Prospects in String Phenomenology

• Eran Palti (Heidelberg)

QCD axion with high scale inflation

• Kiwoon Choi (Daejeon)

We examine the cosmological constraints on QCD axions in high scale inflation scenario, while taking into account that the axion scale during inflation can be generically differet from the present axion scale. Implication of the results for string theoretic realization of the QCD axion is discussed also.

Singlet extensions of the MSSM with Z_4 R-symmetry

• Patrick Vaudrevange (DESY Hamburg)

Singlet extensions of the MSSM with Z_4 R-symmetry are discussed. It is shown that holomorphic zeros can avoid a potentially large coefficient of the term linear in the singlet. The emerging model has both an effective mu-term and a supersymmetric mass term m_N for the singlet which are controlled by the gravitino mass. The mu-term turns out to be suppressed against m_N by about one or two orders of magnitude. We argue that this class of models might provide us with a solution to the little hierarchy problem of the MSSM.

Antibranes in AdS

• Friðrik Freyr Gautason (Leibniz Universität Hannover)

Selection Rules Beyond U(1)’s in F-Theory Compactification

• Christoph Mayrhofer (Heidelberg University)

Anomaly cancelation from geometric symmetries in F-theory

• Andreas Kapfer (MPI Munich)

Building a social network of elliptic fibrations for F-Theory

• Jonas Reuter (University of Bonn)

We discuss the gauge groups and matter content for genus one fibrations with their fiber a hypersurface in one of the 16 2D reflexive polytopes, where some of these were already discussed in the literature. The polyhedrons are connected by geometric transitions on the geometry side which translates into a toric Higgs branch on the field theory side. This network structure is symmetric and reflects the mirror symmetry of the polytopes. This allows the identification of discrete symmetries.

From Torsion to n-sections and Pati-Salam to the Standard Model in F-theory

• Paul-Konstantin Oehlmann (Bonn University)

We give an overview on all F-theory fibrations with the 16 classical 2D polytopes as the fiber. We find examples of Mordell-Weil torsion and discrete symmetries observe a possible connection by mirror symmetry. In the second part of the talk we complete one of the fibrations to a full four dimensional theory possessing exact Pati-Salam symmetry group with three chiral families and break it down to the Standard Model.

Discrete Symmetries in F-theory

• Oskar Till (Heidelberg)

We study the geometric origin of discrete selection rules in F-theory. F-theory on genus-one fibrations are via conifold transitions related to F-theory models with extra abelian gauge groups. We compare the Yukawa structures and show consistency in the tadpole condition.

Moduli Spaces of AdS Vacua in d=7, N=2 Supergravity

• Severin Lüst (Hamburg)

We discuss AdS vacua of N=2 gauged supergravity in seven dimensions. We classify the possible gauge groups which lead to maximally supersymmetric AdS vacua and show that the moduli spaces of these backgrounds can consist only of isolated points.

Systematics on particle physics D6-brane models on T^6/Z2XZ6

• Jill Ecker (PhD student JGU Mainz)

Towards the Standard Model in F-theory

• Ling Lin (Institute for Theoretical Physics Heidelberg)

I will present a class of F-theory compactifications that gives rise to the Standard Model gauge group, augmented by a further U(1) that can serve as a selection rule. I will discuss phenomenological aspects as well as the technical difficulties that arises when we try to match the results to the real Standard Model.

Non-supersymmetric heterotic model building

• Orestis Loukas (LMU Munich)

Inflationary Attractors, f(R)-duals and the Power Spectrum

• Benedict Broy (Deutsches Elektron-Synchrotron DESY)

Inflationary attractors predict the spectral index and tensor-to-scalar ratio to take specific values that are consistent with Planck. An example is the universal attractor for models with a generalised non-minimal coupling, leading to Starobinsky inflation. In this talk, I will demonstrate that it also predicts a specific relation between the amplitude of the power spectrum and the number of e-folds. The length and height of the inflationary plateau are related via the non-minimal coupling: in a wide variety of examples, the observed power normalisation leads to at least 55 flat e-foldings. Prior to this phase, the inflationary predictions vary and can account for the observational indications of power loss at large angular scales. Furthermore, I will investigate whether or not the f(R)-duality of plateau like models survives once higher order corrections to the inflationary potential are considered. Based upon 1408.5905 and 1411.6010

Introduction to Exceptional Field Theory

• Henning Samtleben (ENS Lyon)

Warped M-theory effective actions

• Thomas Grimm (Max Planck Institute for Physics)

Anti-branes in flux backgrounds

• Daniel Junghans (Leibniz Universität Hannover)

Flux vacua on manifolds with SU(5)-structure in terms of generalized complex geometry

• Daniël Prins (Lyon)

The supersymmetry equations are a set of Killing spinor equations that determine supersymmetric flux vacua of type II supergravity. In certain cases for product manifolds R^{1, 9-2n} \times M_2n, these equations have been recast to resemble integrability conditions of generalized almost complex structures: in all such cases, M_2n can be equipped with an SU(n)-structure. This begs the question to what extent this equivalence holds when considering n=5. An obvious obstacle to overcome is that this can only work for Riemannian, rather than Lorentzian manifolds. I will demonstrate that, by making use of complex supergravity, one can show that a necessary but not quit sufficient condition for solutions to the supersymmetry equations on manifolds with SU(5)-structure can indeed be given in terms of generalized almost complex structures.

De Sitter Vacua from a D-term Generated Racetrack Uplift

• Markus Rummel (University of Hamburg)

We propose an uplift mechanism using a structure of multi-Kähler moduli dependence in the F-term potential of type IIB string theory compactifications. This mechanism requires a D-term condition that fixes one modulus to be proportional to another modulus, resulting in a trivial D-term potential. De Sitter minima are realized along with an enhancement of the volume in the Large Volume Scenario and no additional suppression of the uplift term such as warping is required. We further show the possibility to realize the uplift mechanism in the presence of more Kähler moduli such that we expect the uplift mechanism to work in many other compactifications.

Higher Derivative Supergravity and Implications for Moduli Stabilization

• David Ciupke (University of Goettingen)

We study specific classes of four-derivative terms for chiral superfields in N = 1 supersymmetry and supergravity. These terms induce cubic polynomial equations of motion for the chiral auxiliary fields and correct the scalar potential. We discuss the different solutions and argue that only one of them is physically relevant. Special attention is paid to the corrections along flat directions which can be stabilized or destabilized by the higher-derivative terms. As a particular example we show that within α corrected type IIB flux compactifications higher derivative terms could stabilize a large volume without any non-perturbative contribution.

Recent Developments in (String) Cosmology

• Daniel Baumann (Cambridge University)

Non-geometric Strings and Axion Inflation

• Ralph Blumenhagen (Max-Planck-Insititut fuer Physik)

Tuning for Large Field Inflation in String Theory

• Lukas Witkowski (Heidelberg University)

Challenges for Large-Field Inflation and Moduli Stabilization

• Martin Wolfgang Winkler (TU München)

We analyze the interplay between Kahler moduli stabilization and chaotic inflation in supergravity. While heavy moduli decouple from inflation in the supersymmetric limit, supersymmetry breaking generically introduces non-decoupling effects. These lead to inflation driven by a bilinear soft mass term. This scenario needs no stabilizer field, but the stability of moduli during inflation imposes a large supersymmetry breaking scale, m_{3/2} >> H, and a careful choice of initial conditions. This is illustrated in three prominent examples of moduli stabilization: KKLT stabilization, Kahler Uplifting, and the Large Volume Scenario. Remarkably, all models have a universal effective inflaton potential which is flattened compared to quadratic inflation. Hence, they share universal predictions for the CMB observables, in particular a lower bound on the tensor-to-scalar ratio, r > 0.05.

Natural inflation and moduli stabilization in heterotic orbifolds

• Fabian Ruehle (DESY Hamburg)

Yukawa hierarchies at the point of E8 in F-theory

• Diego Regalado (IFT UAM/CSIC)

Realising Axion Inflation in String Theory

• Daniela Herschmann (MPI Munich)

We investigate the realisation of single-field F-term axion monodromy inflation in string theory. Moduli stabilisation in type IIB via the flux induced superpotential is considered. The challenges of keeping one axion massless/light while all other moduli are stabilised at hierarchically higher mass, are discussed. We focus on the axio-dilaton and the complex-structure moduli.

Backreaction of complex structure moduli in axion monodromy inflation

• Fabrizio Rompineve (Heidelberg)

We focus on the backreaction of complex structure moduli in axion monodromy inflation. In our setting, the shift symmetry comes from a partial large complex structure limit of the underlying type IIB orientifold or F-theory fourfold. The coefficient of the inflaton term in the superpotential has to be tuned small to avoid conflict with Kahler moduli stabilisation. To allow such a tuning, this coefficient necessarily depends on further complex structure moduli. At large values of the inflaton field, these moduli are then in danger of backreacting too strongly. To avoid this, further tunings are necessary. We discuss how to realise them in a F-theory fourfold setting and study the resulting scalar potential for the inflaton field.

Tunings in axion monodromy inflation with complex structure moduli

• Patrick Mangat (Heidelberg)

The little hierarchy problem in the light of extra dimensions

• Lucila Zarate (Hamburg)

In this work it was studied within the NMSSM, a requirement upon the soft terms at the GUT scale that alleviates the little hierarchy problem. In particular, for vanishing soft terms at the GUT scale except for the Higgs sector and gaugino masses, a special relation between soft gaugino and Higgs masses was computed that leads to a low electroweak scale. The latter GUT configuration arises from higher dimensional theories with gauge and Higgs fields in the bulk and the supersymmetry breaking field at a spatially separated brane. Furthermore, an explicit example motivated by higher dimensional orbifold GUTs in heterotic string theory was shown to provide the required relation. Soft terms were derived in a model independent way for supersymmetric non renormalizable theories of cutoff $\Lambda$ and applied to the example.

Deforming Z2 singularities in T6/(Z_2 x Z_2N) orbifolds

• Isabel Koltermann (Mainz)

Yukawa couplings for intersecting D-branes on non-factorisable tori

• Christoph Liyanage (Bethe Center for Theoretical Physics)

I will explain how compute Yukawa couplings on a non-factorisable six-torus in the presence of intersecting D6-branes. The talk is based on publication arXiv:1412.3645.

Hyperbolic Geometry and the Lorentz Group

• Norbert Dragon

Radiative effects in decay of metastable vacua: a Green's function approach

• Peter Millington

We introduce a Green's function method for handling radiative effects on the decay of metastable vacua. In the context of phi-4 theory, we are able to calculate analytically both the functional determinant of the quadratic fluctuations about the soliton configuration as well as the first correction to the soliton configuration itself. The latter is made feasible by employing the thin-wall approximation and treating the bubble wall in the planar limit. In so doing, the problem of tunnelling in radiatively generated potentials may be reduced to one of solving one-dimensional ordinary differential equations and integrals.

New exact Results in Supersymmetric Field Theories

• Stefano Cremonesi (London)

2D Gauged Linear Sigma Models and Homological Projective Duality

• Hans Jockers (BCTP, Bonn)

A pair of Calabi-Yau threefolds from a pair of dual non-abelian gauged linear sigma models

• Andreas Gerhardus (Bonn)

Two-dimensional gauge field theories with N=(2,2) supersymmetry, known as gauged linear sigma models (GLSM), may be the ultraviolet completion for a nonlinear sigma model with Calabi-Yau threefold target space. In this case, it is possible to calculate certain topological properties of the Calabi-Yau target space within the GLSM. Recently, a relation between the partition function of the GLSM on the two-sphere and the Kaehler potential on the quantum exact Kaehler moduli space of the Calabi-Yau has been conjectured. We exploit this relation for a pair of non-abelian GLSMs which display both weakly and strongly coupled phases. The fact that their two-sphere partition functions agree provides evidence for a duality between the two models. From a technical point of view the evaluation of the above mentioned partition function involves the calculation of multidimensional Mellin-Barnes integrals. We demonstrate in arbitrary dimension how these integrals are given as sums of Grothendieck residues.

SL(2,C) Chern-Simons theory, quantum curves, and 4d quantum geometry

• Muxin Han (Erlangen)

Topological Strings on Mirror Curves of Genus Two and Siegel Modular Forms

• Thorsten Schimannek (Bonn)

Topological string theory on non-compact geometries has been studied for many years and continues to provide insight in the most diverse areas of mathematical physics. However, at higher worldsheet genus the theory has only been solved for geometries with mirror curves of genus one, where a rich modular structure lies at hand. We present a new almost meromorphic Siegel modular object which provides the generator for higher genus free energies and describe Solutions for two geometries. In particular this gives rise to a generalised Ramanujan identity which reflects the physical conditions on the generator.

Heterotic String in Double field theory

• Rui Sun (MPP)