SFT@Cloud 2021

20 Sept 2021, 07:30 → 24 Sept 2021, 19:00 Europe/Prague

Online

Harold Erbin (MIT)

String Field Theory conference/workshop is an annual meeting for active researchers working in string field theory, worldsheet formalism, and related areas in physics and mathematics. This year, as a variation on the theme, it will also feature a lecture series and several talks on the application of homotopy algebras and Batalin-Vilkovisky formalism in ordinary quantum field theories.

The conference will be held entirely online over five days. The first two days will be dedicated to two lecture series. The final three days will feature 19 talks in the format of 25 +5 and a featured panel discussion.

Time slots will be reserved before and after the talks each day in order to facilitate discussions among the participants. Participants will also be able to communicate during the conference using the String Field Theory Zulip instance. A social event will happen on gather.town on Wednesday morning.

The participants are requested to register to obtain the links for Zoom and to Zulip.

Topics:

• String field theory
• Worldsheet string theory
• String amplitudes
• Pure spinor formalism
• Homotopy algebras in string theory and QFT

Talks are recorded and available on Youtube.

Link to previous workshop: Workshop on Fundamental Aspects of String Theory (June 2020, ICTP-SAIFR & IFT-UNESP, São Paulo, Brazil)

Organizers:

• Subhroneel Chakrabarti (CEICO, Prague)
• Harold Erbin (MIT & IAIFI, Boston; CEA-LIST, Paris)
• Renann Lipinski Jusinskas (CEICO, Prague)
• Jakub Vošmera (ETH, Zurich)

Monday, 20 September

1 Introduction

SFT opening.pdf

2 L-infinity Algebras, Homotopy Transfer and Field Theory (Lecture 1 of 3)

I give a self-contained introduction into L-infinity algebras, the formulation of classical field theories in terms of these, and the notion of homotopy transfer. One goal is to make it self-evident that L-infinity structures are the proper algebraic way to encode the data of classical field theories. In other words, any consistent field theory gives rise to an L-infinity algebra. A second goal is to illustrate that homotopy transfer is the algebraic formulation of the field theory procedure to ``integrate out" degrees of freedom, which may be auxiliary or physical, pure gauge or not.

Speaker: Olaf Hohm

hohm_homotopy_qft_lecture1.pdf

hohm_homotopy_qft_lecture23.pdf

15:00 Break

3 String field theory vertices and hyperbolic geometry (Lecture 1 of 3)

Speaker: Barton Zwiebach (MIT)

16:15 Break

4 String field theory vertices and hyperbolic geometry (Lecture 2 of 3)

Speaker: Barton Zwiebach (MIT)

17:30 Break

5 Q&A (Hohm)

Speaker: Olaf Hohm

6 Q&A (Zwiebach)

Speaker: Barton Zwiebach (MIT)

Tuesday, 21 September

7 Discussion

Speakers: Barton Zwiebach (MIT), Olaf Hohm

8 L-infinity Algebras, Homotopy Transfer and Field Theory (Lecture 2 of 3)

I give a self-contained introduction into L-infinity algebras, the formulation of classical field theories in terms of these, and the
notion of homotopy transfer. One goal is to make it self-evident that L-infinity structures are the proper algebraic way to encode the data of classical field theories. In other words, any consistent field theory gives rise to an L-infinity algebra. A second goal is to illustrate that homotopy transfer is the algebraic formulation of the field theory procedure to ``integrate out" degrees of freedom, which may be auxiliary or physical, pure gauge or not.

Speaker: Olaf Hohm

15:00 Break

9 L-infinity Algebras, Homotopy Transfer and Field Theory (Lecture 3 of 3)

I give a self-contained introduction into L-infinity algebras, the formulation of classical field theories in terms of these, and the
notion of homotopy transfer. One goal is to make it self-evident that L-infinity structures are the proper algebraic way to encode the data of classical field theories. In other words, any consistent field theory gives rise to an L-infinity algebra. A second goal is to illustrate that homotopy transfer is the algebraic formulation of the field theory procedure to ``integrate out" degrees of freedom, which may be auxiliary or physical, pure gauge or not.

Speaker: Olaf Hohm

16:10 Break

10 String field theory vertices and hyperbolic geometry (Lecture 3 of 3)

Speaker: Barton Zwiebach (MIT)

18:10 Break

11 Q&A (Hohm)

Speaker: Olaf Hohm

12 Q&A (Zwiebach)

Speaker: Barton Zwiebach (MIT)

Wednesday, 22 September

13 Conference Brunch

We meet for socialization at gathertown. Link to join will be sent to the registered participants by email.

14 Type II superstring field theory revisited

Speaker: Hiroshi Kunitomo

kunitomo_typeii_wzw.pdf

15 Massless RR Sector in Superstring Field Theory

Speaker: Ashoke Sen (Harish-Chandra Research Institute)

sen_rr_masses.pdf

16 Four Applications of SFT

I will discuss four avenues of applications of string field theory, and open problems thereof: RR flux, time-dependent background, open/closed duality, and D-instantons.

Speaker: Xi Yin (Harvard University)

yin_sft.pdf

15:30 Break

17 Open string amplitudes on superstring D-instanton background

In this talk, I will discuss how to compute disk amplitudes of collective modes on a single D-instanton background in type IIB superstring theory, which requires several interesting ingredients of superstring field theory.

Speaker: Minjae Cho

cho_Dinst_zero_modes.pdf

18 Initial value problem and causality in string-inspired non-local field theory

We investigate causality in a non-local scalar field theory inspired by open SFT. For purely time-dependent configurations, we show that a field redefinition perturbative in a parameter $\xi$, characterizing the non-locality, can turn the theory into a local two-derivative theory with $\xi$-dependent potential. We support this claim by 'taming' the unbounded oscillations of the rolling solution of the non-local theory into a standard rolling solution of the field-redefined potential. For general configurations, we demonstrate that it is possible to field redefine the theory into two-derivative-in-time theory by breaking manifest Lorentz covariance. We discuss light-cone formulation and dispersion relations.

Speaker: Atakan Hilmi Fırat

firat_non_locality.pdf

19 Conformal defects from open string field theory

Unlike conformal boundary conditions, conformal defects of Virasoro minimal models lack classification. Alternatively to the defect perturbation theory and the truncated conformal space approach, we can employ open string field theory (OSFT) to explore the space of conformal defects. I will illustrate the method by an analysis of OSFT around the background associated with the (1,2) topological defect in diagonal unitary minimal models. Numerical analysis of OSFT equations of motion leads to an identification of a nice family of solutions, recovering the picture of infrared fixed points due to Kormos, Runkel and Watts. OSFT provides us with numerical estimates of the g-function and other coefficients of the boundary state.

Speaker: Kasia Budzik

budzik_defects.pdf

17:15 Break

20 The Primitive Domain for Analytic Off-shell Correlators in SFT

The work of de Lacroix, Erbin, and Sen (LES) from 2018 showed that the Feynman loop diagrams (those without any massless internal propagator) in closed superstring field theory are analytic on a domain in complex external momenta variables. We prove an analytic extension of the LES domain to a larger domain, using complex Lorentz transformations and Bochner's tube theorem. Explicit applications of our formula to 2-, 3-, and 4-point functions show that the extension equals the well-known Primitive domain. In the case of 5-point functions, we do the analysis for limited subcases.

Speaker: Ratul Mahanta

mahanta_analyticity_sft.pdf

21 Discussion

Thursday, 23 September

22 Discussion

23 Closed string disk amplitudes in the pure spinor formalism

We describe how to calculate closed string scattering on the disk in the pure spinor approach to string perturbation theory. We exemplify the methods with certain low point functions and compare to the known results of the RNS formalism. Moreover, we discuss some potential applications to the study of higher derivative corrections to D-brane actions.

Speaker: Michael Haack

haack_pure_spinors.pdf

24 From Fields to Strings and Back

I will give a broad brush picture of a program to derive gauge-string duality in some generality. The key elements will include the reorganisation of perturbative large N gauge theory Feynman diagrams as localised integrals over closed string moduli space using the Strebel parametrisation of the latter. The general picture will be concretely illustrated by the special "tensionless string" limits of the $AdS_3$ dual of the free symmetric orbifold CFT and the $AdS_5$ dual to free N=4 Super Yang-Mills theory. In the latter case, I will describe a recent proposal for a candidate worldsheet description involving ambitwistor fields.

Speaker: Rajesh Gopakumar (ICTS-TIFR, Bengaluru)

gopakumar_fields_strings.pdf

25 AdS/CFT at all loop orders

In recent years, the so-called "tensionless" limit of string theory on AdS_3 has been conjectured to be exactly dual to a symmetric product CFT in two dimensions. I review evidence for this correspondence, and demonstrate a method for matching correlation functions at every level in string perturbation theory.

Speaker: Bob Knighton

knighton_ads_cft.pdf

15:30 Break

26 The Disk Partition Function in String Theory

We investigate the disk partition function for the open string. This is a subtle problem because of the presence of a residual gauge group PSL(2,ℝ) on the worldsheet even after fixing the conformal gauge. It naively has infinite volume and leads to a vanishing answer. We use different methods that all demonstrate that PSL(2,ℝ) effectively behaves like a group with finite negative volume in the path integral, which leads to a simple prescription for the computation of the disk partition function. We apply our findings to give a simple rederivation of the D-brane tensions.

Speaker: Sridip Pal

pal_disk_sft.pdf

27 Equivariant BV Formalism for String Worldsheet

Worldsheet diffeomorphisms play a central role in string perturbation theory. In the BV approach to worldsheet theory, we need the measure on the space of Lagrangian submanifolds to be base with respect to diffeomorphisms. We discuss a general construction of such base forms. In particular, we explain that it is equivalent to constructing a representation of some Differential Graded Lie Algebra, which was previously introduced in the context of current algebras and called Dg. This clarifies the procedure of covariant insertion of vertex operators on the string worldsheet.

Speaker: Andrei Mikhailov

mikhailov_bv.pdf

Slides - html

28 The Field Theory of the "World Line"

I will describe an attempt to classify classical field theories that arise from (quotients of) graded super Lie algebras, which may, but need not necessarily originate from the BRST quantisation of the world line. The role of the representation space, usually identified with perturbative excitations, is merely to identify a suitable reduction of the algebra or, to define trace on the latter if one seeks an action functional.

Speaker: Ivo Sachs

sachs_worldline.pdf

17:15 Break

29 Homotopy Intertwining Solution

We give a homotopy algebraic generalization of the argument for background independence of Witten's open bosonic string field theory, with the goal of formulating some conjectures about the nonperturbative vacuum structure of closed string field theory.

Speaker: Ted Erler

erler_intertwining_solution.pdf

30 Discussion

Friday, 24 September

31 Discussion

32 Closed String Deformations in Open String Field Theory

I discuss recent results and attempts to understand how open string physics is affected by a change in the closed string background in the context of bosonic and supersymmetric open string field theory. This is based on the recent papers 2103.04919, 2103.04920, 2103.04921, and on new yet unpublished results.

Speaker: Carlo Maccaferri

maccaferri_openclosed_sft.pdf

33 Panel discussion on "String Field Theory beyond string theory"

The impact of SFT in deciphering string perturbation theory and giving novel insights into certain non-perturbative aspects is widely appreciated. However, the impact of SFT and the techniques it gave rise to has far-reaching applications well beyond stringy physics. For example, open string field theory can be used to gain a new perspective on BCFT. The homotopy algebra and BV formalism, ubiquitous in string field theory, play a prominent role in QFT, leading to several recent new results. Unitarity, Analyticity, Wilsonian action for SFT has also given rise to new insights into QFTs. This panel will discuss the merits of a position that research in SFT has fueled new insights into physics beyond string theory and will continue to do so in the future. It will also be discussed what other similar developments can we expect and in which directions.

Speakers: Nathan Berkovits, Yuji Okawa, Martin Schnabl, Ashoke Sen (Harish-Chandra Research Institute)

okawa_panel.pdf

15:30 Break

34 Gauge Invariant Perturbation Theory via Homotopy Transfer

I will discuss how to express perturbation theory in terms of gauge invariant variables to all orders in perturbations, by using homotopy transfer and the homological perturbation lemma. Then I will demonstrate how this method is applied in cosmological perturbation theory.

Speaker: Allison F. Pinto

pinto_homotopy_cosmology.pdf

35 Doubled Spacetime, Homotopy Algebras, and Puzzles of String Fields on Tori

I will outline the program of obtaining "double field theory" --- the theory of massless string modes on a torus background with both momentum and winding --- beyond cubic order, using the technology of homotopy algebras. I will also point out and resolve some relevant ambiguities (“cocycle signs”) afflicting closed SFT on tori.

Speaker: Alex Arvanitakis

arvanitakis_doubled_spacetime.pdf

36 EL∞-algebras, Generalized Geometry, and Tensor Hierarchies

In this talk, I review the definition and applications of EL∞-algebras given in arXiv:2106.00108. EL∞-algebras are generalizations of L∞-algebras comprising weak Lie ∞-algebras, and they have a number of applications within extended geometry. In particular, they clarify the higher symmetry structure of generalized tangent bundles and double/exceptional field theory. They also provide the algebraic origin for data needed in the definition of higher gauge theories such as the tensor hierarchy of gauged supergravity. This Lie ∞-algebraic perspective now provides a clear path towards finite gauge transformations and a global picture of these higher gauge theories.

Speaker: Christian Saemann

saemann_generalized_geometry.pdf

17:15 Break

37 BV Formalism and Perturbative Algebraic Quantum Field Theory (cancelled)

In this talk I will report on recent results at the intersection of perturbative algebraic quantum filed theory (pAQFT) and the homological approach to perturbative QFT known as the BV formalism. After reviewing the basic notions, I will focus on recent results concerning situations where the given theory has boundary or asymptotic boundary data that have to be taken into account. This can be applied for example to discuss soft modes in QED.

Speaker: Katarzyna Rejzner

SFT2021_Rejzner.pdf

38 Discussion