School of Natural Sciences

Two Freaks and a Conundrum

David Jewitt
September 22, 2020
In the solar system as elsewhere, we learn most from the unexpected. I will describe three recent observational projects challenging existing ideas about solar system objects, and provoking new ones. The freaks are an interstellar object (‘Oumuamua) and a long-period comet (C/2017 K2), active far beyond Uranus. The conundrum concerns the origin of the Trojans of Neptune in the context of planetary migration.

Light-rays and detectors in Wilson-Fisher theory

Petr Kravchuk
Member, School of Natural Sciences, IAS
September 18, 2020
In conformal field theory, in contrast to gapped theories, S-matrix is not well-defined. Similarly, various inclusive observables which make sense in a gapped theory, such as "energy squared" calorimeters, suffer from IR divergences in CFTs. Using the example of Wilson-Fisher theory, I will discuss how these observables can be renormalized and what is the physical meaning of their anomalous dimensions.

Turbulent power-law spectra in the universe

Siyao Xu
September 17, 2020
Turbulence is ubiquitous in astrophysical media and plays an essential role in a variety of fundamental astrophysical processes. The turbulent power-law spectra have been observed in the solar wind, the interstellar medium, the intracluster medium, over a vast range of length scales. In our Galaxy, I will discuss pulsars as a unique tool for statistically studying the turbulence in the multi-phase interstellar medium over different ranges of length scales.

Simulating Multiscale Astrophysics to Understand Galaxy formation

Rachel Somerville
Rutgers University; Flatiron Institute
September 15, 2020
Building genuinely a priori models of galaxy formation in a cosmological context is one of the grand challenges of modern astrophysics. Most large volume simulations of galaxy formation currently adopt phenomenological scaling relations to model "small scale" processes such as star formation, stellar feedback, and black hole formation, growth, and feedback, which limits their predictive power.

Physics and Astrophysics With Gravitational-Wave Observations of Black Hole Binaries

Emanuele Berti
Johns Hopkins University
September 10, 2020
The observation of compact binary mergers by the LIGO/Virgo collaboration marked the dawn of a new era in astronomy. LISA will expand this vision by opening a new observational window at low frequencies. The gravitational radiation emitted by compact binary systems in these two frequency windows encodes important information on their astrophysical formation mechanism. Furthermore, compact objects - whether in isolation or in binaries - are excellent astrophysical laboratories to probe our understanding of high-energy physics and strong-field gravity.

Near Field Star Formation: Surveying Young Stellar Objects and Young Stellar Clusters within 1 kpc of the Sun

Tom Megeath
University of Toledo
September 8, 2020
Surveys of young stellar objects (YSOs) populating nearby molecular clouds are bringing us closer to an integrated picture of star and cluster formation, one that incorporates processes spanning many orders of magnitude in size, from accretion on stellar scales to the formation of clusters and associations on molecular cloud scales. Following a spectacular 15 years of infrared astronomy with Spitzer and Herschel, we now have a nearly compete census of the dusty YSOs (those with disks or infalling envelopes) in the clouds within 500 pc of the Sun.

Partition functions of the tensionless string

Lorenz Eberhardt
Member, School of Natural Sciences, Institute for Advanced Study
August 28, 2020
I discuss string theory on AdS3xS3xT4 in the tensionless limit, with one unit of NS-NS flux. This theory is conjectured to be dual to the symmetric product orbifold CFT. I show how to compute the full string partition function on various locally AdS3 backgrounds, such as thermal AdS3, the BTZ black and conical defects, and find that it is independent of the actual background, but only depends on the boundary geometry.

An update on exact WKB and supersymmetric field theory

Andy Neitzke
Yale University
August 24, 2020
Over the last decade it has become clear that there is a close connection between the BPS sector of N=2 supersymmetric field theories in four dimensions and the exact WKB method for analysis of ordinary differential equations (Schrodinger equations and their higher-order analogues). I will review the basic players in this story and some of the main results, and describe some outstanding puzzles.

Enhanced Corrections to the Page Curve near Holographic Entanglement Transitions

Xi Dong
University of California, Santa Barbara
August 17, 2020
I will present enhanced corrections to the entanglement entropy of a subsystem in holographic states. These corrections appear near phase transitions in the entanglement entropy due to competing extremal surfaces, and they are holographic avatars of similar corrections previously found in chaotic energy eigenstates. I will first show explicitly how to find these corrections in chaotic eigenstates by summing over contributions of all bulk saddle point solutions, including those that break the replica symmetry, and by making use of fixed-area states.