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Tea Break Special Edition
Happy Birthday Higgs Boson
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06 Jul 2022 - 16:00
Abstract
On 4 July 2012, the ATLAS and CMS collaborations at CERN announced the discovery of a Higgs boson-like particle, marking a historical milestone in our understanding of the fundamental interactions. Determining the nature and role of this particle has been a main objective of the LHC experiments, and will remain a crucial theme at future colliders. GGI celebrates the 10th anniversary of the discovery with this special GGI Tea Break’s event. The programme includes three talks. The first talk will illustrate the 30 year-long experimental enterprise that made the Higgs boson discovery possible, its challenges and breakthroughs. The second talk will focus on the theoretical work that led to the prediction and that was instrumental for the discovery. The importance and significance of the discovery will be analyzed by the third talk, offering a modern perspective and an outlook. A general discussion will follow with ample time for questions and comments
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Tracy Slatyer (MIT)
Bound States in Heavy Dark Sectors: from WIMPonium to Squeezeout
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22 Jun 2022 - 17:00
Abstract
The nature of dark matter remains one of the great puzzles of fundamental physics, with potential connections to a plethora of deep questions. While dark matter is often assumed to be collisionless, dark matter particles may interact with each other through either the known forces of the Standard Model of particle physics, or new "dark" forces, while remaining consistent with current constraints. In either case, dark matter may form bound states similar to those we observe in ordinary matter. I will discuss a range of possible implications of the existence of such bound states, including observational signatures in gamma-ray telescopes, and modifications to the history of the cosmos allowing for strikingly heavy dark matter in strongly-interacting dark sectors.
Bio
Tracy Slatyer is a theoretical physicist who is a tenured professor at MIT. She obtained a Ph.D. in physics at Harvard University in 2010. After spending three years at the Institute for Advanced Study in Princeton, she joined the MIT Physics department as a faculty member in 2013. Her research activity is motivated by fundamental questions in particle physics, such as the nature of dark matter, and she looks for new physics signatures in astrophysical and cosmological data. She provided seminal contributions in several aspects of astroparticle physics including theoretical predictions for gamma-ray signals from dark matter annihilations, modeling energy injections in the expansion history of our universe, and the discovery of the giant gamma-ray structures known as the “Fermi Bubbles” erupting from the center of the Milky Way. Her outstanding research results were recognized by several awards including the Bruno Rossi Prize of the American Astronomical Society in 2014 and the New Horizons in Physics Prize in 2021.
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Pasquale Calabrese
Why entanglement matters
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08 Jun 2022 - 17:00
Abstract
One century ago Erwin Schrödinger called entanglement "... the characteristic trait of quantum mechanics, the one that enforces its entire departure from classical lines of thought".
However, only in the last two decades the study of quantum entanglement in many body systems (i.e. field theories) reached such a mature stage to lead to an unprecedented exchange of ideas and concepts between fields that were previously unrelated like quantum information, high-energy physics, statistical mechanics, general relativity, condensed matter and many more.
In this colloquium-style tea break, I will discuss a number of examples taken from different fields in which many-body entanglement is the characteristic physical trait.
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Tomaz Prosen (University of Ljubljana)
Exactly solved models of many-body quantum chaos
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11 May 2022 - 17:00
Abstract
I will discuss the problem of unreasonable effectiveness of random matrix theory for description of spectral fluctuations in extended quantum lattice systems. A class of locally interacting spin systems has been recently identified where the spectral form factor is proven to match with gaussian or circular ensembles of random matrix theory, and where spatiotemporal correlation functions of local observables as well as some measures of dynamical complexity can be calculated analytically. These, so-called dual unitary systems, include integrable, non-ergodic, ergodic, and generically, (maximally) chaotic cases. After reviewing the basic results on dual unitary Floquet circuits, I will argue that correlation functions of these models are generally perturbatively stable with respect to breaking dual-unitarity, and describe a simple result within this framework.
BIO
T. Prosen has received a PhD in theoretical physics in 1995 from University of Ljubljana. After a postdoctoral stay at Institut Henri Poincare in Paris he obtained a permanent position at University of Ljubljana in 1996, first as a researcher, since 1999 as an assistant professor, and since 2008 as a full professor. He is a head of research group on Nonequilibrium quantum and statistical physics at the Faculty of mathematics and physics in Ljubljana, and recipient of the Advanced grant of European research council in 2016. Prosen's main research interests are related to dynamics of interacting systems, both related to Hamiltonian or quantum chaos, and integrability. Among other things, he has developed methods for solving many-body Lindblad equations, in particular in the presence of boundary driving and integrable interactions, which lead to a discovery of quasi-local charges and rigorous lower bounds on previously controversial high temperature ballistic spin transport in XXZ chains.
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Leonardo Rastelli (Yang Institute, Stony Brook)
Pulling yourself up by your bootstraps in quantum gravity
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27 Apr 2022 - 17:00
Abstract
The bootstrap program leverages symmetry and mathematical consistency to study strongly coupled quantum systems. Its flagship result has been the solution of the 3D critical Ising model from abstract principles alone. In this talk I will outline how universal properties of quantum gravity can also be studied from a bootstrap perspective. A surprising discovery has been a connection between black hole thermodynamics and the sphere packing problem, a venerable question in pure mathematics.
BIO
LR got his PhD at MIT in 2000. He was a Dicke Fellow and then a faculty member at Princeton University. Since 2006 he has been at the Yang Institute, Stony Brook, where he currently holds the Renaissance Chair in Physics. He is the director of the Simons Collaboration on the Non-perturbative Bootstrap. He has received a Guggenheim Fellowship and and has been named a Simons Investigator.
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Silvia Pascoli (Università di Bologna)
Neutrinos: from surprising past results, to current unexplained anomalies and questions for the future
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13 Apr 2022 - 17:00
Abstract
In the past twenty years, the discovery of neutrino oscillations has changed our understanding of neutrinos and proved that the Standard Model of particle physics is incomplete. We now know that neutrinos have mass and mix. An impressive progress has been made, thanks to a broad experimental programme, and most of their properties have been determined with precision. In this colloquium, I will briefly review the current knowledge of neutrino properties, highlighting the still open questions, with emphasis on the nature of neutrinos, their masses and leptonic CP violation. I will then discuss the hints for a richer structure beyond three-neutrino mixing, which have been interpreted in terms of sterile neutrinos and/or new neutrino interactions. I will review the experimental status and the expected near future developments and their possible theoretical implications.
BIO
Silvia Pascoli is Professor at the University of Bologna since 2020. After receiving her PhD from SISSA (Trieste) in 2002, she got a postdoctoral position at UCLA and then joined CERN as Fellow. In 2005 she obtained a faculty position at Durham University. Her research activity spans a broad range of topics in neutrino phenomenology, flavour model building, and astroparticle physics. Her main focus is on the physics reach of future neutrino experiments, the origin of neutrino masses, the explanation of the baryon asymmetry via leptogenesis, and links between neutrinos and dark matter.
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Johanna Erdmenger (University of Würzburg)
Berry phases, wormholes and factorization in AdS/CFT
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06 Apr 2022 - 17:00
Abstract
Within the AdS/CFT correspondence, the entanglement properties of the CFT are related to wormholes in the dual gravity theory. This gives rise to questions about the factorisation properties of the Hilbert spaces on both sides of the correspondence. We review these issues and show how the Berry phase, a geometrical phase encoding information about topology, may be used to reveal similarities between the Hilbert space structure on both sides of the correspondence. Mathematical concepts
such as coadjoint orbits play an important role. In addition to its relevance for quantum gravity, this analysis also suggests how to experimentally realise the Berry phase and its relation to entanglement in table-top experiments involving photons or electrons. This provides a new example for relations between very different branches of physics
that follow from the AdS/CFT correspondence and its generalisations.
BIO
Johanna Erdmenger is Chair for Theoretical Physics at the Julius Maximilians University of Würzburg. After obtaining her PhD at the University of Cambridge in 1996, she worked as postdoc at the University of Leipzig and at the Massachusetts Institute of Technology. She was then junior research group leader at the Humboldt University in Berlin for four years, and afterwards research group leader at the Max Planck Institute for Physics in Munich and honorary Professor at LMU in Munich from 2005 until 2016, when she moved to Würzburg for a full professorship. Her research in string theory and quantum field theory is centered on the gauge theory/string theory (AdS/CFT) correspondence, both in its foundational aspects (conformal field theory, quantum information and black holes, higher spin duality) and in a variety of applications to particle physics, condensed matter physics and cosmology.
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Gino Isidori (U. Zurich)
Flavour Physics: Old problems and recent hopes
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30 Mar 2022 - 17:00
Abstract
Flavour physics represents one of the most puzzling aspect of particle physics and, at present, is also one of the most active experimental frontiers. I present a brief introduction to this field, with special emphasis on the subject of Lepton Flavour Universality (LFU).
I review the present hints of LFU violations observed in B decays, discussing their phenomenological interest, and their possible interpretation in terms of physics beyond the Standard Model, both at the EFT level and beyond.
BIO
Gino Isidori is Professor of Theoretical Physics at the Physics Department at the University of Zurich since 2014. He obtained the PhD from the University of Rome La Sapienza in 1996. After that he has been visiting scientist at SLAC (Stanford) in 1997, a CERN Fellow in 2000-2002 and INFN researcher in the Laboratories in Frascati from 2000 till 2014. Since 2021 he is a member of the Science Policy Committee of the CERN Laboratory in Geneva. His research activity focus on the theory and phenomenology of fundamental interactions. He provided seminal contributions in the area of Higgs physics and flavor physics, for instance the demonstration of the metastability of the Standard Model vacuum, the formulation of the hypotheses of Minimal Flavor Violation, and the study of symmetries and symmetry-breaking patterns for theories beyond the Standard Model. Since 2015 his research group at the University of Zurich is playing a leading role in the theoretical interpretation of the B-physics anomalies.
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LianTao Wang (Chicago U.), Daniel Schulte (CERN)
FOCUS MEETING “Challenges and Opportunities of a Muon Collider”
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02 Mar 2022 - 17:00
Abstract
Following the European strategy update, and as a part of the Snowmass studies in the US, high energy muon colliders have received a lot of interest. They have been integrated into the European Accelerator R&D Roadmap. This concept promises to reach very high energies and luminosities because the beam can be accelerated and collided in rings due to the suppression of synchrotron radiation.
On the one hand, the short muon life time, however, poses a number of challenges for the concept, ranging from muon cooling to acceleration, from neutrino radiation to detector design.
On the other hand, recent studies have painted a broad picture of the physics potential of such machines.
In this Focus Meeting, Daniel Schulte (CERN) and Lian-Tao Wang (U. Chicago) will give an overview of the muon collider concept, highlight the associated challenges and review its physics potential.
BIO
Daniel Schulte completed a PhD in 1996 at DESY, Hamburg, on detector backgrounds in future linear collider detectors. He began working at CERN in 1997 as a fellow and since 1998 has been a member of CERN staff. He has worked on many different accelerator and collider projects throughout his career, including both of the proposed linear colliders, the ILC and CLIC, as well as circular collider projects like the LHC and FCC-hh. He lead machine design studies for CLIC and the FCC-hh projects and now he is one of the key participants of the International Muon Collider Collaboration.
LianTao Wang is professor at the University of Chicago. He received his PhD from Michigan University and held postdoctoral positions at Wisconsin and Harvard. He has been professor in Princeton before moving to Chicago. His research activity spans over several aspects of physics beyond the Standard Model including supersymmetric models, dark matter, electroweak physics and collider physics with a focus on developing new techniques for the search of new physics. Recently he has been working on the physics of future colliders, with the aim of understanding the impact of such machines for precision tests of the Standard Model and direct searches.
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Lance Dixon (SLAC National Accelerator Laboratory)
“Scattering Amplitudes in Maximally Supersymmetric Gauge Theory and a New Duality”
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09 Feb 2022 - 17:00
Abstract
Scattering amplitudes are the arena where quantum field theory directly meets collider experiments. An excellent model for scattering in QCD is provided by N=4 super-Yang-Mills theory, particularly in the planar limit of a large number of colors, where the theory becomes integrable, and amplitudes become dual to light-like polygonal Wilson-loop expectation values. The first nontrivial case is the 6-gluon amplitude (hexagonal Wilson loop), which can be computed to 7 loops using a bootstrap which is based on the rigidity of the function space of multiple polylogarithms, together with a few other conditions. It is also possible to bootstrap a particular form factor for the chiral stress-tensor operator to produce 3 gluons, through 8 loops. Remarkably, the two sets of results are related by a mysterious “antipodal” duality, which exchanges the role of branch cuts and derivatives. I will describe how the bootstrapping works and what we know about this new duality.
BIO
Lance Dixon is Professor of Theoretical Particle Physics at the Stanford Linear Accelerator Center (SLAC) at Stanford University. There he is faculty member since 1992, after having been assistant professor at Princeton University, where he obtained his PhD in 1986. Since 1995 Dixon is a Fellow of the American Physical Society. He has been a visiting professor at the École normale supérieure, University of Cambridge and at CERN, and received research chairs from the Perimeter Institute for Theoretical Institute in Canada, Humboldt University Berlin, ETH Zürich and the University of Zurich. His research work is very broad, ranging from early influential work about strings on orbifolds and string corrections to gauge couplings to "pathbreaking contributions to the calculation of perturbative scattering amplitudes, which led to a deeper understanding of quantum field theory and to powerful new tools for computing QCD processes.” The latter is the motivation of the Sakurai Prize for Theoretical Particle Physics which he received, with Bern and Kosower, in 2014. His more recent work in phenomenology focuses on precision calculations in QCD, on the formal side he continues being interested in multi-loop properties of gauge and gravitational theories.
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Eiichiro Komatsu (MPI For Astrophysics, Garching)
Cosmic Birefringence
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02 Feb 2022 - 17:00
Abstract
Polarised light of the cosmic microwave background, the remnant light of the Big Bang, is sensitive to parity-violating physics. In this presentation we report on new measurements of parity violation, called “cosmic birefringence”, from polarisation data of the European Space Agency (ESA)’s Planck satellite. The statistical significance of the measured signal is about 3 sigma. If confirmed with higher statistical significance in future, it would have profound implications for the elusive nature of dark matter and dark energy.
BIO
Eiichiro Komatsu is a cosmologist who enjoys both theoretical and observational work. He has been Director of the Physical Cosmology division at the Max Planck Institute for Astrophysics in Garching, Germany, since 2012. Prior to this he was a professor in the Department of Astronomy and Director of Texas Cosmology Center at the University of Texas at Austin. He obtained his Ph.D. from Tohoku University in Sendai, Japan, in 2001. In recent years he has been trying to find ways to prove that the Universe underwent a period of quasi-exponential, accelerated expansion called “inflation” before the big bang, and to understand why and how the expansion of the current Universe is also accelerating.
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Tea Break Special Edition
Steven Weinberg and his legacy
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19 Jan 2022 - 15:00
ABSTRACT
"The effort to understand the universe is one of the very few things that lifts human life a little above the level of farce, and gives it some of the grace of tragedy."
The Galileo Galilei Institute celebrates Steven Weinberg, a founding father of the theory of fundamental interactions and one of the greatest theoretical physicists of the last century. His work has been a source of inspiration and guidance for generations of physicists and is at the heart of current front-line research. This special GGI Tea Breaks' event is dedicated to the research of Steven Weinberg, its impact and legacy in theoretical physics. The programme includes four talks, each focused on a particular broad area of research where the work of Weinberg led to breakthrough progress. His contribution will be put into historical context and its relevance for present-day research will be discussed.
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Dima Sorokin (INFN Padova)
Non-Linear Electrodynamics and its Applications
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15 Dec 2021 - 17:00
ABSTRACT
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.
BIO
Dmitri Sorokin is a research staff member at Padua Division of INFN. He received his PhD under supervision of Prof. Dmitri Volkov and Dr. Vladimir Tkach at Kharkov University (Ukraine) in 1985. He was a research associate at Kharkov Institute of Physics and Technology, postdoctoral researcher at INFN, Alexander von Humboldt Fellow at Humboldt University of Berlin and visiting professor at Valencia University. He received an Award of the Ministry of Public Education of Poland in 2001 and Ukrainian State Prize in Science and Technology in 2009. His major interests and contributions have been in the geometrical description of string and brane dynamics, symmetries and dualities in field and string theories, higher spin field theories, compactification of higher dimensional supergravities and supersymmetry breaking, and very recently in non-linear electrodynamics.
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Gerald Dunne (University of Connecticut)
Decoding the Path Integral: Resurgence and Non-Perturbative Physics
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01 Dec 2021 - 17:00
ABSTRACT
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.
BIO
Gerald Dunne is a Professor of Physics at the University of Connecticut. He graduated from the University of Adelaide, Australia, and earned a PhD in theoretical physics at Imperial College. He was then a postdoc in the Center for Theoretical Physics at MIT and an Instructor in Applied Math at MIT. His research interests are primarily in non-perturbative methods in quantum field theory, with a particular interest in quantum systems under extreme conditions, such as the Schwinger effect and associated non-linear processes in ultra-high intensity QED physics.
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Raphael Flauger (UC San Diego)
New physics from the CMB: the next decade
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24 Nov 2021 - 17:00
ABSTRACT
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.
BIO
Raphael Flauger is an associate professor at UC San Diego. He received his Ph.D. under the supervision of Dr. Steven Weinberg at the University of Texas in 2009. He held postdoctoral positions at Yale and at the Institute for Advanced Study and New York University before becoming an assistant professor at Carnegie Mellon University in 2014, moving to UT Austin in 2015 and to UC San Diego in 2016. He received the New Horizons in Physics prize in 2016.
He works on models of the early universe and looks for their predictions mostly from cosmic microwave background data. He is also interested in astrophysical processes that must be understood to extract clue about the very early universe. He has been heralded for leading the criticism of the claim by the BICEP2 collaboration to have observed the signature of gravitational waves during a period of cosmic inflation in the early universe. In addition to cosmology, Flauger is interested in both formal aspects and applications of quantum field theories.
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Keith Olive (University of Minnesota)
Big Bang Nucleosynthesis - Post Planck
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17 Nov 2021 - 17:00
ABSTRACT
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.
BIO
Keith Olive holds a Gloria Becker Lubkin Chair in Theoretical Physics at the University of Minnesota. He received a Ph.D. in physics from the University of Chicago and was a research associate at CERN and Fermilab before joining the faculty at the University of Minnesota. His research lies at the interface between particle physics and cosmology, and he provided seminal contributions in several aspects of astroparticle physics including big bang nucleosynthesis, particle dark matter, baryogenesis, and inflation. Among several awards, he was the recipient of the 2018 Hans Bethe Prize and was elected a fellow of the American Physical Society in 2003.
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Igor Klebanov (Princeton University and IAS)
Strong Interactions, Color Confinement, and Strings
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03 Nov 2021 - 17:00
ABSTRACT
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.
BIO
Igor Klebanov is Eugene Higgins Professor of Physics at Princeton University, where he has been a faculty member since 1989, and the Director of the Princeton Center for Theoretical Science. He is a member of the American Academy of Arts and Sciences and of the U.S. National Academy of Sciences, and was awarded the Guggenheim Fellowship in 2010, a prestigious prizes from the University of La Sapienza in Rome in 2014 and the Pomeranchuk Prize from ITEP Moscow in 2017.
Much of his work has focused on the exact relations between quantum field theories in four and three space-time dimensions, and higher dimensional theories which include gravity.
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Subir Sachdev (Harvard & IAS Princeton)
Planckian Metals and Black Holes
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20 Oct 2021 - 17:00
ABSTRACT
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.
BIO
Subir Sachdev is Herchel Smith Professor of Physics at Harvard University and Maureen and John Hendricks Distinguished Visiting Professor at the Institute for Advanced Study, Princeton, specializing in condensed-matter physics.
He was elected to the U.S. National Academy of Sciences in 2014 and Foreign Fellow of the Indian National Science Academy in 2019. He received the Lars Onsager Prize from the American Physical Society and the Dirac Medal from the ICTP in 2018.
His research describes the connection between physical properties of modern quantum materials and the nature of quantum entanglement in the many-particle wavefunction. He has made extensive contributions to the description of the diverse varieties of entangled states of quantum matter. These include states with topological order, with and without an energy gap to excitations, and critical states without quasiparticle excitations.
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Savas Dimopoulos
(Standford U.)
Particle Physics Circa 2021
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13 Oct 2021 - 17:00
ABSTRACT
I will share my personal view of what we learned after half a century of Beyond-the-Standard Model theory and searches
BIO
Savas Dimopoulos is the Hamamoto Family Professor at Stanford University. He obtained his PhD at the University of Chicago, and held positions, among others, at Harvard and CERN. In his long scientific career he is the author of seminal papers on a wide range of topics in elementary particle physics and physics beyond the Standard Model. He made important contributions in the fields of supersymmetry, dynamical symmetry breaking, dark matter, new extra dimensions and fundamental physics at large. For example, his works on supersymmetric unification and his creative ideas in explaining the weakness of gravity with large new extra dimensions have shaped the experimental searches for new physics at the TeV scale in the past decades. In recent years he has been focussing on the study of fundamental physics through atom interferometry, with the aim of testing quantum mechanics and general relativity with unprecedented precision.
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Netta Engelhardt (MIT)
The Black Hole Information Paradox in the Age of Holographic Entanglement Entropy
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06 Oct 2021 - 17:00
ABSTRACT
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.
BIO
Netta Engelhardt is Assistant Professor of Physics at the Massachusetts Institute of Technology since 2019. Prior to that, she worked as postdoctoral fellow at Princeton University, after having obtained her PhD at the University of California, Santa Barbara in 2016. Her research focuses on understanding the dynamics of black holes in quantum gravity, gaining insights from the interplay between gravity and quantum information via the AdS/CFT correspondence. She is the 2019 winner of the Blavatnik Awards for Young Scientists, and one of the 2021 winners of the New Horizons in Physics Prize “for calculating the quantum information content of a black hole and its radiation".
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Gia Dvali (Ludwig-Maximilians University, Munich)
Exclusion of de Sitter Vacua and Naturalness
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14 Jul 2021 - 17:00
ABSTRACT
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.
BIO
Gia Dvali is a professor and chair at Ludwig Maximilians University and a director of Max Planck Institute for Physics in Munich. His research is focused on the physics beyond the Standard Model. His main goal is to understand the fundamental laws of Nature and to link them with experimental signatures in high-energy particle accelerators, cosmology and astrophysics. He also has a very strong interest in many-body quantum systems and quantum information, and has established a link between these two subject areas through black holes and cosmology. His papers on large extra dimensions, together with Nima Arkani-Hamed and Savas Dimopoulos, are some of his most influential works and opened new paths to understand gravity and its weakness compared to other forces.
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Gabriele Veneziano (CERN and College de France)
Reflections on 50+ years of success stories
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07 Jul 2021 - 17:00
ABSTRACT
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.
BIO
Gabriele Veneziano is widely considered the father of string theory. He has conducted most of his scientific activities at CERN, and held the Chair of Elementary Particles, Gravitation and Cosmology at the Collège de France. He is member of the Accademia delle Scienze di Torino, Accademia Nazionale dei Lincei, Académie des Sciences de l’Institut de France.
Among his numerous prizes and awards, he received the Gold medal of Italian Republic, the Dannie Heineman prize of American Physical Society, the Enrico Fermi prize of the Italian Physical Society, the Dirac Medal at ICTP.
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Jesse Thaler (MIT)
The Hidden Geometry of Particle Collisions
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30 Jun 2021 - 17:00
ABSTRACT
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.
BIO
Jesse Thaler is a theoretical particle physicist who is an associate professor at MIT. He obtained his Ph.D. at Harvard University in 2006, and after being a Miller Fellow at the University of California in Berkeley he joined the MIT faculty in 2010. Starting from 2020, he became the inaugural Director of the Institute for Artificial Intelligence and Fundamental Interactions. He is an expert in jets, which are collimated sprays of particles produced at colliders, and he has made outstanding contributions towards understanding their substructure. Besides his research on collider physics, he is also interested in theoretical frameworks beyond the standard model of particle physics and new strategies to probe the nature of dark matter.
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Giuseppe Mussardo (SISSA)
Generalised Riemann Hypothesis and Brownian Motion
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16 Jun 2021 - 17:00
ABSTRACT
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.
BIO
Giuseppe Mussardo is Professor of Theoretical Physics at SISSA in Trieste, where he founded and directed the Statistical Physics group for several years. He is the Editorial Director of the "Journal of Statistical Physics and Applications" (JSTAT) and author of various scientific monographs, such as "Statistical Field Theory", published by Oxford University Press.
He has promoted research in quantum integrable models, where for example he calculated for the first time exactly the correlation functions of the Ising model in the magnetic field, the exact S-matrix of the Yang-Lee model and Toda Field Theories, the correlation functions of the Lieb-Liniger model for cold atoms, and open the study of Truncated Hilbert Space Approach and quantum field theories out of equilibrium. Among his recent research fields there is the relation between Number Theory and Quantum Statistical Physics: in this topic he has proposed and determined exactly a quantum potential having prime numbers as the all and only eigenvalues, and promoted the study of the Riemann conjecture with the methods of statistical mechanics.
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Fabio Maltoni (Bologna U.), Andrea Wulzer (CERN & EPFL, Padova U.)
FOCUS MEETING "The Precision Potential of the (HL-)LHC"
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09 Jun 2021 - 17:00
ABSTRACT
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.
BIO
Fabio Maltoni obtained his PhD at the University of Pisa. He was a postdoc at U. Turin, UIUC, Centro Enrico Fermi and CERN. In 2006 he moved to the Université Catholique de Louvain, while now is professore at U. Bologna. His research interests are focussed on QCD and collider physics, especially related to new physics searches at high energy and precision tests of the Standard Model of particle physics. He introduced the event generator "MadGraph", which is a tool used by the entire high energy community to simulate particle physics processes at colliders.
BIO
Andrea Wulzer received his PhD from the International School for Advanced Studies in Trieste. He held postdoctoral positions at Barcelona, EPFL Lausanne, ETH Zurich, and then moved to University of Padua. He currently holds a joint position at CERN and EPFL Lausanne. His research spans several aspect of physics beyond the Standard Model and he gave several contributions to the field of composite Higgs theories. Recently his focus is on precision tests of the Standard Model, future colliders and machine learning applied to particle physics.
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Gian Giudice (CERN) , Riccardo Rattazzi (EPFL - École polytechnique fédérale de Lausanne)
FOCUS MEETING "Naturalness and the future of High Energy Physics"
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19 May 2021 - 17:00
ABSTRACT
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.
BIO
Gian Francesco Giudice obtained his PhD in theoretical physics from the International School for Advanced Studies in Trieste. He was Research Associate at Fermilab, University of Texas and INFN. He later moved to CERN, where he is currently the Head of the Theoretical Physics Department. His research mainly deals with formulating new theories of the fundamental interactions and studying their implications for the early universe. He made significant contributions in the areas of supersymmetry, extra dimensions, electroweak physics, collider physics, dark matter, and leptogenesis. Among his most influential works are those on the Giudice-Barbieri criterion to test the degree of naturalness, anomaly mediation, split supersymmetry, the Giudice-Masiero mechanism, Minimal Flavor Violation, the Higgs boson potential and quantum criticality.
BIO
Riccardo Rattazzi obtained his PhD at Scuola Normale Superiore, Pisa, and held postdoctoral positions at Berkeley, Rutgers and CERN. He was then researcher at INFN and junior staff at CERN. Since 2006 he is professor of physics at the École Polytechnique Fédérale de Lausanne. His research is focused on the many aspects of quantum field theory, ranging from particle physics to conformal theories, condensed matter systems, and cosmology. He gave significant contributions to effective field theory, supersymmetry, composite Higgs theories and extra dimensions. His work led to the discovery of anomaly mediation in supersymmetry and of galileon theories, as well as to the first practical implementation of the conformal bootstrap method in four dimensions.
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Jan de Boer (Amsterdam University)
Theory Colloquium
Quantum Gravity meets Statistical Physics
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12 May 2021 - 17:00
ABSTRACT
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.
BIO
Jan de Boer has been a professor of theoretical physics at the University of Amsterdam for the past 20 years.
He has worked on a broad range of subjects in theoretical physics with an emphasis on problems in string theory,
black holes, quantum gravity, and holography.
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Jure Zupan (Univ. of Cincinnati)
Flavor Physics: Status and Prospects
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05 May 2021 - 17:00
ABSTRACT
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).
BIO
Jure Zupan received his PhD at University of Ljubljana in 2002, and has held postdoctoral positions at Technion, Carnegie Mellon University and CERN. Since 2010 he is faculty at University of Cincinnati. His primary research area is high energy phenomenology, with a particular focus on flavor physics, the physics of dark matter, and collider physics.
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Mariangela Lisanti (Princeton University)
Galactic Archaeology and the Search for Dark Matter
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28 Apr 2021 - 18:00
ABSTRACT
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.
BIO
Mariangela Lisanti is an Associate Professor at Princeton University. She earned her Ph.D. at Stanford University, and she was an associate research scholar at the Princeton Center for Theoretical Sciences. Her research activity spans from the phenomenology of collider physics to models of dark matter and their experimental signatures.
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Massimo Passera (INFN Padova)
Muon g-2: the showdown
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21 Apr 2021 - 17:00
ABSTRACT
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.
BIO
Massimo Passera is a Research Scientist at INFN, Padua. He received his Ph.D from New York University and worked as a researcher at Brookhaven, Bern, Valencia and CERN. He is a theoretical physicist and he is interested in theories of fundamental interactions, with a focus on phenomenology and precision tests of the Standard Model. In his career he has established himself as one of the world-leading expert of the physics of the muon magnetic moment. In recent years, he has been one of the proponents of the "MUonE" experiment at CERN.
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Renato Renner (ETH Zurich)
TH Colloquium - How to test quantum theory with thought experiments
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14 Apr 2021 - 17:00
ABSTRACT
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.)
BIO
Renato Renner graduated in theoretical physics and completed his PhD in the area of quantum cryptography in 2005. After spending two years in the UK, where he was a HP research fellow in the Department for Applied Mathematics and Theoretical Physics at the University of Cambridge, he joined the ETH Institute for Theoretical Physics as a professor, where he is heading the research group on Quantum Information Theory. His research interests are in the area of quantum information science, quantum thermodynamics, and the foundations of quantum physics.
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Brian Batell
(University of Pittsburgh)
TH Colloquium - "Portals to the Dark Sector"
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24 Mar 2021 - 17:00
ABSTRACT
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.
BIO
Brian Batell obtained his PhD at Minnesota University and was research associate at Perimeter Institute, Chicago University and CERN. He is currently professor at Pittsburg University. His research is focused on the study of fundamental interactions at the intensity and energy frontiers. He has been proposing new observational strategies to search for new phenomena and is an expert of dark matter and of theoretical frameworks involving new dark sectors.
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Adam Riess (JHU) & Licia Verde (ICREA)
FOCUS MEETING - "The trouble with H0”
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17 Mar 2021 - 16:00
ABSTRACT
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.
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Matias Zaldarriaga
(Institute for Advanced Study)
TH Colloquium - Gravitational Wave Astrophysics with LIGO/VIRGO Data
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10 Mar 2021 - 17:00
ABSTRACT
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
BIO
Matias Zaldarriaga has made many influential and creative contributions to our understanding of the early universe, particle astrophysics, and cosmology as a probe of fundamental physics. Much of his work centers on understanding the clues about the earliest moments of our universe encoded in the Cosmic Microwave Background, the faint glow of radiation generated by the Big Bang, and in the distribution of matter in the late universe
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Cumrun Vafa (Harvard University)
The String Landscape and the Swampland
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03 Mar 2021 - 17:00
ABSTRACT
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.
BIO
Cumrun Vafa is the Hollis Professor of Mathematicks and Natural Philosophy in the Physics Department at Harvard University. He is one of the founders of the duality revolution in string theory which has reshaped our understanding of the fundamental laws of the universe. He has uncovered mysteries of black holes using topological aspects of string theory and is the founder of `F-theory’ which is one of the most promising directions in connecting string theory solutions known as the `string landscape’ to particle physics. His ideas related to apparently consistent, but ultimately inconsistent, theories of quantum gravity which he initiated in the `swampland’ project has helped narrow down the vast string landscape and is currently an active area of research with impact on cosmology, as well as particle phenomenology.
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Hirosi Ooguri (Caltech & Kavli IPMU)
Theory colloquium
Tangles to Narnia
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17 Feb 2021 - 17:00
ABSTRACT
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.
BIO
Hirosi Ooguri is a theoretical physicist working on quantum field theory, quantum gravity, superstring theory, and their interfaces with mathematics. He also made fundamental contributions to topological string theory, 2D conformal field theories, D-branes in Calabi-Yau manifolds, the AdS/CFT correspondence, and properties of supersymmetric gauge theories and their relations to superstring theory. He is Fred Kavli Professor of Theoretical Physics and Mathematics and director of the Walter Burke Institute for Theoretical Physics at California Institute of Technology. He is also the director of the Kavli Institute for the Physics and Mathematics at the University of Tokyo and was the president of the Aspen Center for Physics in Colorado.
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Giovanni Villadoro (ICTP)
Theory colloquium
Axion Dark Matter
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10 Feb 2021 - 17:00
BIO
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.
ABSTRACT
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.
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Andreas Ringwald (DESY)
Theory colloquium
The Hunt for the Axion
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03 Feb 2021 - 17:00
ABSTRACT
We review the physics case for the axion and discuss different methods to hunt for it in current and future experiments.
BIO
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.
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Roberto Tateo (University of Turin)
Theory colloquium
What are T-Tbar deformations?
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20 Jan 2021 - 17:00
ABSTRACT
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.
BIO
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.
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Marc Kamionkowski (Johns Hopkins University)
Theory colloquium
Is the ΛCDM model in trouble?
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13 Jan 2021 - 17:00
ABSTRACT
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.
BIO
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.
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