GGI Tea Breaks' Seminars

Jan 1, 2021, 5:00 PM → Dec 31, 2021, 6:30 PM Europe/Rome

GGI Zoom Room

It is a new web-seminar series on the Theory of Fundamental interactions, covering a wide spectrum of arguments. The aim is to discuss the open questions in Fundamental Physics while offering to researches and Ph.D. Students a simple introduction to some of the hottest topics in the field. "GGI Tea Breaks" will include Theory Colloquia given by established experts as  well as Focus Meeting on special topics given by two or more scientists with different viewpoints. Ample space for questions and discussion will be allocated at the end of the Seminars.

If you wish to receive announcements please fill the form: https://docs.google.com/forms/d/e/1FAIpQLSezltPaSJJ6SiSSpxVq3H7Dt4AJx0SoKGDbL-8xsKcsFs5fOg/viewform

Wed, January 13

5:00 PM → 6:30 PM Theory Colloquium "Is the ΛCDM model in trouble?"

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.

Speaker: Marc Kamionkowsky (Johns Hopkins University)

Wed, January 20

5:00 PM → 6:30 PM Theory Colloquium "What are T-Tbar deformations?"

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.

Speaker: Roberto Tateo (TO)

Wed, February 3

5:00 PM → 6:30 PM Theory Colloquium "The Hunt for the Axion"

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

Speaker: Andreas Ringwald (DESY)

Wed, February 10

5:00 PM → 6:30 PM Theory Colloquium "Axion Dark Matter"

While providing a simple dynamical explanation for the smallness of CP violation in strong interactions, the QCD axion is also one of the most compelling candidates of dark matter in the Universe. While the presence of relic QCD axions is almost guaranteed if such particle exists, a reliable computation of its abundance is still lacking. Such information could be pivotal in both focusing the experimental efforts and 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.

Speaker: Giovanni Villadoro

Wed, February 17

5:00 PM → 6:30 PM Theory Colloquium "Tangles to Narnia"

Recently, a new type of holographic pair has been found, in which quantum gravity theories are dual to random ensembles of quantum mechanical systems in one and two dimensions. This discovery has revived questions on role of wormholes in quantum gravity and its implications in the holography. I will discuss their generalization in the context of three-dimensional gravity theories. Mathematical theory of knots and hyperbolic geometries associated to them plays an important role.

Speaker: Hirosi Ooguri (Caltech & Kavli IPMU)

Wed, March 3

5:00 PM → 6:30 PM Theory Colloquium "The String Landscape and the Swampland"

String theory landscape of vacua point to new consistency conditions that a quantum gravitational system must satisfy. There are only a small number of quantum field theories that satisfy these conditions and all the rest belong to the `Swampland' which cannot be consistently coupled to gravity. In this talk I review some of these conditions and their implications for cosmology and particle physics.

Speaker: Cumrun Vafa (Harvard University)

Wed, March 10

5:00 PM → 6:30 PM Theory Colloquium "Gravitational Wave Astrophysics with LIGO/VIRGO Data"

I will describe our recent work re-analyzing the GW data made public by the LIGO collaboration. More broadly I will discuss some of the outstanding questions related to binary black hole mergers, what the data might be saying and what we might expect in the near future.

Speaker: Matias Zaldarriaga (Institute for Advanced Study)

Wed, March 17

4:00 PM → 5:30 PM Focus Meeting "The trouble with H0”

The Hubble constant H0 is one of the most important parameters in the cosmological model, setting the size and age scales of the Universe. The distance ladder relying on supernovae yields values of H0 higher than those inferred from the inverse distance ladder, which is instead based on early-time physics and relies on observations typically involving the cosmic microwave background, in combination with galaxy surveys. Such discrepancy has come to be known as the 'Hubble tension'. In this Focus Meeting Adam Riess and Licia Verde will illustrate the different methods of measurement of H0, and analyze possible resolutions of the Hubble tension.
The Hubble tension has motivated the exploration of extensions to the standard cosmological model in which higher values of H0 can be obtained from CMB measurements and galaxy surveys. The trouble, however, goes beyond H0; such modifications affect other quantities too, such as cosmic times and the matter density. Any Hubble trouble has implications well beyond H0 itself. Licia Verde will analyze the tension in both a model-dependent and a model-independent way, and will propose a new representation of parameter constraints that, hopefully, will help us find a resolution.
A streamlined distance ladder constructed from infrared observations of Cepheids and type Ia supernovae with ruthless attention paid to systematics now provides < 2% precision and offer the means to do much better. By steadily improving the precision and accuracy of the Hubble constant, we now see evidence for significant deviations from the standard model, referred to as LambdaCDM, and thus the exciting chance, if true, of discovering new fundamental physics such as exotic dark energy, a new relativistic particle, or a small curvature to name a few possibilities. Adam Riess will review recent and expected progress, most recently based on measurements from Gaia EDR3 released in December, 2020.

Speakers: Adam Riess (Johns Hopkins University), Licia Verde (ICREA)

Wed, March 24

5:00 PM → 6:30 PM Theory Colloquium "Portals to the Dark Sector"

A handful of open questions, such as the nature of the cosmic dark matter, compel the search for a new paradigm of matter and forces. A novel, yet plausible, element of this framework may be a hidden or dark sector of new elementary particles, which does not experience the familiar strong and electroweak interactions. Such a hidden world may still influence our visible world if there is a very weak interaction, or portal, between the two sectors. I will introduce the basic theoretical framework of dark sectors and portals and highlight the growing experimental program to search for a variety of novel phenomena associated with these theories.

Speaker: Brian Batell (University of Pittsburgh)

Wed, April 14

5:00 PM → 6:30 PM Theory Colloquium "How to test quantum theory with thought experiments"

Quantum theory is one of our most accurate theories ever when it comes to the description of small systems. It is therefore often assumed that the theory can equally well be applied to large objects, sometimes even astronomical ones like black holes. In my talk I will present a thought experiment that indicates that the range of validity of (current) quantum theory may be limited to small systems.
(The talk is based on work with Daniela Frauchiger and Nuriya Nurgalieva.)

Speaker: Renato Renner (ETH Zurich)

Wed, April 21

5:00 PM → 6:30 PM Theory Colloquium "Muon g-2: the showdown"

The Muon g-2 experiment at Fermilab has recently confirmed Brookhaven's earlier measurement of the muon anomalous magnetic moment aμ. This new result increases the discrepancy Δaμ with the Standard Model (SM) prediction and strengthens its "new physics" interpretation as well as the quest for its underlying origin. In this talk I will review the SM prediction of the muon g-2, focusing on some of the latest developments, and discuss the connection of the discrepancy Δaμ to precision electroweak predictions via their common dependence on hadronic vacuum polarization effects.

Speaker: Massimo Passera (INFN Padova)

Wed, April 28

6:00 PM → 7:30 PM Theory Colloquium "Galactic Archaeology and the Search for Dark Matter"

The Gaia mission is in the process of mapping nearly 1% of the Milky Way’s stars, nearly a billion in total. This data set is unprecedented and provides a unique view into the formation history of our Galaxy and its associated dark matter halo. I will review recent results demonstrating how the evolution of the Galaxy can be deciphered from the stellar remnants of massive satellite galaxies that merged with the Milky Way early on. This analysis is an inherently "big data" problem, and I will discuss how to leverage machine learning techniques to advance our understanding of the Galaxy's evolution. Our results indicate that the local dark matter is not in equilibrium, as typically assumed, and instead exhibits distinctive dynamics tied to the disruption of satellite galaxies. The updated dark matter map built from the Gaia data has ramifications for direct detection experiments, which search for the interactions of these particles in terrestrial targets.

Speaker: Mariangela Lisanti (Princeton)

Wed, May 5

5:00 PM → 6:30 PM Theory Colloquium "Flavor Physics: Status and Prospects"

Measurements of rare flavor changing transitions with either quarks or leptons can be used to search for signs of new physics. I will review the status of the field, including the recent anomalies in B physics and anomalous magnetic moment of the muon. I will try to give sense of where the field is going next, driven in a large extent with several ambitious experimental programs coming on line in the near to midterm future (the LHCb upgrade, Belle II, Mu2e, MEG-II, etc).

Speaker: Jure Zupan (U. of Cincinnati)

Wed, May 12

5:00 PM → 6:30 PM Theory Colloquium "Quantum Gravity meets Statistical Physics"

Recent work on quantum gravity has revealed deep connections with subjects like
quantum information, statistical physics and quantum chaos. In particular, low-energy effective
field theories that include gravity turn out to have more access to high-energy degrees of freedom
than their non-gravitational Wilsonian counterparts. While precise microscopic high-energy information
is inaccessible, certain statistical high-energy information does manifest itself in an interesting way at low
energies. I will describe some recent work trying to make this connection more precise, and explain how
it connects to issues like wormholes, baby universes, averaging over theories and the black hole information
paradox.

Speaker: Jan De Boer (Amsterdam University)

Wed, May 19

5:00 PM → 6:30 PM Focus Meeting "Naturalness and the future of High Energy Physics"

Naturalness arguments have been a powerful guiding principle for physicists as they try to construct new theories. While considerations based on simplicity and elegance have characterized the scientific thought since very early times, numerical naturalness, as most clearly formulated by ’t Hooft and Wilson, has been especially influential in the search for theories of fundamental interactions. When applied to our current description of the microscopic world in terms of quantum field theory, it leads to the apparent paradox of the smallness of the electroweak scale and of the cosmological constant as compared to the Planck scale. In this Focus Meeting, Gian Francesco Giudice and Riccardo Rattazzi will review the concept of naturalness and its implications. The seemingly convincing notions of naturalness and simplicity in Effective Field Theory will be introduced and argued that they appear mutually contradictory in both the SM and its natural extensions. This state of things defines the Hierarchy Paradox. The hypotheses on which the naturalness principle rests, the consequences of relaxing some of these hypotheses, and the current attempts to develop new paradigms beyond naturalness will then be discussed.

Speakers: Gian Giudice (CERN), Riccardo Rattazzi (EPFL)

Wed, June 9

5:00 PM → 6:30 PM Focus Meeting "The Precision Legacy of the (HL-)LHC"

The data collected at the LHC and its High-Luminosity successor over the next 20 years will enable a multitude of precise experimental measurements in the Electroweak, Higgs and Top sectors, potentially leading to a systematic program of exploration at the frontier of fundamental physics. The design of this program and its exploitation requires multiple forms of theoretical input, ranging from the definition of the target measurements and their implications on putative new physics scenarios to the development of sufficiently accurate and easily available theoretical predictions as well as of novel analysis data techniques that will be needed to deal with the amazing richness and complexity of the LHC data. In this Focus Meeting, Fabio Maltoni and Andrea Wulzer will review the current status of the field and give a perspective on the future challenges.

Speakers: Andrea Wulzer (CERN & EPFL, Padova U.), Fabio Maltoni (Bologna U.)

Wed, June 16

5:00 PM → 6:30 PM Theory Colloquium "Generalised Riemann Hypothesis and Brownian Motion"

If Number Theory is arguably one of the most fascinating subjects in Mathematics, Theoretical Physics adds to it the standard of clarity, beauty and deepness which have helped us to shape our understanding of the laws of Nature: together, these two subjects present a fascinating story worth telling, one of those vital, wonderful and superb narratives of enquires rarely found in human history.
From this point of view, the seminar presents the main features of the Riemann Hypothesis and discusses its generalisation to an infinite class of complex functions, the so called Dirichlet L-functions, regarded as quantum partition functions on the prime numbers.
The position of the infinite number of zeros of all the Dirichlet L-functions along the axis with real part equal to 1/2 finds a very natural explanation in terms of one of the most basic phenomena in Statistical Physics, alias the Brownian motion. We present the probabilistic arguments which lead to this conclusion and we also discuss a battery of highly non-trivial tests which support with an extremely high confidence the validity of this result.

Speaker: Giuseppe Mussardo (SISSA)

Wed, June 30

5:00 PM → 6:30 PM Theory Colloquium "Artificial Intelligence and Fundamental Interactions"

In this talk, I explain how various concepts and techniques in quantum field theory and collider physics can be naturally translated into a new geometric language. Using the energy mover's distance, which quantifies the minimal amount of "work" required to rearrange one event into another, we can define a distance between pairs of collider events. This distance can then be used to triangulate the "space" of collider events and rigorously define various geometric objects. Many well-known collider observables, jet algorithms, and pileup mitigation schemes have a simple geometric interpretation, as does the important concept of infrared and collinear safety. Intriguingly, these ideas can be lifted from a distance between events into a distance between theories, with potential relevance for visualizing and interpreting data from the LHC.

Speaker: Jesse Thaler (MIT)

Wed, July 7

5:00 PM → 6:30 PM Reflections on 50+ years of success stories

I will share some thoughts prompted by the amazing successes but also by some puzzling aspects of our present description of Nature from the smallest scales of elementary particle physics to the largest ones of gravity and cosmology.

Speaker: Gabriele Veneziano (CERN and College de France)

Wed, July 14

5:00 PM → 6:30 PM Exclusion of de Sitter Vacua and Naturalness

According to the landscape view, the origin of physical parameters, such as the vacuum energy or the Higgs mass, is linked with the existence of a vast landscape of de Sitter vacua, supposedly provided by quantum gravity. The assumed plentitude of such vacua is a necessary ingredient for anthropic selection. In this talk we shall provide evidence that the situation is actually the opposite and that the de Sitter landscape is incompatible with quantum gravity. In this way, quantum gravity/string theory nullifies an outstanding cosmological puzzle of vacuum energy. The exclusion of an eternally inflating Universe raises a number of fundamental questions about past and future cosmology. It also leads to new predictions about cosmological observables and about the nature of dark energy. The lack of anthropic and cosmological selections sharpens other naturalness questions, such as the weak scale hierarchy and strong-CP violation, and correspondingly strengthens the case for new physics.

Speaker: Gia Dvali (Ludwig-Maximilians University, Munich)

Wed, October 6

5:00 PM → 6:30 PM The Black Hole Information Paradox in the Age of Holographic Entanglement Entropy

The black hole information paradox — whether information escapes an evaporating black hole or not — remains one of the greatest unsolved mysteries of theoretical physics. The apparent conflict between validity of semiclassical gravity at low energies and unitarity of quantum mechanics has long been expected to find its resolution in the deep quantum gravity regime. Recent developments in the holographic dictionary and in particular its application to entanglement, however, have shown that a semiclassical analysis of gravitational physics has a hallmark feature of unitary evolution. I will describe this recent progress and discuss some potential new avenues for working towards a resolution of the information paradox.

Speaker: Netta Engelhardt (MIT)

Wed, October 13

5:00 PM → 6:30 PM Particle Physics Circa 2021

I will share my personal view of what we learned after half a century of Beyond-the-Standard Model theory and searches

Speaker: Savas Dimopoulos (Stanford University)

Wed, October 20

5:00 PM → 6:30 PM Planckian Metals and Black Holes

Many modern materials feature a “Planckian metal”: a phase of electronic quantum matter without
quasiparticle excitations, and relaxation in a time of order Planck's constant divided by the absolute
temperature. The semiclassical theory of black holes predicts thermodynamic properties which are
difficult to connect to a unitary quantum theory with a discrete spectrum. I will review recent progress
in understanding these problems in very different fields of physics by using insights from the
Sachdev-Ye-Kitaev model of many-particle quantum dynamics.

Speaker: Sachdev Subir (Harvard & IAS Princeton)

Wed, November 3

5:00 PM → 6:30 PM Strong Interactions, Color Confinement, and Strings

In the 1950s and 60s many strongly interacting particles were discovered. String theory was originally invented to describe them, but Quantum Chromodynamics (QCD)?emerged as the precise theory of the strong nuclear force. A quarter century later it was understood that string theory and certain gauge theories akin to QCD are different descriptions of the same physics. I will review the relations between gauge theories and strings. Their formation in QCD is a manifestation of the confinement of colored quarks and gluons. While the color confinement is observed numerically using Lattice Gauge Theory, its analytic proof remains a deep unsolved problem in theoretical physics. I will conclude by discussing some surprises in lower-dimensional models.

Speaker: Igor Klebanov (Princeton)

Wed, November 17

5:00 PM → 6:30 PM Big Bang Nucleosynthesis - Post Planck

Big bang nucleosynthesis provides a window to the physics of the universe just seconds after the big bang. It predictions of the light element abundances of D, 4He, and 7Li can be compared with observational determinations. Over the last several years, significant progress has been made in the determinations of deuterium and helium abundances and most importantly results from Planck measurements of the microwave background have provided precise values for the baryon density of the universe, a key input used in abundance predictions. Planck data is combined with BBN to test the consistency of the Standard Model. Recent nuclear cross section data and its effect on BBN precision is also discussed. These predictions are sensitive to the conditions when the temperature of the universe was ≈ MeV or ≈ 10^10 K. Using inputs from the standard model of cosmology and particle physics yields excellent agreement between theory and experiment. Thus deviations from the standard model such as the number of particle degrees of freedom (often parametrized as the number of neutrino flavors) can be tested.

Speaker: Keith Olive (University of Minnesota)

Wed, November 24

5:00 PM → 6:30 PM New physics from the CMB: the next decade

Observations of the cosmic microwave background have been key to our understanding of the early universe. The cosmic microwave background also contains invaluable information about particle physics that can be revealed through precision observations of the polarization anisotropies. In this talk I will review the key areas where precision CMB experiments can provide new information and give an overview of the current and next generation CMB experiments.

Speaker: Raphael Flauger (UC San Diego)

Wed, December 1

5:00 PM → 6:30 PM Decoding the Path Integral: Resurgence and Non-Perturbative Physics

There are several important conceptual and computational questions concerning path integrals which have recently been approached from new perspectives motivated by "resurgent asymptotics", a novel mathematical formalism that effectively unifies perturbative and non-perturbative physics. This talk will review the basic ideas behind the connections between resurgent asymptotics and physics, starting from the work of Airy and Stokes, and the development of trans-series by Ecalle, and then turn to several recent applications in quantum mechanics and quantum field theory. The main motivation is to develop a deeper understanding of field theoretic path integrals directly from a saddle point Lefschetz thimble decomposition, and also by reconstruction from perturbative information.

Speaker: Gerald Dunne (University of Connecticut)

Wed, December 15

5:00 PM → 6:30 PM Non-Linear Electrodynamics and its Applications

In 1934 Born and Infeld constructed the first non-linear generalization of Maxwell's electrodynamics that turned out to be a remarkable theory in many respects. In 1936 Heisenberg and Euler computed an effective action describing non-linear corrections to Maxwell's theory due to quantum electron-positron one-loop effects. Since then, these and a variety of other models of non-linear electrodynamics proposed in the course of decades have been extensively studied and used in a wide range of areas of theoretical physics including string theory, gravity, cosmology and condensed matter (CMT). In this talk I will overview general properties of non-linear electrodynamics and the most interesting (from my point of view) models which are distinguished by their symmetry properties, such as a recently discovered unique non-linear modification of Maxwell's electrodynamics which is conformal and duality invariant. I will also sketch how non-linear electromagnetic effects may manifest themselves in physical phenomena (such as vacuum birefringence), in properties of gravitational objects (such as charged black holes) and in the evolution of the universe, and can be used, via gravity/CMT holography, for the description of properties of certain conducting and insulating materials.

Speaker: Dima Sorokin (INFN Padova)