Particle theory

Abstract:

We consider a class of multi-matrix models with an action which is O(D) invariant, where D is the number of NxN Hermitian matrices X_\mu, \mu=1,...,D. The action is a function of all the elementary symmetric functions of the matrix $T_{\mu\nu}=Tr(X_\mu X_\nu)/N$. We address the issue whether the O(D) symmetry is spontaneously broken when the size N of the matrices goes to infinity. The phase diagram in the space of the parameters of the model reveals the existence of a critical boundary where the O(D) symmetry is maximally broken.

Abstract:

A satisfactory theory of quantum gravity will very likely require modification of our classical perception of space-time, perhaps by giving it a 'foamy' structure at scales of order the Planck length. This is expected to modify the propagation of photons and other relativistic particles such as neutrinos, such that they will experience a non-trivial refractive index even in vacuo. The implied spontaneous violation of Lorentz invariance may also result in alterations of kinematical thresholds for key astrophysical processes involving high energy cosmic radiation. We discuss experimental probes of these possible manifestations of the fundamental quantum nature of space-time using observations of distant astrophysical sources such as gamma-ray bursts and active galactic nuclei.

Abstract:

The online silicon vertex tracker (SVT) is the new trigger processor dedicated to the two-dimensional (2-D) reconstruction of charged particle trajectories at the Level 2 of the collider detector at Fermilab (CDF) trigger. The SVT links the digitized pulse heights found within the silicon vertex detector to the tracks reconstructed in the central outer tracker by the Level 1 fast-track finder. Preliminary tests of the system took place during the October 2000 commissioning run of the Tevatron Collider. During the April-October 2001 data taking, it was possible to evaluate the performance of the system. In this paper, we review the tracking algorithms implemented in the SVT and we report on the performance achieved during the early phase of run II.