case study.
Regarding the latter, I will demonstrate in particular the crucial role of the astrophysical uncertainties in assessing the expected constraining power of 21 cm data.
I will conclude emphasizing the complementarity between these two observables as far as new physics searches are concerned.

Speaker: Daniele Gaggero (Istituto Nazionale di Fisica Nucleare)

TASP_DG.pdf

10:12 Early-universe constraints on the electron mass

The aim of this work is to evaluate the effect of a non-standard electron mass $m_e$ in the early Universe picture, in particular considering the neutrino decoupling scenario and Big Bang Nucleosynthesis (BBN).
In the standard case, neutrino interactions with electrons in the early universe maintain the former in equilibrium with the thermal plasma until before electron-positron pairs annihilate away. Modifying the electron mass changes the time at which this happens, thus affecting the neutrino energy density and consequently on the effective number of relativistic species, $N_{\mathrm{eff}}$.
On the other hand, during BBN, weak interactions and therefore the neutron-proton relation depend on the value of the electron mass.
By comparing the light element abundances predicted by BBN with their observed values and applying constraints on $N_{\mathrm{eff}}$, we derive the earliest bound on the value of the electron mass in the early universe, which is remarkably similar to the one measured at terrestrial experiments nowadays. This confirms that the value of the electron mass has been constant throughout most of the life of the Universe.

Speaker: Michela Garramone (Università degli Studi di Torino - Università di Valencia)

presentazione_ridotta_Garramone.pdf

10:24 The Bispectrum of the Relativistic Redshift Drift

With high-precision data about to be released by large-scale cosmological surveys, the development of higher-order perturbative descriptions of cosmological observables is becoming increasingly important.
The so-called Geodesic Light-Cone coordinates are a physically motivated set of coordinates which account for the fact that light-rays propagate on the past light-cone of an observer. They are a powerful tool for studying the late-time universe because, trivializing light-beam propagation throughout an inhomogeneous space-time, they allow for fully non-linear expressions of light-like cosmological observables.
In this talk, I will first review how these coordinates are defined. Then, I will show how a cosmological perturbation theory up to second order can be constructed on top of a background light-cone geometry. Within this new perturbative framework and adopting a fully gauge-invariant approach, higher-order formulae for cosmological observables can be computed. I will focus on the redshift and the redshift drift. In particular, computing the non-linear general relativistic effects of the redshift drift proves that the magnitude of the three-point function is significantly larger than the naive expectation based on perturbative considerations on the two-point function. Consequently, a substantial degree of non-Gaussianity can be inferred from the bispectrum of the redshift drift. In light of future galaxy surveys observations, I will then emphasize how such a high level of non-Gaussianity could be correctly interpreted as evidence of the intrinsic non-linear nature of General Relativity.
[based on 2510.25690, astro-ph.CO and 2601.XXXXX]

Speaker: Pierre Béchaz (Istituto Nazionale di Fisica Nucleare)

10:36 Coffee break

11:06 Searching for gravitational waves with pulsar timing arrays

Pulsar timing arrays (PTAs) provide a unique opportunity to search for gravitational waves (GWs) at nanohertz frequencies, opening a new observational window on supermassive black hole binaries (SMBHBs) and other theoretical astrophysical and cosmological sources. Recently, PTA community has announced the detection of a signal compatible with a GW origin, showing evidence for a red noise process that is common among pulsars and presenting correlation properties expected for a stochastic nano-Hertz GW background (GWB).
After a brief introduction to the general theoretical framework, I will present my research, focusing on simulation-based studies of the GWB. Results are obtained using standard PTA analysis tools such as Enterprise and Discovery, which rely respectively on Markov Chain Monte Carlo and variational inference approaches. Simulations include the use of the radio interferometer LOFAR to investigate the impact of chromatic noise on PTA datasets.
Furthermore, I will discuss searches for GWs from localized SMBHBs using the surfing effect, providing a conceptual overview of the method and its potential for PTA analyses.

Speaker: Danilo Zecca (Università del Salento)

Tasp_2026_Danilo_Zecca.pdf

11:18 Cosmic Gravitational Waves: a Gateway to Early Universe Physics

The exploration of primordial, stochastic gravitational waves opens an extraordinary window into the deep physics of the cosmos, introducing an innovative avenue for advancing our understanding of the physics of the early Universe and examining theoretical fundamental physics. Specifically, the potential detection of gravitational waves across several frequency ranges could yield exclusive insights into the origins of the matter-antimatter asymmetry through the seesaw mechanism. Even in the absence of a detectable signal, stringent constraints could be placed on the parameters of leptogenesis, which are beyond the reach of conventional observational methods

Blockquote

Speaker: Ninetta Saviano (Istituto Nazionale di Fisica Nucleare)

gw_lepto_Bologna.pdf

11:30 Axion inflation in the regime of homogenous backreaction

We investigate the Stochastic Gravitational Wave Background (SGWB) produced in models of axion inflation coupled to gauge fields. Achieving a detectable signal at Pulsar Timing Array, astrometry, or interferometer frequencies requires a sufficiently strong amplification of the gauge fields, at a level that induces significant backreaction on the inflaton background dynamics. Numerical studies based on the approximation of homogeneous backreaction (i.e., neglecting inhomogeneities of the inflaton field) exhibit oscillations in the inflaton velocity, with corresponding peaks in the SGWB spectrum. The most recent lattice simulations have questioned the validity of this regime, showing examples characterized by a rapid increase in the inflaton gradient energy and the breakdown of homogeneous backreaction. We compute this energy density perturbatively within the assumption of homogeneous backreaction, obtaining examples with a detectable SGWB and with an inflaton gradient energy that remains subdominant to the inflaton zero-mode kinetic energy throughout inflation.

Speaker: Nadir Ijaz (Istituto Nazionale di Fisica Nucleare)

TAsP_Meeting2026_Nadir.pdf

11:42 Quantum Recoherence in Presence of Excited States in the Early Universe

We investigate the quantum-to-classical transition of primordial perturbations
within a two-field inflationary framework where an adiabatic mode interacts with an entropic environment. In the case of a massive entropic environment, the attractor Bunch–Davies vacuum plays a special role: it is the only state that can undergo full recoherence, whereas all excited initial states exhibit persistent loss of purity. To characterize this behavior, we parameterize excited Gaussian initial states by their Bogoliubov coefficients and compute the purity and Rényi-2 entropy of the reduced adiabatic state as information-theoretic indicators of decoherence dynamics. We find that excited states display purity-freezing at a non-zero plateau, where residual quantum correlations persist indefinitely, a qualitative departure from the complete recoherence observed for the Bunch–Davies vacuum. This sensitivity to initial conditions highlights the non-generic nature of full recoherence in the quantum-to-classical transition of inflationary perturbations.

Speaker: Dr Simone Scarlatella (Istituto Nazionale di Fisica Nucleare)

Scarlatella_TAsp_BolognaMeeting2026.pdf

11:54 An Introduction to f(R) Gravity and Cosmological Applications

Modified theories of gravity offer a well-motivated theoretical framework to explore possible deviations from General Relativity and to address open questions in cosmology, in particular the origin of late-time cosmic acceleration. Among these approaches, f(R) gravity represents one of the simplest and most extensively studied extensions, obtained by replacing the Ricci scalar in the Einstein–Hilbert action with a generic function of curvature. Despite its simplicity, this class of models exhibits a rich phenomenology and provides a useful laboratory to investigate both theoretical consistency and observational viability of modified gravity scenarios.

In this talk, I will provide an introductory overview of f(R) gravity, discussing its motivation and the main physical questions that can be addressed within this framework, such as effective dark energy behavior, cosmological dynamics, and general viability requirements. I will then focus on a specific f(R) model that is currently under investigation. The construction of the model and its physical motivation will be presented, together with the methods employed to study its cosmological implications.

The talk will emphasize the exploratory nature of this work, highlighting preliminary results, open issues, and future directions. The aim is to illustrate how f(R) gravity can be used as a flexible theoretical tool to test extensions of General Relativity and to gain insight into possible modifications of gravity at cosmological scales.

Speaker: Marco Calo' (Istituto Nazionale di Fisica Nucleare)

F_R__talk_bologna (1).pdf

12:06 Discussion

12:30 → 12:45 Conclusion and farewell