Signatures of Large Extra Dimensions

String theory suggests modifications of our spacetime such as extra dimensions and the existence of a mininal length scale. In models with addidional dimensions, the Planck scale can be lowered to values accessible by future colliders. Effective theories which extend beyond the standart-model by including extra dimensions and a minimal length allow computation of observables and can be used to make testable predictions. Expected effects that arise within these models are the production of gravitons and black holes. Furthermore, the Planck-length is a lower bound to the possible resolution of spacetime which might be reached soon.Comment: 8 pages, no figures, Talk presented at the NATO Advanced Study Institute: Structure and Dynamics of Elementary Matter, Kemer, Turkey, 22 Sep - 2 Oct 2003. Proceedings to be published by Kluwer Academic publisher

Spin network setting of topological quantum computation

The spin network simulator model represents a bridge between (generalised) circuit schemes for standard quantum computation and approaches based on notions from Topological Quantum Field Theories (TQFTs). The key tool is provided by the fiber space structure underlying the model which exhibits combinatorial properties closely related to SU(2) state sum models, widely employed in discretizing TQFTs and quantum gravity in low spacetime dimensions.Comment: Proc. "Foundations of Quantum Information", Camerino (Italy), 16-19 April 2004, to be published in Int. J. of Quantum Informatio

Nonabelian Monopoles from Matrices: Seeds of the Spacetime Structure

We study the expectation value of (the product) of the one-particle projector (s) in the reduced matrix model and matrix quantum mechanics in general. This quantity is given by the nonabelian Berry phase: we discuss the relevance of this with regard to the spacetime structure. The case of the USp matrix model is examined from this respect. Generalizing our previous work, we carry out the complete computation of this quantity which takes into account both the nature of the degeneracy of the fermions and the presence of the space time points belonging to the antisymmetric representation. We find the singularities as those of the SU(2) Yang monopole connection as well as the pointlike singularities in 9+1 dimensions coming from its SU(8) generalization. The former type of singularities, which extend to four of the directions lying in the antisymmetric representations, may be regarded as seeds of our four dimensional spacetime structure and is not shared by the IIB matrix model. From a mathematical viewpoint, these connections can be generalizable to arbitrary odd space dimensions due to the nontrivial nature of the eigenbundle and the Clifford module structure.Comment: 29 pages, Latex, 1 epsf figur

A note on local BRST cohomology of Yang-Mills type theories with free abelian factors

We extend previous work on antifield dependent local BRST cohomology for matter coupled gauge theories of Yang-Mills type to the case of gauge groups that involve free abelian factors. More precisely, we first investigate in a model independent way how the dynamics enters the computation of the cohomology for a general class of Lagrangians in general spacetime dimensions. We then discuss explicit solutions in the case of specific models. Our analysis has implications for the structure of characteristic cohomology and for consistent deformations of the classical models, as well as for divergences/counterterms and for gauge anomalies that may appear during perturbative quantization.Comment: 31 page

Cutoff AdS/CFT duality and the quest for braneworld black holes

We present significant evidence in favour of the holographic conjecture that ``4D black holes localized on the brane found by solving the classical bulk equations in $AdS_5$ are quantum corrected black holes and not classical ones''. The crucial test is the calculation of the quantum correction to the Newtonian potential based on a numerical computation of in Schwarzschild spacetime for matter fields in the zero temperature Boulware vacuum state. For the case of the conformally invariant scalar field the leading order term is found to be $M/45\pi r^3$. This result is equivalent to the result which was previously obtained in the weak-field approximation using Feynman diagrams and which has been shown to be equivalent, via the AdS/CFT duality, to the analogous calculation in Randall-Sundrum braneworlds. This asymptotic behavior was not captured in the analytical approximations for proposed in the literature. The 4D backreaction equations are then used to make a prediction about the existence and the possible spacetime structure of macroscopic static braneworld black holes.Comment: 4 pages, 2 figure

On higher-derivative gauge theories

In this work we study the main properties and the one-loop renormalization of a Yang-Mills theory in which the kinetic term contains also a fourth-order differential operator; in particular, we add to the Yang-Mills Lagrangian the most general contribution of mass dimension six, weighted with a dimensionful parameter. This model is renormalizable; in the literature two values for the beta function for the gauge coupling have been reported, one obtained using the heat kernel approach and one with Feynman diagrams. In this work we repeat the computation using heat kernel techniques confirming the latter result. We also considered coupling with matter. We then study the supersymmetric extension of the model; this is a nontrivial task because of the complicate structure of the higher-derivative term. Some partial results were known, but a computation of the beta functions for the full supersymmetric non-Abelian higher-derivative gauge theory was missing. We make use of the (unextended) supersymmetric higher-derivative Lagrangian density for the Yang-Mills field in six spacetime dimensions derived in arXiv:hep-th/0505082; by dimensional reduction we obtain the N=1 and N=2 supersymmetric higher-derivative super-Yang-Mills Lagrangian in four spacetime dimensions, whose beta function we evaluate using heat kernels. We also deduce the beta function for N=4 supersymmetry.Comment: Based on the thesis prepared as final dissertation for the MSc degree in Physics at the University of Padova. 68 pages; added reference in 1.