Publications (135)443.31 Total impact

Article: Noncommutative/nonassociative IIA (IIB) geometries from Q and Rbranes and their intersections
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ABSTRACT: In this paper we discuss the construction of nongeometric Q and Rbranes as sources of nongeometric Q and Rfluxes in string compactifications. The nongeometric Qbranes, being obtained via Tduality from the NS 5brane or respectively from the KKmonopole, are still local solutions of the standard NS action, where however the background fields G and B possess nongeometric global monodromy properties. We show that using double field theory and redefined background fields $ \widetilde{G} $ and β as well as their corresponding effective action, the Qbranes are locally and globally well behaved solutions. Furthermore the Rbrane solution can be at least formally constructed using dual coordinates. We derive the associated nongeometric Q and Rfluxes and discuss that closed strings moving in the space transversal to the worldvolumes of the nongeometric branes see a noncommutative or a nonassociative geometry. In the second part of the paper we construct intersecting Q and Rbrane configurations as completely supersymmetric solutions of type IIA/B supergravity with certain SU(3) × SU(3) group structures. In the near horizon limit the intersecting brane configurations lead to type II backgrounds of the form AdS 4 × M 6, where the sixdimensional compact space M 6 is a torus fibration with various nongeometric Q and Rfluxes in the compact directions. It exhibits an interesting noncommutative and nonassociate geometric structure. Furthermore we also determine some of the effective fourdimensional superpotentials originating from the nongeometric fluxes.Journal of High Energy Physics 07/2013; 2013(7). · 5.62 Impact Factor 
Article: Basic Concepts of String Theory
Basic Concepts of String Theory: , Theoretical and Mathematical Physics. ISBN 9783642294969. SpringerVerlag Berlin Heidelberg, 2013. 01/2013;  [show abstract] [hide abstract]
ABSTRACT: We discuss the phenomenology and cosmology of a Standardlike Model inspired by string theory, in which the gauge fields are localized on Dbranes wrapping certain compact cycles on an underlying geometry, whose intersection can give rise to chiral fermions. The energy scale associated with string physics is assumed to be near the Planck mass. To develop our program in the simplest way, we work within the construct of a minimal model with gaugeextended sector U(3)B×Sp(1)L×U(1)IR×U(1)L. The resulting U(1) content gauges the baryon number B, the lepton number L, and a third additional Abelian charge IR which acts as the third isospin component of an SU(2)R. All mixing angles and gauge couplings are fixed by rotation of the U(1) gauge fields to a basis diagonal in hypercharge Y and in an anomalyfree linear combination of IR and BL. The anomalous Z′ gauge boson obtains a string scale Stückelberg mass via a 4D version of the GreenSchwarz mechanism. To keep the realization of the Higgs mechanism minimal, we add an extra SU(2) singlet complex scalar, which acquires a VEV and gives a TeVscale mass to the nonanomalous gauge boson Z′′. The model is fully predictive and can be confronted with dijet and dilepton data from LHC8 and, eventually, LHC14. We show that MZ′′≈3–4 TeV saturates current limits from the CMS and ATLAS Collaborations. We also show that for MZ′′≲5 TeV, LHC14 will reach discovery sensitivity ≳5σ. After that, we demonstrate in all generality that Z′′ milliweak interactions could play an important role in observational cosmology. Finally, we examine some phenomenological aspects of the supersymmetric extension of the Dbrane construct.Physical review D: Particles and fields 06/2012; 86(6).  [show abstract] [hide abstract]
ABSTRACT: We discuss direct production of Regge excitations in the collisions of massless fourdimensional superstring states, focusing on the first excited level of open strings ending on Dbranes extending into higher dimensions. We construct covariant vertex operators and identify “universal” Regge states with the internal parts either trivial or determined by the worldsheet SCFT describing superstrings propagating on an arbitrary Calabi–Yau manifold. We evaluate the amplitudes involving one such massive state and up to three massless ones and express them in the helicity basis. The most important phenomenological applications of our results are in the context of lowmass string (and large extra dimensions) scenarios in which excited string states are expected to be produced at the LHC as soon as the string mass threshold is reached in the centerofmass energies of the colliding partons. In order to facilitate the use of partonic cross sections, we evaluate them and tabulate for all production processes: gluon fusion, quark absorbing a gluon, quark–antiquark annihilation and quark–quark scattering.Nuclear Physics B 02/2011; 843(3):570–601. · 4.33 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We address the question how string compactifications with Dbranes are consistent with the black hole bound, which arises in any theory with number of particle species to which the black holes can evaporate. For the KaluzaKlein particles, both longitudinal and transversal to the Dbranes, it is relatively easy to see that the black hole bound is saturated, and the geometric relations can be understood in the language of speciescounting. We next address the question of the black hole evaporation into the higher string states and discover, that contrary to the naive intuition, the exponentially growing number of Regge states does not preclude the existence of semiclassical black holes of substringy size. Our analysis indicates that the effective number of string resonances to which such micro black holes evaporate is not exponentially large but is bounded by N = 1/gs2, which suggests the interpretation of the wellknown relation between the Planck and string scales as the saturation of the black hole bound on the species number. In addition, we also discuss some other issues in Dbrane compactifications with a low string scale of order TeV, such as the masses of light moduli fields.Fortschritte der Physik 05/2010; 58(6):505  527. · 0.98 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We consider instanton solutions of Euclidean HořavaLifshitz gravity in four dimensions satisfying the detailed balance condition. They are described by geometric flows in three dimensions driven by certain combinations of the Cotton and Ricci tensors as well as the cosmologicalconstant term. The deformation curvature terms can have competing behavior leading to a variety of fixed points. The instantons interpolate between any two fixed points, which are vacua of topologically massive gravity with Λ > 0, and their action is finite. Special emphasis is placed on configurations with SU(2) isometry associated with homogeneous but generally nonisotropic Bianchi IX model geometries. In this case, the combined RicciCotton flow reduces to an autonomous system of ordinary differential equations whose properties are studied in detail for different couplings. The occurrence and stability of isotropic and anisotropic fixed points are investigated analytically and some exact solutions are obtained. The corresponding instantons are classified and they are all globally \mathbbR S3 \mathbb{R} \times {S^3} and complete spaces. Generalizations to higherdimensional gravities are also briey discussed. KeywordsSolitons Monopoles and InstantonsDifferential and Algebraic GeometryClassical Theories of GravityJournal of High Energy Physics 01/2010; 2010(4):158. · 5.62 Impact Factor 
Article: Strings at the LHC
Fortschritte Der Physikprogress of Physics  FORTSCHR PHYS. 01/2010; 58:833838.  [show abstract] [hide abstract]
ABSTRACT: We extend the study of scattering amplitudes presented in “The LHC String Hunter's Companion” [1] to the case of fivepoint processes that may reveal the signals of low mass strings at the LHC and are potentially useful for detailed investigations of fundamental Regge excitations. In particular, we compute the fullfledged string disk amplitudes describing all 2→3 parton scattering subprocesses leading to the production of three hadronic jets. We cast our results in a form suitable for the implementation of stringy partonic cross sections in the LHC data analysis. We discuss the universal, modelindependent features of multiparton processes and point out the existence of even stronger universality relating Ngluon amplitudes to the amplitudes involving N−2 gluons and one quark–antiquark pair. We construct a particularly simple basis of two functions describing all universal fivepoint amplitudes. We also discuss modeldependent amplitudes involving four fermions and one gauge boson that may be relevant for studying jets associated to Drell–Yan pairs and other processes depending on the spectrum of Kaluza–Klein particles, thus on the geometry of compact dimensions.Nuclear Physics B 08/2009; · 4.33 Impact Factor 
Article: LHC phenomenology for string hunters
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ABSTRACT: We consider extensions of the standard model based on open strings ending on Dbranes, with gauge bosons due to strings attached to stacks of Dbranes and chiral matter due to strings stretching between intersecting Dbranes. Assuming that the fundamental string mass scale is in the TeV range and the theory is weakly coupled, we discuss possible signals of string physics at the Large Hadron Collider (LHC). In previous works, direct channel excitations of Regge recurrences in parton–parton scattering supplied the outstanding new signature. The present work considers the deviation from standard model expectations for the 4fermion processes qq→qq and qq′→qq′, in which the schannel excitation of string resonances is absent. In this case, we find that Kaluza–Klein recurrences at masses somewhat less than the string scale generate effective 4fermion contact terms which can significantly enhance the dijet R ratio above its QCD value of about 0.6. The simultaneous observation of a nearby resonant structure in the dijet mass spectrum would provide a “smoking gun” for TeV scale string theory. In this work, we also show that (1) for Mstring<3.5 TeV, the rates for various topologies arising from the pp→Z0+jet channel could deviate significantly from standard model predictions and (2) that the sizeable cross sections for Regge recurrences can allow a 6σ discovery for string scales as large as 3 TeV after about 1 year of LHC operation at and .Nuclear Physics B 04/2009; · 4.33 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We consider string theory compactifications of the form AdS with orientifold sixplanes, where is a sixdimensional compact space that is either a nilmanifold or a coset. For all known solutions of this type we obtain the fourdimensional lowenergy effective theory by computing the superpotential, the Kähler potential and the mass spectrum for the light moduli. For the nilmanifold examples we perform a crosscheck on the result for the mass spectrum by calculating it alternatively from a direct Kaluza–Klein reduction and find perfect agreement. We show that in all but one of the coset models all moduli are stabilized at the classical level. As an application we show that all but one of the coset models can potentially be used to bypass a recent nogo theorem against inflation in type IIA theory.Classical and Quantum Gravity 01/2009; 26(2):025014. · 3.56 Impact Factor 
Article: Can we see strings at the LHC?
Fortschritte Der Physikprogress of Physics  FORTSCHR PHYS. 01/2009; 57:434445.  [show abstract] [hide abstract]
ABSTRACT: We update the D3/D7brane inflation model on K3×T2/Z2 with branes and fluxes. For this purpose, we study the low energy theory including gs corrections to the gaugino condensate superpotential that stabilizes the K3 volume modulus. The gauge kinetic function is verified to become holomorphic when the original N=2 supersymmetry is spontaneously broken to N=1 by bulk fluxes. From the underlying classical N=2 supergravity, the theory inherits a shift symmetry which provides the inflaton with a naturally flat potential. We analyze the fate of this shift symmetry after the inclusion of quantum corrections. The field range of the inflaton is found to depend significantly on the complex structure of the torus but is independent of its volume. This allows for a large kinematical field range for the inflaton. Furthermore, we show that the D3/D7 model may lead to a realization of the recent CMB fit by Hindmarsh et al. with an 11% contribution from cosmic strings and a spectral index close to ns=1. On the other hand, by a slight change of the parameters of the model one can strongly suppress the cosmic string contribution and reduce the spectral index ns to fit the WMAP5 data in the absence of cosmic strings. We also demonstrate that the inclusion of quantum corrections allows for a regime of eternal D3/D7 inflation.Nuclear Physics B 01/2009; · 4.33 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: Assuming that the fundamental string mass scale is in the TeV range and the theory is weakly coupled, we discuss possible signals of string physics at the Large Hadron Collider (LHC). In Dbrane constructions, the dominant contributions to fullfledged string amplitudes for all the common QCD parton subprocesses leading to dijets are completely independent of the details of compactification, and can be evaluated in a parameterfree manner. We make use of these amplitudes evaluated near the first resonant pole to determine the discovery potential of LHC for the first Regge excitations of the quark and gluon. Remarkably, the reach of LHC after a few years of running can be as high as 6.8 TeV. Even after the first 100 pb(1) of integrated luminosity, string scales as high as 4.0 TeV can be discovered. Data on pp>directgamma + jet can provide corroboration for string physics at scales as high as 5 TeV.Physical Review Letters 12/2008; 101(24):241803. · 7.94 Impact Factor 
Article: The LHC string Hunter's companion
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ABSTRACT: The mass scale of fundamental strings can be as low as few TeV/c2 provided that spacetime extends into large extra dimensions. We discuss the phenomenological aspects of weakly coupled low mass string theory related to experimental searches for physics beyond the Standard Model at the Large Hadron Collider (LHC). We consider the extensions of the Standard Model based on open strings ending on Dbranes, with gauge bosons due to strings attached to stacks of Dbranes and chiral matter due to strings stretching between intersecting Dbranes. We focus on the modelindependent, universal features of low mass string theory. We compute, collect and tabulate the fullfledged string amplitudes describing all 2→2 parton scattering subprocesses at the leading order of string perturbation theory. We cast our results in a form suitable for the implementation of stringy partonic cross sections in the LHC data analysis. The amplitudes involving four gluons as well as those with two gluons plus two quarks do not depend on the compactification details and are completely modelindependent. They exhibit resonant behavior at the parton center of mass energies equal to the masses of Regge resonances. The existence of these resonances is the primary signal of string physics and should be easy to detect. On the other hand, the fourfermion processes like quark–antiquark scattering include also the exchanges of heavy Kaluza–Klein and winding states, whose details depend on the form of internal geometry. They could be used as “precision tests” in order to distinguish between various compactification scenarios.Nuclear Physics B 08/2008; · 4.33 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: In this talk we discuss various aspects of the string landscape: Dbrane model building and their statistics, the generation of nonperturbative superpotentials from Dbrane instantons, moduli stabilization by fluxes and nonperturbative effects, the relation between flux vacua and BPS black holes, the construction of AdS4 vacua and related domain wall solutions, transitions between flux vacua and also some constraints on the string landscape from black hole considerations.Fortschritte der Physik 07/2008; 56(7‐9):694  722. · 0.98 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We construct the gravity dual of a field theory with flavour in which there are FayetIliopoulos (FI) terms present. For this purpose we turn on a constant KalbRamond B field in four internal space directions of AdS5 × S5 together with a D7 brane probe wrapping AdS5 × S3. The B field induces noncommutativity on the four internal directions of the D7 brane probe perpendicular to the AdS boundary. We argue that the moduli space of the Higgs part of mixed CoulombHiggs states in the dual field theory is described by the ADHM equations for noncommutative instantons on the four internal directions of the D7 brane probe. In particular, the global symmetries match. The FI term arises as the holographic dual of an antiselfdual B field. We discuss possible applications for this construction.Journal of High Energy Physics 07/2008; 2008(07):068. · 5.62 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We review some aspects of Dinstantons in intersecting Dbrane models. In particular, we present applications of the recently proposed instanton calculus to computations of charged matter superpotential couplings and corrections to the gauge kinetic function in the low energy effective action of type IIA orientifolds. As an interesting byway, we also discuss how oneloop corrections to the gauge kinetic function can be deduced from gauge threshold corrections in the type IIA setting.Fortschritte der Physik 04/2008; 56(4‐5):313  323. · 0.98 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: Nonperturbative Dbrane instantons can generate perturbatively absent though phenomenologically relevant couplings for type II orientifold compactifications with Dbranes. We discuss the generation of the perturbatively vanishing SU(5) GUT Yukawa coupling of type <10 10 5(H)>. Moreover, for a simple globally consistent intersecting D6brane model, we discuss the generation of mass terms for matter fields. This can serve as a mechanism for decoupling exotic matter.Physical Review Letters 02/2008; 100(6):061602. · 7.94 Impact Factor  Fortschritte Der Physikprogress of Physics  FORTSCHR PHYS. 01/2008; 56:309311.
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ABSTRACT: In this paper we discuss the strong coupling limit of chiral N=1 supersymmetric gauge theory via their embedding into Mtheory. In particular we focus on N=1 brane box models and show that after a Tduality transformation their Mtheory embedding is described by supersymmetric 3cycles. Brane box models with uniform bending lead to 3cycles which consist out of intersecting SeibergWitten curves. We discuss a few aspects of the intersection pattern in case of two intersecting tori which corresponds to N=1 SUSY QCD with N c =N f =4.05/2007: pages 434445;
Publication Stats
3k  Citations  
443.31  Total Impact Points  
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Institutions

1982–2013

LudwigMaximilianUniversity of Munich
 Arnold Sommerfeld Center for Theoretical Physics (ASC)
München, Bavaria, Germany


2005–2012

Max Planck Institute of Physics
München, Bavaria, Germany


2010

New York University
 Department of Physics
New York City, NY, United States


2009

Northeastern University
 Department of Physics
Boston, MA, United States


2008–2009

University of Wisconsin  Milwaukee
 Department of Physics
Milwaukee, WI, United States


1998–2009

Stanford University
 Department of Physics
Palo Alto, California, United States 
Martin Luther University of HalleWittenberg
HalleontheSaale, SaxonyAnhalt, Germany


1994–2004

HumboldtUniversität zu Berlin
 Department of Physics
Berlin, Land Berlin, Germany


2000

Columbia University
New York City, New York, United States


1999

Massachusetts Institute of Technology
 Center for Theoretical Physics
Cambridge, MA, United States 
University of California, Santa Barbara
 Kavli Institute for Theoretical Physics
Santa Barbara, California, United States 
Universiteit Utrecht
 Institute for Theoretical Physics
Utrecht, Provincie Utrecht, Netherlands


1998–1999

Humboldt State University
Arcata, California, United States


1997

University of Pennsylvania
 Department of Physics and Astronomy
Philadelphia, PA, United States


1985–1994

CERN
 Physics Department (PH)
Genève, Geneva, Switzerland


1986–1987

California Institute of Technology
Pasadena, California, United States
