30th Nordic Network Meeting on "Strings, Fields, and Branes"

room 4204 (Nordita, Stockholm)

room 4204

Nordita, Stockholm

Agnese Bissi (Uppsala University), Henrik Johansson (Uppsala University and Nordita), Marco Chiodaroli (Uppsala University), Paolo Di Vecchia (Nordita)


Nordita, Stockholm, Sweden


The 30th Nordic Network Meeting on ''Strings, Fields and Branes'' will be held 22-24 November 2021 and hosted by Nordita, which is located near the AlbaNova University Center in Stockholm. The meeting will start on Monday the 22nd at 13.00 and end on Wednesday the 24th at around 13.00. The lectures and talks will be in the new Nordita building, lecture room 4204 (4th floor). The new Nordita building is located north of the AlbaNova building (towards the lake).


The program will consist of lectures by invited plenary speakers, and short talks by students and young researchers who wish to contribute. The lectures include

  • Fridrik Freyr Gautason (Iceland U.): From Janus interfaces to holographic conformal manifolds
  • Charlotte Kristjansen (NBI): Defects & D-branes as Integrable Boundary states
  • Eirik Eik Svanes (Stavanger U.) :  Moduli and topological field theories: A heterotic case study


For participants that wish to apply for the opportunity to give a short talk, or that need accommodation, the deadline is 1 November, 2021Added note: the registration for in-person participation closed on 15 November, 2021.  Non-registered participation is available through Zoom.

Zoom Coordinates

The meeting can be attended through Zoom via the following link.

Meeting ID: 696 2266 4454

Accommodation and Financial Support

Accommodation (for two nights) will be available free of charge for Nordic and Baltic participants that apply before the deadline 1 November, 2021. Travel expenses can unfortunately not be covered by Nordita.

Lunch and Dinner

Lunch will be provided on Tuesday and Wednesday, and a workshop dinner will be organized on Tuesday evening.  


Local organizing committee: Agnese Bissi, Marco Chiodaroli, Paolo Di Vecchia, and Henrik Johansson

Sponsored by

  • Agnese Bissi
  • Alessandro Georgoudis
  • Alex Edison
  • Alexander Söderberg
  • Andres Luna
  • Anne Spiering
  • Azeem Hasan
  • Bram Verbeek
  • Charles Thull
  • Charlotte Kristjansen
  • Daniel Panizo
  • Dinh-Long VU
  • Dongsheng Ge
  • Edoardo Vescovi
  • Eirik Eik Svanes
  • Filippo Maria Balli
  • Florian Niedermann
  • Francesco Alessio
  • Fridrik Freyr Gautason
  • Gerben Oling
  • Giulia Fardelli
  • Henrik Johansson
  • Ingrid Vazquez-Holm
  • Jacopo Sisti
  • Javier Murgas
  • Javier Subils
  • Johannes Lahnsteiner
  • Jose Manuel Penin Ascariz
  • Juan S. Cruz
  • Kays Haddad
  • Konstantin Zarembo
  • Lorenzo Ruggeri
  • Lucia Maria Garozzo
  • Lucile Cangemi
  • Magdalena Larfors
  • Maor Ben-Shahar
  • Marco Chiodaroli
  • Martin Sloth
  • Matthew Magill
  • Max Guillen
  • Maxim Zabzine
  • Michele Del Zotto
  • Nicolò Piazzalunga
  • Niels Obers
  • Nils Matthes
  • Oscar Henriksson
  • Paolo Di Vecchia
  • Paolo Pichini
  • Rahul Poddar
  • Robin Marzucca
  • Rodolfo Panerai
  • Roman Mauch
  • Ronnie Rodgers
  • Salvatore Raucci
  • Simon Ekhammar
  • Sourav Sarkar
  • Usman Naseer
  • Victoria Martin
  • Watse Sybesma
  • Yong Zhang
  • Yuta Sekiguchi
  • Ziqi Yan
    • 12:55 PM 1:00 PM
      Welcome: Niels Obers (Director of Nordita) 5m
    • 1:00 PM 2:30 PM
      Moduli and topological field theories: A heterotic case study 1h 30m
      Speaker: Eirik Eik Svanes (Stavanger U.)
    • 2:30 PM 3:00 PM
      Break 30m
    • 3:00 PM 3:20 PM
      On Analytic Bootstrap for Interface and Boundary CFT 20m

      We use analytic bootstrap techniques for a CFT with an interface or a boundary (near four and six dimensions). Exploiting the analytic structure of the bulk and boundary conformal blocks we extract the CFT data. The method presented is general, and it is illustrated in the context of perturbative Wilson-Fisher theories.

      Speaker: Alexander Söderberg
    • 3:25 PM 3:45 PM
      Non-Lorentzian Supergravity in Ten Dimensions 20m

      In this talk, I describe recent progress in understanding the background field dynamics of the non-relativistic string theory pioneered by Gomis and Ooguri. Building on earlier developments, I present a non-Lorentzian supergravity theory and explain how it constrains the dynamics of the background fields. Special attention will be given to the exotic geometric structures that arise in this theory. I will compare the results with those coming from beta function calculations. In the final part of my talk, I will comment on non-Lorentzian T-duality and an intriguing relation with double field theory.

      Speaker: Johannes Lahnsteiner (Ph.D. Student)
    • 3:50 PM 4:10 PM
      Hidden Conformal Symmetries from Killing Tensors 20m

      I will discuss the recent paper 2110.10723, in which we generalize the notion of hidden conformal symmetry in Kerr/CFT to Kerr- (A)dS black holes in arbitrary dimensions. We build the SL(2,R) generators directly from the Killing tower, whose Killing tensors and Killing vectors enforce the separability of the equations of motion. Our construction amounts to an explicit relationship between hidden conformal symmetries and Killing tensors: we use the Killing tower to build a novel ten- sor equation connecting the SL(2,R) Casimir with the radial Klein-Gordon operator. For asymptotically flat black holes in four and five dimensions we recover previously known re- sults that were obtained using the “near-region” limit and the monodromy method. We then perform a monodromy evaluation of the Klein-Gordon scalar wave equation for all Kerr-(A)dS black holes, finding explicit forms for the zero mode symmetry generators. We also extend this analysis to the large-dimensional Schwarzschild black hole as a step towards buliding a Large-D/CFT correspondence.

      Speaker: Victoria Martin (University of Iceland)
    • 4:10 PM 4:40 PM
      Break 30m
    • 4:40 PM 5:00 PM
      Quarter-BPS operators in $\mathcal{N}=4$ SYM: a case study 20m

      In this work we start a systematic study of quarter-BPS operators in $\mathcal{N}=4$ SYM with gauge group SU($N$) at large $N$. In particular we consider $\mathcal{O}_{pq}$, operators transforming in the $[q,p,q]$ representation of the SU(4) R-symmetry: when expanded in $\mathcal{N}=2$ supermultiplets, they contain Schur operators making it possible to derive the Ward Identities through the chiral algebra. Our focus will be on the simplest non trivial example, namely the operator in the $[2,0,2]$ representation. In the planar limit this is a double trace operator and, because of that, its OPE analysis will give access to unexplored information on higher trace operators, whose knowledge is crucial to investigate $\mathcal{N}=4$ SYM away from the leading orders in the large $N$ expansion.
      I will discuss the results that we obtained in this context by means of modern analytic CFT techniques such as chiral algebra and Lorentzian inversion formula.

      Speaker: Giulia Fardelli (Uppsala University)
    • 5:05 PM 5:25 PM
      Bonuses from G2 structures 20m

      A $G_2$ structure on a manifold can be defined in terms of the existence of a covariantly constant spinor, so naturally arise in SUSY preserving string compactifications. Such manifolds always admit extra structures, tied to the existence of families of nowhere vanishing vector fields. I will introduce these structures and some of their properties, and indicate the relevance for physics.

      Speaker: Matthew Magill (Uppsala University)
    • 5:30 PM 5:50 PM
      Compton Black-Hole Scattering for s≤5/2 20m

      Quantum scattering amplitudes for massive matter have received new attention in connection to classical calculations relevant to gravitational-wave physics. Amplitude methods and insights are now employed for precision computations of observables needed for describing the gravitational dynamics of bound massive objects such as black holes. An important direction is the inclusion of spin effects needed to accurately describe rotating (Kerr) black holes. Higher-spin amplitudes introduced by Arkani-Hamed, Huang and Huang at three points have by now a firm connection to the effective description of Kerr black-hole physics. The corresponding Compton higher-spin amplitudes remain however an elusive open problem. Here we draw from results of the higher-spin literature and show that physical insights can be used to uniquely fix the Compton amplitudes up to spin 5/2, by imposing a constraint on a three-point higher-spin current that is a necessary condition for the existence of an underlying unitary theory. We give the unique effective Lagrangians up to spin 5/2, and show that they reproduce the previously-known amplitudes. For the multi-graviton amplitudes analogous to the Compton amplitude, no further corrections to our Lagrangians are expected, and hence such amplitudes are uniquely predicted. As an essential tool, we introduce a modified version of the massive spinor-helicity formalism which allows us to conveniently obtain higher-spin states, propagators and compact expressions for the amplitudes.

      Speaker: Paolo Pichini (Uppsala University)
    • 9:15 AM 10:45 AM
      Defects & D-branes as Integrable Boundary states 1h 30m
      Speaker: Charlotte Kristjansen (NBI)
    • 10:45 AM 11:15 AM
      Break 30m
    • 11:15 AM 11:35 AM
      The Price of Curiosity: Information Recovery in de Sitter Space 20m

      Is it possible for a static patch observer in de Sitter space to recover information that lies beyond their de Sitter horizon by collecting Gibbons-Hawking radiation? (How) will back-reaction interfere with their experiment? In this talk I will discuss insights regarding information recovery in de Sitter space obtained by utilizing the so-called island prescription, which has been used to shed new light on the information paradox for black holes utilizing quantum extremal surfaces. Effects of back-reaction are modeled by studying two-dimensional semi-classical models of de Sitter space. One finds that the observer’s curiosity comes at a price, which turns out to be essential for evading quantum cloning paradoxes. I will also discuss further implications such as a connection to de Sitter holography and scrambling times.

      Speaker: Watse Sybesma (University of Iceland)
    • 11:40 AM 12:00 PM
      SUSY enhancement on the squashed three-sphere 20m

      In this talk, I will discuss mass deformed $\mathcal{N}=2$ theories on the squashed three-sphere. By embedding all the background fields into an extended supergravity I show how fine-tuning the mass leads to an enhancement of the supersymmetry to $\mathcal{N}=4$. In the case where the 3d partition function is a limit of a 4d index only states annihilated by additional supercharges contribute to the 4d index at these specific mass points. The enhanced supersymmetry leads to simplifications of the localized partition function. Notably we can use it to explain the recently observed squashing independence of the free energy in mass deformed ABJ(M) theory. I will report on ongoing work on $\mathcal{N}=4$ dualities on the squashed three-sphere.

      Speaker: Charles Thull (Uppsala University)
    • 12:05 PM 12:25 PM
      Towards holographic integrable deformations of Warped CFTs 20m

      Integrable deformations of 2-dimensional quantum field theories include the $T\bar T$ and $J \bar T$ deformations. These deformations are well defined in any translationally invariant quantum field theory, including QFTs without Lorentz invariance, such as Warped CFTs. Warped CFTs have been shown to be holographically realized through so-called lower spin gravity. By adapting the deformed boundary conditions recently discussed in the context of holographic dual to $T\bar T$ and $J \bar T$ deformed CFTs to the warped geometry context, we investigate how a $T\bar T$ deformed Warped CFT affects a bulk geometry.

      Speaker: Rahul Poddar (University of Iceland)
    • 12:25 PM 2:30 PM
      Lunch 2h 5m
    • 2:30 PM 4:00 PM
      From Janus interfaces to holographic conformal manifolds 1h 30m
      Speaker: Fridrik Freyr Gautason (Iceland U.)
    • 4:00 PM 4:30 PM
      Break 30m
    • 4:30 PM 4:50 PM
      Gradient effects on false vacuum decay in gauge theory and general estimates 20m

      We study false vacuum decay for a gauged complex scalar field in a polynomial potential with nearly degenerate minima. Radiative corrections to the profile of the nucleated bubble as well as the full decay rate are computed in the planar thin-wall approximation using the effective action. This allows to account for the inhomogeneity of the bounce background and the radiative corrections in a self-consistent manner. In addition to the renormalization of the couplings, we employ a gradient expansion in order to systematically construct the counterterm for the wave-function renormalization. Further advances using these techniques are presented. The full decay rate however does not rely on such an expansion and accounts for all gradient corrections at the chosen truncation of the loop expansion. The ensuing gradient effects are shown to be of the same order of magnitude as nonderivative one-loop corrections.

      Speaker: Juan S. Cruz (SDU - CP3)
    • 4:55 PM 5:15 PM
      Color-kinematics duality for Chern-Simons theory 20m

      Many gauge theories possess a hidden duality between color and kinematics in
      their on-shell scattering amplitudes. An open problem is to formulate an off-shell realizationof the duality, thus manifesting a kinematic algebra. We show that 3D Chern-Simons (CS) theory in Lorenz gauge obeys off-shell color-kinematics duality. This holds both for the CS field and the BRST ghosts, and the duality is manifest in the Feynman rules. A kinematic algebra emerges through the second-order differential operator in the propagator-numerator, and it corresponds to the algebra of diffeomorphism of functions in the Lorenz gauge. We consider several admissible 3D off-shell double-copy constructions. While the double copy is in principle well formulated off shell, the scattering amplitudes vanish due to the topological nature of CS theory.

      To obtain non-vanishing amplitudes, we deform Chern-Simons theory by including adjoint matter, which we take to be maximally supersymmetric. This gives a formulation of a $N=4$ CS-matter theory, whose double-copy with itself corresponds to maximally supersymmetric $N=8$ Dirac-Born-Infeld theory.

      Speaker: Maor Ben-Shahar (Uppsala University)
    • 5:20 PM 5:40 PM
      Scattering amplitudes and algebraic geometry --- Elliptics and beyond 20m

      In this talk I will describe scattering amplitudes from the point of view of algebraic geometry. This leads to extra structure on the intervening amplitudes which is very useful in both theory and practice. The focus of this talk will lie on integrals related to elliptic curves, but time permitting I will also sketch what lies beyond.

      Speaker: Nils Matthes
    • 9:15 AM 9:35 AM
      Black brane evaporation through D-brane bubble nucleation 20m

      Gravitational solutions describing black branes in asymptotically anti-de Sitter spacetimes, holographically dual to field theory states at finite temperature and density, can exhibit an instability due to brane nucleation. This allows the black brane to evaporate by emitting D-branes. Working in the setting of D3-branes on the conifold, we construct static Euclidean solutions describing this nucleation to leading order, i.e. D3-branes bubbling off the horizon. Furthermore, we analyze the late-time dynamics of such a D3-brane bubble as it expands and find a steady-state solution including the wall profile and its speed.

      Speaker: Oscar Henriksson (University of Helsinki)
    • 9:40 AM 10:00 AM
      Novel Methods for Cuts and Integrands applied to Six Loops in $\mathcal{N}=4$ super-Yang-Mills 20m

      We construct the complete (planar and non-planar) integrand for the
      six-loop four-point amplitude in maximal $D\le10$ super-Yang-Mills.
      This construction employs new advances that combat the
      proliferation of loops and state-sums when evaluating
      multi-loop $D$-dimensional unitarity cuts. Concretely, we introduce
      two graph-based approaches, applicable in a range of theories, to
      evaluating generalized unitarity cuts in $D$ dimensions: 1)
      recursively from lower-loop cuts, or 2) directly from known
      higher-loop planar cuts. Neither method relies on explicit state
      sums or any sewing of tree-level amplitudes. The first method
      meshes particularly well with the Method of Maximal Cuts to allow
      direct construction of the complete six-loop integrand.

      Speaker: Alexander Edison (Uppsala University)
    • 10:05 AM 10:25 AM
      Risking your NEC 20m

      Energy conditions, especially the null energy condition (NEC), are generically imposed on solutions to retain a physically sensible classical field theory and they also play an important role in the AdS/CFT duality. Using this duality, we study non-trivially deformed strongly coupled quantum field theories at large-Nc. For this, we construct the corresponding dual classical gravity solutions, which entail the use of radially non-monotonic D-brane distributions. The distributions are phenomenological in the sense that they do not correspond to the smearing of known probe D-brane embeddings. These gravity backgrounds are supersymmetric and hence perturbatively stable, and do not possess curvature singularities. There are no short-cuts through the bulk spacetime for signal propagation which assures that the field theory duals are causal. Nevertheless, some of the constructed solutions violate the NEC in the gravity dual. In these cases the non-monotonicity of the D-brane distributions is reflected in the properties of the renormalization group flow: none of the c-functions proposed in the literature are monotonic. This further suggests that the non-monotonic behavior of the c-functions within previously known anisotropic backgrounds does not originate from the breaking of Lorentz invariance. We surmise that NEC violations induced by quantum corrections also need to be considered in holographic duals, but can be studied already at the classical level

      Speaker: Jose Manuel Penin (University of Helsinki)
    • 10:25 AM 10:55 AM
      Break 30m
    • 10:55 AM 11:15 AM
      Probing confinement in holography 20m

      I will present a family of solutions of Type IIA supergravity that holographically describe gauge theories with interesting IR dynamics. We will examine how this family interpolates between conformal and confining regimes and study the different physics that Wilson loops and entanglement entropies can probe in these theories. Finally, we will uncover a rich finite temperature phase diagram, endowed with a triple point, a critical point where a second order phase transition occurs and a branch of phase transitions occurring at finite temperature but vanishing entropy.

      Speaker: Javier Subils (Stockholm University)
    • 11:20 AM 11:40 AM
      Solving the two-(spinning-)body problem with QFT techniques 20m

      In this talk, I will briefly review recent developments in the application of techniques in quantum field theory (the scattering amplitudes program, the double copy, etc.) to the description of the dynamics of a binary of (spinning) black holes.

      Speaker: Andres Luna (NBIA)
    • 11:45 AM 12:05 PM
      SYM on Quotients of Spheres and Complex Projective Spaces 20m

      We introduce a generic procedure to reduce a supersymmetric Yang-Mills (SYM) theory along the Hopf fiber of squashed $S^{2r-1}$ with $U(1)^r$ isometry, down to the $\mathbb{CP}^{r-1}$ base. This amounts to fixing a Killing vector $v$ generating a $U(1)\subset U(1)^r$ rotation and dimensionally reducing either along $v$ or along another direction contained in $U(1)^r$. To perform such reduction we introduce a $\mathbb{Z}_p$ quotient freely acting along one of the two fibers. For fixed $p$ the resulting manifolds $S^{2r-1}/\mathbb{Z}_p\equiv L^{2r-1}(p,\pm 1)$ are a higher dimensional generalization of lens spaces. In the large $p$ limit the fiber shrinks and effectively we find theories living on the base manifold. Starting from $\mathcal{N}=2$ SYM on $S^3$ and $\mathcal{N}=1$ SYM on $S^5$ we compute the partition functions on $L^{2r-1}(p,\pm 1)$ and, in the large $p$ limit, on $\mathbb{CP}^{r-1}$, respectively for $r=2$ and $r=3$. We show how the reductions along the two inequivalent fibers give rise to two distinct theories on the base. Reducing along $v$ gives an equivariant version of Donaldson-Witten theory while the other choice leads to a supersymmetric theory closely related to Pestun's theory on $S^4$. We use our technique to reproduce known results for $r=2$ and we provide new results for $r=3$. In particular we show how, at large $p$, the sum over fluxes on $\mathbb{CP}^2$ arises from a sum over flat connections on $L^{5}(p,\pm 1)$. Finally, for $r=3$, we also comment on the factorization of perturbative partition functions on non simply connected manifolds.

      Based on https://arxiv.org/abs/2110.13065

      Speaker: Lorenzo Ruggeri
    • 12:05 PM 2:00 PM
      Lunch 1h 55m