Publications (76)279.46 Total impact
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ABSTRACT: Using a novel, string theoryinspired formalism based on a Hamiltonian constraint, we obtain a conformal mechanical system for the spatially flat fourdimensional RobertsonWalker Universe. Depending on parameter choices, this system describes either a relativistic particle in the RobertsonWalker background or metric fluctuations of the RobertsonWalker geometry. Moreover, we derive a treelevel M theory matrix model in this timedependent background. Imposing the Hamiltonian constraint forces the spacetime geometry to be fuzzy near the big bang, while the classical RobertsonWalker geometry emerges as the Universe expands. From our approach, we also derive the temperature of the Universe interpolating between the radiation and matter dominated eras.Physical Review Letters 07/2007; 98(26):261301. · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We motivate and summarize our analysis of hepth/0610276 in which we consider D7brane probe embeddings in the PolchinskiStrassler background with = 2 supersymmetry. The corresponding dual gauge theory is given by the = 2* theory with fundamental matter. Based on a talk given by C. Sieg at the RTN Workshop 2006, Napoli.Fortschritte der Physik 04/2007; 55(5‐7):639  643. · 0.98 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study the gauge/gravity dual of a finite temperature field theory at finite isospin chemical potential by considering a probe of two coincident D7branes embedded in the AdSSchwarzschild black hole background. The isospin chemical potential is obtained by giving a vacuum expectation value to the time component of the nonAbelian gauge field on the brane. The fluctuations of the nonAbelian gauge field on the brane are dual to the SU(2) flavor current in the field theory. For the embedding corresponding to vanishing quark mass, we calculate all Green functions corresponding to the components of the flavor current correlator. We discuss the physical properties of these Green functions, which go beyond linear response theory. In particular, we show that the isospin chemical potential leads to a frequencydependent isospin diffusion coefficient.Physical review D: Particles and fields 01/2007; 76(4):046001046001. 
Article: Quarks and Mesons from String Theory
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ABSTRACT: In the context of the generalized AdS/CFT correspondence, we review the stringtheoretical description of QCDlike field theories with fundamental matter. We present a gravitational realization of chiral symmetry breaking, as well as a gravity description of a first order thermal phase transition. We also review nonperturbative results about the meson spectra that are obtained by solving the gravity equations of motion.Nuclear Physics B  Proceedings Supplements 01/2007; 164:280283. · 0.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Recent work on adding flavor to the generalized AdS/CFT correspondence is reviewed. In particular, we consider instanton configurations on two coincident D7 brane probes. These are matched to the Higgs branch of the dual field theory. In AdS5 × S5, the instanton generates a flow of the meson spectrum. For nonsupersymmetric gravity backgrounds, the Higgs branch is lifted by a potential, which has nontrivial physical implications. In particular these configurations provide a gravity dual description of BoseEinstein condensation and of a thermal phase transition.01/2007;  [Show abstract] [Hide abstract]
ABSTRACT: As an extension of holography with flavour, we analyze in detail the embedding of a D7brane probe into the PolchinskiStrassler gravity background, in which the breaking of conformal symmetry is induced by a 3form flux G_3. This corresponds to giving masses to the adjoint chiral multiplets. We consider the N=2 supersymmetric case in which one of the adjoint chiral multiplets is kept massless while the masses of the other two are equal. This setup requires a generalization of the known expressions for the backreaction of G_3 in the case of three equal masses to generic mass values. We work to second order in the masses to obtain the embedding of D7brane probes in the background. At this order, the 2form potentials corresponding to the background flux induce an 8form potential which couples to the worldvolume of the D7branes. We show that the embeddings preserve an SU(2) x SU(2) symmetry. We study possible embeddings both analytically in a particular approximation, as well as numerically. The embeddings preserve supersymmetry, as we investigate using the approach of holographic renormalization. The meson spectrum associated to one of the embeddings found reflects the presence of the adjoint masses by displaying a mass gap. Comment: LaTeX, 50 pages, 9 figuresJournal of High Energy Physics 10/2006; · 5.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: For a generic twodimensional 0A string background, we map the DiracBornInfeld action to a matrix model. This is achieved using a canonical transformation. The action describes D0branes in this background, while the matrix model has a potential which encodes all the information of the background geometry. We apply this formalism to specific backgrounds: For Rindler space, we obtain a matrix model with an upsidedown quadratic potential, while for AdS_2 space, the potential is linear. Furthermore we analyze the black hole geometry with RR flux. In particular, we show that at the Hagedorn temperature, the resulting matrix model coincides with the one for the linear dilaton background. We interpret this result as a realization of the string/black hole transition. Comment: 1+36 pages, No figure; an interpretation changed, Refs. added; Connection to Liouville theory added, to be published in CQGClassical and Quantum Gravity 10/2006; · 3.56 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We propose a holographic description of heavylight mesons, i.e. of mesons containing a light and a heavy quark. In the semiclassical string limit, we look at the dynamics of strings tied between two D7 branes. We consider this setup both in an AdS background and in the nonsupersymmetric ConstableMyers geometry which induces chiral symmetry breaking. We compute the meson masses in each case. Finally we discuss the relevance of this result for phenomenological comparison to the physical bquark sector. Comment: 22 pages, 7 figures; discussion of 't Hooft coupling dependence includedJournal of High Energy Physics 05/2006; · 5.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Recent work on adding flavour to the generalized AdS/CFT correspondence is reviewed. In particular, we consider instanton configurations on two coincident D7 brane probes. These are matched to the Higgs branch of the dual field theory. In AdS_5 x S^5, the instanton generates a flow of the meson spectrum. For nonsupersymmetric gravity backgrounds, the Higgs branch is lifted by a potential, which has nontrivial physical implications. In particular these configurations provide a gravity dual description of BoseEinstein condensation and of a thermal phase transition. Comment: 12 pages, 5 figures. Based on talk given by J. Erdmenger at the RTN Workshop``Constituents, Fundamental Forces and Symmetries of the Universe'',Corfu,Greece, 2026th September 2005. Contribution to the ProceedingsFortschritte der Physik 01/2006; · 0.98 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We consider D7 brane probes embedded in deformed AdS5 x S5 supergravity backgrounds which are nonsupersymmetric in the interior. In the context of the generalised AdS/CFT correspondence, these setups are dual to QCDlike theories with fundamental matter which display chiral symmetry breaking by a quark condensate. Evaluating the D7 action for a surface instanton configuration gives rise to an effective potential for the scalar Higgs vev in the dual field theory. We calculate this potential for two specific supergravity backgrounds. For a metric due to Constable and Myers, we find that the potential is asymptotically bounded by a 1/Q^4 behaviour and has a minimum at zero vev. For the YangMills* background we find that the Higgs potential scales quadratically with the Higgs vev. This corresponds to a canonical mass term and the embedding is again stable. Comment: 13 pages, 2 figures, calculation for the ConstableMyers geometry revisedJournal of High Energy Physics 09/2005; · 5.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We use AdS/CFT duality to study the thermodynamics of a strongly coupled N=2 supersymmetric large Nc SU(Nc) gauge theory with Nf =2 fundamental hypermultiplets. At finite temperature T and isospin chemical potential mu, a potential on the Higgs branch is generated, corresponding to a potential on the moduli space of instantons in the AdS description. For mu =0, there is a known first order phase transition around a critical temperature Tc. We find that the Higgs VEV is a suitable order parameter for this transition; for T>Tc, the theory is driven to a nontrivial point on the Higgs branch. For nonzero mu and T=0, the Higgs potential is unbounded from below, leading to an instability of the field theory due to BoseEinstein condensation. Comment: 23 pages, 5 figuresPhysical review D: Particles and fields 04/2005;  [Show abstract] [Hide abstract]
ABSTRACT: We use AdS/CFT duality to study the large N_c limit of the meson spectrum on the Higgs branch of a strongly coupled, N=2 supersymmetric SU(N_c) gauge theory with N_f =2 fundamental hypermultiplets. In the dual supergravity description, the Higgs branch is described by SU(2) instanton configurations on D7branes in an AdS background. We compute the spectral flow parameterized by the size of a single instanton. In the large N_c limit, there is a sense in which the flow from zero to infinite instanton size, or Higgs VEV, can be viewed as a closed loop. We show that this flow leads to a nontrivial rearrangement of the spectrum. Comment: v2; 16 pages, 3 figures, LaTeX + JHEP class, 3 refs added, accepted for publication by JHEPJournal of High Energy Physics 02/2005; · 5.62 Impact Factor 
Article: Spacetime dependent couplings in Script N = 1 SUSY gauge theories: anomalies and central functions
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ABSTRACT: We consider Script N = 1 supersymmetric gauge theories in which the couplings are allowed to be spacetime dependent functions. Both the gauge and the superpotential couplings become chiral superfields. As has recently been shown, a new topological anomaly appears in models with spacetime dependent gauge coupling. Here we show how this anomaly may be used to derive the NSVZ betafunction in a particular, welldetermined renormalisation scheme, both without and with chiral matter. Moreover we extend the topological anomaly analysis to theories coupled to a classical curved superspace background, and use it to derive an allorder expression for the central charge c, the coefficient of the Weyl tensor squared contribution to the conformal anomaly. We also comment on the implications of our results for the central charge a expected to be of relevance for a fourdimensional Ctheorem.Journal of High Energy Physics 01/2005; 6(06):004004. · 5.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In view of extending gauge/gravity dualities with flavour beyond the probe approximation, we establish the gravity dual description of mesons for a threedimensional super YangMills theory with fundamental matter. For this purpose we consider the fully backreacted D2/D6 brane solution of Cherkis and Hashimoto in an approximation due to Pelc and Siebelink. The lowenergy field theory is the IR fixed point theory of threedimensional N=4 SU(N_c) super YangMills with N_f fundamental fields, which we consider in a large N_c and N_f limit with N_f/N_c finite and fixed. We discuss the dictionary between mesonlike operators and supergravity fluctuations in the corresponding nearhorizon geometry. In particular, we find that the mesons are dual to the lowenergy limit of closed string states. In analogy to computations of glueball mass spectra, we calculate the mass of the lowestlying meson and find that it depends linearly on the quark mass.Journal of High Energy Physics 09/2004; · 5.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Following a purely algebraic procedure, we provide an exhaustive classification of local Weylinvariant scalar densities in dimension D=8. Comment: LaTeX, 19 pages, typos corrected, one reference addedClassical and Quantum Gravity 05/2004; · 3.56 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study gravity duals of large N nonsupersymmetric gauge theories with matter in the fundamental representation by introducing a D7brane probe into deformed AdS backgrounds. In particular, we consider a D7brane probe in both the AdS Schwarzschild black hole solution and in the background found by Constable and Myers, which involves a nonconstant dilaton and S5 radius. Both these backgrounds exhibit confinement of fundamental matter and a discrete glueball and meson spectrum. We numerically compute the Ψ̅ Ψ condensate and meson spectrum associated with these backgrounds. In the AdS–blackhole background, a quarkbilinear condensate develops only at a nonzero quark mass. We speculate on the existence of a third order phase transition at a critical quark mass where the D7 embedding undergoes a geometric transition. In the ConstableMyers background, we find a chiral symmetry breaking condensate as well as the associated Goldstone boson in the limit of small quark mass. The existence of the condensate ensures that the D7brane never reaches the naked singularity at the origin of the deformed AdS space.Physical review D: Particles and fields 03/2004; 69(6).  [Show abstract] [Hide abstract]
ABSTRACT: We establish a holographic description of chiral symmetry breaking for a particular confining large N nonsupersymmetric gauge theory with matter in the fundamental representation. The gravity dual of this theory is obtained by introducing a D7brane probe into a deformed Antide Sitter background found by Constable and Myers. We numerically compute the \bar\psi\psi condensate and meson spectrum by solving the equation of motion of the D7brane probe in this background. We find a symmetry breaking condensate as well as the associated, pionlike, Goldstone boson in the limit of small quark mass. The existence of the condensate ensures that the D7brane never reaches the naked singularity at the origin of the deformed AdS space. Comment: Talk given by I.K. at 36th International Symposium Ahrenshoop on the Theory of Elementary Particles: Recent Developments in String/MTheory and Field Theory, Berlin, Germany, 2630 Aug 2003, to appear in Fortsch.PhysFortschritte der Physik 12/2003; · 0.98 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study a defect conformal field theory describing D3branes intersecting over two spacetime dimensions. This theory admits an exact Lagrangian description which includes both two and fourdimensional degrees of freedom, has (4,4) supersymmetry and is invariant under global conformal transformations. Both two and fourdimensional contributions to the action are conveniently obtained in a twodimensional (2,2) superspace. In a suitable limit, the theory has a dual description in terms of a probe D3brane wrapping an AdS3×S1 slice of AdS5×S5. We consider the AdS/CFT dictionary for this setup. In particular we find classical probe fluctuations corresponding to the holomorphic curve wy=cα′. These fluctuations are dual to defect fields containing massless twodimensional scalars which parametrize the classical Higgs branch, but do not correspond to states in the Hilbert space of the CFT. We also identify probe fluctuations which are dual to BPS superconformal primary operators and to their descendants. A nonrenormalization theorem is conjectured for the correlators of these operators, and verified to order g2.Physical Review D 11/2003; 68(10). · 4.69 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study brane recombination for supersymmetric configurations of intersecting branes in terms of the worldvolume field theory. This field theory contains an impurity, corresponding to the degrees of freedom localized at the intersection. The Higgs branch, on which the impurity fields condense, consists of vacua for which the intersection is deformed into a smooth calibrated manifold. We show this explicitly using a superspace formalism for which the calibration equations arise naturally from F and Dflatness. Comment: References addedJournal of High Energy Physics 09/2003; · 5.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The defect conformal field theory describing intersecting D3branes at a C^2/Z_k orbifold is used to (de)construct the theory of intersecting M5branes, as well as M5branes wrapping the holomorphic curve xy=c. The possibility of a 't Hooft anomaly due to tensionless strings at the intersection is discussed. This note is based on a talk given by Zachary Guralnik at the 35th International Symposium Ahrenshoop on the Theory of Elementary Particles. Comment: latex, one figure, 9pages. Talk given by Z.G. at the 35th International Symposium Ahrenshoop on the Theory of Elementary ParticlesFortschritte der Physik 12/2002; · 0.98 Impact Factor
Publication Stats
2k  Citations  
279.46  Total Impact Points  
Top Journals
Institutions

2006–2012

Max Planck Institute of Physics
München, Bavaria, Germany


2011

Università degli Studi di Perugia
Perugia, Umbria, Italy


2002–2005

Humboldt University of Berlin
 Department of Physics
Berlín, Berlin, Germany


2001

Massachusetts Institute of Technology
 Center for Theoretical Physics
Cambridge, MA, United States


1998–2000

University of Leipzig
 Institute of Theoretical Physics
Leipzig, Saxony, Germany
