[Show abstract][Hide abstract] ABSTRACT: We give a detailed account and extensions of a holographic flavor superconductivity model which we have proposed recently. The model has an explicit field theory realization as strongly coupled N=2 Super Yang-Mills theory with fundamental matter at finite temperature and finite isospin chemical potential. Using gauge/gravity duality, i.e. a probe of two flavor D7-branes in the AdS black hole background, we show that the system undergoes a second order phase transition with critical exponent 1/2. The new ground state may be interpreted as a rho meson superfluid. It shows signatures known from superconductivity, such as an infinite dc conductivity and a gap in the frequency-dependent conductivity. We present a stringy picture of the condensation mechanism in terms of a recombination of strings. We give a detailed account of the evaluation of the non-Abelian Dirac-Born-Infeld action involved using two different methods. Finally we also consider the case of massive flavors and discuss the holographic Meissner-Ochsenfeld effect in our scenario. Comment: 23 pages, 22 figures. v2: small corrections and section about dynamical mass generation revised
Journal of High Energy Physics 03/2009; 2009(10). DOI:10.1088/1126-6708/2009/10/067 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this talk we present applications of the AdS/CFT correspondence to strongly coupled systems at finite temperature and particle density. The model we investigate contains adjoint matter described by the gauge multiplet of N=4, as well as fundamental matter given by the hypermultiplet of N=2 Super Yang-Mills theory. In some aspects these systems can be thought of as models for the quark-gluon plasma. In the first part we review some properties of meson spectra obtained from these holographic models. We discuss the implications of finite temperature and particle density in these string-theory motivated setups. In particular, we find a broadening of the vector meson peaks in the relevant spectral function at finite density. However, we do not observe a movement of the resonances to lower frequencies. Moreover, we analyze the effects of strong coupling on heavy meson diffusion in medium. To do so, we make use of an effective model with dipole interaction, which is valid for heavy quarks at arbitrary coupling strength. We calculate the momentum broadening -- normalized to the in-medium mass shift -- and compare the large 't Hooft coupling AdS/CFT result with a perturbative result for weak coupling. We find that the momentum broadening is reduced at large 't Hooft coupling, leading to increased relaxation time. Comment: 6 pages, 3 figures, prepared for the proceedings of the 8th Conference "Quark Confinement and the Hadron Spectrum", September 1st-6th 2008, Mainz, Germany; to appear in Proceedings of Science, based on a talk given by Felix Rust
[Show abstract][Hide abstract] ABSTRACT: Aharony, Bergman, Jafferis, and Maldacena have proposed that the low-energy description of multiple M2-branes at a C4/Zk singularity is a (2+1)-dimensional N=6 supersymmetric U(Nc) x U(Nc) Chern-Simons matter theory, the ABJM theory. In the large-Nc limit, its holographic dual is supergravity in AdS4 x S7/Zk. We study various ways to add fields that transform in the fundamental representation of the gauge groups, i.e. flavor fields, to the ABJM theory. We work in a probe limit and perform analyses in both the supergravity and field theory descriptions. In the supergravity description we find a large class of supersymmetric embeddings of probe flavor branes. In the field theory description, we present a general method to determine the couplings of the flavor fields to the fields of the ABJM theory. We then study four examples in detail: codimension-zero N=3 supersymmetric flavor, described in supergravity by Kaluza-Klein monopoles or D6-branes; codimension-one N=(0,6) supersymmetric chiral flavor, described by D8-branes; codimension-one N=(3,3) supersymmetric non-chiral flavor, described by M5/D4-branes; codimension-two N=4 supersymmetric flavor, described by M2/D2-branes. Finally we discuss special physical equivalences between brane embeddings in M-theory, and their interpretation in the field theory description.
Journal of High Energy Physics 01/2009; · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigate the thermodynamics of a thermal field theory in presence of both a baryon and an isospin chemical potential. For this we consider a probe of several D7-branes embedded in the AdS-Schwarzschild black hole background. We determine the structure of the phase diagram and calculate the relevant thermodynamical quantities both in the canonical and in the grand canonical ensemble. We discuss how accidental symmetries present reflect themselves in the phase diagram: In the case of two flavors, for small densities , there is a rotational symmetry in the plane spanned by the baryon and isospin density which breaks down at large densities, leaving a Z 4 symmetry. Finally, we calculate vector mode spectral functions and determine their dependence on either the baryon or the isospin density. For large densities, a new excitation forms with energy below the known supersymmetric spectrum. Increasing the density further, this excitation becomes unstable. We speculate that this instability indicates a new phase of condensed mesons.
Journal of High Energy Physics 12/2008; 0811(031):2008-65. DOI:10.1088/1126-6708/2008/11/031 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We consider thermal strongly-coupled N=2 SYM theory with fundamental matter at finite isospin chemical potential. Using gauge/gravity duality, i.e. a probe of two flavor D7-branes embedded in the AdS black hole background, we find a critical temperature at which the system undergoes a second order phase transition. The critical exponent of this transition is one half and coincides with the result from mean field theory. In the thermodynamically favored phase, a flavor current acquires a vev and breaks an Abelian symmetry spontaneously. This new phase shows signatures known from superconductivity, such as an infinite dc conductivity and a gap in the frequency-dependent conductivity. The gravity setup allows for an explicit identification of the degrees of freedom in the dual field theory, as well as for a dual string picture of the condensation process.
Physics Letters B 10/2008; 680(5-680):516-520. DOI:10.1016/j.physletb.2009.09.029 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We construct electrically charged AdS_5 black hole solutions whose charge, mass and boost-parameters vary slowly with the space-time coordinates. From the perspective of the dual theory, these are equivalent to hydrodynamic configurations with varying chemical potential, temperature and velocity fields. We compute the boundary theory transport coefficients associated with a derivative expansion of the energy momentum tensor and R-charge current up to second order. In particular, we find a first order transport coefficient associated with the axial component of the current. Comment: 31 pages, v2: published version; added some references, discussion of the charge-current changed, results unchanged
Journal of High Energy Physics 09/2008; 2009(01). DOI:10.1088/1126-6708/2009/01/055 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We consider a heavy meson moving slowly through high temperature non-abelian plasmas. Using a simple dipole effective Lagrangian, we calculate the in-medium mass shift and the drag coefficient of the meson in $\N=4$ Super Yang Mills theory at weak and strong coupling. As anticipated, in the large $N$ limit the mass shift is finite while the drag is suppressed by $1/N^2$ . After comparing results to perturbative QCD estimates (which are also calculated), we reach the conclusion that relative to weak coupling expectations the effect of strong coupling is to reduce the momentum diffusion rate and to {\it increase} the relaxation time by up to a factor of four.
Journal of High Energy Physics 09/2008; 2008(10). DOI:10.1088/1126-6708/2008/10/098 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We construct the gravity dual of a field theory with flavour in which there are Fayet-Iliopoulos (FI) terms present. For this purpose we turn on a constant Kalb-Ramond 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 Coulomb-Higgs 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 anti-selfdual B field. We discuss possible applications for this construction.
Journal of High Energy Physics 07/2008; 2008(07):068. DOI:10.1088/1126-6708/2008/07/068 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Gauge/gravity duals with flavour such as D7 probe branes added to deformed AdS_5 × S^5 backgrounds provide dual descriptions of spontaneous chiral symmetry breaking and light mesons, as well as of a first order phase transition for the fundamental degrees of freedom at finite temperature in the deconfined phase. The quasiparticle degrees of freedom are studied using the appropriate spectral function at both finite temperature and density.
[Show abstract][Hide abstract] ABSTRACT: We review recent progress in studying mesons within gauge/gravity duality, in the context of adding flavour degrees of freedom
to generalizations of the AdS/CFT correspondence. Our main focus is on the “top-down approach” of considering models constructed
within string theory. We explain the string-theoretical constructions in detail, aiming at non-specialists. These give rise
to a new way of describing strongly coupled confining large-N gauge theories similar to large-N QCD. In particular, we consider gravity dual descriptions of spontaneous chiral symmetry breaking, and compare with lattice
results. A further topic covered is the behaviour of flavour bound states in finite-temperature field theories dual to a gravity
background involving a black hole. We also describe the “bottom up” phenomenological approach to mesons within AdS/QCD. Some
previously unpublished results are also included.
European Physical Journal A 01/2008; 35(1):81-133. DOI:10.1140/epja/i2007-10540-1 · 2.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We consider gauge/gravity duality with flavor for the finite-temperature field theory dual of the AdS-Schwarzschild black hole background with embedded D7-brane probes. In particular, we investigate spectral functions at finite baryon density in the black hole phase. We determine the resonance frequencies corresponding to meson-mass peaks as function of the quark mass over temperature ratio. We find that these frequencies have a minimum for a finite value of the quark mass. If the quotient of quark mass and temperature is increased further, the peaks move to larger frequencies. At the same time the peaks narrow, in agreement with the formation of nearly stable vector meson states which exactly reproduce the meson mass spectrum found at zero temperature. We also calculate the diffusion coefficient, which has finite value for all quark mass to temperature ratios, and exhibits a first-order phase transition. Finally we consider an isospin chemical potential and find that the spectral functions display a resonance peak splitting, similar to the isospin meson mass splitting observed in effective QCD models. Comment: 15 pages, REVTeX, 12 figures, Typos corrected, extended discussion of the dependence of the spectra on changes in the quark mass
[Show abstract][Hide abstract] ABSTRACT: We investigate gauge/gravity duals with flavour for which pure-gauge Kalb-Ramond B fields are turned on in the background, into which a D7 brane probe is embedded. First we consider the case of a magnetic field in two of the spatial boundary directions. We show that at finite temperature, i.e. in the AdS-Schwarzschild background, the B field has a stabilizing effect on the mesons and chiral symmetry breaking occurs for a sufficiently large value of the B field. Then we turn to the electric case of a B field in the temporal direction and one spatial boundary direction. In this case, there is a singular region in which it is necessary to turn on a gauge field on the brane in order to ensure reality of the brane action. We find that the brane embeddings are attracted towards this region. Far away from this region, in the weak field case at zero temperature, we investigate the meson spectrum and find a mass shift similar to the Stark effect. Comment: 34 pages, 18 figures, v2: added references and comments on mode decoupling, on thermodynamics and holographic renormalisation, JHEP style, v3: Final published version
Journal of High Energy Physics 09/2007; 2007(12). DOI:10.1088/1126-6708/2007/12/091 · 6.11 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 D7-branes embedded in the AdS-Schwarzschild black hole background. The isospin chemical potential is obtained by giving a vacuum expectation value to the time component of the non-Abelian gauge field on the brane. The fluctuations of the non-Abelian 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 frequency-dependent isospin diffusion coefficient.
[Show abstract][Hide abstract] ABSTRACT: In the context of gauge/gravity duals with flavor, we examine heavy-light mesons which involve a heavy and a light quark. For this purpose we embed two D7 brane probes at different positions into the gravity background. We establish the non-Abelian Dirac-Born-Infeld (DBI) action for these probes, in which the U(2) matrix describing the embedding is diagonal. The fluctuations of the brane probes correspond to the mesons. In particular, the off-diagonal elements of the U(2) fluctuation matrix correspond to the heavy-light mesons, while the diagonal elements correspond to the light-light and heavy-heavy mesons, respectively. The heavy-light mesons scale differently with the 't Hooft coupling than the mesons involving quarks of equal mass. The model describes both scalar and vector mesons. For different dilaton-deformed gravity backgrounds, we also calculate the Wilson loop energy, and compare with the meson masses.
Journal of High Energy Physics 07/2007; 09(09). DOI:10.1088/1126-6708/2007/09/111 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Using a novel, string theory-inspired formalism based on a Hamiltonian constraint, we obtain a conformal mechanical system for the spatially flat four-dimensional Robertson-Walker Universe. Depending on parameter choices, this system describes either a relativistic particle in the Robertson-Walker background or metric fluctuations of the Robertson-Walker geometry. Moreover, we derive a tree-level M theory matrix model in this time-dependent background. Imposing the Hamiltonian constraint forces the spacetime geometry to be fuzzy near the big bang, while the classical Robertson-Walker 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.
[Show abstract][Hide abstract] ABSTRACT: We motivate and summarize our analysis of hep-th/0610276 in which we consider D7-brane probe embeddings in the Polchinski-Strassler 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.
[Show abstract][Hide abstract] ABSTRACT: In the context of the generalized AdS/CFT correspondence, we review the string-theoretical description of QCD-like 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 non-perturbative results about the meson spectra that are obtained by solving the gravity equations of motion.
[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 non-supersymmetric gravity backgrounds, the Higgs branch is lifted by a potential, which has non-trivial physical implications. In particular these configurations provide a gravity dual description of Bose-Einstein condensation and of a thermal phase transition.
[Show abstract][Hide abstract] ABSTRACT: As an extension of holography with flavour, we analyze in detail the embedding of a D7-brane probe into the Polchinski-Strassler gravity background, in which the breaking of conformal symmetry is induced by a 3-form 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 D7-brane probes in the background. At this order, the 2-form potentials corresponding to the background flux induce an 8-form potential which couples to the worldvolume of the D7-branes. 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 figures
Journal of High Energy Physics 10/2006; DOI:10.1088/1126-6708/2007/01/079 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: For a generic two-dimensional 0A string background, we map the Dirac-Born-Infeld action to a matrix model. This is achieved using a canonical transformation. The action describes D0-branes 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 upside-down 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 CQG
Classical and Quantum Gravity 10/2006; DOI:10.1088/0264-9381/23/23/017 · 3.17 Impact Factor