Robust constraints on tensor perturbations from cosmological data: A comparative analysis from Bayesian and frequentist perspectives
20/12/2024
One of the central challenges in modern Cosmology is the precise characterization of the primordial tensor power spectrum, a cornerstone prediction of numerous cosmological models, particularly inflationary scenarios. These tensor perturbations carry distinctive imprints that can reveal their physical origins, making the robust reconstruction of their spectrum a pivotal goal for contemporary research. In this talk, I will present methods for constraining key parameters of the tensor power spectrum, such as the tensor-to-scalar ratio and the spectral tilt, with a particular emphasis on the statistical methodologies underpinning these inferences. I will critically examine the strengths and limitations of the standard Bayesian framework commonly employed in this context. Furthermore, I will demonstrate how complementary insights from a frequentist approach can deepen our understanding of the Bayesian results, offering a more nuanced perspective on the interplay between these statistical paradigms.
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Wave dark matter
17/12/2024
We will explore the possibility that dark matter is composed of sufficiently light particles that it effectively behaves as a collection of waves. We will review the particle physics motivations and the rich wave phenomenology, and discuss the implications for astronomical observations and experimental detection.
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Galaxy Clusters from adolescence to maturity: challenges for simulations
12/12/2024
In my talk I will review our understanding, through cosmological simulations, of the evolution of galaxy clusters from redshift z~2-3, to the recent cosmic epoch. Through a comparison with observational data at different wavelengths I will assess the capability of simulations to trace the fast evolution of such cosmic structures from their proto-cluster stage, characterized by a strongly star forming galaxy population embedded in a dynamically disturbed inter-galactic medium, to their relaxed stage at low redshift, characterized by a passive galaxy population immersed in a relatively relaxed intra-cluster medium. In this context, I will highlight successes of simulations, and critically assess their limitations and what we should learn from them.
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Lighting up Blazar Physics at the Spectrum’s Edge: VHE and VLBI Synergies
12/12/2024
Blazars, a class of active galactic nuclei with jets aligned towards Earth, offer a unique opportunity to study extreme astrophysical processes. Their powerful jets emit across the entire electromagnetic spectrum, providing data at all wavelengths for investigation. This presentation focuses on the synergy between Very High Energy (VHE) gamma-ray observatories and VLBI arrays—two distinct facilities operating at opposite ends of the spectrum—used to uncover the mechanisms driving the non-thermal emission of blazars. VHE observations probe the highest energy emissions from these objects, while VLBI provides high-resolution imaging of their jet structures. Together, they enable the study of particle acceleration processes, jet kinematics, and emission variability across multiple scales. I will introduce the basics of VHE observations and the tools employed at the two extremes of the spectrum. Finally, I will present studies showing how this combined approach deepens our understanding of blazar physics, from the origins of high-energy photons to the dynamic behaviour of jets in their most compact regions.
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Breaking the distance-duality relation to address cosmic tensions
11/12/2024
Persistent cosmic tensions arise from discrepancies in the cosmological distance ladder constructed from different distance observables, such as BAO and SnIa, which are calibrated using measurements from either the early or late Universe. These tensions are typically evaluated under the assumption that the distance-duality relation (DDR) holds, allowing for a direct comparison between measurements of the luminosity and angular diameter distances. In this talk, we will examine the implications of relaxing this assumption and considering more general relations. We will discuss how this approach impacts the interpretation of current cosmic tensions and its potential to clarify whether new physics is needed to address these discrepancies.
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Extended AGN jets as a direct test to the ΛCDM model
03/12/2024
Current small-scale cosmological controversies are coming down to the precision level of observations. The key point is whether a better understanding of baryonic physics, dark matter physics, or both is required to address these challenges. In this talk, I will describe how very long baseline interferometric observations of extended AGN jets (sometimes gravitationally lensed) are contributing to understanding some of these small-scale cosmological issues while simultaneously providing insights on the jet physics up to the earliest epochs (z>6).
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The nature and fate of the most obscured high-z massive galaxies
28/11/2024
The early assembly of the most massive galaxies, and their contribution to the SFR density of the universe is currently one of the main challenges for galaxy formation models. Recently, a population of massive red sources already in place at z>2-3 have been discovered, and called HST-dark, because they are missed by optical/UV search but detected at MIR and often in the mm.
Their characterisation remains uncertain, due to limited information available, and to different selection techniques. JWST is now allowing us to investigate the nature of HST-dark galaxies,
and to reveal new populations of early massive galaxies.
I will discuss the main properties of HST-dark galaxies, compared to those of JWST NIR-dark.
For those ALMA detected, the molecular gas mass and depletion times show that they are
likely on the way to quenching their SF. For ALMA HST-dark, there is a consensus on the presence of large amounts of dust, posing the problem of high-z dust production.
To constrain dust properties and obscured SF at high-z we need to observe in the FIR.
I will present the recently selected NASA PRobe far-Infrared Mission for Astrophysics (PRIMA),
a FIR (25-235 μm) observatory operating in the 2030s in spectroscopy and imaging, that will allow us a leap forward in our knowledge of the high-z obscured universe.
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Gamma-Ray Burst Polarimetry: History and Future Prospects
25/11/2024
Gamma-Ray Bursts (GRB) are the brightest electromagnetic events in the Universe since the Big Bang. As such they have intrigued the astrophysical community since their accidental discovery in 1967. Despite almost 60 years of intense research, resulting in over 10000 GRB detections, very little remains known about these violent events. While we know that these events are related to the death of massive stars or the merger of compact objects, we still lack an understanding of how, and where, the gamma-rays which give these events their name, are produced. Attempts to understand this have thus far focussed primarily on measurements of the time of arrival, the direction and energy of the gamma-ray emission. Measurements of the 4th parameter, the polarization, are rare, despite their significant potential to resolve theoretical models. In this talk I will discuss this potential in detail, while in parallel addressing the reasons for the lack of polarization measurements. Finally, I will present an overview of past missions as well as the missions which aim to provide the first detailed measurements in the coming decade.
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Recent observations of the near-Earth radiation environment: a plethora of galactic, solar and magnetospheric particles
22/11/2024
The near-Earth radiation space is a unique environment where particle populations of different origins coexist and evolve dynamically over time and space, spanning a wide energy range. Galactic cosmic rays – entering the heliosphere – are continuously modulated by the change in the solar wind and the associated heliospheric magnetic field. Moreover, changes in galactic particle fluxes show a very clear time-dependence, which is directly related to the periodical activity of the Sun. However, the Sun acts as both a modulator and a source of space radiation – especially during maxima of solar activity – with powerful emissions of the so-called solar energetic particles (SEPs). Despite notable improvements in the latest decades, the complex mechanisms underlying their origin and transport still challenge the development of a comprehensive picture of SEP events. Many efforts have also been directed at modelling the Earth’s trapped charged particle environment, as in the case of the South Atlantic Anomaly (SAA). Observations of the SAA radiation environment are crucial to validate these models (e.g., the NASA AE9/AP9 models), as well as to investigate the temporal evolution of the geomagnetic field, to study perturbations generated by space weather events (such as geomagnetic storms), and, last but not least, to safeguard spacecraft systems and human crew health. After the foundational results of successful past (PAMELA) and present (AMS-02) spaceborne missions, the CSES (China Seismo-Electromagnetic Satellite) mission aims to continue the study of the near-Earth radiation environment, through a constellation of low-Earth orbit satellites. This presentation will review the main results achieved by the High-Energy Particle Detector (HEPD-01) on board the CSES-01 satellite, which will be followed by the launch of the improved HEPD-02 detector on the CSES-02 satellite in December 2024.
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Magnetic field amplification in neutron star mergers and the role of the MRI
21/11/2024
The first detection of a binary neutron star merger has made sharp reality the long-standing paradigm that these cosmic fireworks are exciting laboratories for extreme physics. To get the most out of present and future observations, however, we require accurate models of the merger dynamics, which can only be achieved through numerical relativity simulations. One of the key factors in these simulations is the magnetic field, which plays a crucial role in shaping the dynamics of the system. It is also instrumental in the launching of relativistic jets and the associated gamma-ray bursts. In this seminar I will discuss the main mechanisms responsible for the amplification of the magnetic field, with a particular focus on the magneto-rotational instability and its potential role in binary neutron star mergers."
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