Processes of particle production during inflation can increase the amplitude of the scalar metric perturbations. We show that such a mechanism can naturally arise in supergravity models where an axion-like field drives large field inflation. In this class of models one generally expects instanton-like corrections to the superpotential. We show, by deriving the equations of motion in models of supergravity with a stabilizer, that such corrections generate an interaction between the inflaton and its superpartner. This inflaton-inflatino interaction term is rapidly oscillating, and can lead to copious production of inflatinos during inflation, filling the Fermi sphere up to momenta much larger than the Hubble parameter. In their turn, those fermions source inflaton fluctuations, increasing their amplitude, and effectively lowering the tensor-to-scalar ratio for the model. This allows, in particular, to bring the model where the inflaton potential is quadratic (plus negligibly small instanton corrections) to agree with all existing observations.

We construct vacua of string theory in which all moduli are stabilized and the magnitude of the cosmological constant is exponentially small. The vacua are supersymmetric AdS4 solutions in flux compactifications of type IIB string theory on orientifolds of Calabi-Yau hypersurfaces. I will explain the advances in computing topological data in Calabi-Yau compactifications that led to these solutions, then speculate about implications for the cosmological constant problem. The vacuum energy is small because we ensure the exact cancellation of all perturbative contributions, through an explicit choice of integer parameters determined by the topology and quantized fluxes. The nonperturbative contributions that remain are exponential in these integers. Finding cosmological constants of small magnitude in this landscape is exponentially easier than in Bousso-Polchinski landscapes. Extending this approach to positive cosmological constants in realistic universes is a difficult open problem.

We reinterpret the OSV formula for the on-shell action/entropy function of asymptotically flat BPS black holes as a fixed point formula that is formally equivalent to a recent gluing proposal for asymptotically AdS4 black holes. This prompts a conjecture that the complete perturbative answer for the most general gravitational building block of 4d N=2 supergravity at a single fixed point takes the form of a Nekrasov-like partition function with equivariant parameters related to the higher-derivative expansion of the prepotential. In turn this leads to a simple localization-like proposal for a set of supersymmetric partition functions in (UV completed) 4d N=2 supergravity theories. The conjecture is shown to be in agreement with a number of available results for different BPS backgrounds with both Minkowski and AdS asymptotics. In particular, it follows that the OSV formula comes from the unrefined limit of the general expression including only the so-called W tower of higher derivatives, while the on-shell action of pure (Euclidean) AdS4 with round S3 boundary comes from the NS limit that includes only the T tower.

In recent years Adam Riess' SH0ES collaboration has made it fashionable to question Lambda-CDM through a series of steadily more precise local determinations of the Hubble constant, the latest of which currently stands at H0 = 73 ± 1 km/s/Mpc. On the other hand, questioning the FLRW paradigm is still taboo. However, if there is a 5 sigma discrepancy with Planck, then a good explanation is required. In the talk, I will explain why H0 should be bounded above by H0 ~ 71 km/s/Mpc in any FLRW cosmology, before presenting some observations that appear to challenge the working FLRW assumption that the Universe is isotropic and homogeneous. Time permitting, I will spell out the implications of a higher local H0 for dark energy models.

The black hole information paradox has been tightened to a precise contradiction by the small corrections theorem. Resolving the puzzle thus needs an order unity correction to semiclassical dynamics at the horizon. Remarkably, in string theory we find that microstates of black holes are `fuzzballs' with no horizon, which resolves the paradox. An alternative to the fuzzball paradigm is has been sought through a `wormhole paradigm' where the horizon would be continue to be described by semiclassical physics on a code subspace of the full quantum degrees of freedom. This wormhole paradigm can however can be ruled out by an extension of the small corrections theorem. We argue that the notions of ER=EPR etc underlying the wormhole paradigm are incorrect, and that the error arises from using the eternal spacetime geometry which is itself inconsistent with the requirements of unitarity.

I shall review some key features of the three ten-dimensional string models with broken supersymmetry that are free of tachyonic modes. Their leading back-reactions are runaway “tadpole potentials”, which have important effects on their ambient spacetimes. When these are explored in detail within the low-energy effective theory, some surprising features emerge: ·Tadpole potentials can drive interesting spontaneous compactifications; ·In Cosmology, they can lead to the peculiar “climbing scenario” for fast-to-slow-roll transitions. Puzzling instabilities typically accompany broken supersymmetry in String Theory. However, they are absent in the former setting, and point to a mere breakdown of isotropy in the latter, which resonates with the very emergence of compact dimensions. I shall address these issues, trying to emphasize potential lessons and some key open questions.

Cosmological inflation predicts the existence of a stochastic background of gravitational waves (GW), whose features depend on the model of inflation under consideration. There exist well motivated frameworks leading to an enhancement of the primordial GW spectrum at frequency scales testable with GW experiments, with specific features as parity violation, anisotropies, and non-Gaussianity. I will explain the properties of such scenarios, and their distinctive predictions for what respect GW observables. I will then discuss perspectives for testing these predictions with future GW experiments.

After reviewing the role Quasi-Normal Modes (QNMs) play in the Gravitational Wave (GW) signals emitted in the ring-down phase of Black-Hole (BH) mergers, we present a novel efficient approach to compute QNMs of BHs, D-branes and fuzz-balls, based on quantum Seiberg-Witten (SW) curves for N=2 supersymmetric Yang-Mills (SYM) theories. We find remarkable agreement with numerical results obtained by means of Leaver's method of continuous fractions and with `semi-classical' results obtained in the eikonal approximation, based on geodetic motion. Finally we discuss the extension to D3-branes and their bound states of Couch-Torrence (CT) conformal inversions, that exchange horizon and infinity, and show that they keep the photon-sphere (or photon-halo) fixed.

Almost all existing calculations that concern the Higgs mass are performed within the framework of an effective field theory. While sufficient for certain purposes, such calculations throw up problems to do with fine-tuning and naturalness in particular the famous hierarchy problem. This makes most attempts within field theory to understand the Higgs mass pretty much futile. Even most phenomenology done within string theory does not respect the full string symmetries that are responsible for many of the remarkable finiteness properties for which string theory is famous. Chief among these symmetries is worldsheet modular invariance, which is an exact symmetry of all perturtubative closed-string vacua. And yet if the UV is tamed by this symmetry then it should be exact even today! In this talk I will discuss the many things one can learn from this fact. For example that a gravitational modular anomaly generically relates the Higgs mass to the one-loop cosmological constant, yielding a string-theoretic connection between the two fundamental quantities which are known to suffer from hierarchy problems in the absence of spacetime supersymmetry. In addition one learns about the use and interpretation of modular invariant regulators in string theory, which in turn dictates how string theory arranges its UV/IR-mixing to make itself finite. Finally, I discuss how the effective field theory emerges showing that ultimately the Higgs mass can be understood as arising from an infinite “stringy” sum of Coleman-Weinberg effective potentials in such theories. The results can therefore serve as the launching point for a rigorous investigation of hierarchy problems in a UV complete theory.

The Bethe-Gauge Correspondence (BGC) of Nekrasov and Shatashvili, which relates 1d quantum integrable spin chains to two-dimensional supersymmetric gauge theories with \mathcal{N}=2 supersymmetry, is one of the instances of the deep connection between supersymmetric gauge theories and integrable models. The question that will be the main content of the talk is the origin of this correspondence. I will explain how the BGC could be naturally realized within superstring theory. Toward this aim, I will first explain The Bethe Side (noncompact rational integrable \mathfrak{gl}(m|n) superspin chains) and the corresponding Gauge Side of the BGC. I will then discuss the brane setup for the realization of The Gauge Side. Using string dualities, this brane setup will be mapped to another setup, which realizes The Bethe Side of the correspondence. An important role in this duality frame is played by the 4d Chern-Simons Theory of Costello which explains the integrability of The Bethe Side. If time permits, I will also explain the story for the compact rational integrable \mathfrak{gl}(m|n) superspin chains. This talk is based on the joint work (arXiv:2110.15112) with Nafiz Ishtiaque, Surya Raghavendran, and Junya Yagi.

In this talk I will give an overview of recent and ongoing work regarding rotating black holes in dynamical Chern-Simons (dCS) gravity. dCS gravity is a well motivated modified theory of gravity which has been extensively studied in gravitational and cosmological contexts. I will first discuss unique geometric structures, `the Chern-Simons caps,' which slowly rotating black holes in dCS gravity were recently found to possess. Motivated by the dCS caps, I will then discuss superradiance in the context of slowly rotating dCS black holes and show that there are corrections to the usual solution for a Kerr black hole. Lastly, I will comment on the observable implications for these corrections and point towards avenues for future work.

Conformal defects can be characterised by their contributions to the Weyl anomaly. The coefficients of these terms, often called defect central charges, depend on the particular defect insertion in a given conformal field theory. I will review what is currently known about defect central charges across dimensions, and present novel results. I will discuss many examples where they can be computed exactly without requiring any approximations or limits. These include defects in free theories, and recently developed tools for defects in superconformal field theories.

Hawking famously argued, based on semiclassical calculations, that the radiation from evaporating black holes is contains no information about the matter that fell in. This would be inconsistent with the unitarity of quantum mechanics. In this talk, I will show that, in more careful ‘replica trick’ calculations, the gravitational path integral becomes dominated at late times by saddles containing spacetime wormholes. These wormholes cause the entropy to decrease after the Page time, consistent with unitarity, and allow information to escape from the interior of the black hole.

Over the past decade we have witnessed the emergence of a plethora of correspondences between QFTs in various dimensions arising from higher dimensional SCFTs. In this talk I will overview another strategy to produce correspondences building upon geometric engineering techniques. As applications I will touch upon higher DT theory for Calabi-Yau 3-folds, the algebra of G(2) instantons, and generalizations of level/rank dualities.

I will cover some of the most recent developments on classical spinning black holes and their perturbations. The reinterpretation of them in terms of a classical limit of QFT three-point amplitudes, where the black hole is modeled as a massive spinning particle, sheds light on many fundamental properties such as integrability, the Newman-Janis construction, and the so-called classical double copy relating the solution to gauge theory.

Lattice field theory provides a non-perturbative regularization suitable for strongly interacting systems, which has proven crucial to the study of quantum chromodynamics among many other theories. Lattice investigations of supersymmetric field theories have a long history but often struggle due to the interplay of supersymmetry with the lattice discretization of space-time. I will discuss a way around these difficulties for d-dimensional supersymmetric Yang--Mills theories with at least 2^d supercharges. After informally reviewing some highlights of the lattice formulation, I will survey a selection of results from recent and ongoing numerical studies, including tests of holographic dualities.

I will describe recent studies of bound states of NS5 branes carrying momentum and/or fundamental string charge, in the decoupling limits leading to little string theory and to AdS3/CFT2 duality. This work involves a class of exactly solvable worldsheet models that describe families of BPS and non-BPS black hole microstates. These models have enabled studies of string and D-brane probes of these microstates, yielding insight into their stringy structure in the gravitational bulk description.