We investigate aspects of the four-dimensional effective description of brane world scenarios based on warped compactification on anti-de Sitter space. The low-energy dynamics is described by visible matter gravitationally coupled to a “dark” conformal field theory. We give the linearized description of the 4d stress tensor corresponding to an arbitrary 5d matter distribution. In particular a 5...

In this easy introduction to higher gauge theory, we describe parallel transport for particles and strings in terms of 2-connections on 2-bundles. Just as ordinary gauge theory involves a gauge group, this generalization involves a gauge ‘2-group’. We focus on 6 examples. First, every abelian Lie group gives a Lie 2-group; the case of U(1) yields the theory of U(1) gerbes, which play an importa...

It has been suggested that codimension-two braneworlds might naturally explain the vanishing of the 4D effective cosmological constant, due to the automatic relation between the deficit angle and the brane tension. To investigate whether this cancellation happens dynamically, and within the context of a realistic cosmology, we study a codimension-two braneworld with spherical extra dimensions c...

We study 4d simplicial quantum gravity in the dynamical triangulation approach with a non-trivial class of measures. We find that the measure contribution plays an important role, influencing the phase diagram and the nature of the (possible) critical theory. We discuss how the lattice theory could be used to fix the quantum measure in a non-ambiguous

The technique of generating new solutions to 4D gravity/matter systems by dimensional reduction to a σ-model is extended to supersymmetric configurations of supergravity. The conditions required for the preservation of supersymmetry under isometry transformations in the σ-model target space are found. Some examples illustrating the technique are given. e-mail: [email protected] e-mail: parviz@ph...

The key to membrane theory is to enlarge the diffeomorphism group until 4D gravity becomes almost topological. Just one ghost survives and its central charges can cancel against matter. A simple bosonic membrane emerges, but its flat D = 28 target space is unstable. Adding supersym-metry ought to give calculable (2,2) membranes in 12 target dimensions, but (2,1) membranes won't work.

We discuss the “gravitationally dressed” beta functions in the Gross– Neveu model interacting with 2d Liouville theory and in SU(N) gauge theory interacting with the conformal sector of 4d quantum gravity. Among the effects that we suggest may feel the gravitational dressing are the minimum of the effective potential and the running of the gauge coupling. ∗ [email protected] ∗∗ percacci@...

We propose a model which represents a four-dimensional version of Ponzano and Regge’s three-dimensional euclidean quantum gravity. In particular we show that the exponential of the euclidean Einstein-Regge action for a 4d-discretized block is given, in the semiclassical limit, by a gaussian integral of a suitable 12j-symbol. Possible developments of this result are discussed.