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Instability of the Reissner-Nordström solution and new hairy black holes in d = 5 dimensions
Get PDFThe d = 5 Reissner-Nordström black hole becomes unstable when considered as a solution of Einstein– Yang-Mills–Chern-Simons theory. The existence of a marginally stable mode gives rise to a new branch of black holes with non-Abelian magnetic fields outside the horizon. These solutions carry a nonzero electric charge and have finite mass. We argue that these features manifest themselves both for Minkowski and (Anti-)de Sitter asymptotics. The properties of solutions in a de Sitter background are new to the present work and are emphasised. All solutions constructed have finite mass by virtue of the presence of the Chern-Simons term, which in d = 5 plays the role of a higher order term scaling appropriately for this purpose
Towards Unquenched Holographic Magnetic Catalysis
Get PDFWe propose a string dual to the SU(N_c) N = 4 SYM coupled to N_f massless fundamental flavors in an external magnetic field. The flavors are introduced by homogeneously smeared N_f D7–branes and the external magnetic field via a non-trivial Kalb-Ramond B–field. Our solution is perturbative in a parameter that counts the number of internal flavor loops. In the limit of vanishing B–field the background reduces to the supersymmetric one obtained in hep-th/0612118. We introduce an additional probe D7–brane and in the supersymmetric limit of vanishing B–field perform a holographic renormalization of its “on-shell” action. We consider also non-supersymmetric probes with fixed worldvolume gauge field corresponding to a magnetic field coupled only to the fundamental fields of the probe brane. We study the influence of the backreacted flavors on the effect of dynamical mass generation. Qualitatively the physical picture remains unchanged. In the next step we consider the case when the magnetic field couples to both the backreacted and the probe fundamental degrees of freedom. At sufficiently strong magnetic field the meson spectrum signals an instability of the probe D7–brane, which we interpret as reflecting an instability of the supergravity background
Numerical Hermitian Yang-Mills connections and Kähler cone substructure
Get PDFWe further develop the numerical algorithm for computing the gauge connection of slope-stable holomorphic vector bundles on Calabi-Yau manifolds. In particular, recent work on the generalized Donaldson algorithm is extended to bundles with Kähler cone substructure on manifolds with h^1,1 > 1. Since the computation depends only on a one-dimensional ray in the Kähler moduli space, it can probe slope-stability regardless of the size of h^1,1 . Suitably normalized error measures are introduced to quantitatively compare results for different directions in Kähler moduli space. A significantly improved numerical integration procedure based on adaptive refinements is described and implemented. Finally, an efficient numerical check is proposed for determining whether or not a vector bundle is slope-stable without computing its full connection
Pressure and volume in the first law of black hole thermodynamics
Get PDFThe mass of a black hole is interpreted, in terms of thermodynamic potentials, as being the enthalpy, with the pressure given by the cosmological constant. The volume is then defined as being the Legendre transform of the pressure and the resulting relation between volume and pressure is explored in the case of positive pressure. A virial expansion is developed and a van der Waals like critical point determined. The first law of black hole thermodynamics includes a PdV term which modifies the maximal efficiency of a Penrose process. It is shown that, in four dimensional space-time with a negative cosmological constant, an extremal charged rotating black hole can have an efficiency of up to 75%, while for an electrically neutral rotating back hole this figure is reduced to 52%, compared to the corresponding values of 50% and 29% respectively when the cosmological constant is zero
Generalized baryon form factors and proton structure functions in the Sakai–Sugimoto model
Get PDFWe investigate the production of positive parity baryon resonances in proton electromagnetic scattering within the Sakai-Sugimoto model. The latter is a string model for the non-perturbative regime of large N_c QCD. Using holographic techniques we calculate the generalized Dirac and Pauli form factors that describe resonance production. We use these results to estimate the contribution of resonance production to the proton structure functions. Interestingly, we find an approximate Callan-Gross relation for the structure functions in a regime of intermediate values of the Bjorken variable
The 24-cell and Calabi-Yau threefolds with Hodge numbers (1,1)
Get PDFCalabi-Yau threefolds with h^(11)(X) = h^(21)(X) = 1 are constructed as free quotients of a hypersurface in the ambient toric variety defined by the 24-cell. Their fundamental groups are SL(2, 3), Z_3 × Z_8 , and Z_3 × Q_8
Notes on Yang-Mills–Higgs monopoles and dyons on R^D, and Chern-Simons–Higgs solitons on R^{D-2}: Dimensional reduction of Chern-Pontryagin densities
Get PDFWe review work on construction of Monopoles in higher dimensions. These are solutions to a particular class of models descending from Yang–Mills systems on even dimensional bulk, with Spheres as codimensions. The topological lower bounds on the Yang–Mills action translate to Bogomol’nyi lower bounds on the residual Yang-Mills–Higgs systems. Mostly, consideration is restricted to 8 dimensional bulk systems, but extension to the arbitrary case follows systematically. After presenting the monopoles, the corresponding dyons are also constructed. Finally, new Chern–Simons densities expressed in terms of Yang-Mills and Higgs fields are presented. These are defined in all dimensions, including in even dimensional spacetimes. They are constructed by subjecting the dimensionally reduced Chern–Pontryagin densites to further descent by two steps