# Plenary sessions and the public talk take place in the room 0.03 on the ground floor

# Parallel sessions take place in the room 1.01 (Cosmo), 1.02 (Strings 1, 3, 4), 1.03 (Strings 2, Pheno) on the first floor

# MON (2/7)

## 8:30 – 9:10 Registration

9:10 – 9:15 Welcome

## 9:15 – 9:45 Liam McAllister *Threefolds with Large Picard Number*

# Threefolds with Large Picard Number

## I will describe an ensemble of Calabi-Yau threefold hypersurfaces obtained by triangulating two million polytopes from the Kreuzer-Skarke list, including all polytopes with $240 \le h^{1,1} \le 491$. We find that the Kahler cone is very narrow at large $h^{1,1}$, and as a result, control of the curvature expansion is correlated with the presence of ultralight axions.

## 9:45 – 10:15 Anne-Christine Davis *Recent Developments in Modified Gravity*

# Recent Developments in Modified Gravity

## I will discuss modified gravity models and show how they can be tested and constrained. I will review some laboratory tests for a class of such models. The implications of GW170817 will be discussed and shown how it can constrain models, or even rule them out.

## 10:15 – 10:45 Coffee break

## 10:45 – 11:15 Ignatios Antoniadis *Inflation from supersymmetry breaking*

# Inflation from supersymmetry breaking

## I will discuss the problem of scale hierarchies in particle physics and cosmology and propose ways to address it. In particular I will present a framework of obtaining inflation from supersymmetry breaking by identifying the inflaton with the superpartner of the goldstino and will describe its phenomenological consequences.

## 11:15 – 11:45 Stephan Stieberger *Strings on Celestial Sphere *

# Strings on Celestial Sphere

## We transform superstring scattering amplitudes into the correlation functions of primary conformal fields on two-dimensional celestial sphere. The points on celestial sphere are associated to the asymptotic directions of (light-like) momenta of external particles, with the Lorentz group realized as the SL(2,C) conformal symmetry of the sphere. The energies are dualized through Mellin transforms into the parameters that determine dimensions of the primaries. We focus on four-point amplitudes involving gauge bosons and gravitons in type I open superstring theory and in closed heterotic superstring theory at the tree-level.

## 11:45 – 12:15 Marika Taylor *Asymptotic symmetries and their observational consequences *

# Asymptotic symmetries and their observational consequences

## There has been considerable recent interest in the deep relationships between asymptotic symmetries, soft scattering theorems and gravitational memory effects. In this talk we will discuss new results on asymptotic symmetries in general dimensions, and explore the potential consequences in terms of scattering and memory.

## 12:15 – 14:00 Lunch break

## 14:00 – 14:30 Andre Lukas *Calabi-Yau Manifolds and SU(3) Structure*

# Calabi-Yau Manifolds and SU(3) Structure

## The constructing non-trivial SU(3) structures on Calabi-Yau manifolds and their possible application to string compactifications is discussed. Among the wide range of SU(3) structures which emerge we find Strominger-Hull systems, suitable for heterotic or type II string compactifications, on all complete intersection Calabi-Yau manifolds. Provided they can be supported by suitable sourced in the Bianchi identity, they lead to Calabi-Yau compactifications of string theory with a non Ricci-flat, physical metric which can be written down explicitly and in analytic form.

## 14:30 – 15:00 Michele Cicoli *Cosmology of Fibre Inflation models*

# Cosmology of Fibre Inflation models

## I will describe several features of type IIB Fibre Inflation models like: (i) how to construct a chiral global embedding into consistent Calabi-Yau orientifold compactifications; (ii) the presence of an inflaton upper bound from the Kahler cone conditions; (iii) the details of perturbative reheating and the associated production of dark radiation; (iv) the generation of primordial black holes during inflation and their contribution to dark matter; (v) open issues with light axionic spectator fields during inflation.

## 15:00 – 15:30 Sven Krippendorf *Explorations in SUSY and String Theory Parameter Space*

## 15:30 – 16:00 Coffee break

## 16:00 – 16:30 Patrick Vaudrevange *To chart the Landscape of Heterotic Orbifold Models*

# To chart the Landscape of Heterotic Orbifold Models

## Due to its enormous size, the landscape of heterotic orbifold models is still widely undiscovered. Hence, one has to assume that there are many islands of MSSM-like models to be found in this landscape. We give an overview of recent attempts to improve the situation using, for example, techniques from machine learning.

## 16:30 – 17:00 Fabian Ruehle *Reinforcement learning in string theory *

# Reinforcement learning in string theory

## When studying the vacua of string theory, we often want to find solutions with specific properties, but do not know how to select the string geometry that gives rise to such vacua. We explain how reinforcement learning, a semi-supervised approach to machine learning, can be used to explore the landscape of string solutions autonomously, and give some examples for applications.

## 17:00 – 17:30 James Halverson *String Theory and Data Science*

# String Theory and Data Science

## Techniques in data science are increasing making breakthroughs in fields outside of physics. In this talk I will demonstrate how some of those techniques can be utilized to study string compactifications, focusing on applications in F-theory and in the Bousso-Polchinski model.

# TUE (3/7)

## 9:15 – 9:45 Hans Peter Nilles *CP violation from strings *

## 9:45 – 10:15 Fernando Marchesano *The type IIA flux potential and Freed-Witten anomalies*

# The type IIA flux potential and Freed-Witten anomalies

## I will discuss the classical 4d scalar potential in type IIA Calabi-Yau orientifolds in the presence of fluxes and D6-branes. As we will see, such a potential can be written as a bilinear form V = ZAB ρAρB, where the ρ are in one-to one correspondence with the fluxes of the compactification. The ρ only depend on the internal fluxes, the axions and the topological data of the compactification, and are fully determined by the Freed-Witten anomalies of branes that appear as 4d string defects. The quadratic form Z only depends on the saxionic partners of these axions. In general, the ρ can be seen as the basic invariants under the discrete shift symmetries of the 4d effective theory, and therefore the building blocks of any flux-dependent quantity.

## 10:15 – 10:45 Coffee break

## 10:45 – 11:15 Emilian Dudas *Axions in gauge anomalous U(1)’s effective models*

# Axions in gauge anomalous U(1)’s effective models

## We discuss the possibility of light axions and their low-energy couplings in effective string models with anomalous U(1)’s and Green-Schwarz anomaly cancelation conditions.

## 11:15 – 11:45 Iñaki García Etxebarria *Anomalies, string universality, and model building*

# Anomalies, string universality, and model building

## I will discuss various aspects of non-perturbative gauge anomalies, with a particular emphasis on those aspects helpful in constraining the possibilities for string model building in various dimensions.

## 11:45 – 12:15 Miguel Montero *More on global anomalies*

# Dai-Freed anomalies in particle physics

## Anomaly cancellation conditions place strong constraints on many physical theories. In the traditional framework, local and global anomalies are detected by computing an eta invariant on a mapping torus. Recent research, mostly in the condensed matter context, has uncovered the existence of finer anomaly cancellation conditions, not visible in these traditional settings. These anomalies refine the Ibañez-Ross constraints on discrete gauge symmetries, such as proton triality in the MSSM. I will also discuss the constraints for continuous gauge groups of relevance to the SM and GUTs.

## 12:15 – 14:00 Lunch break

## 14:00 – 14:30 Ivonne Zavala *Mechanisms for Primordial Black Hole Production in String Inflation*

# Mechanisms for Primordial Black Hole Production in String Inflation

## I will discuss mechanisms for producing a significant population of primordial black holes (PBHs) within string theory inspired single field models of inflation.

The production of PBHs requires a large amplification in the power spectrum of curvature perturbations between scales associated with CMB and PBH formation. In principle, this can be achieved by temporarily breaking the slow-roll conditions during inflation. I will discuss two string setups that can realise this process: string axion models of inflation where subleading non-perturbative effects can superimpose steep cliffs and gentle plateaus onto the leading axion potential. The cliffs can momentarily violate the slow-roll conditions, and the plateaus can lead to phases of ultra slow-roll inflation.

DBI models of inflation, where a sharp increase in the speed of sound sourced by a steep downward step in the warp factor can drive the amplification.

## 14:30 – 15:00 Raffaele Savelli *Global Aspects of T-branes*

# Global Aspects of T-branes

## T-branes are bound states of ordinary D-branes, characterized by non-commuting expectation values for the worldvolume scalars. They defy usual geometric intuition and feature a variety of unconventional brane-model-building phenomena. In this talk I will discuss some general global properties of the vacuum solutions corresponding to T-branes, and show how their existence as stable supersymmetric configurations puts strong constraints on the geometry supporting them.

## 15:00 – 15:30 Irene Valenzuela *Massless Towers of States, Field Distances and the Swampland*

# Massless Towers of States, Field Distances and the Swampland

## Consistency with quantum gravity can have significant consequences on low energy physics. Recently substantial effort has been dedicated to understand the quantum gravity constraints that distinguish the string landscape from the swampland. I will focus on the Swampland Distance Conjecture, for which at infinite distances in field space there must be an infinite tower of states becoming massless exponentially fast in the proper field distance. This puts an upper bound on the field range of a scalar field, with potential implications for inflation. We present new evidence for the conjecture by studying infinite distance singularities in the complex-structure moduli space of Calabi-Yau manifolds and identifying an infinite tower of BPS states becoming exponentially light. We show that the monodromy transformation at the singularity generates an infinite orbit within the spectrum of BPS states, and the infinite distance itself emerges upon integrating out this infinite orbit of states.

## 15:30 – 16:00 Coffee break

## 16:00 – 16:30 Ulf Danielsson *Riding a dark bubble*

# Riding a dark bubble

## Finding dark energy in string theory has turned out to be a great challenge, and there are even hints that de Sitter space is in the swampland. In this talk we discuss a possibility to induce dark energy that turns the problem of instabilities into a virtue.

## 16:30 – 17:00 Marek Lewicki *Cosmic Archaeology with Gravitational Waves from Cosmic Strings*

# Cosmic Archaeology with Gravitational Waves from Cosmic Strings

## Cosmic strings are generic cosmological predictions of many extensions of the Standard Model of particle physics, such as a U(1)′ symmetry breaking phase transition in the early universe. Unlike other topological defects, cosmic strings can reach a scaling regime that maintains a small fixed fraction of the total energy density of the universe from a very early epoch until today. If present, they will oscillate and generate gravitational waves with a frequency spectrum that imprints the dominant sources of total cosmic energy density throughout the history of the universe. We demonstrate that current and future gravitational wave detectors, such as LIGO and LISA, could be capable of measuring the frequency spectrum of gravitational waves from cosmic strings and discerning the energy composition of the universe at times well before primordial nucleosynthesis and the cosmic microwave background where standard cosmology has yet to be tested.

# WED (4/7)

## 9:15 – 9:45 Burt Ovrut *Non-Perturbative Bundle Moduli Superpotentials in Heterotic String Theory*

# Non-Perturbative Bundle Moduli Superpotentials in Heterotic String Theory

## We study the non-perturbative superpotential in $E_8 times E_8$ heterotic string theory on a non-simply connected Calabi-Yau manifold $X$, as well as on its simply connected covering space $tilde{X}$. The superpotential is induced by the string wrapping holomorphic, isolated, genus 0 curves. According to the residue theorem of Beasley and Witten, the non-perturbative superpotential must vanish in a large class of heterotic vacua. There are however, heterotic vacua for which the residue theorem is not directly applicable. We present a specific example in which the superpotential is non-zero both on $tilde{X}$ and on $X$. The reason for the non-vanishing of the superpotental on $X$ is that the second homology class contains “discrete torsion”. As a result, the curves with the same area are distributed among different torsion classes and, as a result, do not cancel each other.

## 9:45 – 10:15 Gary Shiu *Topological Data Analysis for Cosmology and String Phenomenology*

# Topological Data Analysis for Cosmology and String Phenomenology

## Topological data analysis (TDA) is a multi-scale approach in computational topology used to analyze the “shape” of large datasets by identifying which homological characteristics persist over a range of scales. In this talk, I will discuss how TDA can be used to extract physics from cosmological datasets (e.g., primordial non-Gaussianities generated by cosmic inflation) and to explore the structure of the string landscape.

## 10:15 – 10:45 Steven Abel *TBA*

## 10:45 – 11:15 Coffee break

## 11:15 – 12:30

## Cosmo 1

## Strings 1

## Strings 2

## 11:15 – 11:30

## Veronica Guidetti

*Chiral Global Embedding of Fibre Inﬂation Models*

# Chiral Global Embedding of Fibre Inﬂation Models

## I will present explicit examples of ﬁbre inﬂation models which are globally embedded in type IIB compactifications with explicit choice of orientifold involution, gauge fluxes and brane setup which lead to chiral matter and moduli stabilisation compatible with inflation driven by string loops and higher derivative eﬀects.

## Nana Geraldine Cabo Bizet

*Non abelian T-dualities in Gauged Linear Sigma Models*

# Non abelian T-dualities in Gauged Linear Sigma Models

## Abelian T-duality in Gauged Linear Sigma Models (GLSM) forms the basis of the physical understanding of Mirror Symmetry. We consider an alternative formulation of abelian T-duality on GLSM’s by gauging a U(1) global symmetry with the addition of Lagrange multipliers. This extends to non-Abelian T-duality in the presence of global non-Abelian symmetries. We study the SU(2) gauged group, exploring first a family of Abelian dualities; the dual model Lagrangian depends on twisted chiral superfields with a twisted superpotential. We explore non-perturbative instanton corrections in the dual theories, matching the effective potential for the U(1) field strength. More general SU(2) non-Abelian dual models are obtained and analyzed via the geometry of their supersymmetric vacua. The duality connects different regions of the string landscape, and allows to explore mirror symmetry in CYs embedded in non toric ambient spaces.

## Federico Carta

*Supersymmetry enhancement via T-branes*

# Supersymmetry enhancement via T-branes

## In the last couple of years it was discovered that some 4d N=1 quantum field theories flow in the IR to 4d N=2 superconformal field theories (often of generalized Argyres-Douglas type), therefore showing a phenomenon of Supersymmetry Enhancement at the IR fixed point. The N=2 IR theory is often non-lagrangian while the N=1 UV theory is lagrangian, therefore such flows are extremely useful to learn features of the IR non-lagrangian theory, by using the UV formulation to compute RG flow protected quantities as for example the superconformal index. However, up to date it is not completely clear why such flows exist, and how the SUSY enhancement happens. Limiting ourself to the case of rank one theories, we show how it is possible to understand the enhancement phenomenon in a geometric way, by condering a D3 brane probing a local singularity in F-theory corresponding to a T-brane of seven-branes. (Work in progess with R.Savelli and S.Giacomelli)

## 11:30 – 11:45

## Tetiana Obikhod

*D-brane description of charged black holes with the help of the Dixmier-Douady invariant*

# D-brane description of charged black holes with the help of the Dixmier-Douady invariant

## Quantum gravity in the framework of string theory provides a microscopic quantum description of charged black holes using D-brane-soliton objects in string theory. Such a D-brane is represented in the form of a brane-antibranch configuration characterized by a magnetic charge, taking on a value in the Hilbert space. Thus, the singularities of black holes are described by the vacuum space-time, which is identified with the physical Hilbert space. According to Rosenberg, the principal bundles over a locally compact space X with fibers isomorphic to compact operators on an infinite-dimensional Hilbert space, K, define sections that represent the C * algebra of sections of the principal bundle. A characteristic class associated with such an algebra is called the Dixmier-Douady invariant corresponding to the Neveu-Schwartz field, H. According to the Rosenberg theorem, there is the morphism which corresponds to a phase transition from one soliton state of the D-brane to another.

## Andreas Muetter

*Group Theory Aspects of Non-Supersymmetric Heterotic Partition Functions*

# Group Theory Aspects of Non-Supersymmetric Heterotic Partition Functions

## For supersymmetry breaking heterotic orbifolds, we develop a formalism that links the non-vanishing of the partition function to the representation theory of the underlying orbifold point group. In this way, we are able to show that only specific sectors are responsible for the non-vanishing of the partition function. This analysis provides us with valuable data considering the possible vanishing of the cosmological constant in non-supersymmetric heterotic orbifolds, e.g. by the virtue of Atkin-Lehner symmetry, and gives us hints for loopholes in earlier no-go theorems concerning that issue.

## Seung-Joo Lee

*Gravity and U(1)s in F-theory*

# Gravity and U(1)s in F-theory

## We study how the F-theory EFTs behave in 6d as we take some limits for the internal geometry, appropriately controlling the strengths of gravitational and/or U(1) interactions. In particular, we discuss the fate of U(1) gauge symmetries upon decoupling gravity and also touch upon quantum gravity conjectures in the context of F-theory vacua.

## 11:45 – 12:00

## Tomasz Krajewski

*Higgs domain walls in the Standard Model and beyond*

# Higgs domain walls in the Standard Model and beyond

## Cosmological domain walls have been widely studied in numerical lattice simulations in the past. The main effort was to understand the dynamics of domain walls in the case of spontaneous breaking of global discrete symmetries which are often present in supersymmetric theories. It was found that networks formed by cosmological domain walls are (meta)stable if vacua between which walls interpolate are connected by the (approximate) symmetry. However, the scenario in which vacua belong to different orbits of the action of the symmetry group is possible too. It is realized, for example, by domain walls of the Higgs field in the Standard Model. Investigating the dynamics of Higgs domain walls in extensions of the Standard Model we found that degeneracy of minima of the potential is insufficient to ensure longevity of the networks. Results of our studies on the influence of asymmetry of the potential on the dynamics of cosmological domain walls will be presented.

## Sebastian Schwieger

*Stability Walls for T-branes on del-Pezzo Surfaces*

# Stability Walls for T-branes on del-Pezzo Surfaces

## In the past it has been shown that bound states of 7-branes, so called T-branes, may not be stable on 4-cycles of positive or vanishing curvature. We will show how defect fields localised on the intersection curves with other 4-cycles may relax these criteria by acquiring a vev. Starting from this observation we will then investigate wall-crossing phenomena in Kähler moduli space.

## Pierre Corvilain

*Circle compactification, Anomalies and Field Distances*

# Circle compactification, Anomalies and Field Distances

## Circle compactifications play a central role in string phenomenology, especially in the context of F-theory. Properly integrating the KK tower can sometimes be subtle, but also more instructive than expected. We show that chiral anomalies are preserved under a circle compactification from 4D to 3D, arising as field-dependent Chern-Simons terms in 3D, if the regulator used decompactifies at high energies. This then implies, when the F/M-theory duality can be used, that the 4D effective field theories coming from F-theory don’t have chiral anomaly. We relate this method to the species bound of [1] and use the latter to compute correction to the metric of the radius modulus. We explain how this connects with the Swampland Distance Conjecture [2] and the idea explored in [3], that the infinite distance singularities are emerging from integrating out infinitely many light modes.

[1] Dvali 0706.2050 [2] Ooguri, Vafa hep-th/0605264 [3] Grimm, Palti, Valenzuela 1802.08264

## 12:00 – 12:15

## Pramod Shukla

*LVS flat directions and inflaton field range*

# LVS flat directions and inflaton field range

## I will discuss a new challenge for consistently realizing large field inflation in the LVS framework. It turns out that the directions which remain flat after LVS moduli stabilization are bounded by logarithm of the stabilized volume of the Calabi Yau threefold, which arises from the Kaehler cone conditions. I will also discuss the specifics of the subsequent challenges, and the possible resolutions in the context of Fibre inflation model.

## Hiroyuki Abe

*Moduli stabilization and F-term uplifting in semi-realistic magnetized orbifold models*

# Moduli stabilization and F-term uplifting in semi-realistic magnetized orbifold models

## Magnetized orbifold models provide a well-motivated background for particle phenomenology, where the standard model gauge groups, chiral structures, generations of quarks and leptons and Yukawa hierarchies are determined by the magnetic fluxes. Within such a framework, we construct a concrete model realizing both visible and hidden sectors, and show that the anti-de Sitter vacuum of the nonperturbative moduli potential can be uplifted to a Minkowski minimum by the vacuum energy created by a dynamical supersymmetry breaking in the hidden sector.

## Erik Parr

*How an unsupervised Neural Network sees the Heterotic Orbifold Landscape*

# How an unsupervised Neural Network sees the Heterotic Orbifold Landscape

## We explore the Heterotic Orbifold Landscape and generate a two-dimensional map of it. The starting point is the Orbifolder software, which we use to generate millions of random data points in the landscape and to classify them by their spectra. Each data point is represented by up to 128 parameters, called Shifts and Wilson lines. In order to handle this data, we use machine learning techniques to find non-linear structures in the landscape. The first step in this process is the preprocessing of the data, i.e. transformation of the models to an invariant representation. Then, we utilize a Neural Network, i.e. a so-called Autoencoder, to find – via unsupervised learning – a lower dimensional representation of the string landscape. This allows us to identify new fertile patches, i.e. clusters in the landscape with a high concentration of MSSM-like models. The main common properties of these clusters are then investigated by techniques like decision trees.

## 12:15 – 12:30

## Mateusz Duch

*Kinetic decoupling and gauge invariance of the resonant annihilation in a vector dark matter model*

# Kinetic decoupling and gauge invariance of the resonant annihilation in a vector dark matter model

## In models with resonantly enhanced dark matter annihilation, the coupling of dark sector to the visible one is suppressed with respect to non-resonant scenarios. Consequently the cross section for the scattering of dark matter on light states in the thermal bath is diminished and temperatures of the kinetic and chemical decoupling are similar. This leads to the interesting interplay between dark matter temperature and density. Moreover for a vector dark matter model, the calculation of the resonant annihilation cross-section requires the proper treatment of the mediator self-energy. I will present formulas that satisfy the conditions of gauge-invariance and unitarity obtained within the pinch technique. Finally I will discuss quantitatively the consequences for the calculation of dark matter relic abundance and bounds from direct and indirect detection experiments in the Abelian vector dark matter model.

## Yoshiyuki Tatsuta

*Effects of fixed-point localized mu-terms in flux compactifications*

# Effects of fixed-point localized mu-terms in flux compactifications

## We discuss effects of mu-terms in the minimal supersymmetric standard model (MSSM) at fixed points of a fluxed two-dimensional orbifold. Supposing non-trivial flux background on a toroidal orbifold, it is well known that there appear multiple Kaluza-Klein (KK) modes of matter fields in each of KK levels. Then, we can identify the multiple lowest modes with a family structure and such a family-generating mechanism provides a variety of extra dimensional model buildings. However, it is pointed out that there appear family-like multiple Higgs bosons via flux in many setups, and also that such models are disfavored by unmeasurement of flavor changing neutral current. In this talk, we plan to suggest mu-terms localized at fixed points, and show possibilities to realize an effectively light mu-term between single pair of MSSM Higgs multiplets.

## David Andriot

### Dimensional reduction on curved manifolds: low energy, swampland, de Sitter

# Dimensional reduction on curved manifolds: low energy, swampland, de Sitter

## In string compactifications, considering a compact manifold M that is not Ricci flat (e.g. most group manifolds) provides several interesting features for phenomenology. For instance, specific moduli can then be stabilized classically; also, classical de Sitter solutions require a negative Ricci scalar for M. In this talk, I will present recent results regarding the physics on such manifolds.

In view of deriving a string four-dimensional low energy effective theory on a group manifold, we determined the spectrum of the Laplacian operator. We first found an interesting low energy truncation of that spectrum. We used that knowledge to study different points in field space that could be in tension with the swampland distance conjecture. Finally, related thoughts concerning the recent de Sitter swampland criterion will be presented.

## 12:30 – 14:00 Lunch break

## 14:00 – 15:15

## Cosmo 2

## Strings 3

## Pheno 1

## 14:00 – 14:15

## Viraf Mehta

*Axions and Non-linear Effects*

# Axions and Non-linear Effects

## We discuss various objects appearing once simulations of axion inflation models go beyond leading order, including the appearance of oscillons in a variety of scenarios. We touch upon the occurence of these objects in other cosmological settings – like fuzzy dark matter – and find these non-linear effects to be generically long-lived in various setups.

## Timm Wrase

*de Sitter extrema and the swampland*

# de Sitter extrema and the swampland

## Following the recent claim in 1806.08362 that dS extrema are in the swampland, I will review and scrutinize existing constructions of type II flux compactifications that use only classical ingredients. I will review some no-go results against dS extrema but also show that explicit constructions of (unstable) dS extrema exist that are inconsistent with the conjecture in 1806.08362. I will scrutinize all potential assumptions that go into these existing constructions.

## Andrei Constantin

*Physical Yukawa Couplings in Heterotic String Theory from Localisation*

# Physical Yukawa Couplings in Heterotic String Theory from Localisation

## We propose an analytic method to calculate the matter field Kähler metric in heterotic compactifications on smooth Calabi-Yau three-folds with Abelian internal gauge fields. The matter field Kähler metric determines the normalisations of the N = 1 chiral superfields, which enter the computation of the physical Yukawa couplings. It turns out that, due to large internal gauge flux, the normalisation integrals localise around certain points on the compactification manifold and can, hence, be calculated approximately without precise knowledge of the Ricci-flat Calabi-Yau metric. In a final step, we show how this local result can be expressed in terms of the global moduli of the Calabi-Yau manifold.

## 14:15 – 14:30

## Stephen Angus

*Einstein Double Field Equations*

# Einstein Double Field Equations

## The closed-string massless sector hints at a natural augmentation to General Relativity, in which the metric, B-field, and dilaton together comprise the fundamental gravitational multiplet. The O(D,D)-covariant formalism of Double Field Theory provides a concrete geometrical foundation for this `Stringy Gravity’. In this talk I will introduce the on-shell conserved stringy energy-momentum tensor which appears in the `Einstein Double Field Equations’, i.e. the doubled generalization of Einstein’s equations in the presence of matter. I will then consider the most general D = 4, static, spherically symmetric solution with nontrivial matter localized only up to a finite radius. The exterior vacuum geometry has four parameters—this additional freedom allows gravity to be modified at small values of the dimensionless radius normalized by mass, R/MG, which may be relevant to the dark matter and dark energy problems.

## Hajime Otsuka

*SO(32) Heterotic Line Bundle Models*

# SO(32) Heterotic Line Bundle Models

## We search for the three-generation standard-like and/or Pati-Salam models from the SO(32) heterotic string theory on smooth, quotient complete intersection Calabi-Yau threefolds with multiple line bundles, each with structure group U(1). These models are S- and T-dual to intersecting D-brane models in type IIA string theory. We find that the stable line bundles and Wilson lines lead to the standard model gauge group with an extra U(1)B−L via a Pati-Salam-like symmetry and the obtained spectrum consists of three chiral generations of quarks and leptons, and vector-like particles. Green-Schwarz anomalous U(1) symmetries control not only the Yukawa couplings of the quarks and leptons but also the higher-dimensional operators causing the proton decay.

## Eduardo Gonzalo Badia

*Constraints on the SM Higgs from the WGC*

# Constraints on the SM Higgs from the WGC

## It has been recently argued that the presence of any non-SUSY AdS stable vacua implies that a theory cannot be consistently coupled to gravity (Ooguri-Vafa conjecture). The application of this conjecture to the SM and its compactifications to two or three dimensions has lead to interesting predictions on low energy physics. One of these predictions is an upper bound on the Higgs vev, determined by the cosmological constant, that appears when trying to avoid the formation of an AdS minima around the neutrino scale. We will show that, when the number of quark/lepton generations is bigger or equal than three, the Higgs vev is also bounded from below by $Lambda_{text{QCD}}$. These bounds force the EW and QCD scale to be relatively close. They also imply that the Higgs vev is stable against quantum corrections, leading to a reassessment of the SM hierarchy problem.

## 14:30 – 14:45

## Victor Alfonzo Diaz

*Primordial Black Holes from String Inflation*

# Primordial Black Holes from String Inflation

## We present a single-field string inflationary model which allows for the generation of primordial black holes in the low mass region where they can account for a significant fraction of the dark matter abundance. The potential is typical of type IIB fibre inflation models and features a plateau at CMB scales and a near inflection point at small distance scales where the power spectrum is enhanced due to a period of ultra slow-roll. The tunability of the underlying parameters may be guaranteed by scanning through the string landscape and their stability against quantum corrections ensured by an effective shift symmetry.

## Mehmet Demirtas

*On Calabi-Yau Compactifications with Large Picard Number*

# On Calabi-Yau Compactifications with Large Picard Number

## We study Calabi-Yau threefold hypersurfaces with $1 ll h^{1,1} le 491$, and we characterize some of their topological properties as functions of $h^{1,1}$. We triangulate $1.8 times 10^6$ polytopes from the Kreuzer-Skarke database and compute the Mori cones of the associated toric varieties $V$. We show that the K”ahler cone of $X$ is very narrow at large $h^{1,1}$, and study the consequences.

## Florian Wolf

*Challenging the Refined Swampland Distance Conjecture*

# Challenging the Refined Swampland Distance Conjecture

## By constructing phenomenological models from String Theory, it became more and more apparent that not every effective theory, consistent at low-energy in 4 dimensions, can be coupled to Quantum Gravity. Theories that are not able to be consistently coupled to Quantum Gravity are dubbed to be in the Swampland and can never arise from fully fledged string compactifications. The aim of this talk is to challenge the (Refined) Swampland Distance Conjecture, which is an important criterium to decide whether an effective theory lies inside the Swampland. The focus will be in particular on the different phases of various two-parameter moduli spaces of Calabi-Yau compactifications. We will highlight special points, such as conifold, Landau-Ginzburg and large complex structure point in the context of the Swampland Distance Conjecture. Consequences for large-field inflation in String Theory are briefly described as well.

## 14:45 – 15:00

## Francisco Pedro

*Inflationary non-linear sigma models*

# Inflationary non-linear sigma models

## Non-linear sigma models appear naturally in the context of string inflation models and can feature a rich phenomenology even in the quasi single field limit. In this talk I will present an overview of their dynamics and clarify some issues about their stability.

## Yifan Chen

*Perturbative moduli stabilisation in type IIB/F-theory framework*

# Perturbative moduli stabilisation in type IIB/F-theory framework

## We propose a new mechanism of (geometric) moduli stabilisation in type IIB/F-theory four-dimensional compactifications on Calabi-Yau manifolds, in the presence of 7-branes, that does not rely on non-perturbative effects. Complex structure moduli and the axion-dilaton system are stabilised in the standard way, without breaking supersymmetry, using 3-form internal fluxes. K”ahler class moduli stabilisation utilises perturbative string loop corrections, together with internal magnetic fields along the D7-branes world-volume leading to Fayet-Iliopoulos D-terms in the effective supergravity action. The main ingredient that makes the stabilisation possible at a de Sitter vacuum is the logarithmic dependence of the string loop corrections in the large two-dimensional transverse volume limit of the 7-branes.

## Saul Ramos-Sanchez

*Flavor in MSSM-like heterotic orbifolds*

# Flavor in MSSM-like heterotic orbifolds

## In this talk, we study the flavor symmetries emerging in Abelian orbifolds of the E8×E8 heterotic string, including those with rototranslations. We study the breaking of flavor symmetry groups when Wilson lines are present and focus on models where the MSSM is obtained. We perform the widest scan so far in order to obtain models of this kind, determining the most frequent flavor symmetries appearing in semi-realistic string compactifications. Some aspects about the flavor phenomenology of these models are discussed.

## 15:00 – 15:15

## Amjad Ashoorioon

*Extended Effective Field Theory of Inflation*

# Extended Effective Field Theory of Inflation

## I present a general framework where the effective field theory of single field inflation is extended by the inclusion of operators with mass dimension 3 and 4 in the unitary gauge. These higher dimensional operators introduce quartic and sextic corrections to the dispersion relation. I study the regime of validity of this extended effective field theory of inflation and the effect of these higher dimensional operators on the CMB observables associated with scalar perturbations, such as the speed of sound (including the time-dependent case), the amplitude of the power spectrum and the tensor-to-scalar ratio. Tensor perturbations remain instead, unaltered.

## Eirik Eik Svanes

*Non Perturbative Superpotentials and Counting Associatives*

# Non Perturbative Superpotentials and Counting Associatives

## We conjecture that certain G2 manifolds contain an infinite number of associative sub, manifolds, i.e. three-cycles calibrated with respect to the G2 holonomy three-form. Using a sequence of string dualities, we connect these to a non-perturbative superpotential of the Donagi-Grassi-Witten type.

## 15:15 – 15:45 Coffee break

## 15:45 – 17:15

## Cosmo 3

## Strings 4

## Pheno 2

## 15:45 – 16:00

## Taro Mori

*Multi-field effects in a simple extension of R^2 inflation*

# Multi-field effects in a simple extension of R^2 inflation

## We consider inflation in the system containing a Ricci scalar squared term and a canonical scalar field with quadratic mass term. In the Einstein frame this model takes the form of a two-field inflation model with a curved field space, and under the slow-roll approximation contains four free parameters corresponding to the masses of the two fields and their initial positions. Our analysis is based on the δN formalism, which allows us to determine predictions for the non-Gaussianity of the curvature perturbation. Depending on the choice of parameters, we find predictions that range from those of R2 inflation to those of quadratic chaotic inflation, with the non-Gaussianity of the curvature perturbation always remaining small. Using our results we are able to put constraints on the masses of the two fields.

## Wieland Staessens

*A Song of D-branes and Fluxes*

# A Song of D-branes and Fluxes

## Type IIA compactifications with RR and NS fluxes are characterized by perturbative scalar potentials suitable to stabilize closed string moduli. In recent times the structure of the scalar potential has been elucidated in terms of generalized axion monodromies, which remain present in the presence of D6-branes. Generically D6-branes are required to construct fully global models, but might complicate the identification of vacua with stabilized moduli. In this talk, we consider D6-branes with displacement moduli and discuss the interplay between moduli stabilization and supersymmetry breaking. A straightforward application of such set-ups are supersymmetric DFSZ axion models, in which the strong CP problem can be addressed. We will also comment on the construction of inflationary models in Type IIA flux compactifications in light of the Ooguri-Vafa swampland conjectures.

## Marcin Badziak

*Asymptotically Free Supersymmetric Twin Higgs*

# Asymptotically Free Supersymmetric Twin Higgs

## Twin Higgs (TH) models explain the absence of new colored particles responsible for natural electroweak symmetry breaking. All known ultraviolet completions of TH models require some non-perturbative dynamics below the Planck scale. A new type of supersymmetric Twin Higgs model is presented in which the TH mechanism is introduced by a new asymptotically free gauge symmetry. The model features natural electroweak symmetry breaking for squarks and gluino heavier than 2 TeV even if supersymmetry breaking is mediated around the Planck scale, and has interesting flavor phenomenology including the top quark decay into the Higgs and the up quark which may be discovered at the LHC. The talk will be primarly based on arXiv:1707.09071 and arXiv:1711.11040.

## 16:00 – 16:15

## Quentin Bonnefoy

*Axions in a highly protected gauge symmetry model*

# Axions in a highly protected gauge symmetry model

## I will discuss a model of an accidental global symmetry, and its axionic Goldstone mode, obtained from an abelian quiver with scalar bifundamental fields. This model corresponds to the latticization of a 5d abelian theory on a linear dilaton background and can accommodate a protected QCD axion (or DM axion-like particles). Indeed, explicit breaking contributions to the axion mass are already much suppressed for few quiver sites. I will also comment on axion couplings in such protected theories of a QCD axion, which may or may not require an additional sector.

## Anthony Ashmore

*Moduli and obstructions of N=1 heterotic backgrounds*

# Moduli and obstructions of N=1 heterotic backgrounds

## A recurring problem in heterotic compactifications is the plethora of moduli fields in the resulting low-energy theories which we do not observe in nature. One might be able to lift these moduli by moving to non-Kahler compactifications. The general N=1 heterotic solution with a 4d Minkowski vacuum is described by the Strominger system. The compactification manifold is non-Kahler, there is H flux and one has a non-trivial Bianchi identity to deal with. The moduli of these solutions has been a mystery until recently. I will present work on understanding the moduli of these compactifications to higher orders using the heterotic superpotential. Obstructions to integrating the deformations appear as non-zero Yukawa couplings in the low-energy theory. I will also comment on links to generalised geometry and a generalisation of Kodaira-Spencer gravity.

## Michał Iglicki

*Multicomponent Dark Matter – a vector-fermion model*

# Multicomponent Dark Matter – a vector-fermion model

## Mono-component WIMP Dark Matter scenario is not sufficient to explain the current experimental data. In this talk I will discuss a vector-fermion model of DM including (dependending on parameters) 2 or 3 dark components, with special emphasis of DM self-interaaction and possibility of distinguishing special cases in collider experiments.

## 16:15 – 16:30

## Guillem Domenech

*Dilatonic couplings and the late time universe*

# Dilatonic couplings and the late time universe

## Dilatonic couplings provide interesting models for dark energy. In this talk, I will show how a dilatonic coupling to (only) dark matter alleviates the coincidence problem and provides non-trivial Horndeski model that satisfy the bounds on the propagation of gravitational waves.

## Ehsan Hatefi

*Highly Symmetric D-brane-Anti-D-brane Effective Actions*

# Highly Symmetric D-brane-Anti-D-brane Effective Actions

## To deal with symmetries of string amplitudes as well as their all order α′ corrections we first address a four point function of one closed string Ramond-Ramond (RR) and two real tachyons on the world volume of brane-anti brane system. We then focus on symmetries of string theory as well as universal tachyon expansion to achieve both string and effective field theory of an RR and three tachyons where the complete algebraic analysis for the whole S-matrix was also revealed. Finally we work out with symmetries of theory and show that tachyon expansion is universal and precisely discover all order singularity structures of D-brane-anti-D-brane effective actions of string theory. Various remarks about the so called generalised Veneziano amplitude and new string couplings are elaborated as well.

## Da Huang

*Electroweak Baryogenesis and Dark Matter from a Complex Singlet Scalar*

# Electroweak Baryogenesis and Dark Matter from a Complex Singlet Scalar

## We connect the electroweak (EW) baryogenesis and the dark matter physics in a complex singlet scalar S extension of the Standard Model. We impose the additional CP and Z_2 symmetries on the scalar potential. With the complex vacuum expectation value of S at the temperature higher than the EW phase transition, the CP symmetry is spontaneously broken and a strong first-order EW phase transition is easily realized. Together with a dimension-6 effective operator that gives new complex contributions to the top quark mass, we show that it is easy to yield the observed baryon asymmetry in our Universe. On the other hand, the CP and Z_2 symmetries are recovered after the EW phase transition. The lighter real state in S can be the dark matter candidate, and the strong constraints of CP violations can be avoided. With the scan of parameter space, we can find models which can explain the dark matter relic abundance and the baryon asymmetry simultaneously while satisfying all constraints.

## 16:30 – 16:45

## Michał Artymowski

*Uphill inflation with gravitational reheating*

# Uphill inflation with gravitational reheating

## I will present the idea of uphill inflation in the scalar-tensor theory. The inflaton field rolls uphill the Jordan frame potential generating quasi-de Sitter expansion of the Universe. I will assume gravitational reheating and I will show how it influences inflation, thermal history of the Universe and the spectrum of primordial gravitational waves.

## Markus Dierigl

*Global Tensor-Matter Transitions in F-Theory*

# Global Tensor-Matter Transitions in F-Theory

## In this talk I will explain how anomaly considerations, including Abelian and gravitational anomalies, can constrain allowed tensor-matter transitions in F-theory. Since these transitions pass through a point of strong coupling, they are a promising way of studying the consistent coupling of 6d SCFTs to gravity. Moreover, most of the allowed transitions can be easily constructed in a toric framework.

## Zofia Fabisiewicz

*A systematic mass insertion approach to lepton flavor violation in the MSSM*

# A systematic mass insertion approach to lepton flavor violation in the MSSM

## In this talk we analyze the sources of lepton flavor violation in the Minimal Supersymmetric Standard Model (MSSM) in the processes $l → l’ gamma$ and $h → ll’$. Using the Flavor Expansion Theorem, a recently developed technique of a purely algebraic mass-insertion expansion of the amplitudes, we recover the direct analytic dependence of the results on the MSSM Lagrangian parameters. Both flavor-violating off-diagonal terms and flavor-conserving mass-insertions are considered. We also study the decoupling features of the amplitudes in the limit of heavy SUSY spectrum. The results are compared with calculations in the mass eigenstates basis (i.e. using the exact diagonalization of the mass matrices).

## 16:45 – 17:00

## Manki Kim

### Monodromy Charge in D7-brane Inflation

# Monodromy Charge in D7-brane Inflation

## In axion monodromy inflation, traversing N axion periods corresponds to accumulating N units of a quantized charge. In models with moving D7-branes, this monodromy charge is D5-brane or D3-brane charge induced on the D7-branes. The stress-energy of the monodromy charge affects the internal space, changing the inflaton potential and potentially limiting the field range. We compute the backreaction of monodromy charge in the fluxbrane and Higgs-otic scenarios.

## Eduardo Garcia-Valdecasas Tenreiro

*From D-brane instantons to Bipartite Field Theories*

# From D-brane instantons to Bipartite Field Theories

## In this talk we present a method for realising Bipartite Field Theories in string theory starting from D3-branes probing toric CY singularities. Adding a D-brane instanton will deform the theory into a BFT. In this way many BFT’s can be embedded in string theory.

## Alvaro Herraez

*AdS-Phobia: confronting the SM and SUSY with the WGC*

# AdS-Phobia: confronting the SM and SUSY with the WGC

## After recalling that the sharpened version of the WGC proposed by Ooguri and Vafa implies that any stable non-SUSY AdS vacuum is in the swampland, we will present some of the consequences that this may have for the SM and some of its extensions. First, we will argue why it is interesting to consider compatifications of the SM to 2D on $T^2/Z_N$. From these we can conclude that the SM is not robust against the appearance of AdS vacua in 2D and hence would be, by itself, inconsistent with quantum gravity. However, if the SM is embedded at some scale into a supersymmetric version, these AdS vacua present in the non-SUSY case disappear or become unstable, suggesting that the WGC favors supersymmetry. Finally, we present different scenarios in which embedding the orbifold action into different gauge symmetries can lead to additional constraints.

## 17:00 – 17:15

## Michał Wieczorek

### On reheating in alpha attractor models of inflation

# On reheating in alpha attractor models of inflation

## With increasing accuracy of CMB data, a thorough, quantitative understanding of the post-inflationary reheating era becomes more and more important for constraining different models of inflation. In particular, a precise computation of the non- omogeneous field evolution during preheating is desirable. In this talk I will present the results of such computation for alpha-attractor models of inflation. I will show the Floquet analysis of field perturbations evolution, as well as the results of full non-linear simulations. I will discuss the importance of studying the dynamics of both scalar fields present in the model.

## Kilian Mayer

*Black strings, one-loop Chern-Simons terms, and F-theory*

# Black strings, one-loop Chern-Simons terms, and F-theory

## In this talk I will present a macroscopic analysis of black strings in six-dimensional F-theory compactifications in the presence of a multi-centered Taub-NUT space. These strings have an AdS3×S3/Zm near horizon geometry and are realized in F-theory as D3-branes wrapping a curve in the compactification manifold. Starting from a six-dimensional point of view we compute central charges and levels of the dual conformal field theory, which enjoys N=(0,4) supersymmetry, up to sub-subleading order. Taking account the full geometry, in particular the asymptotic Taub-NUT space transverse to the string, and including one-loop Chern-Simons arising from integrating out massive Kaluza-Klein modes turn out to be the crucial ingredients to obtain the expected results.

## Damian Kaloni Mayorga Pena

*U(1) SYMMETRIES WITH HIGHER CHARGE SINGLETS IN F-THEORY AND TYPE IIB*

# U(1) SYMMETRIES WITH HIGHER CHARGE SINGLETS IN F-THEORY AND TYPE IIB

## We consider the Sen limit of several global F-theory compactifications exhibiting a single U(1) gauge symmetry and singlets with U(1) charges higher than 2. We show that these indeed have a consistent limit where they can be viewed as resulting from an intersecting D-brane configuration in type IIB. We discuss the match of the fluxes and the spectrum in detail. We used the intuition gained from existing F-theory models in order to systematically explore all constant massless particle spectra for models with a single U(1) symmetry on the perturbative type IIB side.

# THU (5/7)

## 9:15 – 9:45 Misao Sasaki *Scalaron as a heavy field and formation of primordial black holes*

# Scalaron as a heavy field and formation of primordial black holes

## A model of two-stage inflation in which a scalar field, chi, is non-minimally coupled to Starobinsky’s R2 gravity is discussed.

The scalaron in Starobinsky’ model drives the first stage of inflation, and chi drives the second. At the end of the first stage, the scalaron becomes heavy and undergoes damped oscillations. This causes enhancement and oscillatory features in the curvature perturbation power spectrum. The peak in these features may give rise to copious production of primordial black holes (PBHs). For a suitably chosen set of model parameters, these PBHs may even be identified as the CDM of the Universe.

## 9:45 – 10:15 Keith Dienes *Darkness from the Bulk: An Alternative Approach to Dark-Matter Physics*

# Darkness from the Bulk: An Alternative Approach to Dark-Matter Physics

## TBA

## 10:15 – 10:45 Wilfried Buchmuller *Flux compactifications and the hierarchy problem*

# Flux compactifications and the hierarchy problem

## We consider gauge-Higgs unification in six dimensions, compactified on a magnetized torus. It is shown that in the effective four-dimensional theory a shift symmetry of the Wilson-line scalar is preserved, despite the presence of Yukawa and gauge couplings.

## 10:45 – 11:15 Coffee break

## 11:15 – 11:45 Thomas Van Riet *Is dS space in the Swampland?*

# Is dS space in the Swampland?

## I discuss the constructions of dS space in string theory. And in particular the KKLT scenario since it is the prime example supporting evidence for the landscape of dS vacua. I will emphasize how the 6d backreaction and the associated singularities claimed in the literature might be resolved. But that a new problem, concerning 4d backreaction has recently come to the surface. One potential way around the problem of 4d backreaction is racetrack finetuning. I explain why racetrack finetuning gives super-Planckian decay constants and is hence potentially worry-some. I then make a bold conjecture that dS space is in the Swampland and why that does not need to contradict observations. Finally I discuss exotic theories, like Vasiliev theory or Hull’s star string theories and how such theories can have dS vacua which are fully stable and even be supersymmetric and therefore allow a dS/CFT description.

## 11:45 – 12:15 Mirjam Cvetic *Global F-theory Standard Models*

## 12:15 – 12:45 Robert Brandenberger *Superstring Theory and Nonsingular Cosmology*

## 12:45 – 13:15 Coffee

## Free afternoon

## 18:00 – 19:15 Public talk by Fernando Quevedo *The Search for the Fundamental Theory of the Universe*

## 19:45 Reception at the Kazimierzowski Palace (Main Campus of the University)

To board the buses 128 and 175 one needs to go to the bus stop at Żwirki i Wigury Street, located near the corner of Banacha and Żwirki i Wigury (in the direction towards the city center).