* denotes the organizer responsible for participant diversity
** denotes a scientific advisor

May 26 - September 15
Individual Research

Physicists are encouraged to apply as individual researchers to work on their own projects for up to five weeks at any time during the summer. We provide a serene atmosphere to complete work. The individual researcher may also choose to attend any workshop meetings or chat with other scientists in residence in addition to working on his or her own research. Click here for more information.

May 26 - September 15
Working Group

Working groups of between two and six physicists are encouraged. Click here for more information.

May 26 - June 9
String Theory and the Hidden Universe

*Jim Halverson, Northeastern University
Liam McAllister, Cornell University
Matt Reece, Harvard University
**Arthur Hebecker, University of Heidelberg

The hidden universe --- encompassing dark matter, dark energy, inflation, and possible further hidden sector degrees of freedom --- is one of the central mysteries in modern physics.  String theory offers a fundamental perspective on the puzzles posed by this hidden world. To realize the potential of this theoretical, top-down approach, the present workshop plans to bring together experts in three different areas: the formal study of the string theory landscape, the predictions of string compactifications for cosmology, and theoretical astrophysics and cosmology with a focus on dark sectors.  Topics to be discussed include the swampland program, the signatures of inflation and reheating in string theory, hidden gauge sectors, moduli domination, supersymmetry breaking, and the measure problem.

May 26 - June 16
Progress after Impasse: New Frontiers in Dark Matter

*Priyamvada Natarajan, Yale University
Kerstin Perez, MIT
**Gianfranco Bertone, UvA, Netherlands
Tim Tait, University of California Irvine

Current cosmological observations suggest that we live in a universe dominated by dark matter and dark energy while their nature remains elusive. Compelling evidence for the existence of dark matter derives from the gravitational influence exerted on the motions of stars and galaxies as well as the bending of light. Meanwhile, finding the dark matter particle has been challenging due to its inertness. Despite this, we have a successful dark matter-based theory of structure formation in the universe. Although the theory has been validated from many independent lines of compelling evidence, there are a few gaps—a few observations that challenge the paradigm. At this juncture a comprehensive exploration of all possibilities is warranted, including those that radically question the current picture to help frame and refine alternatives. Alternatives to the dark matter model include modifications to Newtonian gravity; generalizations of Einstein’s theory of general relativity; and extensions to the standard model of particle physics that open up an entirely new window—the dark sector—for the putative dark matter particle. In this workshop we plan to discuss the status of the current cold dark matter picture and the WIMP paradigm; devising and assessing alternative models with axions and sterile neutrinos, and theories; and debating whether and where a radical rethinking is likely to take us and how we might be able to test and verify such alternatives with new experiments. Taking stock of the experimental and observational status of dark matter searches, we will address some hard questions about current approaches:

  1. At what sensitivity do nuclear recoil experiments begin to lose the luster? How do expected accelerator and astrophysical results bear on this question? How far should we push before the WIMP model is no longer tenable?
  2. What is the right combination of axion and sterile neutrino experiments to more fully probe these candidates? What is parameter space for viable searches for these candidates?
  3. Are primordial black holes of any mass excluded as the dominant component of dark matter? How and when can such black holes form in the early universe and grow without jeopardizing the ionization history of the universe?
  4. What can gravitational waves tell us if anything about the nature of dark matter?
  5. What is the right combination of observations and astrophysical data that would be needed to probe new ideas beyond LambdaCDM?
  6. What role can simulations play in helping discriminate between alternate dark matter models? And what kinds of new numerical techniques and approaches would be required to do so?

 We intend to hold a unique inter-disciplinary exploration that consolidates the current status and outlines a vision for future work in terms of experimental, theoretical and numerical approaches.

June 2 - June 23
The Turbulent Life of Cosmic Baryons

Marcus Brüggen, University of Hamburg
**Eliot Quataert, University of California Berkeley
*Evan Scannapieco, Arizona State University
**Ellen G. Zweibel, University of Wisconsin Madison

Turbulence is ubiquitous within and around galaxies, as gravitational instabilities, supernovae, and feedback from active galactic nuclei drive supersonic, high-Reynolds number flows, often threaded by strong magnetic fields. Recent high-resolution, UV, optical, infrared, and radio observations and innovative numerical simulations are opening up a new window into the complex evolution of diffuse material over cosmic time.  The program will take advantage of these advances, bringing together experts in theory, computation, and observation to achieve a better understanding of the life cycle of cosmic baryons, and the crucial role that turbulence plays on sub-galactic, galactic, and intergalactic scales.
Among the specific topics to be discussed are:
  • The role of turbulence in the formation history of galaxy disks and bulges 

  • The impact of turbulence in rapidly star-forming galaxies and its connection to the 
driving of galaxy outflows
  • The physics of turbulent mixing in the interstellar and intergalactic media 

  • The role of hydrodynamic and plasma instabilities in galaxies and galaxy clusters
  • The physics of turbulent dissipation in multi-phase astrophysical media from hot and 
diffuse to cold and dense 
  • Observational constraints of turbulence in the intracluster and circumgalactic media 

  • The role of turbulence in particle acceleration and magnetic field amplification

June 9 - June 30
Active and Driven Matter: Connecting Quantum and Classical Systems

Aparna Baskaran, Brandeis University
*Silke Henkes, University of Bristol
Jonathan Keeling, University of St. Andrews
Aditi Mitra, New York University

This program aims to establish and explore the connections between two fields: Active matter and driven quantum matter. Active matter studies how the paradigms of statistical physics and hydrodynamics are modified by the introduction of active elements that consume energy and do work. Driven quantum matter refers to quantum systems with external drives such as optical, THz, or microwave radiation. Both fields are focused around the fundamental question of how sources and sinks of energy modify the collective behavior, i.e. the statistical physics, of many coupled elements.  The aim of this meeting is to develop connections between these fields, in terms of methods, paradigms of understanding driven behavior, and classes of problems that can be addressed. In particular, we have identified three themes that provide clear links between the two fields:

  1. Periodic driving and non-equilibrium steady states
  2. Effective theories and emergent Hamiltonian methods
  3. Topological phenomena

June 16 - July 7
Moiré Materials: Strong Correlations in Synthetic Superlattices 

Michael Zaletel, Princeton University
**Eva Andrei, Rutgers University
Leonid Levitov, MIT
*Andrea Young, University of California Santa Barbara

Recent advances in the fabrication of two-dimensional heterostructures have opened up a new approach to engineering strongly interacting quantum matter. By sandwiching together layers of different honeycomb materials such as graphene, we can now design a panoply of two-dimensional materials, all while preserving pristine device quality. When the neighboring layers have a small lattice mismatch, long-wavelength beating between them leads to the formation of tunable “moiré superlattices” in which interactions can dominate over bandwidth. Recently there has been a trio of dramatic experimental discoveries in such systems: fractional quantum Hall effects, Mott insulators, and superconductivity. This program will bring together the theorists and experimentalists working to understand these rapid experimental developments, as well as brainstorm the new ways in which moiré materials might be used to understand long-standing problems in strongly correlated quantum matter.

June 23 - July 14
Quantum Spin Liquids

Senthil Todadri, MIT
*Young Lee, Stanford University
Chandra Varma, New York University

Quantum spin liquids are phases of magnetic matter  characterized by long range quantum mechanical entanglement between the local moments. This underlies a number of novel phenomena these states of matter are thought to display: these include excitations with fractional quantum numbers/statistics, emergence of gauge fields, etc. In the last 15 years or so a number of experimental systems have been studied as potential realizations of the quantum spin liquid.  The present period is an exciting one with many surprising experimental discoveries which are then spurring theory development. We encourage condensed matter experimentalists and theorists broadly interested in quantum many body physics to apply.

July 7 - July 28
Information Processing in Single Cells

Edo Kussell, New York University
Hanna Salman, University of Pittsburgh
*Lydia Robert, CNRS & Sorbonne University
Marco Cosentino-Lagomarsino, CNRS & Sorbonne University

Biological systems consist of collections of cells that work together to extract energy from their environments, to survive in stressful conditions, and ultimately to reproduce or replicate their basic structures. Complex cellular processes underlie the integration of signals from the environment with the ability of cells to rapidly respond to changes. Over the last decade, it has become possible, in diverse systems from bacteria to human cells, to study the variability in the genetic programs at the single cell level. This has opened the door to a range of new questions on how single cells process information, and has led to new conceptual developments. These include understanding the role of memory in regulating genetic networks that respond to stress, the role of heterogeneity in chemotaxis and cellular motility, and the relationship between cell size regulation, cell cycle progression, and population growth. New insights are also emerging into the rich behaviors exhibited by single cells under fluctuating conditions, where information processing capacity is intimately related to long-term survival. The workshop will focus on common themes in information processing across a wide range of biological systems, to enable new theoretical and quantitative formulations of biology at the single cell level. These focal themes are:

  • Memory and Stochasticity in Information Processing
  • Survival Under Stress
  • Cell Growth, Cell-Cycle Progression, and Cell Division

July 14 - August 4
Realizations and Applications of Quantum Coherence in Non-Equlibrium Systems

Norman Yao, University of California Berkeley
Felix von Oppen, Freie University Berlin
*Chris Laumann, Boston University
Gil Refael, Caltech

The control of complex, open quantum systems and the development of next-generation quantum measuring devices forms one of the central challenges at the interface between AMO physics, condensed matter, and quantum information. Progress here is expected to revolutionize computing, allow novel and secure multiparty communication protocols, and usher vast improvements in the performance of sensors.  Surprisingly, recent insights have demonstrated that the stabilization of such quantum systems can rise out of their own complexity, originating for example from: external driving, engineered dissipation, or intrinsic disorder. The goal of this workshop will be to survey experimental developments of relevance to non-equilibrium, many-body quantum phases as well as recent theoretical progress with the purpose of identifying fruitful future areas for exploration. Focal themes include:

  • Periodically Driven (Floquet) Quantum Systems
  • Quantum simulation in cold atomic systems
  • Non-Abelian topological phases
  • Quantum enhanced metrology
  • Disordered systems

July 28 - August 18
Generalized Symmetries, Anomalies, and Observables

Dan Freed, University of Texas Austin
David Ben-Zvi, University of Texas Austin
Anton Kapustin, Caltech
**Zohar Komargodski, Institute for Advanced Study

Higher symmetries appear in many situations in high energy and condensed matter theory.  They act on non-local excitations and, like ordinary symmetries, they may be spontaneously broken, softly broken, may have 't~Hooft anomalies, and can be coupled to background (higher) gauge fields. Higher symmetries have applications to phases of quantum field theories, to bosonization in higher dimensions, and to formulations of the hydrodynamic theory of strongly interacting plasmas, among others.  The workshop will cover not only groups, but also algebras of higher symmetries. Their structure can be expressed using the emerging theory of factorization algebras, which play an important role in some mathematical approaches to field theory.  Examples include vertex algebras, which have recently re-emerged in a prominent role in supersymmetric gauge theory.  We encourage high energy theorists, condensed matter theorists, and mathematicians interested in this area to apply.

August 4 - August 25
Scattering Amplitudes and the Conformal Bootstrap

Henriette Elvang, Univeristy of Michigan
*David Simmons-Duffin, Caltech
David Poland, Yale University
Jacob Bourjaily, Niels Bohr Institute

The focus of the program will be on new approaches to quantum field theory, with a particular emphasis on two highly active areas: the bootstrap approach to conformal field theories (CFTs) and modern on-shell methods for scattering amplitudes. The two fields are conceptually related, sharing both mathematical tools and a philosophical outlook focusing on physical observables, and we expect fruitful results to follow from bringing experts from both camps together in Aspen for an extended period. The organizers plan to encourage communication between participants from the two main areas by requiring talks to be aimed at the audience from the other field and having presentations focused on explaining potential overlaps in interests.

August 11 - September 15
The Energy Frontier Beyond LHC Run 2

*Anson Hook, University of Maryland
Zhen Liu, Fermilab
Benjamin Nachman, Lawrence Berkeley National Laboratory
Jessie Shelton, University of Illinois Urbana-Champaign

The picture of the electroweak scale that is emerging from the enormously successful experimental program at the Large Hadron Collider (LHC) is becoming ever more clear, yet remains deeply puzzling. The long shutdown period following the close of LHC Run 2 in 2018 will be a critical opportunity to reflect on the lessons learned and opportunities available for the future.  The full statistical power of the Run 2 dataset will be valuable for informing the development of many new directions, including machine learning, long-lived particle searches, and the design of custom detectors. Meanwhile, the high-energy physics community has also been revisiting and reimagining common motivations for physics beyond the SM.  Developing new approaches to the hierarchy problem, to dark matter, and establishing the resulting implications for the search program at the LHC will be cornerstones of this program.  To aid in the development of a new understanding of naturalness and map out the long journey at the energy frontier, this workshop will gather both theorists and experimentalists to crystallize and explore these new ideas.

August 18 - September 15
Astrophysics in the LIGO/Virgo Era

Brad Cenko, NASA Goddard Space Flight Center
Ryan Foley, University of California Santa Cruz
*Enrico Ramirez-Ruiz, University of California Santa Cruz
Vicky Kalogera, Northwestern University

The direct detection of gravitational waves by the Laser Interferometric Gravitational-Wave Observatory (LIGO) and the European Virgo detector has opened an entirely new window to study the Universe.  LIGO and Virgo have uncovered an entirely new population of binary black holes with masses up to 30 times that of our Sun, and the origin of these systems remains hotly debated.  The first discovery of the merger of two neutron stars in August 2017 was a watershed event for astrophysics, with associated emission detected across the entire electromagnetic spectrum.  From just this single binary neutron star merger we have placed some of the tightest constraints on the equation of state of dense material to date, and have determined that such systems appear to be the dominant source of heavy “r-process” elements in the Universe.  Our objective with this workshop is to bring together astronomers and physicists across a diverse range of topics to address some of the most exciting astrophysical questions that have been raised by these gravitational wave discoveries, including: What is the origin of the binary black hole systems discovered by LIGO and Virgo? What constraints on the neutron star equation of state can be derived from joint gravitational wave and electromagnetic observations? Are neutron star mergers indeed the dominant source of heavy (r-process) elements in the Universe?  The workshop will take place in the middle of the O3 observing run, and so should be a timely opportunity to discuss these topics (and more).

August 25 - September 15
Non-Standard Cosmology Probes

*Bozena Czerny, Center for Theoretical Physics, Warsaw, Poland
Guido Risaliti, University of Florence
**Tomasso Treu, University of California Los Angeles

The accelerated expansion of the Universe is a topic of great interest to both the physical and astronomical communities. To settle the issue whether new physics is   required, we need precise and reliable measurements of cosmological parameters. In this era of precision cosmology, the issue of systematic errors will ultimately limit our progress in understanding the nature of dark energy. Assessment of systematic errors in any given method is difficult, and therefore new cosmology tools are needed as a way to provide independent cross-checks. We aim at organizing a brain storm meeting of scientists developing various methods based on gravitational waves, active galactic nuclei, gamma-ray bursts, galaxy clusters imaged in mm and X-ray band, and strong gravitational lensing. The workshop will be used to perform two apparently contradictory tasks:
  1. assignment of the relative importance of all new tools in the timescale of the next ten years
  2. collaboration of researchers coming from different fields in establishing a reliable and consistent astro-statistical approach.