Contributed Talks

Thursday 24 September

Firdevs Karakus - Scattering and Tunneling in Real Quantum Mechanics

We establish the general form of the evolution equation and study scattering and tunneling in real quantum mechanics. We prove an analogue of Stone’s theorem for a real Kahler space and derive the corresponding general evolution equation, whose evolution operator is both orthogonal and symplectic. We formulate scattering theory in terms of real wave operators and the associated S-matrix. For the class of potentials considered, we show that the differential scattering cross section is equivalent to that obtained in standard complex quantum mechanics. We also show that the tunneling probability in real quantum mechanics is identical to that in complex quantum mechanics.

M. Efe Özkara - Spinning Shadow Coefficients using Weight-Shifting Operators

In this talk, I will review two techniques used in the conformal bootstrap: the shadow transform and weight-shifting operators. The shadow transform is a tool of conformal harmonic analysis and shadow coefficients relate conformal partial waves to conformal blocks. For spinning operators, the transform can mix different three-point tensor structures, so these coefficients generally form a matrix. I will 

explain how weight-shifting operators generate spinning structures from scalar seeds and how this leads to recursive relations for their shadow coefficients. I will also discuss our Mathematica implementation of this approach for bosonic operators.

Shivam Singh Kushwah - $\zeta/eta$, Photoproduction in Paramagnetic MQGP and (Almost) Contact Structures 

We compute the bulk-to-shear viscosity ratio for thermal QCD-like theories at intermediate coupling using an O(R⁴)-corrected M-theory uplift [Yadav, Misra, ATMP 26(2022)10, 3801-3894], finding results consistent with lattice QCD via the MQGP limit's Contact 3-Structures [Misra, Yadav, IJGMMP (2025) 2550284]. We show the dual is paramagnetic and compute the photoproduction spectral function from D6-brane gauge-field fluctuations, matching 5D gauged supergravity results [Avilla et al., PRD 107(2023)6, 066010]. We conjecture that failures of N-path connectedness in the relevant Contact Structures correspond to branch-point singularities in the complexified viscosity ratio, and that this Contact Structure becomes Almost Contact in the UV.

Aviral Aggarwal - G2-orbifold resolutions in scale-separated AdS$_3$

String compactification on toroidal orbifolds have been long studied and are useful for finding scale separated vacua of string theory. The presence of singularities on the compactified manifold and the presence of intersecting orientifold planes, which are essential to such construction, makes such solutions pathological. This has been long argued as a consistency argument in favor of the swampland program which calls for such vacua to be in swampland. Here we provide a new scale separated solution with similar ingredients compactified on a G2 manifold but we cure the pathology by resolving the singularity of these manifolds. We explicitly show that compactification on these manifolds can be resolved into a smooth manifold and the blow up moduli can be stabilized in the right regime of the supergravity. We then also show that once resolved the apparent intersection of O planes on these singularities no longer exists. This eliminates the criticism of these solutions from the view point of singularities of the internal manifold and asks for further checks from other perspectives.

Daniele Mauri - Towards Quadratic Quasi-normal modes of black holes

Although linear perturbations of black hole solutions have been studied in great detail, much less is known about quadratic fluctuations. Recent studies of black hole ring-down have shown that quadratic quasi-normal modes (QNMs) can reach approximately 10% of the amplitude of the dominant linear mode, motivating a deeper study of perturbations beyond linear order. In this work, we explore this 

nonlinear regime by first analyzing simple toy models — the Inverted Hydrogen Atom and anti-de Sitter (AdS) spacetime — constructing solutions for scalar perturbations at quadratic order. We then consider the gravity-scalar sector of a four-dimensional N=2 supergravity on a Schwarzschild-anti-de Sitter (SAdS) spacetime. Using the previously obtained AdS solutions, we construct linear and quadratic QNMs in SAdS perturbatively in the black hole mass.

Tommaso Antonelli - Higher order differentiability of static and spherically symmetric geometries

I will present a result about the classification of singularities in static and spherically symmetric spacetimes. The theorem will allow us to conclude from fairly simple mathematical conditions the presence or absence of singular behaviour in some popular black hole solutions. These results are very general and stem from considerations of differential geometry, without resorting to any particular model of gravitational theory, and hence they can be useful in several different approaches of quantum gravity that try to solve the singularity problem.

Friday 25 September

Keremcan Doğan - An Algebroid Perspective on Exceptional Geometry and U-Duality

Compactifications of string and M-theory provide a natural arena in which duality symmetries emerge in lower-dimensional effective theories and motivate geometric structures extending conventional differential geometry. In particular, toroidal compactifications of eleven-dimensional supergravity give rise to the exceptional U-duality groups, and exceptional geometry provides a geometric framework for encoding these symmetries together with the associated geometric and non-geometric fluxes. In this talk, I will present an algebroid perspective on the structures underlying U-duality, extending the familiar chain from Poisson-Lie T- duality and Drinfel’d doubles to bialgebroids and generalized geometry on Courant algebroids. The framework is based on calculi over pairs of vector bundles that need not be ordinary duals of one another, allowing Drinfel’d double constructions adapted to the exceptional tangent bundles appearing in string/M-theory compactifications [1, 2]. For the SL(5) U-duality case, with exceptional bundle TM ⊕ Λ2T*M, a Nambu-Poisson trivector acts as a twist that induces the dual calculus and the corresponding exceptional Drinfel’d algebroid [3]. The resulting bracket reproduces the non-constant fluxes of the SL(5) exceptional Drinfel’d algebra, while its compatibility conditions encode the associated quadratic constraints. The same viewpoint extends to the E6(6) U-duality case, where the enlarged generalized tangent bundle TM ⊕ Λ2T*M ⊕ Λ5T*M naturally brings in H- and R-type twists and leads from bialgebroids to proto bialgebroids [4]. This provides an algebroid level geometric realization of exceptional Drinfel’d structures associated with distinct compactifications, and places duality, fluxes and exceptional geometry in a common frame independent calculus-based framework.

[1] A. Çatal-Özer, K. Doğan, C. Yetişmişoğlu, “Drinfel’d Double of Bialgebroids for String and M Theories: Dual Calculus Framework,” Journal of High Energy Physics (2024), arXiv:2312.06584 [hep-th].

[2] A. Çatal-Özer, K. Doğan, C. Yetişmişoğlu, “Drinfel’d Doubles, Twists and All That... in Stringy Geometry and M Theory,” Journal of High Energy Physics (2025), arXiv:2409.11973 [hep-th].

[3] A. Çatal-Özer, K. Doğan, C. Yetişmişoğlu, “Exceptional Drinfel’d Algebroids and Rackoids,” to be submitted (2026).

[4] A. Çatal-Özer, K. Doğan, C. Yetişmişoğlu, “E6(6) Exceptional Drinfel’d Algebras from Proto Bialgebroids,” submitted (2026).

Okan Gunel - Wrapping M5-branes on a non-spin manifold: spin^h structures and AdS₇ black holes

We compactify the 7D gauged maximal supergravity on the non-spin manifold SU(3)/SO(3) (Wu manifold), and SL(3,R)/SO(3). We embed SO(3) in the SO(5) gauge group to use the spin$^h$ structure on the Wu manifold. The solutions preserve supersymmetry. The AdS$_2$ x Wu manifold solution is later generalised to a BPS extremal non-Abelian AdS$_7$ black hole and a nonextremal one. The thermodynamic properties are given, and holographic applications are discussed. The solution can be uplifted to 11D supergravity by considering an $S^4$ bundle over the Wu manifold twisted by SO(3) gauge fields.

Mehmet Gumus - Tracking S-matrix bounds across dimensions

Based on 2512.24474. We study massive two-to-two scattering of identical scalar particles in spacetime dimensions d=3 to 11 using non-perturbative S-matrix bootstrap techniques. Treating d as a continuous parameter, we compute two-sided numerical bounds on low-energy observables and find smooth branches of extremal amplitudes separated by sharp kinks at d=5 and d=7. The kinks coincide with a transition in the analytic behavior at the two particle threshold and the loss of some well-known dispersive positivity constraints. I will discuss possible implications of our results for ultraviolet completions in higher-dimensional quantum field theory and string theory.

Francesco Ferrarin - Resumming alpha’ corrections via worldsheet functional RG

We study the worldsheet sigma model describing string perturbation theory by applying the techniques of the functional renormalization group, allowing us to resum α’ corrections to all orders. By imposing the cancellation of the Weyl anomaly, we determine higher-derivative corrections to the spacetime field equations. We start from a truncation matching the classical Polyakov action, which we then generalize, and by means of the Tseytlin reconstruction, we derive an effective action for string theory with higher-derivative corrections on generic backgrounds. We then discuss the resulting solutions arising from the infinite tower of α’ corrections.

Vittorio D'Alelio - Quantum Anisotropies as Pre-inflationary Relics in the Primordial Power Spectrum

We investigate the quantum dynamics of the inflationary Universe, asking whether primordial quantum anisotropies can leave observable relics in the scalar perturbation spectrum even when their classical counterparts are efficiently suppressed by inflation. Starting from the Wheeler-DeWitt equation, we first implement a Born–Oppenheimer separation between the slow gravitational sector and the fast matter degrees of freedom. We then perform a WKB expansion in a quadratic Planckian scale proportional to the squared Planck mass. The slow gravitational sector consists of an isotropic inflationary de Sitter background supplemented by small homogeneous Bianchi IX anisotropies, which are treated as genuine quantum degrees of freedom. A physical notion of time is introduced through a reference fluid, allowing the quantum constraints to be recast in terms of an effective Schrödinger evolution. At the lowest orders, the semiclassical background dynamics and the Schrödinger evolution of matter perturbations are recovered. At the next order, the quantum anisotropies contribute to the corrected Gaussian state of each scalar mode. After tracing over the anisotropic degrees of freedom, we derive a correction to the primordial power spectrum that separates into an isotropic quantum-gravitational contribution and a genuinely anisotropic term. Both contributions may exhibit a nontrivial dependence on the comoving scale (k), although their functional forms need not coincide. A central question is therefore whether the isotropic and anisotropic corrections can be distinguished through their different scale dependence, which is controlled by the dynamics and initial state of the corresponding gravitational sectors.

Saturday 26 September

Ceren Ayse Deral - Supersymmetric Null and Timelike Warped AdS and Stringsin D = 3, N = 2 Gauged Supergravity

We study the supersymmetric solutions of D=3, N=2 gauged supergravity [2] extended with a Fayet-Iliopoulos term [3]. In this talk, we present some interesting solutions, including null and timelike warped AdS spacetimes, as well as charged string solutions. A well-defined black hole can be obtained via periodic identification from the null z-warped AdS. We also show, with a few examples, that the charged string solutions interpolate between two supersymmetric AdS or Minkowski extrema of the scalar potential. One of them corresponds to a horizon with a singularity behind it, and the other determines the asymptotic geometry.

[1] N. S. Deger and C. A. Deral, [arXiv:2510.25652 [hep-th]].

[2] N. S. Deger, A. Kaya, E. Sezgin and P. Sundell, Nucl. Phys. B 573, 275-290 (2000) [arXiv:hep-th/9908089 [hep-th]].

[3] M. Abou-Zeid and H. Samtleben, Phys. Rev. D 65, 085016 (2002) [arXiv:hep-th/0112035 [hep-th]].

Altay Etkin - Volume time in Jackiw-Teitelboim gravity: a holographic clock

How is a “bulk clock” encoded holographically? We address this in JT gravity, where a natural physical clock emerges by promoting the vacuum energy to a dynamical variable: the vacuum cosmological constant becomes a top form degree of freedom conjugate to spacetime volume, thereby defining a notion of bulk physical time. This construction is naturally formulated in the Henneaux-Teitelboim (HT) framework. We show that the boundary dynamics is the Schwarzian mode coupled to a free particle on U(1), matching the universal low-energy effective action of the complex SYK model. By further clarifying the role of the vacuum cosmological constant as a top form, we establish the equivalence between JT gravity coupled to two-dimensional Maxwell theory and 2d HT gravity via an explicit field redefinition. The initial question is addressed: we show that the resulting boundary theory can itself be rewritten as an observer action, equivalently a (0+1)-dimensional HT theory. This yields a direct identification of the boundary clock with the U(1) phase mode, and makes its relation to the bulk clock explicit.

Farbod Sayyed Rassouli - Volume as a Clock: Observers and Topology Change in Quantum Gravity

Different notions of time arise from different choices of observer. In cosmological settings, a particularly natural choice is spacetime volume, which is conjugate to the cosmological constant. This gives rise to unimodular time, deparametrizing the Wheeler–DeWitt equation into a Schrödinger-like evolution equation. I will first explain how this construction appears in arbitrary dimensions, with particular emphasis on the four-dimensional case.

I will then use a two-dimensional toy model to quantise global Lorentzian de Sitter space, where quantum mechanically there is a region in which topology change can occur. More generally, I will explain how adding these types of observers and clocks classically encodes topology change and orientation change, and how this structure can be associated with a Morse function. If time permits, I will also comment on the holography of such observers.

Hiroki Kawai - On the universality of giant graviton integrated correlators

We discuss half-BPS four-point integrated correlators in N=4 super Yang-Mills theory involving various heavy operators. We demonstrate that the correlators can be computed exactly using supersymmetric localisation and the complex matrix model at both large and finite N. The eigenvalue density in the complex plane corresponds to the free-fermion description of half-BPS operators. The free-fermion description provides a natural explanation for the universal structure of those correlators in the strong-coupling regime, which is independent of the detailed data of the heavy operator and can be interpreted as stringy α' corrections. 

Francesco Arcofora - TBA

TBA

Federico Arrighi - Precision tests of AdS/CFT correspondence: one-loop divergences for Kaluza-Klein theories on AdS x S spaces.

In this talk I discuss precision holography which is the programme of matching quantum corrections on both sides of AdS/CFT beyond the classical approximation. In particular, I present a new systematic framework for computing the logarithmically divergent part of one-loop partition functions on product spaces AdS × S of arbitrary dimension.

I begin by explaining how to compute the logarithmic divergence of the free energy of some simple physical theories in both pure AdS or S spaces and product AdS x S spaces. Then, I briefly introduce the AdS/CFT correspondence and specialise it to the case of interest, namely the AdS_4 x S^7 solution of 11D supergravity and ABJM theory at level k = 1 on S^3. After that, I discuss the application of our framework to the complete multiplet of the theory where we recover in a 4d language the known result of Marino, Sen et al. [arXiv:1210.6057] that the only non-vanishing logarithmic divergence originates entirely from the 2-form AdS mode in the ghost sector, which reproduces the correction to the ABJM free energy predicted by supersymmetric localization. I will conclude by giving some comments on our technique and outlining some intriguing further applications of it.