## AdS(Algeometry, duality and Strings) seminar

## 报告人简介

**2019-6-6**

**Speaker:** Sung-Soo Kim (UESTC)

**Title: **New developments in 5d SCFTs and 5-brane webs

**Abstract:** In this talk, we will first review 5d superconformal theories
(SCFTs) and its salient features. As geometric engineering, we then discuss how
one can construct 5d SCFTs from Type II string theory or M-theory. We finally
report recent developments in 5-brane web in Type II string theory including
constructions of spinor representations and rank-3 antisymmetric
hypermultiplets and their connection to 6d SCFTs.

** **

**2019-5-30**

**Speaker:** Bartek Czech (IASTU)

**Title: **Holographic Entropy Cone with Time Dependence

**Abstract:** In the AdS/CFT correspondence, if a CFT state is dual to a
semiclassical spacetime, its entanglement entropies (minimal surface areas)
must obey certain inequalities. The best-known examples are the strong
subadditivity of entanglement entropy (SSA) and the monogamy of mutual
information (MMI). Together, such inequalities define the so-called holographic
entropy cone. It is an interesting object because (a) it quantifies what is
special about holography--how holographic CFTs are different from general
quantum mechanical systems, and (b) it highlights special entanglement structures
(bipartite, perfect tensor), which are the atomic ingredients for building up
holographic spacetimes.

The holographic entropy cone is known for static states, but it is not known for time-dependent states. Is it possible to use time dependence to construct more general bulk spacetimes, which violate conditions that hold in static geometries? I will show that this does not happen in the AdS3/CFT2 correspondence. The argument has many interesting aspects: (a) it completely dispenses with any notion of a bulk slice, (b) it operates directly in kinematic space (space of CFT intervals), (c) it reduces to repeated applications of the strong subadditivity of entanglement entropy. I hope we will discuss the significance of these facts together.

** **

**2019-5-23**

**Speaker:** Dandan Xu (IASTU)

**Title: **Legend of Sealed Book

**Abstract:** In this talk, I will review a brief history of cosmology
studies since the beginning of last century, in particular how the current
cosmological picture is reached, its success and drawbacks. In particular, I
will talk about a powerful astronomical tool named gravitational lensing, using
which various theories on cosmology and galaxy formation can be tested and
constrained.

** **

**2019-5-16**

**Speaker:** Dongmin Gang (KIAS)

**Title: **Magnetically charged Ads4 (Ads5) black hole from
class R (class S) theories

**Abstract:** I will talk about twisted index computation of 3d theory of class R
associated hyperbolic 3-manifold M. Using 3d-3d relation, the index is given in
terms of simple 3-manifold invariant, analytic torsion. From the expression, we
found 1) a curious integral properties of analytic torsion at finite N, 2) full
perturbative 1/N corrections at large N. The leading and log N subleading
nicely match the supergravity computation and other perturbative terms give
predictions on holographic dual gravity computation. I briefly comment on
similar story for 4d class R theory on S1xM.

** **

**2019-5-9**

**Speaker:** Babak Haghighat (YMSC)

**Title: **M5 branes and theta functions

**Abstract:** We propose quantum states for Little String Theories (LSTs) arising
from M5 branes probing A- and D-type singularities. This extends Witten's
picture of M5 brane partition functions as theta functions to this more general
setup. Compactifying the world-volume of the five-branes on a two-torus, we
find that the corresponding theta functions are sections of line bundles over
complex 4-tori. This formalism allows us to derive Seiberg-Witten curves for
the resulting four-dimensional theories. Along the way, we prove a duality for
LSTs observed by Iqbal, Hohenegger and Rey.

** **

**2019-4-25**

**Speaker:** Marcus Sperling (YMSC)

**Title: **From discrete quotients of Coulomb branches to
magnetic quivers

**Abstract:** Coulomb branches of 3-dimensional N=4 gauge theories are
hyper-Kähler singularities with non-trivial quantum corrections; in contrast to
Higgs branches of theories with 8 supercharges. The monopole formula, defined
as Hilbert series of the Coulomb branch chiral ring, provides one approach to
study these moduli spaces. Remarkably, Coulomb branches have been used recently
to describe Higgs branches of 5d and 6d theories with 8 supercharges at
infinite gauge coupling, where no classical Higgs branch description is
applicable. After a brief reminder of the set-up, I discuss discrete quotients
of 3d N=4 Coulomb branches and prove equalities of Hilbert series for a number
of different cases. Among others, the results prove a recent 'discrete gauging'
conjecture on Higgs branches of certain 6-dimensional N=(0,1) theories. In the second
half, I focus on Higgs branches of 6d N=(1,0) theories associated to the
physics of M5 branes placed near an M9 plane on an A-type ALE singularity.
There are tensionless strings whenever two M5 branes coincide or whenever an M5
brane approaches the M9 plane. Previous works suggest the conjecture that a new
Higgs branch arises whenever a BPS-string becomes tensionless. Previewing joint
work with Santiago Cabrera and Amihay Hanany, a formalism is proposed that
allows to derive a novel object from a brane configuration, called the
'magnetic quiver'. The main features are (i) the 3d Coulomb branch of the
magnetic quiver yields the Higgs branch of the 6d system, (ii) all 'discrete
gauging' and 'small E8 instanton transitions' have an explicit brane realisation,
and (iii) exceptional symmetries arise directly from brane configurations.

** **

**2019-4-18**

**Speaker:** Alejandra Castro (University of Amsterdam)

**Title: **New aspects of nAdS2/nCFT1 correspondence

**Abstract:** The linchpin of nAdS2/nCFT1 is the non-linear realisation of
symmetries, where the conformal symmetry of AdS2 is spontaneously broken and
also broken by an anomaly. In this talk I'll discuss aspects of this
correspondence that are relevant for the holographic description of
near-extremal rotating black holes. And if time allows, I will discuss the role
of gravitational anomalies in nAdS2 holography.

** **

**2019-4-11**

**Speaker:** Joonho Kim (KIAS)

**Title: **Cardy Formula of 4d N=1 SCFT

**Abstract: **We study the asymptotic behavior of the modiﬁed superconformal index in 4d N=1 gauge theory. This index has the
same amount of information as the conventional one, and only differs by an
extra phase factor dressing each short multiplet’s contribution. The high
‘temperature' limit of this index can be written in terms of the conformal
anomalies, (3c-2a). We ﬁnd that the entropy from our asymptotic
free energy is always positive for interacting SCFTs. Especially for the
holographic SCFTs dual to AdS_5 × Y^{p,p}, the entropy from the index accounts
for the Bekenstein-Hawking entropy of large BPS black holes.

** **

**2019-4-4**

**Speaker:** Xuening Bai (IAS, Tsinghua University)

**Title: **Cosmic-ray Streaming Instability: Introduction and
ab initio Simulations

**Abstract: **The interstellar medium in the Galaxy is filled
with gas, magnetic fields, and cosmic-rays (CRs). Being relativistic particles,
the CRs naturally tends to escape from thee Galaxy. Howeveer, CRs streaming
along magnetic fields are subject to the cosmic-ray (CR) streaming instability,
which is gyro-resonant in nature and occurs when the bulk CR streaming speed
exceeds the Alfven velocity of background gas. It is believed to play a crucial
role in CR transport, leading to growth of Alfven waves at small scales that
scatter CRs, and impacts the interaction of CRs with the interstellar medium on
large scales. Employing our recently developed
magnetohydrodynamic-particle-in-cell (MHD-PIC) method, we conduct the first
simulations that quantitatively demonstrate the growth and saturation of the
instability. By implementing the delta-f method, we are able to accurately
capture wave growth over a broad spectrum, and accurately follow the subsequent
quasi-linear diffusion. Full isotropization of the CRs in the wave frame
requires pitch angles of most CRs to efficiently cross 90deg, which is achieved
by non-linear wave-particle interaction. We anticipate our methodology will
open up opportunities for future investigations that incorporate additional
physics.

** **

**2019-3-21**

**Speaker:** Junbao Wu (Tianjin University)

**Title: **Holographic Wilson Loops in AdS4/CFT3 Correspondence
Revisited

**Abstract: **The duality between bosonic 1/2-BPS Wilson loops
and probe M2-branes in dual M-theories were proposed in Farquet and Sparks in
2013. Though passed some checks, we found this duality should be reconsidered.
The reason is that we found fermionic BPS Wilson loops in such theories
including ones coupled with all nodes and the arrows in the quiver diagrams.
The precise duality between fermionic BPS Wilson loops and probe M2-branes are
found for N=2 orbifold ABJM theory. The duality in more general theories are to
be studied. This talk is based on joint work done with A. Mauri, H. Ouyang, S.
Penati and J.-j. Zhang.

**2019-3-7 **

**Speaker: **Song He, ITP

**Title: **ABCD of causal diamonds, cluster associahedra and
scattering amplitudes

**Abstract:** Recently it has been realized that scattering amplitudes in various
theories can be viewed as "volume" of certain polytopes that live in
kinematic space, which can make properties/symmetries of amplitudes manifest. I
will introduce perhaps the simplest class of such polytopes, namely generalized
associahedra for finite-type cluster algebra. It is remarkable even
combinatorially trivalent scalar Feynman diagrams at tree and one-loop level
form polytopes of type A, B/C and D, and our realizations of the latter in
kinematic space provide new representation for these scalar amplitudes. As a
byproduct, such realizations are naturally related to causal diamonds and
positive solutions of wave equations in 1+1 D, which can be viewed as the
continuum limit of our associahedra. (Based on part I of series of works in
progress with Arkani-Hamed et al, which aim to provide a combinatorial origin
for scattering of particles and strings and connect them with positive
geometries, cluster algebra, periods etc.)

**2019-2-28**

**Speaker:** Dan Xie, Tsinghua University

**Title: **W algebra and four dimensional N=2 Argyres-Douglas
theory

**Abstract:** One can associate a two dimensional vertex operator algebra (VOA)
to a four dimensional N=2 SCFT. In this talk, I will discuss the associated VOA
for 4d N=2 SCFTs engineered using 6d (2,0) theory, and the result is a class of
W algebras which has been intensively studied by physicists and mathematicians
in the past few years. Various interesting results of 4d theory and 2d theory
will be discussed. This is a joint work with Wenbin Yan.