Iberian Strings Meetings 

22/01/2021, 17:30 — 18:00 —
Alessandro Mininno, Universidad Autónoma de Madrid

Dynamical Tadpoles and Weak Gravity Constraints

Non-supersymmetric string models are plagued with tadpoles for dynamical fields, which signal uncanceled forces sourced by the vacuum. We argue that in certain cases, uncanceled dynamical tadpoles can lead to inconsistencies with quantum gravity, via violation of swampland constraints. We describe an explicit realization in a supersymmetric toroidal $Z_2 \times Z_2 $ orientifold with $D7$-branes, where the dynamical tadpole generated by displacement of the $D7$-branes off its minimum leads to violation of the axion Weak Gravity Conjecture. In these examples, cancellation of dynamical tadpoles provides consistency conditions for the configuration, of dynamical nature (as opposed to the topological conditions of topological tadpoles, such as RR tadpole cancellation in compact spaces). We show that this approach provides a re-derivation of the Z-minimization criterion for $AdS$ vacua giving the gravitational dual of a-maximization in $4d \ N=1$ toric quiver SCFTs.

See also

Mininno-IberianStrings2021.pdf

22/01/2021, 17:00 — 17:30 — Online
Max Wiesner, Universidad Autónoma de Madrid

Quantum Corrections in 4d $N=1$ Infinite Distance Limits and the Weak Gravity Conjecture

We study quantum corrections in four-dimensional theories with $N = 1$ supersymmetry in the context of Quantum Gravity Conjectures. According to the Emergent String Conjecture, infinite distance limits in quantum gravity either lead to decompactification of the theory or result in a weakly coupled string theory. We verify this conjecture in the framework of $N = 1$ supersymmetric F-theory compactifications to four dimensions including perturbative $\alpha'$ as well as non-perturbative corrections. After proving uniqueness of the emergent critical string at the classical level, we show that quantum corrections obstruct precisely those limits in which the scale of the emergent critical string would lie parametrically below the Kaluza-Klein scale. Limits in which the tension of the asymptotically tensionless string sits at the Kaluza-Klein scale, by contrast, are not obstructed.

In the second part of the talk we discuss the effect of quantum corrections for the Weak Gravity Conjecture away from the strict weak coupling limit. We propose that gauge threshold corrections and mass renormalisation effects modify the super-extremality bound in four dimensions. For the infinite distance limits in F-theory the classical super-extremality bound is generically satisfied by a sublattice of states in the tower of excitations of an emergent heterotic string. By matching the F-theory $\alpha'$-corrections to gauge threshold corrections of the dual heterotic theory we predict how the masses of this tower must be renormalised in order for the Weak Gravity Conjecture to hold at the quantum level.

See also

Iberian_Strings2021_wiesner.pdf

22/01/2021, 16:30 — 17:00 — Online
Zachary Elgood, Universidad Autónoma de Madrid

The first law of heterotic stringy black hole mechanics at zeroth order in $\alpha'$

We re-derive the first law of black hole mechanics in the context of the Heterotic Superstring effective action compactified on a torus to leading order in $\alpha'$, using Wald's formalism, covariant Lie derivatives and momentum maps. The Kalb-Ramond field strength of this theory has Abelian Chern-Simons terms which induce Nicolai-Townsend transformations of the Kalb-Ramond field. We show how to deal with all these gauge symmetries deriving the first law in terms of manifestly gauge-invariant quantities. In the presence of Chern-Simons terms, several definitions of the conserved charges exist, but the formalism picks up only one of them to play a role in the first law. The derivation of a first law is a necessary step towards the derivation of a manifestly gauge-invariant entropy formula which is still lacking in the literature. In its turn, this entropy formula is needed to compare unambiguously macroscopic and microscopic black hole entropies.

See also

iberian2021_zach.pdf

22/01/2021, 15:30 — 16:00 — Online
Nana Geraldine Cabo Bizet, Universidad de Guanajuato

Testing Swampland Conjectures with Machine Learning

We consider Type IIB string theory compactification on an isotropic torus with geometric and non geometric fluxes. Employing supervised machine learning, consisting of an artificial neural network coupled to a genetic algorithm, we determine more than sixty thousand flux configurations yielding a scalar potential with at least one critical point. Stable AdS vacua with large moduli masses and small vacuum energy as well as unstable dS vacua with small tachyonic mass and large energy are absent, in accordance to the Refined de Sitter Conjecture. Hierarchical fluxes favor perturbative solutions with small values of the vacuum energy and moduli masses, as well as scenarios with the lightest modulus mass much smaller than the AdS vacuum scale.

22/01/2021, 14:30 — 15:30 — Online
Timo Weigand, University of Hamburg

The Swampland - From Conjectures to Theorems

Review lecture on The Swampland.

The `swampland’ has become known as a term to describe effective field theories which, while consistent as quantum field theories, cannot be completed into fully consistent theories of quantum gravity. A growing web of conjectures has been developed in the literature as to when a theory belongs to the swampland. In this talk I will review some of these so-called `Quantum Conjectures’, summarise the general and often times heuristic arguments in their support and highlight various connections between them. Despite the speculative character of many of the involved ideas, we will see that some of the quantum gravity conjectures can be made extremely precise and even be proven within large classes of string constructions.

See also

Weigand-IberianStrings21.pdf

22/01/2021, 12:30 — 13:00 — Online
Pablo Enmanuel León Torres, University of Antofagasta

Massive supermembrane in ten non-compact dimensions

We discuss a formulation of the M2-brane theory in ten non-compact dimensions that exhibits mass terms in the Hamiltonian. The existence of these mass terms improves the quantum behaviour of the theory in comparison with the known compactifications of the M2 to ten dimensions. On the other hand, this formulation of the M2-brane can be interpreted as a realization in ten non-compact dimensions of the central charge condition. This result could be interesting, since it represent another well behaved sector of the M2-brane and it might yield new information about massive Romans supergravity in ten dimensions.

See also

PabloLeon.pdf

22/01/2021, 12:00 — 12:30 — Online
Martí Rosselló, Instituto Superior Técnico, Universidade de Lisboa

Arithmetic of decay walls through continued fractions: a new exact dyon counting solution in $\mathcal{N} =4$ CHL models

We use continued fractions to perform a systematic and explicit characterization of the decays of two-centred dyonic black holes in $4D$ $\mathcal{N} =4$ heterotic $\mathbb{Z}_N$ CHL models. Thereby we give a new exact solution for the problem of counting decadent dyons in these models.

See also

slides iberian strings_marti.pdf

22/01/2021, 11:30 — 12:00 — Online
Tomas Andrade, Universitat de Barcelona

Violations of weak cosmic censorship in black hole collisions

We simulate collisions of stable rotating black holes in six and seven dimensions. We find that if the angular momentum of the system is sufficiently large, the post-merger configuration is an elongated dumbbell which is Gregory-Laflamme unstable. As such, it displays a cascade of satellite formation which ultimately leads to pinching off of the horizon, thus violating the weak cosmic censorship conjecture.

22/01/2021, 11:00 — 11:30 — Online
Marija Tomasevic, Universitat de Barcelona

Multi-mouth traversable wormholes

We describe the construction of traversable wormholes with multiple mouths in four spacetime dimensions and discuss associated quantum entanglement. Our solutions are asymptotically flat up to the presence of magnetic fluxes that extend to infinity. The construction begins with a two-mouth traversable wormhole supported by backreaction from quantum fields. Inserting a sufficiently small black hole into its throat preserves traversability between the original two mouths. This black hole can be the mouth of another wormhole connecting the original throat to a new distant region of spacetime. Our wormholes are traversable between any pairs of mouths. This work is based on arxiv:2012.07821.

See also

marija.pdf

22/01/2021, 10:00 — 10:30 — Online
Roberto Emparan, ICREA Barcelona

Quantum BTZ black hole

The study of quantum effects on black holes including their gravitational backreaction is an important but notoriously hard problem. I will begin by reviewing how the framework of braneworld holography allows to solve it for strongly-coupled quantum conformal fields. Then I will describe a holographic construction of quantum rotating BTZ black holes (quBTZ) using an exact dual four-dimensional bulk solution. Besides yielding the quantum-corrected geometry and the renormalized stress tensor of quBTZ, we use it to show that the quantum black hole entropy, which includes the entanglement of the fields outside the horizon, rather non-trivially satisfies the first law of thermodynamics, while the Bekenstein-Hawking-Wald entropy does not.

See also

quBTZ_IbStrings.pdf

22/01/2021, 09:00 — 10:00 — Online
Lárus Thorlacius, University of Iceland

Entanglement islands

Review on Entanglement islands.

See also

islands_220121.pdf

21/01/2021, 17:30 — 18:30 — Online
Roberto Emparan, ICREA Barcelona

The ultimate trap: a tale of horizons, singularities, and black holes. Outreach colloquium on the occasion of The Nobel Prize in Physics 2020

Outreach colloquium on black hole formation as a robust prediction of the general theory of relativity.

More than fifty years ago, a young mathematician called Roger Penrose revolutionized the study of gravity and spacetime by introducing the idea of a “trapped surface”: a region where the pull of gravity is so strong that spacetime is inevitably led to a mysterious singularity. This result is so important that last year Penrose was awarded the Nobel Prize in Physics for “showing that Einstein's theory leads to the formation of black holes, those monsters in time and space”. Isn't it fascinating? Sure, but, actually, what does it mean?

See also

blackholes.pdf

21/01/2021, 16:30 — 17:00 — Online
Max Schwick, Instituto Superior Técnico

Resurgent properties of minimal string theory: part II

We will illustrate the importance of the above concepts in known solutions of the Painlevé equations (tronquée and tritronquée phases). Furthermore, we will expand on the above solutions by introducing some specific characteristics of these equations like resonance, relations between Stokes constants.Then, we will expand on this by explaining a conjecture on the analytic form of these constants that has been checked with our numerical method up to very high precision. Finally, we will talk about possible future directions.

See also

IberianStringsTalkMaxSchwick.pdf

21/01/2021, 16:00 — 16:30 — Online
Roberto Vega Álvarez, Instituto Superior Técnico, Universidade de Lisboa

Resurgent properties of minimal string theory: part I

In these talks we will report the findings of our unpublished work on resurgent properties of the Painlevé I and II equations. These equations play a fundamental role in Minimal String Theories as the specific heat of 2D (Super)-Quantum Gravity. We will do a short introduction to the topic of resurgence and explain the role of Stokes constants when constructing solutions to these equations. While reviewing these tools, we will present our new method for numerically calculating these constants in very general setups to reasonably high precision.

21/01/2021, 15:30 — 16:00 — Online
Zhenghao Zhong, Imperial College London

$5$d SCFTs, 5-brane webs and (orthosymplectic) magnetic quivers

The Higgs branches of $5d \ N=1$ SQCD theories at infinite gauge coupling (UV superconformal fix point) is often inaccessible via standard tools. The recently introduced concept of magnetic quivers proves to be a powerful tool able to probe the finite and infinite coupling limits in a uniform manner. In this talk, I will focus on $5d \ N=1$ SQCD theories whose Higgs branches at infinite coupling exhibit exceptional global symmetries. By realizing these theories as 5-brane web configurations with orientifold planes, I will discuss how to derive the corresponding orthosymplectic magnetic quivers. This allows us to study the geometry of the enlarged Higgs branches of $5d \ N=1$ theories with $Sp(k)$ and $SO(k)$ gauge groups at the UV fix point.

See also

Iberian Strings_zhenghao.pdf

21/01/2021, 14:30 — 15:30 — Online
Daniel Hernández Ruipérez, University of Salamanca

Supermoduli of supersymmetric curves with punctures

Review lecture:

We introduce super schemes (super algebraic varieties) and super analytic spaces and their basic properties. We then focus on SUSY curves (supersymmetric Riemann surfaces) without and with NS and RR punctures and construct a supermoduli for them. It has the structure of an Artin algebraic superspace, that is, it is the quotient of an étale equivalence relation of superschemes (superalgebriac varieties). We also report on compactifications of the supermoduli.

See also

Lisboa21_3_ruiperez.pdf

21/01/2021, 12:30 — 13:00 — Online
Mario Herrero, SISSA

Amplitudes Positivity and IR-UV connections in Graviton Exchange

Positivity bounds are standard tools to assess the validity of EFTs for which a unitary, local and Lorentz Invariance UV completion is assumed. They impose positivity of certain (combination of) Wilson coefficients by connecting IR physics to features of the UV completion through dispersion relations of scattering amplitudes. If the corresponding EFT does not satisfy these bounds, it is assumed to lay on the Swampland.

However, the standard derivation of positivity bounds fails when the exchange of a massless particle is possible, which excludes the very important case of gravitational interactions. In this talk we show how to derive new positivity bounds that take into account this issue. We generalize the standard derivation by writing dispersion relations which are valid when production of massless particles is included.

Furthermore, we show that one can obtain efficient bounds in the case of gravity if one assumes the high energy limit of the scattering amplitude to be of the Regge form, as implied from String Theory. We will discuss implications of these bounds for different physical settings, such as models of interacting scalar fields, scalar QED, and the Weak Gravity Conjecture.

See also

IS_2021_herrero.pdf

21/01/2021, 12:00 — 12:30 — Online
Mattia Cesaro, Universidad Autónoma de Madrid

Kaluza-Klein fermion mass matrices from Exceptional Field Theory and $N=1$ spectra

Using Exceptional Field Theory, the infinite-dimensional mass matrices for the gravitino and spin-1/2 Kaluza-Klein perturbations above a class of anti-de Sitter solutions of M-theory and massive type IIA string theory with topologically-spherical internal spaces can be determined. These mass matrices can be employed to compute the spectrum of Kaluza-Klein fermions about some solutions in this class with internal symmetry groups containing $SU(3)$. Combining these results with previously known bosonic sectors of the spectra, I will present the complete spectra about some $N=1$ and some non-supersymmetric solutions in this class, together with certain generic features they are shown to enjoy.

See also

Iberian Strings Presentation - Mattia.pdf

21/01/2021, 11:30 — 12:00 — Online
Gabriel Larios, Universidad Autónoma de Madrid

Kaluza-Klein spectra and consistent truncations

Kaluza-Klein spectra on string/M-theory solutions depend significantly on whether the solution can be obtained from uplift of a maximal gauged supergravity. For some solutions of M-theory, mIIA and IIB obtained from uplift, I will present the spectrum of KK gravitons and discuss a persistent form of universality when solutions with same (super)symmetry and supergravity spectrum are present in different theories. In the second part of the talk, I will discuss the spectrum of KK gravitons around the $N=2 \ AdS_4$ solution that is dual to the IR of a cubic deformation of ABJM. This solution cannot be obtained from uplift of an $N=8 \ D=4$ theory, and this seems to be linked to the fact that its metric cannot be isometrically embedded in $R^8$. Further, the allocation of modes with different spins in $N=2$ supermultiplets cannot be made KK level by KK level, but needs space invaders.

See also

Kaluza-Klein spectra and consistent truncations.pdf

21/01/2021, 11:00 — 11:30 — Online
Salvatore Baldino, Instituto Superior Técnico, Universidade de Lisboa

Seiberg-Witten theory, string theory and WKB analysis

In this talk, we will explore the relationship between non critical string theories, $SU(2)$ supersymmetric gauge theories and WKB analysis. In particular, we will examine the role of Seiberg-Witten geometry in the context of $SU(2)$ theories, and how this is related to the concept of string duality. We will examine the role of WKB analysis in solving the equations that come out in this context. We will focus on the physical interpretation of the various quantities that can be computed in WKB analysis, and how they can be related to observables in Seiberg-Witten theory or string theory. We will conclude by presenting the author's work on WKB analysis of finite difference equations, that naturally appear in this context.

See also

ibstringsseminar_salvatore.pdf