Marco M. Caldarelli

We construct solutions for thin black rings in Anti-deSitter and deSitter spacetimes using approximate methods. Black rings in AdS exist with arbitrarily large radius and satisfy a bound |J| \leq LM, which they saturate as their radius becomes infinitely large. For angular momentum near the maximum, they have larger area than rotating AdS black holes. Thin black rings also exist in deSitter space, with rotation velocities varying between zero and a maximum, and with a radius that is always strictly below the Hubble radius. Our general analysis allows us to include black Saturns as well, which we discuss briefly. We present a simple physical argument why supersymmetric AdS black rings must not be expected: they do not possess the necessary pressure to balance the AdS potential. We discuss the possible existence or absence of `large AdS black rings' and their implications for a dual hydrodynamic description. An analysis of the physical properties of rotating AdS black holes is also included.

The old suggestive observation that black holes often resemble lumps of fluid has recently been taken beyond the level of an analogy to a precise duality. We investigate aspects of this duality, and in particular clarify the relation between area minimization of the fluid vs. area maximization of the black hole horizon, and the connection between surface tension and curvature of the fluid, and surface gravity of the black hole. We also argue that the Rayleigh-Plateau instability in a fluid tube is the holographic dual of the Gregory-Laflamme instability of a black string. Associated with this fluid instability there is a rich variety of phases of fluid solutions that we study in detail, including in particular the effects of rotation. We compare them against the known results for asymptotically flat black holes finding remarkable agreement. Furthermore, we use our fluid results to discuss the unknown features of the gravitational system. Finally, we make some observations that suggest that asymptotically flat black holes may admit a fluid description in the limit of large number of dimensions.

We present non-extremal magnetic black string solutions in five-dimensional gauged supergravity. The conformal infinity is the product of time and S^1xS_h, where S_h denotes a compact Riemann surface of genus h. The construction is based on both analytical and numerical techniques. We compute the holographic stress tensor, the Euclidean action and the conserved charges of the solutions and show that the latter satisfy a Smarr-type formula. The phase structure is determined in the canonical ensemble, and it is shown that there is a first order phase transition from small to large black strings, which disappears above a certain critical magnetic charge that is obtained numerically. For another particular value of the magnetic charge, that corresponds to a twisting of the dual super Yang-Mills theory, the conformal anomalies coming from the background curvature and those arising from the coupling to external gauge fields exactly cancel. We also obtain supersymmetric solutions describing waves propagating on extremal BPS magnetic black strings, and show that they possess a Siklos-Virasoro reparametrization invariance.

The supersymmetric solutions of N=2, D=4 minimal ungauged and gauged supergravity are classified according to the fraction of preserved supersymmetry using spinorial geometry techniques. Subject to a reasonable assumption in the 1/2-supersymmetric time-like case of the gauged theory, we derive the complete form of all supersymmetric solutions. This includes a number of new 1/4- and 1/2-supersymmetric possibilities, like gravitational waves on bubbles of nothing in AdS_4.