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