Journal club

We are organizing a seminar on string field theory (SFT) and related topics (worldsheet theory, string amplitudes, compactifications, homotopy algebras…) on Thursday every 2 weeks. Talks are typically 1.5 hours long, but they may be longer for topics when necessary.

Our goal is to offer reviews, mini-lectures and communications of recent results. In the latter case, the recommended format is a general introduction of 30 min for students and non-specialists, followed by 1 hour of talk + discussions intertwined. However, speakers are free to organize their time differently. Speakers can present one of their papers, work in progress or even other papers they want to discuss. We hope that this regular journal club will help foster discussions within the SFT community and related fields and seed new collaborations and applications.

Structure (reference timezone is CEST, see this website for conversion):

  • 15:00 – 16:30 (CEST) [9:00 (EST), 19:30 (IST), 23:00 (JST)] : talk

Please register on the mailing list for announcements and obtaining the Zoom link. If you don’t see emails, please check your spam folder and, if necessary, mark the email as non-spam.


  • Subhroneel Chakrabarti
  • Harold Erbin
  • Renann Lipinski Jusinskas

Talks will be announced on this page and through the mailing list. You can also consult the calendar or events pages or subscribe to the SFT Google Calendar (ics version). Talks are also listed on Everyone is invited to discuss on Zulip.

Videos of the recorded talks will be posted in the String field theory Youtube channel.

Past seminars:

You can contact us for suggesting speakers.


  • Thursday 26 October 2023 : Olaf Hohm (Humboldt U.)
    Title: Double Copy, Double Field Theory & Homotopy Algebras

    Abstract: The double copy denotes a technology to relate the scattering amplitudes of Yang-Mills theory to those of gravity. While enormously successful at the level of scattering amplitudes, until recently there was no first-principle understanding of how to derive such relations. Such an understanding would be needed in order to describe, for instance, a double copy of classical solutions. I present an approach based on homotopy algebras such as L-infinity algebras that allows one to provide such a first-principle derivation, at least to some finite order in perturbation theory. To this end I review how to formulate Yang-Mills theory as an L-infinity algebra, how to “strip off” color to obtain a different kind of homotopy algebra and, finally, how to combine two copies of these exotic algebras to obtain the L-infinity algebra of gravity in the form of double field theory.

  • Thursday 16 November 2023 : Minjae Cho (Princeton U.)
    Title: On the symplectic form of the open string field theory

    Abstract: We explore the construction of the symplectic form on the phase space of classical solutions in open string field theory. We demonstrate its practical application by computing the energy of open string rolling tachyon solutions, which agrees with Sen’s proposal based on boundary conformal field theory.

  • Thursday 25 January 2024 : Georg Stettinger (Institute of Physics of The Czech Academy of Sciences)
    Title: Open String Field Theory with Stubs

    Abstract: There are various reasons why adding stubs to the vertices of open string field theory (OSFT) is interesting: Not only can the stubs tame certain singularities and make the theory more well-behaved, but also the new theory shares a lot of similarities with closed string field theory, which helps to improve our understanding of its structure and possible solutions. In this talk, I will explain in detail how to implement stubs into the framework of OSFT, resulting in an A-infinity-algebra with infinitely many vertices. Moreover, properties and examples of cohomomorphisms that map solutions of Witten theory to solutions of the stubbed theory are discussed. In the second part, I will generalize the whole construction to the sliver frame and construct solutions of the stubbed theory explicitly.

  • Thursday 22 February 2024 : Aninda Sinha (Indian Institute of Science)
    Title: From Euler to Veneziano and Back

    Abstract: What links Madhava, Euler, and string theory? I will present new QFT motivated representations of the Euler Beta function and related functions which make appearances in string theory. Pushing the analogy between Feynman diagrams in quantum field theory and string theory leads to new physics inspired representations of Zeta functions as well as pi, finding that the QFT formulas interpolate between standard representations and faster converging ones. The new representations sum over all channels and include contact interactions very much in the spirit of quantum field theory and what is anticipated from string field theory, enabling efficient level truncation. I will briefly touch upon the status of this calculation in string field theory and what is missing to enable a derivation of an analytic formula using string field theory.

  • Thursday 28 March 2024 : Alberto Ruffino (Università di Torino)
    Title: Quantum stubs for String Field Theories

    Abstract: We present a systematic algebraic procedure for adding stubs to a generic quantum String Field Theory. This method extends the approach of adding stubs through homotopy transfer techniques, as pointed out by Schnabl-Stettinger and Erbin-Firat, to the quantum scenario. To start with, we pedagogically apply our method to a “quantum” cubic theory and then delve into proper solutions to the BV quantum master equation, such as open-closed SFT, where we extract the explicit expression for the stubbed multi-string open-closed products. We also describe how our algebraic method matches the geometric interpretation of adding stubs, focusing on the concrete example of the open string one-loop tadpole within the framework of open-closed SFT.

  • Thursday 18 April 2024: Lucien Heurtier (King’s College London)
    Title: Exact Schwinger Proper Time Renormalisation

    Abstract: We derive an exact version of the Schwinger Proper Time Renormalisation Group flow equation from first principles from the complete path integral, without using any perturbative expansion. We study the advantages of this flow equation as compared to the canonical Exact Renormalisation Group flow equation, which uses a regulator in momentum space. We use our flow equation to recover the convexity of the effective scalar potential in the IR limit and apply it to the study of false-vacuum decay.

  • Thursday 25 April 2024: Michael Kroyter (Holon Institute of Technology)
    Title: On Democratic String Field Theories

    Abstract: We reexamine democratic open string field theories, namely, theories in which string fields are not constrained to a single picture number and picture changing is obtained as a gauge transformation. We describe several possibilities for regular free theories and attempt to construct the lowest order interaction term and identify the lowest order gauge transformation for some of these theories. We also discuss projections over string field spaces that might be needed for a consistent off-shell implementation of picture changing.