The existence of a minimal observable length has long been suggested in quantum gravity as well as in string theory. In this context a generalized uncertainty relation has been derived which quantum theoretically describes the minimal length as a minimal uncertainty in position measurements. Here we study in full detail the quantum mechanical structure which underlies this uncertainty relation. DAMTP/94-105, hep-th/9412167, and Phys.Rev.D52:1108 (1995) * supported by Studienstiftung des Deutschen Volkes, BASF-fellow, a

In the early universe, neutrinos are slightly coupled when electron-positron pairs annihilate transferring their entropy to photons. This process originates non-thermal distortions on the neutrino spectra which depend on neutrino flavour, larger for nu_e than for nu_mu or nu_tau. We study the effect of three-neutrino flavour oscillations on the process of neutrino decoupling by solving the momentum-dependent kinetic equations for the neutrino spectra. We find that oscillations do not essentially modify the total change in the neutrino energy density, giving N_eff=3.046 in terms of the effective number of neutrinos, while the small effect over the production of primordial 4He is increased by O(20%), up to 2.1 x 10^{-4}. These results are stable within the presently favoured region of neutrino mixing parameters.Comment: 18 pages, 2 figure

We present an up-to-date review of Big Bang Nucleosynthesis (BBN). We discuss the main improvements which have been achieved in the past two decades on the overall theoretical framework, summarize the impact of new experimental results on nuclear reaction rates, and critically re-examine the astrophysical determinations of light nuclei abundances. We report then on how BBN can be used as a powerful test of new physics, constraining a wide range of ideas and theoretical models of fundamental interactions beyond the standard model of strong and electroweak forces and Einstein's general relativity.

Studies in string theory and quantum gravity suggest the existence of a finite lower limit ∆x 0 to the possible resolution of distances, at the latest on the scale of the Planck length of 10 −35 m. Within the framework of the euclidean path integral we explicitly show ultraviolet regularisation in field theory through this short distance structure. Both rotation and translation invariance can be preserved. An example geometry is studied in detail.

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