Quantum Universe

• Slava Mukhanov

A Slippery Slope in the Inflationary Landscape

• Ben Freivogel (Amsterdam U.)

Vacuum Selection on Axionic Landscapes

• Thorsten Battefeld (Goettingen U.)

Random potentials are often used to model the string theoretical landscape. Taking axionic landscapes as a simple example, I discuss the distribution of minima that are reached dynamically, both numerically and analytically. Such landscapes are well suited for inflationary model building due to the presence of shift symmetries and possible alignment effects (the KNP mechanism). The resulting distribution of dynamically reached minima differs considerably from the naive expectation based on counting all vacua. These differences are more pronounced in the presence of many fields due to dynamical selection effects. We show that common analytic arguments based on random matrix theory in the large D-limit to estimate the distribution of minima are insufficient for quantitative arguments pertaining to the dynamically reached ones. This discrepancy is not restricted to axionic potentials. I further comment on additional changes to the distribution induced by instabilities with respect to tunneling.

On the origin of adiabatic perturbations

• Enrico Pajer (Utrecht U.)

Axion Monodromy and the Weak Gravity Conjecture

• Fabrizio Rompineve (ITP Heidelberg)

Axions with broken discrete shift symmetry (axion monodromy) have recently played a central role both in the discussion of inflation and the `relaxion' approach to the hierarchy problem. We suggest a very minimalist way to constrain such models by the weak gravity conjecture for domain walls: While the electric side of the conjecture is always satisfied if the cosine-oscillations of the axion potential are sufficiently small, the magnetic side imposes a cutoff, Λ^(3)∼mfMpl, independent of the height of these `wiggles'. We also briefly discuss the non-trivial question which version, if any, of the weak gravity conjecture for domain walls should hold. In particular, we show that string compactifications with branes of different dimensions wrapped on different cycles lead to a `geometric weak gravity conjecture' relating volumes of cycles, norms of corresponding forms and the volume of the compact space. Imposing this `geometric conjecture', e.g. on the basis of the more widely accepted weak gravity conjecture for particles, provides at least some support for the (electric and magnetic) conjecture for domain walls.

M-theory compactifications on G_2 manifolds

• Thaisa Guio (Bonn U.)

M-theory compactifications on G_2 manifolds give rise to interesting 4d N=1 SUGRA theories. We review a method pioneered by Kovalev to construct compact G_2 manifolds via a compatible gluing of a pair of asymptotically cylindrical Calabi-Yau threefolds, and show that these indeed give rise to a rich landscape of 4d N=1 M-theory vacua. In a certain limit we are able to analyse explicitly the target space of G_2 metrics on M-theory compactifications based on the moduli space of Kovalev's geometrical building blocks.

Recent Developments of Flux-Scaling Scenarios of Moduli Stabilisation

• Florian Wolf (MPI for Physics)

At first, I will summarise the basic concepts and construction strategy of flux-scaling scenarios of moduli stabilisation in string theory. Characteristic differences to other moduli stabilisation scenarios will be discussed as well as the application to F-term axion monodromy inflation. In the main part I will comment on recent developments in particular concerning deSitter uplift and the possibility for sequestering.

How Potent is Nilpotent Inflation?

• Clemens Wieck (IFT/UAM)

We study the embedding of inflation with nilpotent multiplets in supergravity, in particular the decoupling of the sgoldstino scalar field. Instead of being imposed by hand, the nilpotency constraint on the goldstino multiplet arises in the low energy-effective theory by integrating out heavy degrees of freedom. We find that the inflaton potential receives two types of corrections which are otherwise missed. One is from the backreaction of the sgoldstino, the other from the heavy fields generating its mass. Because these scale oppositely with the Volkov-Akulov cut-off scale, a consistent decoupling of the sgoldstino is questionable. Still, we identify a parameter window in which sgoldstino-less inflation can take place, up to corrections which flatten the inflaton potential.

Free fermionic and orbifold models

• Viraf Mehta (Heidelberg U.)

We provide a dictionary relating free fermionic and symmetric toroidal orbifold descriptions of the heterotic string, and detail the general approach as well as giving an illustrative example.

On Mirror Symmetry for Calabi-Yau Fourfolds with Three-Form Cohomology

• Sebastian Greiner (MPI for Physics / ITP Utrecht)

We study the action of mirror symmetry on two-dimensional N=(2,2) effective theories obtained by compactifying Type IIA string theory on Calabi-Yau fourfolds. Our focus is on fourfold geometries with non-trivial three-form cohomology. The couplings of the massless zero-modes arising by expanding in these forms depend both on the complex structure deformations and the Kahler structure deformations of the Calabi-Yau fourfold. We argue that two holomorphic functions of the deformation moduli capture this information. These are exchanged under mirror symmetry, which allows us to derive them at the large complex structure and large volume point. We discuss the application of the resulting explicit expression to F-theory compactifications and their weak string coupling limit. In the latter orientifold settings we demonstrate compatibility with mirror symmetry of Calabi-Yau threefolds at large complex structure. As a byproduct we find an interesting relation of no-scale like conditions on Kahler potentials to the existence of chiral and twisted-chiral descriptions in two dimensions.

Aspects of non-geometric flux vacua

• Daniela Herschmann (MPI Munich)

Various aspects of non-geometric flux vacua are discussed, like soft supersymmetry breaking, de Sitter minima and applications to inflation.

Conserved Currents for Arbitrary Helicity

• Norbert Dragon (Leibniz Universität Hannover)

We present the unitary representation of the Poincaré group on massless states of arbitrary helicity and construct a conserved current. Such a current seemed to be excluded by arguments of Witten and Weinberg. Taking into account the nontriviality of the Hopf bundle we clarify and correct their statements and other folklore.

The structure of quantum periods for Calabi-Yau fourfolds

• Andreas Gerhardus (Bonn U.)

In this talk we discuss the structure of integral periods for Calabi-Yau fourfolds globally over the entire quantum Kaehler moduli space and deduce their monodromy behavior around singular points. While for Calabi-Yau threefolds the dimension of the period vector is solely determined by the dimension of the moduli space, this is in general not true anymore for Calabi-Yau fourfolds. We comment on implications of these findings for flux induced superpotentials in compactification scenarios.

Higher-Derivative Supergravity, $\alpha'$-Corrections and Phenomenological Applications

• David Ciupke (DESY)

String phenomenology on twisted tori

• David Andriot (AEI Potsdam-Golm)

When trying to relate string theory to four-dimensional observable physics, the starting ten-dimensional space-time is usually split as a four-dimensional Minkowski or de Sitter space-time, times a six-dimensional compact manifold M. In this talk I will focus on M being a twisted torus, also known as nil- or solvmanifold. In addition of being classified and easy to handle, most of these manifolds are negatively curved, which is advantageous for phenomenology. I will first present and comment on newly discovered Minkowski backgrounds. I will then report on a cosmological inflation mechanism proposed in this context, and on the difficulties in its concrete realisation. I will finally discuss dimensional reduction on such manifolds, and their use in simple extra dimensions models for dark matter.

Aspects of Inflation

• Benedict Broy (DESY)

Recent Issues in String Cosmology

• Arthur Hebecker

Baryogenesis from strings

• Michele Cicoli (ICTP, Trieste and Bologna University)

I will present an explicit realisation of Affleck-Dine baryogenesis in the framework of sequestered type IIB models where inflation is driven by a Kahler modulus.

Brownian motion in the landscape

• Francisco Pedro (IFT/UAM)

From Type II string theory towards BSM/dark sector physics

• Gabriele Honecker (Johannes-Gutenberg-Universität Mainz)

Contrary to early "anything goes" statements, consistency of string theory compactifications severely constrains new physics scenarios, including the way the recently much-advocated axions can occur. These constraints will be discussed in the context of D-brane models in Type II string theory.

Recent Developments in Particle Phenomenology and the LHC

• Christophe Grojean

Killing the cMSSM softly

• Philip Bechtle (DESY)

We investigate the constrained Minimal Supersymmetric Standard Model (cMSSM) in the light of constraining experimental and observational data from precision measurements, astrophysics, direct supersymmetry searches at the LHC and measurements of the properties of the Higgs boson, by means of a global fit using the program Fittino. As in previous studies, we find rather poor agreement of the best fit point with the global data. We also investigate the stability of the electro-weak vacuum in the preferred region of parameter space around the best fit point. We find that the vacuum is metastable, with a lifetime significantly longer than the age of the Universe. For the first time in a global fit of supersymmetry, we employ a consistent methodology to evaluate the goodness-of-fit of the cMSSM in a frequentist approach by deriving p-values from large sets of toy experiments. We analyse analytically and quantitatively the impact of the choice of the observable set on the p-value, and in particular its dilution when confronting the model with a large number of barely constraining measurements. Finally, for the preferred sets of observables, we obtain p-values for the cMSSM below 10%, i.e. we exclude the cMSSM as a model at the 90% confidence level.

The Dynamics of Electroweak Relaxation

• Lukas Witkowski (Heidelberg University)

We explore the proposal of Cosmological Relaxation for generating a hierarchically small Higgs vacuum expectation value. In particular, we discuss its capacity for solving the electroweak hierarchy problem. To do so, we study the dynamics of the model and determine the relation between the fundamental input parameters and the electroweak vacuum expectation value. Depending on the input parameters the model exhibits three qualitatively different regimes, two of which allow for a hierarchically small Higgs vacuum expectation value. In one case we obtain standard electroweak symmetry breaking whereas in the other electroweak symmetry is mainly broken by a Higgs source term. While the latter is not acceptable in a model based on the QCD axion, in non-QCD models this may lead to new and interesting signatures in Higgs observables.

Hunting ALPs in galaxy clusters

• Markus Rummel (University of Oxford)

Recursion relations from soft theorems

• Lui Huo (UHH)

We establish a set of new on-shell recursion relations for amplitudes satisfying soft theorems. The recursion relations can apply to those amplitudes whose additional physical inputs from soft theorems are enough to overcome the bad large-z behaviour. This work is a generalization of the recursion relations for amplitudes in scalar effective field theories with enhanced vanishing soft behaviours, which can be regarded as a special case of those with non-vanishing soft limits. We apply the recursion relations to tree-level amplitudes in various theories, including amplitudes in the Akulov-Volkov theory and amplitudes containing dilatons of spontaneously-broken conformal symmetry.

Non-locality in QFT due to Quantum Effects in Gravity

• Xavier Calmet (Sussex U)

I show that General Relativity coupled to a quantum field theory generically leads to non-local effects in the matter sector. These non-local effects can be interpreted in terms of quantum black holes. This interpretation fits nicely with thought experiments that point towards the existence of a minimal length in Nature. Using effective field theory techniques, one can describe this non-locality using higher dimensional operators. In the case of scalar fields, these operators have an approximate shift symmetry. We then apply our results to inflationary models. We find that small non-Gaussianities are a generic feature of models based on General Relativity coupled to matter fields. However, these effects are too small to be observable in the Cosmic Microwave Background.

De Sitter vacua with two axions

• Markus Dierigl (DESY)

We first describe in general terms how to derive Minkowski or de Sitter vacua from N=1 SUGRA with two axions. Then we discuss a possible embedding in a 6D flux compactification model with two axions involved in a Green-Schwarz mechanism that cancels an anomaly related to a U(1) flux which breaks SUSY at a high scale.

Moduli Spaces of AdS_{5} vacua in N=2 supergravity

• Constantin Muranaka (UHH)

I will talk about the conditions for maximally supersymmetric AdS_5 vacua of five-dimensional gauged N=2 supergravity coupled to vector-, tensor- and hypermultiplets charged under an arbitrary gauge group. Moreover I will explain the moduli space of these vacua and show that it carries a natural Kaehler structure.

Supersymmetric AdS Solutions in Supergravity

• Severin Luest (UHH)

We study anti-de Sitter solutions in supergravity in arbitrary dimension and derive a simple criterion for the existence of AdS solutions that do not break any supersymmetry.

Higgs mass from SUSY breaking sector

• Masaki Asano (Bonn U.)

Gauge mediation is one of the plausible scenario, but the observed Higgs mass may conflict to a minimal realization of such a scenario (because the A-term is very small). We show that a meson in the SUSY breaking sector can play a role of the singlet S in the next-to-MSSM. In our framework, the hidden strong dynamics, which provides a meta-stable SUSY breaking vacuum, is responsible also for forming S, and the soft SUSY breaking mass for S, which is a key to explain the correct electroweak symmetry breaking. Thus, all the ingredients for successful phenomenology originate from the common dynamics.(Based on arXiv:1510.08033)

Sasakian quiver gauge theory on the conifold

• Jakob Geipel (Hanover U.)

This talk describes the quiver gauge theory on the Sasaki-Einstein manifold $T^{1,1}$ and its metric cone, the conifold, which is obtained by imposing an equivariance condition. The results are compared with those for the Kaehler coset $CP^1 \times CP^1$. A description of the moduli space of Hermitian Yang-Mills instantons in terms of adjoint orbits is given.

6D SCFTs and stringy geometry

• Stefano Massai (LMU Munich)

The large symmetry group of string theory leads to new geometric structures of spacetime, whose description remains very elusive. We will discuss a realization of such geometries obtained from six-dimensional, torus fibered heterotic compactifications with T-duality monodromy. These are described by a fibration of an auxiliary surface whose degenerations define stringy, “non-geometric” branes. We will study these objects by constructing F-theory dual models that admit Calabi-Yau resolutions, from which we can extract the low-energy physics. This leads to a set of 6D (1,0) SCFTs that we fully classify.

The DBI action and higher derivative SUSY

• Sjoerd Bielleman (IFT Madrid)

We study the effective action of the scalar position moduli of Type IIB Dp-branes. We find that in many instances the kinetic term is modified by a term proportional to the scalar potential itself. This can be linked to the appearance of higher-dimensional supersymmetric operators correcting the Kähler potential. We identify the supersymmetric dimension 8 operators describing the alpha' corrections captured by the DBI action. An example where this study could be useful in the future is in models of inflation where the inflaton is the position modulus of a Dp-brane.

Towards a world-sheet description of double field theory

• Erik Plauschinn (LMU Munich)

On the physical realization of Seiberg dual phases in branes at singularities

• Mikel Berasaluce-Gonzalez (Mainz U.)

Branes located at (toric) singularities may give rise to several quiver gauge theories related by Seiberg duality. Our goal is to study where in the Kähler moduli space each of them is being physically realized.

Model building on the non-factorisable type IIA T6/(Z4x\Omega R) orientifold

• Alexander Seifert (Mainz U.)

We studied the geometry of the non-factorizable toroidal Z4-orientifold and verified the anologies and differences to the factorizable case. The non-factorizable structure gives rise to additional constraints on the wrapping numbers for building fractional cycles and Lagrangian cycles. Thus, we can extend model building with intersecting D6-branes to non-factorizable orientifolds. We found that some global supersymmetric Pati-Salam-models with four generations are possible.

A hitchhikers guide to complete intersection fibers in F-theory

• Thorsten Schimannek (Bonn U.)

We refine the recent classification of complete intersection Calabi-Yau onefolds in three-dimensional toric ambient spaces. We provide F-theory fibers with novel features and our analysis supports the duality between Mordel-Weil torsion and Tate-Shafarevich degree that was observed for toric hypersurfaces. We explain the duality for the latter and comment on a possible extension to a general proof for complete intersection fibers.

Recent Developments in Superconformal Field Theories

• Alberto Zaffaroni

Integrability and Exact Results in N = 2 gauge theories

• Elli Pomoni (DESY)

Any N=2 gauge theory in four dimensions contains a set of local operators made only out of fields in the N=2 vector multiplet that is closed under renormalization to all loops, with SU(2,1|2) symmetry. We present a diagrammatic argument that for any planar N=2 theory the SU(2,1|2) Hamiltonian acting on infinite spin chains is identical to all loops to that of N=4 SYM, up to a redefinition of the coupling constant g^2 → f(g^2). Thus, this sector is integrable and anomalous dimensions can be read off from the N=4 ones up to this redefinition. The functions f(g^2) dubbed as effective couplings encode the relative, finite renormalization between the N=2 and the N=4 gluon propagator and thus can be computed in perturbation theory using Feynman diagrams. For each N=2 theory exact effective couplings can be obtained by computing different exact results for localizable observables such as Wilson loops and the Bremsstrahlung function and by comparing them with their N = 4 counterparts.

Worldsheet string theory in AdS/CFT and lattice

• Valentina Forini (Max Planck Institute for Gravitational Physics, Albert Einstein Institute)

It is discussed how the integrable structure underlying the AdS/CFT system and the cross-fertilization of established field-theretical tools to strings can be used to enhance our knowledge on the relevant string sigma model, and thus the predictivity of the duality.

Heterotic string model building without supersymmetry

• Stefan Groot Nibbelink (ASC, LMU)