Andrei Mesinger (Scuola Normale Superiore, Pisa)
Forward modeling the first billion years
Friday, May 26th, 2023, 11am – Aula D (old SISSA building) & streaming
Abstract The birth of the first stars, black holes and galaxies heralded the end of the cosmic Dark Ages and the beginning of the Cosmic Dawn. The light from these objects heated and ionized almost every atom in existence, culminating in the Epoch of Reionization: the final major phase change of the Universe. This final frontier of astrophysical cosmology is undergoing a transition from an observationally-starved epoch to a “Big Data” field. This process is set to culminate with upcoming Square Kilometre Array interferometric observations of the redshifted 21-cm line: providing a 3D map of the first billion years of our Universe. With the SKA, we will be able to actually study the UV and X-ray properties of the first galaxies, as well as physical cosmology, which are encoded in the large-scale structure of the 21-cm signal. I will review the current status of observations of the EoR and Cosmic Dawn, before discussing the main challenges in modeling the 21-cm signal: a huge range of relevant scales and a large parameter space of astrophysical uncertainties. I will review how simulations have adapted to address these challenges. I show how the unprecedented size of the upcoming SKA dataset will allow us to recover properties of the (unseen!) first galaxies, in addition to providing clean probes of cosmology through accoustic oscilations. Finally I will demonstrate how simulation-based inference will be a powerful tool to study these upcoming (non-Gaussian) datasets.
Contact: Matteo Viel
Video – Andrei Mesinger’s webpage
John Webb (University of Cambridge)
Searching for new physics – spacetime variations of fundamental constants
Friday, April 28th, 2023, 11am – Aula D (old SISSA building) & streaming
Abstract Following Dirac’s proposed “Large Number Hypothesis”, a new research field emerged: the search for spacetime variations of fundamental constants. Today, the theoretical motivations are quite different. Higher dimensional unification theories naturally predict variations. One of the main science drivers of expensive new instrumentation like ESPRESSO on the VLT, and soon the ELT, is this topic. The discovery of any change would violate the Einstein Equivalence Principle and revolutionise physics. On the other hand, increasingly stringent upper limits on any change rule out certain classes of unification theories. I will describe this background and then discuss recent developments to finally establish the theoretical and numerical techniques needed for this tricky measurement. I will summarise the observational status and show data from quasar spectroscopy that hints at a change in the fine structure constant.
Contact: Dinko Milaković
Vivian Poulin (LUPM, Montpellier)
Towards a new “Concordance Cosmology”
Friday, April 21st, 2023, 11am – Aula D (old SISSA building) & streaming
Abstract. With the latest results from Planck, we have entered a new era of “precision cosmology”. However, some predictions of the canonical cosmological model namely Lambda-Cold-Dark-Matter (LCDM), calibrated on data from the early universe, are being challenged by high-accuracy measurements with probes of the late-universe. In particular, the famous “H0 Tension” and “S8 tension” between direct measurements of the Hubble parameter (H0) and clustering amplitude (S8) respectively, and the prediction from the Planck/LCDM model, have now reached a high level of statistical significance. After a brief review of the measurements and (some) possible systematic errors that could affect these measurements, I will discuss new physics scenarios that have been suggested and draw some guidelines towards a new “concordance cosmology”
Contact: Matteo Viel
Slides – Video – Vivian Poulin’s website
Alan Heavens (Imperial College, London)
Cosmic shear as a probe of Dark Energy and Modified Gravity
Friday, March 17th, 2023, 11am – Room 205 & streaming
Abstract In this talk I’ll review the physics of cosmic shear, showing how it gives us a window into Dark Energy properties, and how it can alert us to deficiencies in Einstein gravity. The relative simplicity of the gravitational physics involved motivates surveys such as Euclid and LSST, but there are challenges from astrophysics that break the original simplicity. Furthermore, the signatures of Dark Energy and modifications to gravity are subtle, so all aspects of the scientific analysis need to be under control, from accurate theoretical calculations, through exquisite control of observational systematics, to very careful statistical analysis. I’ll focus on the last of these, showing how we are able to use new forward-modelling techniques, based on powerful Bayesian Hierarchical Modelling and Simulation-Based Inference, to extract information from the surveys with far greater precision than traditional methods.
Contact: Roberto Trotta
Video – Alan Heavens’s webpage
Fulvio Ricci (Università la Sapienza, Roma)
Gravitational Wave Detection, a multidisciplinary experimental challenge
Friday, February 24th, 2023, 11am – Aula D (old SISSA building) & streaming
Abstract The detection of Gravitational Waves with interferometers on Earth such as LIGO and Virgo has been the result of a long process of experimental activity which has involved several research areas. Weak GW signal requires beating a long list of noise sources that limit detector sensitivity. Seismic, thermal and optical noises are the main limitations; each of these sources requires a dedicated strategy, which exploits new technologies and new ideas to improve the performance of the detector and to explore ever deeper into the Universe. The construction of a third generation GW interferometer, such as the Einstein Telescope, is a new experimental venture. In this talk we will try to highlight the main experimental challenges and present some of the ideas to achieve its ambitious goal of sensitivity.
Contact: Matteo Viel
Fulvio Ricci’s website
Licia Verde (University of Barcelona)
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.
Video – Slides – Katherine 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
Video – Slides – Will Percival’s webpage