### Past Events

### Conformal Bootstrap lecture series

2018-07-17Conformal bootstrap lecture series organized by Aryeh Fortinsky

### Conformal Bootstrap lecture series

2018-07-16Conformal bootstrap lecture series organized by Aryeh Fortinsky.

### [Lecture] "Massless higher spins and cosmology" by Prof. Ergin Sezgin

2018-07-01We present a Freedman-Robertson-Walker solution of higher spin theory in four dimesions. It is obtained by employing a holomorphic factorization in noncommutative twistor space and gauge functions. We interpret the FRW solution in the context of inflationary cosmology. In interpreting the solution in terms of Fronsdal-type fields in spacetime, a field-dependent higher spin transformation is required, which is implemented at leading order. We also observe that the factorization method provides a convenient framework for setting up a perturbation theory around the exact solutions, and we propose that the nonlinear completion of particle excitations over FRW requires black hole-like states.

### [Lecture] "Self-Duality and Chiral Higher Spin Theories" by Dr. Dmitry Ponomarev

2018-07-01In this talk I will review recent results revealing the connection between chiral higher spin theories and self-duality as well as discuss consequences of this connection.

### [Lecture] "Soft hair on black hole and cosmological horizons in any dimension" by Prof. Daniel Grumiller

2018-07-01Starting from a generic near horizon expansion in any spacetime dimension greater than two we derive all near horizon symmetries and discover a wealth of novel results: 1. Any non-extremal horizon has an infinite set of near horizon symmetries and associated soft hair excitations. 2. The near horizon symmetries can be represented as generalization of the Bondi-Metzner-Sachs algebra. 3. For horizons that are either flat or non-rotating the near horizon symmetries can be represented as Heisenberg algebras, with one quarter of the inverse of Newton's constant playing the role of Planck's constant. 4. Not only black holes, but also cosmological horizons are equipped with soft hair. We discuss implications of soft hair for horizon thermodynamics and entropy, and comment on open problems and further developments, including possible applications to higher spin theories.

### [Lecture] "Supersymmetry and de Sitter Holography" by Gerben Venken

2018-06-30There is a no-go theorem stating that de Sitter space cannot be supersymmetric, unless the theory violates unitarity. The nonunitary can manifest itself for instance by the presence of ghost fields. We point out that Vasiliev higher spin gravity evades the assumptions of the no-go theorem and provide evidence that dS space can be consistently supersymmetrized. This relates to the fact that the supersymmetric AdS-Vasiliev/U(N) model duality can be consistently Wickrotated into a supersymmetric dS-Vasiliev/U(-N) duality, providing a concrete supersymmetric dS/CFT duality. Using dS/CFT, we compute the dS Hartle-Hawking wavefunction for a range of deformations. We show that the wavefunction is peaked at undeformed dS space and large deformations are supressed, indicating an absence of ghosts. We speculate on the possibility of a stringy interpetation of dS/CFT in terms of exotic string theories. Based in part on [1709.06024] JHEP 02 (2018) 024.

### [Lecture] "Tensionless String Spectra in AdS_3" by Prof. Rajesh Gopakumar

2018-06-30We examine the spectrum of superstrings on backgrounds of the form AdS_3\times S^3\times M at their minimal radius (or tensionless limit). We focus on a very natural subsector which consists of states at the bottom of the so-called spectrally flowed continuous representations. We find that this entire subsector matches precisely with that of a symmetric product CFT. This can be viewed as a signature of an unbroken Higher Spin Square (HSS) symmetry at this point. This HSS symmetry had previously appeared at a very different tensionless point in the parameter space of the string theory on AdS_3.

### [Seminar] "Gravity and differential forms" by Prof. Kirill Krasnov

2018-06-19Speaker: Prof. Kirill Krasnov, University of Nottingham

Date : Tuesday, June 19, 2018

Time : 3:00pm-4:00pm

### [Seminar] "New triangulation of the Amplituhedron from sign flip" by Ryota Kojima

2018-06-05Speaker: Ryota Kojima, KEK, Japan

Date : Tuesday, June 5, 2018

Time : 3:00pm-4:00pm

### [Seminar] "Black holes in loop quantum gravity: Emergence of non-singular quantum space-time" by Dr. Suddhasattwa Brahma

2018-06-01Speaker: Dr. Suddhasattwa Brahma, APCTP, Korea

Date : Friday, June 1, 2018

Time : 4pm-5pm