AdS Background Research Articles

On integrable backgrounds self-dual under fermionic T-duality

We study the fermionic T-duality symmetry of integrable Green-Schwarz sigma-models on AdS backgrounds with Ramond-Ramond fluxes in various dimensions. We show that sigma-models based on supercosets of PSU supergroups, such as AdS_2 \times S^2 and AdS_3 \times S^3 are self-dual under fermionic T-duality, while supercosets of OSp supergroups such as non-critical AdS_2 and AdS_4 models, and the critical AdS_4 \times CP^3 background are not. We present a general algebraic argument to when a supercoset is expected to have a fermionic T-duality symmetry, and when it will fail to have one.

Chemical potential in the gravity dual of a2+1dimensional system

We study probe D5 branes in D3 brane AdS5 and AdS5-Schwarzschild backgrounds as a prototype dual description of strongly coupled 2+1 dimensional quasiparticles. We introduce a chemical potential through the U(1)R symmetry group, U(1) baryon number, and a U(1) of isospin in the multiflavor case. We find the appropriate D5 embeddings in each case—the embeddings do not exhibit the spontaneous symmetry breaking that would be needed for a superconductor. The isospin chemical potential does induce the condensation of charged meson states.

Cosmological topologically massive gravitons and photons**Some of these results were reported in abbreviated form in [1

We study topologically massive (2+1)-dimensional gravity with a negative cosmological constant. The masses of the linearized curvature excitations about AdS3 backgrounds are not only shifted from their flat background values but also, more surprisingly, split according to chirality. For all finite values of the topological mass, we find a single bulk degree of freedom with positive energy, and exhibit a complete set of normalizable, finite-energy wave packet solutions. This model can also be written as a sum of two higher-derivative Chern–Simons theories, weighted by the central charges of the boundary conformal field theory. At two particular ‘critical’ values of the couplings, one of these central charges vanishes, and linearized topologically massive gravity becomes equivalent to topologically massive electromagnetism; however, the physics of the bulk wave packets remains unaltered here.

HAGEDORN BEHAVIOR OF STRINGS IN AdS3/BTZ

We study a finite temperature string in curved space, especially in AdS3 and BTZ black hole background. We extract Hagedorn behavior of strings and argue thermodynamic properties in thermal AdS3 as well as in BTZ black hole background. In particular, we find the Hagedorn temperature of string on AdS3, which depends on the AdS3 curvature scale. We also find a tachyonic divergence for a BTZ black hole of string scale.

Electroweak symmetry breaking from a holographic fourth generation

We consider a model with four generations of standard model fermions propagating in an extra dimension with an AdS background metric. We show that if the zero modes of the fourth generation are highly localized towards the infrared brane, it is possible to break the electroweak symmetry via their condensation, partly driven by their interactions with the Kaluza-Klein excitations of the gauge bosons, as well as by the presence of bulk higher-dimensional operators. This dynamical mechanism results in a composite Higgs, which is highly localized and generally heavy. The localization of fermions in the five-dimensional bulk naturally leads to the standard model Yukawa couplings via the action of the bulk higher-dimensional operators, which are suppressed by the Planck scale. We obtain the spectrum of the model and explore some of its phenomenological consequences, both for electroweak precision constraints as well as at the Large Hadron Collider.

On T-duality and integrability for strings on AdS backgrounds

We discuss an interplay between T-duality and integrability for certain classical non-linear sigma models. In particular, we consider strings on the AdS5 ? S5 background and perform T-duality along the four isometry directions of AdS5 in the Poincar? patch. The T-dual of the AdS5 sigma model is again a sigma model on an AdS5 space. This classical T-duality relation was used in the recently uncovered connection between light-like Wilson loops and MHV gluon scattering amplitudes in the strong coupling limit of the AdS/CFT duality. We show that the explicit coordinate dependence along the T-duality directions of the associated Lax connection (flat current) can be eliminated by means of a field dependent gauge transformation. As a result, the gauge equivalent Lax connection can easily be T-dualized, i.e. written in terms of the dual set of isometric coordinates. The T-dual Lax connection can be used for the derivation of infinitely many conserved charges in the T-dual model. Our construction implies that local (Noether) charges of the original model are mapped to non-local charges of the T-dual model and vice versa.

Running anti-de Sitter radius from QCD-like strings

We consider renormalization effects for a bosonic QCD-like string, whose partons have 1/p2 propagators instead of Gaussian. Classically this model resembles (the bosonic part of) the projective light-cone (zero-radius) limit of a string on an AdS5 background, where Schwinger parameters give rise to the fifth dimension. Quantum effects generate dynamics for this dimension, producing an AdS5 background with a running radius. The projective light-cone is the high-energy limit: Holography is enforced dynamically.

Black strings with a negative cosmological constant: inclusion of electric charge and rotation

We generalize the vacuum static black string solutions of Einstein's equations with negative cosmological constant recently discussed in literature, by including an electromagnetic field. These higher-dimensional configurations have no dependence on the ‘compact’ extra dimension, while their boundary topology is the product of time and Sd−3 × S1 or Hd−3 × S1. Rotating generalizations of the even dimensional black string configurations are considered as well. Different from the static, neutral case, no regular limit is found for a vanishing event horizon radius. We explore numerically the general properties of such classical solutions and, using a counterterm prescription, we compute their conserved charges and discuss their thermodynamics. We find that the thermodynamics of the black strings follows the pattern of the corresponding black hole solutions in AdS backgrounds.

Integrability of type II superstrings on Ramond-Ramond backgrounds in various dimensions

We consider type II superstrings on AdS backgrounds with Ramond-Ramond flux in various dimensions. We realize the backgrounds as supercosets and analyze explicitly two classes of models: non-critical superstrings on AdS_{2d} and critical superstrings on AdS_p\times S^p\times CY. We work both in the Green--Schwarz and in the pure spinor formalisms. We construct a one-parameter family of flat currents (a Lax connection) leading to an infinite number of conserved non-local charges, which imply the classical integrability of both sigma-models. In the pure spinor formulation, we use the BRST symmetry to prove the quantum integrability of the sigma-model. We discuss how classical \kappa-symmetry implies one-loop conformal invariance. We consider the addition of space-filling D-branes to the pure spinor formalism.

Electromagnetic properties of Kerr–anti-de Sitter black holes

We examine the electromagnetic properties of Kerr-anti-de Sitter (Kerr-AdS) black holes in four and higher spacetime dimensions. Assuming that the black holes may carry a test electric charge we show that the Killing one-form which represents the difference between the timelike generators in the spacetime and in the reference background can be used as a potential one-form for the associated electromagnetic field. In four dimensions the potential one-form and the Kerr-AdS metric with properly rescaled mass parameter solve the Einstein-Maxwell equations, thereby resulting in the familiar Kerr-Newman-AdS solution. We solve the quartic equation governing the location of the event horizons of the Kerr-Newman-AdS black holes and present closed analytic expressions for the radii of the horizons. We also compute the gyromagnetic ratio for these black holes and show that it corresponds to g=2 just as for ordinary black holes in asymptotically flat spacetime. Next, we compute the gyromagnetic ratio for the Kerr-AdS black holes with a single angular momentum and with a test electric charge in all higher dimensions. The gyromagnetic ratio crucially depends on the dimensionless ratio of the rotation parameter to the curvature radius of the AdS background. At the critical limit, when the boundary Einstein universe ismore » rotating at the speed of light, it tends to g=2 irrespective of the spacetime dimension. Finally, we consider the case of a five-dimensional Kerr-AdS black hole with two angular momenta and show that it possesses two distinct gyromagnetic ratios in accordance with its two orthogonal two-planes of rotation. In the special case of two equal angular momenta, the two gyromagnetic ratios merge into one leading to g=4 at the maximum angular velocities of rotation.« less

Heavy-light mesons from the AdS/CFT correspondence

We propose a holographic description of heavy-light mesons, i.e. of mesons containing a light and a heavy quark. In the semi-classical 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 non-supersymmetric Constable-Myers 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 b-quark sector.

Weak gravity conjecture in the asymptotical dS and AdS background

The cosmological observations provide a strong evidence that there is a positive cosmological constant in our universe and thus the spacetime is asymptotical de Sitter space. The conjecture of gravity as the weakest force in the asymptotical dS space leads to a lower bound on the U(1) gauge coupling $g$, or equivalently, the positive cosmological constant gets an upper bound $\rho_V \leq g^2 M_p^4$ in order that the U(1) gauge theory can survive in four dimensions. This result has a simple explanation in string theory, i.e. the string scale $\sqrt{\alpha '}$ should not be greater than the size of the cosmic horizon. Our proposal in string theory can be generalized to U(N) gauge theory and gives a guideline to the microscopic explanation of the de Sitter entropy. The similar results are also obtained in the asymptotical anti-de Sitter space.

Tools for deconstructing gauge theories in AdS5

We employ analytical methods to study deconstruction of 5D gauge theories in the AdS5 background. We demonstrate that using the so-called q-Bessel functions allows a quantitative analysis of the deconstructed setup. Our study clarifies the relation of deconstruction with 5D warped theories.

Quasi-normal modes of the scalar hairy black hole

We calculate quasi-normal modes of the scalar hairy black hole in the AdS background using the Horowitz–Hubeny method for the potential that is not known in an analytical form. For some black hole parameters we found pure imaginary frequencies. Increasing the scalar field mass does not cause the imaginary part to vanish, it reaches some minimum and then increases; thus, in the case under consideration, the infinitely long living modes (quasi-resonances) do not appear.

Holographic model for hadrons in deformed AdS5 background

Several physical quantities of light hadrons are examined by a new holographic model of QCD, which is the modified version of the one proposed by Erlich et al. defined on AdS5. In our model, AdS5 is deformed by a non-trivial bulk scalar, this is corresponding to adding the mass term of the adjoint fermions to the 4d SYM theory dual to the gravity on AdS5. We find that this deformation should be taken to be rather small, but its important effects are also seen.

Anti-de Sitter D-brane dynamics

We study the anti-de Sitter D-brane dynamics in Hamiltonian formulation. By exploiting the existence of certain conserved charges, we solve the equation of motion for a D1-brane in the AdS3 background and find the space-time dependent solutions. We further study the dynamics by mapping the problem to that of the open string tachyon, and examine the time dependent solutions in some detail.

Thermodynamics of Newman-Unti-Tamburino charged spaces

We discuss and compare at length the results of two methods used recently to describe the thermodynamics of Taub-NUT solutions in a deSitter background. In the first approach ($\mathbb{% C}$-approach), one deals with an analytically continued version of the metric while in the second approach ($\mathbb{R}$-approach), the discussion is carried out using the unmodified metric with Lorentzian signature. No analytic continuation is performed on the coordinates and/or the parameters that appear in the metric. We find that the results of both these approaches are completely equivalent modulo analytic continuation and we provide the exact prescription that relates the results in both methods. The extension of these results to the AdS/flat cases aims to give a physical interpretation of the thermodynamics of nut-charged spacetimes in the Lorentzian sector. We also briefly discuss the higher dimensional spaces and note that, analogous with the absence of hyperbolic nuts in AdS backgrounds, there are no spherical Taub-Nut-dS solutions.

ENERGY AND MOMENTUM DISTRIBUTIONS OF THE MAGNETIC SOLUTION TO (2+1) EINSTEIN–MAXWELL GRAVITY

We use Møller's energy–momentum complex in order to explicitly evaluate the energy and momentum density distributions associated with the three-dimensional magnetic solution to the Einstein–Maxwell equations. The magnetic spacetime under consideration is a one-parametric solution describing the distribution of a radial magnetic field in a three-dimensional AdS background, and representing the superposition of the magnetic field with a 2+1 Einstein static gravitational field.

Spectral flow on the Higgs branch and AdS/CFT duality

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 D7-branes 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 non-trivial rearrangement of the spectrum.

Hadronic Spectrum of a Holographic Dual of QCD

We compute the spectrum of light hadrons in a holographic dual of QCD defined on AdS5 x S5 which has conformal behavior at short distances and confinement at large interquark separation. Specific hadrons are identified by the correspondence of string modes with the dimension of the interpolating operator of the hadron's valence Fock state. Higher orbital excitations are matched quanta to quanta with fluctuations about the AdS background. Since only one parameter, the QCD scale Lambda(QCD), is used, the agreement with the pattern of physical states is remarkable. In particular, the ratio of delta to nucleon trajectories is determined by the ratio of zeros of Bessel functions.