Matthew Yu - KLT Factorization and Nonrelativistic String Theory Room: Lärosal 5 I will describe new aspects of KLT factorization for relativistic string theory where the strings carry both momentum and winding. This gives rise to an interesting D-brane configuration in spacetime when we consider the open string amplitudes. I will then present a zero Regge slope limit of the KLT relations between winding string amplitudes. Such a limit of string theory requires a critically tuned Kalb-Ramond field in the compact directions, and results in the D-branes carrying an electric potential. Finally I will present the one loop open string amplitudes which extends the work of Gomis and Ooguri for closed strings.

Jan Rosseel - Minimal Stringy Non-Relativistic Supergravity Room: Lärosal 5 In this talk I will discuss a non-relativistic limit of minimal ten-dimensional supergravity that yields a supergravity theory with underlying String Newton-Cartan geometry. I will argue that after taking the limit, the theory is invariant under emergent dilatation and fermionic Stueckelberg symmetries that lead to a shortening of the supergravity multiplet. Even though the supersymmetry transformation rules diverge in the limit, regularity and consistency of the procedure can then be maintained by imposing a set of dilatation covariant and supersymmetric intrinsic torsion constraints. Finally, I will discuss how this non-relativistic minimal stringy supergravity theory is natural when viewed through the lense of longitudinal T-duality and use the latter to obtain supergravity solutions corresponding to non-relativistic fundamental and unwound strings.

Kevin van Helden - Intrinsic torsion for non-Lorentzian p-branes from a mathematician's perspective Room: Lärosal 5 In non-Lorentzian geometries, it is not always possible to find a connection that has no torsion. The components of torsion that persist under taking the differences of connections are called intrinsic. We will provide a mathematical framework and dictionary to physics of intrinsic torsion. We will also classify all the subrepresentations of intrinsic torsion of both Galilei and Caroll p-brane gravity and tell about their geometric interpretations.

Jørgen Musaeus - On the 1/c-expansion of gravity Room: Lärosal 5 In this talk I present the covariant 1/c-expansion of general relativity and how it relates to the well-known post-Newtonian expansion. The 1/c-expansion is an expansion of general relativity around the limit in which the tangent space lightcone flattens. This differentiates the 1/c-expansion from the post-Newtonian expansion, as it does not assume the gravitational field strength to be weak a priori. Thus, the 1/c-expansion is able to capture strong gravitational effects, such as gravitational time dilation, giving rise to a new approximation of general relativity. However, the main part of this talk is going to be focused on how to filter out the strong field effects and make contact with the post-Newtonian approximation. This is an important step in understanding the 1/c-expansion and its capabilities as we, among other things, are forced to confront its limited region of validity and incorporate it into a broader approximation scheme by way of matched asymptotic expansions. Additionally, this gives us a new framework for post-Newtonian gravity based on Newton-Carton geometry, the novel feature of which is covariance. This will allow us to deviate from the standard harmonic gauge that much of modern post-Newtonian theory relies on. Finally, I will give an outlook on other potential uses of this new framework and summarise what we have learned about the covariant 1/c-expansion as a whole.

Troels Harmark - Non-relativistic strings in weakly coupled gauge theory Room: Lärosal 7

Silvia Penati - Supersymmetric Galilean Electrodynamics: A renormalizable non-linear sigma model Room: Lärosal 7 I will discuss quantum properties of galilean supersymmetric theories in d =2+1, primarily focusing on the non-relativistic version of N=2 SuperQED. Compared with its relativistic cousin, this model exhibits a very different behavior at quantum level. In fact, it is featured by an infinite number of marginal couplings that turn on along the RG flows. Superconformal invariance is preserved in correspondence of a non-trivial conformal manifold of fixed points where the theory is gauge-invariant and interacting.

Rishi Mouland - Black Holes in Non-Relativistic Holography Room: Lärosal 7 I will first review the basic ideas of holography for non-relativistic conformal field theories, and describe a systematic approach to construct black hole solutions in the corresponding dual theories of gravity. I will then focus on an explicit such duality, that identifies a concrete superconformal quantum mechanics with M-theory on a particular background. Through an asymptotic study of the superconformal index in the supergravity regime, I will provide a precise microstate counting for a broad class of BPS black holes. I will finally discuss some subtle and somewhat counter-intuitive features of holographic dualities of this type, and speculate on the role that non-relativistic string theory and its low-energy effective description can play towards a better understanding thereof.

Jelle Hartong - Longitudinal Galilean and Carrollian limits of Non-relativistic Strings Room: Lärosal 7

Kevin Morand - On non-Riemannian geometries and singularities in Double Field Theory Room: Lärosal 7 Admitting non-Riemannian geometries, Double Field Theory (DFT) extends the notion of spacetime beyond the Riemannian paradigm. In this talk, we will review the non-Riemannian sector of DFT and discuss some of its implications regarding the singularity problem in General Relativity.

Stephen Ebert - The Anisotropic Compactification of Non-Relativistic M-Theory Room: Lärosal 7 This talk will focus on new developments and the structure of M-theory explored in the non-relativistic limit. As an example, I reveal the new structure of a non-relativistic M5-brane propagating in an eleven-dimensional non-Lorentzian supergravity background, and its compactification on a novel, anisotropic torus, which realizes the manifest SL(2, Z)-invariant D3-brane’s intricate structure in type IIB non-relativistic superstring theory. These new developments in this non-relativistic limit of M-theory are foundational to realizing its U-duality symmetry from higher dimensional anisotropic toroidal compactifications and Matrix theory.

Utku Zorba - Nonrelativistic IIB supergravity Room: Lärosal 7 In this talk, we present the nonrelativistic limit of IIB supergravity at the level of action. This limit is based on reparameterizing the background fields of type IIB superstring theory. Recently, it was shown that the cancellation of the divergencies between Einstein-Hilbert and the Kalb-Ramond term in the NS-NS sector is based on the critical limit. In addition to this, we show that taking the limit of the action leads to additional divergent terms in the RR sector. However, these extra terms can be written as two terms without a leading divergence upon introducing an auxiliary field. After taking the limit, the auxiliary field becomes a Lagrange multiplier imposing a constraint on some RR fluxes. Interestingly, the equation of motion of the Lagrange multiplier is precisely one of the self-duality conditions resulting from the non-relativistic limit of the relativistic condition. We then show that the action is invariant under boosts, gauge symmetries, dilatations, and SL(2,R) transformations. In particular, we will argue that these symmetries uniquely fix the nonrelativistic IIB action.

Arjun Bagchi - Tensionless tales Room: Lärosal 7 I will review recent progress in the understanding of tensionless null strings where the worldsheet becomes Carrollian and BMS3 appears as the residual gauge symmetry algebra replacing the two copies of the Virasoro algebra of the tensile string. After a recap of the classical aspects, I will focus on the quantum theory, which has many surprises in store including the appearance of three different theories from a single classical one, novel closed to open string transitions and Rindler physics on the worldsheet. In the final part of the talk, I will give some details of a model of microstates of the BTZ black hole based on a null string construction.

Emil Have - Nonrelativistic expansion of string theory Room: Lärosal 7 In this talk, I will discuss a stringy "post-Newtonian" expansion of string theory. At each order in 1/c², where c is the speed of light, this produces a new string theory which "remembers" the preceding string theories that appear at lower orders. The next-to-leading order (NLO) theory reduces to the Gomis-Ooguri string once a suitable "strong" foliation constraint is imposed. In general, the geometry to which these strings couple is the string 1/c² expansion of Lorentzian geometry, subject to a foliation constraint arising from the string 1/c² expansion of the string β-functions to lowest order in α'. I will showcase the expansion of closed bosonic string theory up to NNLO and make some comments on the expansion of the open string.

Susanne Reffert - The Large-Charge Expansion Room: Lärosal 7 Working in a sector of fixed and large global charge leads to important simplifications in the study of strongly-coupled CFTs. It is possible to calculate the conformal data as an expansion in inverse powers of the large charge which acts as a control parameter. Fixing the charge leads to spontaneous symmetry breaking both in the global and space-time symmetries. The fixed-charge theory as a result exhibits non-relativistic traits in the spectrum of Goldstone excitations. It is also possible to use the large-charge approach directly on non-relativistic systems, so called non-relativistic CFTs which are invariant under the Schrödinger group. An interesting example of this class is the unitary Fermi gas which can be realized in the laboratory.

Eric Bergshoeff, Jan de Boer, Elias Kiritsis - Panel discussion Room: Lärosal 7

Andrea Fontanella - Integrability in non-relativistic string theory Room: Lärosal 7 It is known that relativistic string theory in AdS5xS5 is integrable, as it admits a Lax pair (classical integrability) and an R-matrix (quantum integrability). The property of being integrable opened the road to many powerful applications which allowed to compute observables, such as the spectrum, useful in making impressive quantitative checks of the AdS5/CFT4 correspondence. Integrability of relativistic string theory also extends to symmetric space backgrounds, where AdS5xS5 is a particular example. The question we pose is: How much do we know about integrability in non-relativistic string theory? In this talk I will report on recent progress in understanding classical integrable structures present in non-relativistic string theory propagating in string Newton-Cartan AdS5xS5. I will elaborate on the coset construction of the non-relativistic action, present the Lax pair associated with its equations of motion and discuss a preliminary work on constructing a spectral curve. This talk is based on work done in collaboration with J. Nieto, O. Ohlsson Sax, A. Torrielli, S. van Tongeren.

Johannes Lahnsteiner - Wrapped Membranes, Supergravity, and U-Duality Room: Lärosal 7 In this talk, I revisit the wrapped membrane sector of M theory. It is defined as the zero Planck length limit with a critically tuned three-form and decouples the wrapping modes from the rest of the spectrum. I will present the underlying background geometry and extend it by including supersymmetry. This will lead me to introduce a new supergravity multiplet in eleven dimensions. Contrary to the usual multiplet, it is manifestly non-Lorentzian. Finally, I will conjecture dualities to other limits of M theory.