A Simple Signal of Noncommutative Space

We propose a simple low-energy classical experiment in which the effects of noncommutativity can be clearly separated from commutative physics. The ensuing bound on the noncommutative scale is remarkable, especially in view of its elementary derivation.Comment: latex, 5 page

Path Integral Formulation of Noncommutative Quantum Mechanics

We propose a phase-space path integral formulation of noncommutative quantum mechanics, and prove its equivalence to the operatorial formulation. As an illustration, the partition function of a noncommutative two-dimensional harmonic oscillator is calculated.Comment: Latex, 7 page

Effects of Magnetic Fields on String Pair Creation

The rate of pair production of open strings in general uniform electromagnetic fields is calculated in various space-time dimensions. The corrections with respect to the case of pure electric backgrounds are displayed. In particular, a contribution in the form of a Born-Infeld action is derived and its role in the present context emphasizedComment: LaTeX, 13 pages, one LaTeX figure; several clarifying remarks and one equation added; section 3 shortened, a few misprints correcte

A path integral leading to higher-order Lagrangians

We consider a simple modification of standard phase-space path integrals and show that it leads in configuration space to Lagrangians depending also on accelerations.Comment: 6 page

Lagrangian versus Quantization

We discuss examples of systems which can be quantized consistently, although they do not admit a Lagrangian description.Comment: 8 pages, no figures; small corrections, references adde

Pair Production of Open Strings - Relativistic versus Dissipative Dynamics

We study the pair production of open strings in constant electric fields, using a general framework which encodes both relativistic string theory and generic linearly extended systems as well. In the relativistically invariant case we recover previous results, both for pair production and for the effective Born-Infeld action. We then derive a non-relativistic limit - where the propagation velocity along the string is much smaller than the velocity of light - obtaining quantum dissipation. We calculate the pair nucleation rate for this case, which could be relevant for applications.Comment: 22 pages; 1 LaTeX figur