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
VideoAlan 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)
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