2019-9-12

Speaker: 李理 Li Li (中科院理论所)

Title: Intertwined orders in holography: Pair and Charge Density Waves

Abstract: We construct spatially modulated black holes where a U(1) symmetry and translational invariance are broken spontaneously at the same time.  Our construction provides an example of a system with pair density wave order, in which the superconducting order parameter is spatially modulated but has a zero average. In addition, the charge density oscillates at twice the frequency of the scalar condensate. Depending on the choice of parameters, it also admits a state with coexisting superconducting and charge density wave orders, in which the scalar condensate has a uniform component. The transport behavior and fermionic response are considered in our holographic setup.

2019-9-5

Speaker: Kazunobu Maruyoshi (Sekei University)

Title: Deformations of 4d SCFTs and Supersymmetry Enhancing RG Flows

Abstract: We study remarkable RG flows in 4d QFT where supersymmetry enhances from N=1 to N=2 in the IR. This is triggered by the N=1 preserving deformation of 4d N=2 SCFTs with non-Abelian flavor symmetry by adding a chiral multiplet in the adjoint representation of the flavor symmetry and giving a nilpotent vev to the chiral multiplet. When the original N=2 SCFT and choice of the vev satisfy certain conditions, the resulting RG flows give N=2 Argyres-Douglas theories in the IR. These flows thus enable us to compute partition functions of Argyres-Douglas theories via localization. We also consider the more general and systematic deformation procedure which is applicable to any N=1 SCFTs and thus includes the above nilpotent one. Starting from N=1 SCFTs we allow all possible relevant deformations and/or coupling to a free chiral sector. We apply this to simple N=1 SCFTs and discuss the landscape of the IR fixed points, focusing on the enhancement of supersymmetry.

-------------------------------History-------------------------------

2019-8-15

Speaker: Philsang Yoo(Yale)

Title: Twisted S-duality

Abstract: IS-duality is a fundamental duality identifying physical theories in the context of quantum field theory and string theory. Its mathematical incarnations also have been of interest to many subjects including geometric Langlands program. Based on a conjectural description of twisted supergravity theories due to Costello and Li, we suggest a definition of a twisted version of S-duality. From this, we derive some consequences on 4-dimensional supersymmetric gauge theory and hint at some generalization of geometric Langlands theory.

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.