Publications (48)
The Higgs Mechanism in Heterotic Orbifolds
Stefan Forste, Hans Peter Nilles, Akin Wingerter
We study spontaneous gauge symmetry breaking in the framework of orbifold compactifcations of heterotic string theory. In particular we investigate the electroweak symmetry breakdo…
Measurement and Teleportation in the cSYK/JT Correspondence
Raphael Brinster, Stefan Forste, Yannic Kruse +1
We consider two complex SYK models entangled in a thermofield double (TFD) state and investigate the effect of one-sided projective measurements. As measurement operator we choose…
Grand Canonical vs Canonical Krylov Complexity in Double-Scaled Complex SYK Model
Stefan Forste, Yannic Kruse, Saurabh Natu
We consider the complex SYK model in the double-scaling limit. We obtain the transfer matrix for the grand canonical ensemble and symmetrize it. In the (n,Q)- basis of chord states…
Deformations of JT Gravity via Topological Gravity and Applications
Stefan Forste, Hans Jockers, Joshua Kames-King +1
We study the duality between JT gravity and the double-scaled matrix model including their respective deformations. For these deformed theories we relate the thermal partition func…
Heterotic Brane World
Stefan Forste, Hans Peter Nilles, Patrick K. S. Vaudrevange +1
Orbifold compactification of heterotic E8 x E8 string theory is a source for promising grand unified model building. It can accommodate the successful aspects of grand unification…
Stringy Corrections to the Wilson Loop in N=4 Super Yang-Mills Theory
Stefan Forste, Debashis Ghoshal, Stefan Theisen
We study stringy fluctuations as a source for corrections to the Wilson loop as obtained from the superstrings on (adS_5 x S^5)/ N=4 SYM correspondence. We give a formal expression…
Geometry of Rank Reduction
Stefan Forste, Hans Peter Nilles, Akin Wingerter
We introduce continuous Wilson lines to reduce the rank of the gauge group in orbifold constructions. In situations where the orbifold twist can be realised as a rotation in the ro…
Instanton effects in string cosmology
Klaus Behrndt, Stefan Forste, Stefan Schwager
We consider the gauge dyonic string solution of the K3 compactified heterotic string theory in a four dimensional cosmological context. Since for this solution Green-Schwarz as wel…
Nearly AdS2 Sugra and the Super-Schwarzian
Stefan Forste, Iris Golla
In nearly AdS2 gravity the Einstein-Hilbert term is supplemented by the Jackiw-Teitelboim action. Integrating out the bulk metric gives rise to the Schwarzian action for the bounda…
A truly marginal deformation of SL(2,R) in a null direction
Stefan Forste
We perform a marginal deformation of the SL(2,R) WZW model in a null direction. If we send the deformation parameter to infinity we obtain a linear dilaton background plus two free…
Orientifolds with branes at angles
Stefan Forste, Gabriele Honecker, Ralph Schreyer
We present supersymmetry breaking four dimensional orientifolds of type IIA strings. The compact space is a torus times a four dimensional orbifold. The orientifold group reflects…
Nontrival Cosmological Constant in Brane Worlds with Unorthodox Lagrangians
Stefan Forste, Hans Peter Nilles, Ivonne Zavala
In self-tuning brane-world models with extra dimensions, large contributions to the cosmological constant are absorbed into the curvature of extra dimensions and consistent with fl…
Duality in String Theory
Stefan Forste, Jan Louis
In this lecture we review some of the recent developments in string theory on an introductory and qualitative level. In particular we focus on S-T-U dualities of toroidally compact…
Bottom Up Meets Heterotic Strings
Stefan Forste, Akin Wingerter
In this talk we argue that a certain class of heterotic orbifolds can be the underlying fundamental theory for recently studied field theory GUTs. In addition we demonstrate that s…
Non critical super strings on world sheets of constant curvature
Stefan Forste
We consider correlation functions in Neveu--Schwarz string theory coupled to two dimensional gravity. The action for the 2D gravity consists of the string induced Liouville action…
Half-Wormholes in a Supersymmetric SYK Model
Stefan Forste, Saurabh Natu
We identify half-wormhole contributions to the non averaged supersymmetric SYK model in which time has been reduced to a point. As in previously studied examples,…
Proton Hexality in Local Grand Unification
Stefan Forste, Hans Peter Nilles, Saul Ramos-Sanchez +1
Proton hexality is a discrete symmetry that avoids the problem of too fast proton decay in the supersymmetric extension of the standard model. Unfortunately it is inconsistent with…
Strings, Branes and Extra Dimensions
Stefan Forste
This review is devoted to strings and branes. Firstly, perturbative string theory is introduced. The appearance of various types of branes is discussed. These include orbifold fixe…
Current-Current Deformations of Conformal Field Theories, and WZW Models
Stefan Forste, Daniel Roggenkamp
Moduli spaces of conformal field theories corresponding to current-current deformations are discussed. For WZW models, CFT and sigma model considerations are compared. It is shown…
Oddness from Rigidness
Stefan Forste, Ivonne Zavala
We revisit the problem of constructing type IIA orientifolds on T^6/(Z2 x Z2) which admit (non)-factorisable lattices. More concretely, we consider a (Z2 x Z2') orientifold with to…
Supersymmetric Black Holes and the SJT/nSCFT Correspondence
Stefan Forste, Andreas Gerhardus, Joshua Kames-King
We consider 1/4 BPS black hole solutions of gauged supergravity in . The near horizon geometry is and supersymmetry is enhanced. In the first…
The Cosmological Constant Problem from a Brane-World Perspective
Stefan Forste, Zygmunt Lalak, Stéphane Lavignac +1
We point out several subtleties arising in brane-world scenarios of cosmological constant cancellation. We show that solutions with curvature singularities are inconsistent, unless…
Rigid D6-branes on T6/[Z(2)xZ(2M)xOmegaR] with discrete torsion
Stefan Forste, Gabriele Honecker
We give a complete classification of T6/[Z(2)xZ(2M)xOmegaR] orientifolds on factorisable tori and rigid D6-branes on them. The analysis includes the supersymmetry, RR tadpole cance…
D-branes in a marginally deformed WZW model
Stefan Forste
In this talk we discuss symmetry preserving D-branes on a line of a marginally deformed SU(2) WZW model. A semiclassical and a quantum theoretical approach are presented.
A note on inflationary string cosmology
Stefan Forste
Cosmological solutions are obtained by continuation of black D-brane solutions into the region between the horizons. It is investigated whether one can find exponential expansion w…
Wilson loop via AdS/CFT duality
Stefan Forste, Debashis Ghoshal, Stefan Theisen
The Wilson loop in N=4 supersymmetric Yang-Mills theory admits a dual description as a macroscopic string configuration in the adS/CFT correspondence. We discuss the correction to…
Towards the Holographic Dual of N = 2 SYK
Stefan Forste, Joshua Kames-King, Max Wiesner
The gravitational part of the holographic dual to the SYK model has been conjectured to be Jackiw-Teitelboim (JT) gravity. In this paper we construct an AdS2 background in N = (2,2…
Ensemble Averages of Orbifold Classes of Narain CFTs
Stefan Forste, Hans Jockers, Joshua Kames-King +2
In this work we study families of orbifolds of toroidal conformal field theories based on both factorizable and non-factorizable target space tori. For these classes…
Z_2 x Z_2 Heterotic Orbifold Models of Non Factorisable Six Dimensional Toroidal Manifolds
Alon E. Faraggi, Stefan Forste, Cristina Timirgaziu
We discuss heterotic strings on Z_2 x Z_2 orbifolds of non factorisable six-tori. Although the number of fixed tori is reduced as compared to the factorisable case, Wilson lines ar…
Strings from Orientifolds
Stefan Forste, Debashis Ghoshal
We construct models in 1+1 dimensions with chiral (0,N) supersymmetry by taking orientifolds of type IIB on an eight-torus identified by different numbers of reflections. The resul…
General self-tuning solutions and no-go theorem
Stefan Forste, Jihn E. Kim, Hyun Min Lee
We consider brane world models with one extra dimension. In the bulk there is in addition to gravity a three form gauge potential or equivalently a scalar (by generalisation of ele…
Orientifold's Landscape: Non-Factorisable Six-Tori
Stefan Forste, Cristina Timirgaziu, Ivonne Zavala
We construct type IIA orientifolds on T6/(Z2 x Z2) which admit non factorisable lattices. We describe a method to deal with this kind of configurations and discuss how the compacti…
Gauging Flavour in Meta-Stable Susy Breaking Models
Stefan Forste
We modify the first ISS model (hep-th/0602239) by gauging a diagonal flavour symmetry. We add additional multiplets transforming as fundamentals and anti-fundamentals under the gau…
Non-Factorisable Z2 times Z2 Heterotic Orbifold Models and Yukawa Couplings
Stefan Forste, Tatsuo Kobayashi, Hiroshi Ohki +1
We classify compactification lattices for supersymmetric Z2 times Z2 orbifolds. These lattices include factorisable as well as non-factorisable six-tori. Different models lead to d…
An orientifold of the solitonic fivebrane
Stefan Forste, Debashis Ghoshal, Sudhakar Panda
We study an orientifold of the solitonic fivebrane of type II string theory. The consideration is restricted to a space-time domain which can be described by an exact conformal fie…
Tuning the Cosmological Constant, Broken Scale Invariance, Unitarity
Stefan Forste, Paul Manz
We study gravity coupled to a cosmological constant and a scale but not conformally invariant sector. In Minkowski vacuum, scale invariance is spontaneously broken. We consider sma…
Yukawa couplings for intersecting D-branes on non-factorisable tori
Stefan Forste, Christoph Liyanage
We compute Yukawa couplings in type IIa string theory compactified on a six-torus in the presence of intersecting D6-branes. The six-torus is generated by an SO(12) root lattice. Y…
A Comment on Self-Tuning and Vanishing Cosmological Constant in the Brane World
Stefan Forste, Zygmunt Lalak, Stephane Lavignac +1
In this note we elaborate on various five dimensional contributions to the effective 4D cosmological constant in brane systems. In solutions with vanishing 5D cosmological constant…
Non-Abelian T-duality for open strings
Stefan Forste, Alexandros A. Kehagias, Stefan Schwager
In the first part of the talk we discuss T-duality for a free boson on a world sheet with boundary in a setting suitable for the generalization to non-trivial backgrounds. The gaug…
Membrany corrections to the string anti-string potential in M5-brane theory
Stefan Forste
We study the potential between a string and an anti-string source in M5-theory by using the adS/CFT duality conjecture. We find that the next to leading order corrections in a sadd…
Fine-Tuning of the Cosmological Constant in Brane Worlds
Stefan Forste
We discuss how the fine-tuning of the cosmological constant enters brane world setups. After presenting the Randall Sundrum model as a prototype case, we focus on single brane mode…
Yukawa couplings from magnetized D-brane models on non-factorisable tori
Stefan Forste, Christoph Liyanage
We compute Yukawa couplings in type IIB string theory compactified on a non factorisable six-torus in the presence of D9 branes and fluxes. The setting studied in detail, is obtain…
Deformations of WZW models
Stefan Forste
Current-current deformations for WZW models of semisimple compact groups are discussed in a sigma model approach. We start with the abelian rank one group U(1). Afterwards, we keep…
Supersymmetric Z_N times Z_M Orientifolds in 4D with D-Branes at Angles
Stefan Forste, Gabriele Honecker, Ralph Schreyer
We construct orientifolds of type IIA string theory. The theory is compactified on a T^6/Z_N times Z_M orbifold. In addition worldsheet parity in combination with a reflection of t…
D-branes on a Deformation of SU(2)
Stefan Forste
We discuss D-branes on a line of conformal field theories connected by an exact marginal deformation. The line contains an SU(2) WZW model and two mutually T-dual SU(2)/U(1) cosets…
T-duality for open strings with respect to non-abelian isometries
Stefan Forste, Alexandros A. Kehagias, Stefan Schwager
We gauge the non-abelian isometries of a sigma model with boundaries. Forcing the field strength of the gauge fields to vanish renders the gauged model equivalent to the ungauged o…
Lyapunov exponents in supersymmetric Jackiw-Teitelboim gravity
Ruben Campos Delgado, Stefan Forste
We study supersymmetric Jackiw-Teitelboim (JT) gravity at finite temperature coupled to matter. The matter fields are related to superconformal primaries by AdS/CFT…
Scattering amplitudes in strongly coupled N=4 SYM from semiclassical strings in AdS
Steven Abel, Stefan Forste, Valentin V. Khoze
Very recently in arXiv:0705.0303 Alday and Maldacena gave a string theory prescription for computing (all) planar amplitudes in N=4 supersymmetric gauge theory at strong coupling u…