Licia Verde (University of Barcelona)
Hubble Troubles
Friday, November 11th, 2022, 11am – Aula D (old SISSA building) & streaming

Abstract The current expansion rate of the Universe is captured by the so-called Hubble constant, which is a key parameter in the, extremely successful,  standard model of cosmology. As such, The Hubble constant  can be measured in several different ways: looking at the light of the “early Universe”, looking at bright objects in the “late Universe” (an approach close to  Hubble original approach) and  other in-between  options,   each  measuring the  expansion of the Universe in its peculiar way. Each of these measurements is very precise:  error-bars are at the percent level. However,  their values do not seem to agree. These are exquisitely sophisticated, and challenging,  measurements. Yet one may ask:  can this be a signature that the cosmological model starts showing some cracks and  that we might need to invoke new physics?  The ‘Hubble tension’ has motivated the exploration of extensions to the standard cosmological model.The Hubble trouble, I will argue, goes beyond H0.   I will introduce this modern-day cosmic puzzle,  discuss  its implications, what this tension has taught us so far  and possible future prospects.

Contact: Matteo Viel
Video (partial) – Licia Verde’s website

Katherine Freese (University of Texas at Austin)
Dark Matter in the Universe
Friday, October 14th, 2022, 11am – Aula D (old SISSA building) & streaming

Abstract The nature of the dark matter in the Universe is among the longest and most important outstanding problems in all of modern physics. The ordinary atoms that make up the known universe, from our bodies and the air we breathe to the planets and stars, constitute only 5% of all matter and energy in the cosmos. The remaining 95% is made up of a recipe of 25% dark matter and 70% dark energy, both nonluminous components whose nature remains a mystery.  I’ll begin by discussing the evidence that dark matter is the bulk of the mass in the Universe, and then turn to the hunt to understand its nature.  Leading candidates are fundamental particles including Weakly Interacting Massive Particles (WIMPs), axions, sterile neutrinos, as well as primordial black holes.  I will discuss multiple experimental searches:  at CERN in Geneva; in underground laboratories; with space telescopes; with gravitational wave detectors; and even with DNA.  I’ll tell you about our novel idea of Dark Stars, early stars powered by dark matter heating, and the possibility that the James Webb Space Telescope could find them.  At the end of the talk, I’ll turn to dark energy and its effect on the future of the Universe.

VideoSlidesKatherine Freese’s webpage

Contact: Patrick Stengel
Katherine Freese’s website

Will Percival (University of Waterloo)
Can galaxy surveys answer the question: what is Dark Energy?
Friday, September 30th, 2022, 11am – Aula D (old SISSA building) & streaming

Abstract The present day energy-density in the Universe is dominated by an unknown component called Dark Energy that gives rise to acceleration of the cosmological scale. Understanding this component represents one of the major challenges for modern physics. Using maps of galaxies we can measure both the accelerating expansion and structure growth within it, obtaining complementary information about how Dark Energy behaves that can distinguish between models for it. There are a number of ways that information is extracted from galaxy surveys including techniques known as Baryon Acoustic Oscillations, Redshift-Space Distortions and Voids. Looking ahead to the future, measurements from the Dark Energy Spectroscopic Instrument and Euclid experiments made using these techniques will transform our understanding of Dark Energy within the next few years. Key to extracting the information will be understanding statistical and systematic errors for the measurements: in many ways the errors placed on the measurements and the way they are used to distinguish between models are as important as the measurements themselves. In this talk I will provide an overview of this field of research highlighting various pieces of work and ideas in a way that is highly biased towards my research and that of my research group.

Contact: Pierluigi Monaco
VideoSlidesWill Percival’s webpage

Tom Abel (KIPAC, Stanford University)
Dark Matter Dynamics
Friday, July 1st, 2022, 11am – Aula D (old SISSA building) & streaming

Abstract We have a standard paradigm that quantitatively succeeds to describe the origin, formation and evolution of structure in the Universe. Dark matter is needed in this model to describe details of the Cosmic Microwave Background radiation, the appearance of high-redshift galaxies as well as many details of the clustering of galaxies. This broadly seems to works for the abundance of massive galaxy clusters, the prevalence of sheets, filaments and voids and the existence of ultra-faint dwarf galaxies. For Dark Matter made of an unknown particle that only interacts via gravity we have made predictions about how structure forms in the Universe using N-body techniques originally developed for plasma physics. These numerical investigations have led to many insights and enabled quantitative comparisons of the real and these simulated Universes. In this talk I describe and show visualizations from recently developed complimentary numerical methods that can describe the dark matter collisionless fluid in the continuum limit. These techniques follow three dimensional manifolds (“sheets”) as they evolve through the six dimensional phase space. The full geometry of the sheets is followed and consequently the noise of traditional N-body methods can be avoided completely. The caustics and detailed phase space structures inherent to the Hamiltonian dynamics of the particles are fully captured. These techniques also explain the origin of the shortcomings of traditional N-body such as artificial fragmentation evident in Warm Dark Matter models. These new approaches now also find application in modeling massive neutrinos in cosmology as well as applications in Laboratory Plasma Physics. The correspondence of the phase space sheet techniques  allow for high precision comparisons of simulations and analytical calculations promising an avenue to improve the analytic techniques and supersede standard perturbative approaches.

Contact: Matteo Biagetti
VideoTom Abel’s webpage

Luigi Guzzo (Università di Milano)
Here comes the flood: cosmology with galaxy surveys in the Euclid era
Friday, May 27th, 2022, 11am – Aula D (old SISSA building) & streaming

Abstract A new generation of galaxy surveys to map the Universe has started, pushed by the need to uncover the nature of dark matter and dark energy, the mysterious ingredients dominating the highly successful standard model of cosmology.  Among these, the ESA Euclid mission stands out as the most comprehensive endeavour, tackling the intertwined nature of gravity and the dark sector through percent precision measurements of cosmic expansion and structure growth.  In my talk I will review the current state of affairs approaching Euclid’s launch, currently planned for 2023.  Achieving the mission ambitious goals will require the ability to process complex data on one side, while efficiently and intelligently extracting information from large multi-dimensional data sets.  I will present some instructive examples on how we are preparing for this. I will also mention how Machine Learning techniques have the potential to produce a paradigm shift in all such applications.

Contact: Emiliano Sefusatti
VideoLuigi Guzzo’s webpage

Marta Volonteri (Institut d’Astrophysique de Paris)
Massive black hole pairs and binaries in the cosmos
Friday, March 25th, 2022, 11am – streaming

Abstract Massive black holes weighing from a few thousands to tens of billions of solar masses inhabit the centers of most galaxies. During their cosmic evolution the galaxies hosting massive black holes interact and merge: this gives rise to pairs of massive black holes that can be observed as dual active galactic nuclei. As the dynamical evolution of the pairs proceeds, eventually binaries are formed, whose coalescence driven by emission of gravitational waves can be detected with ESA’s planned satellite LISA and with Pulsar Timing Arrays.  I will discuss the physical processes through which massive black holes pair and bind and present the analysis of cosmological simulations to investigate the properties of dual active galactic nuclei, merging massive black holes and their host galaxies.

Contact: Valentina D’Odorico
VideoSlidesMarta Volonteri’s webpage

Raffaele Tito D’Agnolo (Institut de Physique Théorique, CEA-Saclay)
A New Chapter in the Quest for Dark Matter: The Ultralight Regime
Friday, February 25th, 2022, 11am – Giambiagi lecture hall (ICTP Adriatico GH) & streaming

Abstract Dark Matter was discovered more than 90 years ago through its gravitational effects. It makes up 80% of the matter in our Universe and about a quarter of its present energy density. We have spent decades trying to detect it in the laboratory, but to date its microscopic origin remains mysterious. The vast majority of our theoretical and experimental effort has been devoted to the exploration of relatively heavy dark matter candidates, with masses comparable to particles that we can produce at our highest energy colliders. In this talk I will review how in the last five to ten years a new perspective has emerged in particle theory, shifting our attention to ultralight dark matter candidates, in particularly the axion. This has generated a flurry of experimental activity, with a few pioneering efforts now setting up prototypes, and new ideas appearing almost weekly on the arXiv. I will review both the theoretical appeal of these dark matter candidates and the new ideas proposed to detect them experimentally. Furthermore, ultralight dark matter is well described in the laboratory as a coherent classical field. Its detection has interesting overlaps with that of high-frequency gravitational waves.

Contact: Paolo Creminelli

Gary Mamon (Institut d’Astrophysique de Paris)
What lurks in the centers of globular clusters? Intermediate-mass black holes, stellar mass black holes, compact stars, or nothing special?
Friday, January 28th, 2022, 11am – Aula D (old SISSA building) & streaming

Abstract Globular star clusters are the largest self-gravitating systems that are collisional (short 2-body relaxation times). Their inner dynamics are complicated by three- and four-body encounters, mass loss from stellar evolution, and astrophysical phenomena that lead to ejection. I will present recent analyses of the stellar kinematics in nearby globular clusters using proper motions from Gaia and HST. This allows us to map the inner mass profile and test for the existence and extent of a possible dark inner component, which could be an intermediate-mass black hole or populations of stellar-mass black holes, neutron stars, or white dwarfs. This helps answer the question: are globular clusters prime locations for the emission of gravitational waves in the Universe?

Contact: Andrea Biviano
VideoSlidesGary Mamon’s webpage

Antonio Riotto (Geneva University)
Primordial Black Holes in the era of Gravitational Wave Astronomy
Friday, December 3rd, 2021, 11am – Giambiagi lecture hall (ICTP Adriatico GH) & streaming

Abstract The  discovery of a gravitational wave  signal coming from the merger of two black holes by the LIGO/Virgo collaboration  has initiated the new era of gravitational wave astronomy.  Primordialblack holes ( were immediately suggested to be responsible for such a signal  thus initiating aflourish research activity on the subject on which we will report the state of the art.

Contact: Matteo Biagetti
VideoSlidesAntonio Riotto’s webpage

Fiorenza Donato (Università di Torino)
Challenges in cosmic ray physics: galactic sources, antimatter, dark matter
Friday, November 19th, 2021, 4pm – Aula D (Old SISSA building) & streaming

Abstract The unprecedented precision of data cosmic rays and gamma rays challenges our understanding of the origin and of the behavior of cosmic rays in the Galaxy. We will discuss possible interpretations of the nuclear component, in terms of sources and propagation in the Galaxy. Special emphasis will be payed to the antimatter channels, where a possible contribution from dark matter annihilation has been argued. Finally, the leptonic component – both positrons and electrons – will be critically assessed in connection with the most recent gamma-ray observations from single Galactic sources.

Contact: Piero Ullio
VideoSlidesFiorenza Donato’s webpage

Marica Branchesi (Gran Sasso Science Institute)
Multi-messenger astronomy including gravitational-waves
Friday, October 29th, 2021, 11am – streaming

Abstract A new exploration of the Universe has recently started through multi-messenger observations including gravitational-waves. The detection of gravitational-waves and multi-wavelength electromagnetic emissions from a binary neutron star merger has demonstrated the enormous potential of multi-messenger astronomy to investigate the most energetic transients in the sky, probing relativistic astrophysics, nuclear physics, nucleosynthesis, and cosmology. The talk will give an overview of the astrophysical implications of gravitational-wave and multi-messenger observations, the prospects and challenges of the current and future gravitational-wave detectors, such as Einstein Telescope which is expected to undergo a revolution for transient (astro)physics.

Contact: Enrico Barausse
VideoSlidesMarica Branchesi’s webpage

John Miller (University of Oxford & SISSA)
Binary neutron star coalescence – after the merger
Friday, October 1st, 2021, 11am – Giambiagi lecture hall (ICTP Adriatico GH) & streaming

Abstract This talk will give an overview of current understanding of what happens after the coalescence of neutron star binaries, focussing on the particular case of the gravitational wave source GW170817.

Contact: Enrico Barausse
VideoSlidesJohn Miller‘s webpage

Pasquale Serpico (LAPTH, Annecy)
Massive sterile neutrinos in supernovae and the early Universe
Friday, September 17th, 2021, 11am – Kastler lecture hall (ICTP Adriatico GH) & streaming

Abstract After reviewing some motivation and the relevant parameter space, I will illustrate the impact of massive sterile neutrinos (tens or hundreds of MeV) on core collapse supernovae. An introduction to the topic of neutrinos in supernovae will be included for those unfamiliar with the relevant astrophysics. In particular, I will discuss constraints in the mass-mixing plane and interesting phenomenological signatures measurable at existing or forthcoming neutrino detectors. Cosmological probes (primordial nucleosynthesis, CMB) are also sensitive to some allowed parameter space. I will present recent calculations of the thermal decoupling of these states and the impact on the observables Neff  and Y. Current constraints and forecasts for the reach of the Stage-IV CMB observations will be discussed.

Contact: Piero Ullio, Emiliano Sefusatti
VideoSlidesPasquale Serpico‘s webpage