GGI Tea Breaks' Seminars

Person Person

Andreas Ringwald

The Hunt for the Axion

03 Feb 2021 - 17:00 GGI zoom room

Andreas Ringwald is a research scientist at DESY, Hamburg. He studied physics and obtained his PhD at Heidelberg University. He was scientist at CERN before joining the DESY staff. He is a leading expert in both the theory and phenomenology of axions and other weakly-coupled hypothetical particles beyond the standard model. Among other things, he is one of the initiators of the ALPS and WISPDMX experiments at DESY and of the SHIPS helioscope at Hamburg Observatory. He has been the leader of the ALPS working group at DESY since 2013.

We review the physics case for the axion and discuss different methods to hunt for it in current and future experiments.

Giovanni Villadoro

Axion Dark Matter

10 Feb 2021 - 17:00 GGI zoom room

Giovanni Villadoro is Research Scientist at ICTP, Trieste. He obtained his Ph.D. from the University of Rome La Sapienza and worked at Harvard, CERN and SLAC. He is mainly interested in theories of fundamental interactions, including quantum gravity and cosmology, and beyond-the-Standard Model phenomenology. His research contributions span from lattice gauge theories and flavor physics to supersymmetry and string theory. Since a few years he has been carrying out a fruitful research programme on the physics of axions and is a world expert on this subject.

While providing a simple dynamical explanation for the smallnessof CP violation in strong interactions the QCD axion is also oneof the most compelling candidates of dark matter in the Universe. While the presence of relic QCD axions is almost guaranteed if suchparticle exists a reliable computation of its abundance is still lacking. Such information could be pivotal in both focusing the experimental effortsand drawing the right theoretical conclusions should such particle be found. In this talk I will review the challenges of such computation and the most recent developments.

Roberto Tateo (University of Turin)
What are T-Tbar deformations?
20 Jan 2021 - 17:00

Roberto Tateo is full Professor at the University of Torino. He is mainly working on integrable models and their applications to the AdS/CFT duality, the ODE/IM correspondence and PT-symmetry. He received his PhD in Physics in 1994 and worked as a Postdoc at the University of Durham, the University of Amsterdam, and at the Service de Physique Théorique in Saclay.

The presence of an irrelevant field in a quantum field theory is usually not good news, as far as understanding the high-energy physics of the model is concerned. In two space-time dimensions, the T-Tbar deformation is solvable. We can describe physical observables of interest, such as the S-matrix and the finite-volume spectrum, in terms of the corresponding undeformed quantities. For this irrelevant perturbation, we can reverse the renormalization group trajectory and gain exact information about ultraviolet physics. The outcome is stunning: low-energy physics resembles that of a conventional local quantum field theory while at high-energy the density of states on a cylinder shows Hagedorn growth similar to that of a string theory.

Marc Kamionkowski (Johns Hopkins University)
Is the ΛCDM model in trouble?
13 Jan 2021 - 17:00

Marc Kamionkowski is a theoretical physicist. His research is in cosmology, astrophysics, and elementary-particle theory. His main focus has been on particle dark matter, inflation and the cosmic microwave background, and cosmic acceleration. He also worked on neutrino and nuclear physics and astrophysics, large-scale-structure and galaxy formation, intrinsic galaxy alignments and gravitational lensing, gravitational waves, phase transitions in the early Universe, alternative-gravity theories, the first stars and the epoch of reionization, and a bit in stellar and high-energy astrophysics.

We’ve known since the late 1920s that the Universe is expanding. However, the expansion rate currently inferred from measurements of the cosmic microwave background now disagrees with that obtained from supernova measurements. Over the past few years, theorists have been exploring the possibility that this Hubble tension is explained by some new “early dark energy”: a new component of matter that may have been dynamically important several hundred thousand years after the Big Bang.