Universes encircling 5-dimensional black holes
Universes inside a $Λ$ black hole
Universes out of almost empty space
Unmissing the Missing Matter in Neo-Kaluza-Klein Universes
Unparticle inspired corrections to the Gravitational Quantum Well
Unpolarized radiative cylindrical spacetimes: Trapped surfaces and quasilocal energy
Unruh Effect for General Trajectories
Unruh effect with back reaction--A first quantized treatment
Unruh model for the Einstein-Rosen charge: Squealing Wormholes?
Unruh response functions for scalar fields in de Sitter space
Unruh--DeWitt detectors in spherically symmetric dynamical space-times
Unspeakables and the Epistemological path towards Quantum Gravity
Unstable Anisotropic Loop Quantum Cosmology
Unstable circular null geodesics of static spherically symmetric black holes, Regge poles and quasinormal frequencies
Unstable even-parity eigenmodes of the regular static SU(2) Yang-Mills-dilaton solutions
Unstable Fields in Kerr Spacetimes
Unusual Features of Varying Speed of Light Cosmologies
Unusual Properties of Four-Fermion Gravitational Interaction
Unwrapping Closed Timelike Curves
Up to eleven: radiation from particles with arbitrary energy falling into higher-dimensional black holes