Cell Microtubules as Cavities: Quantum Coherence and Energy Transfer?

A model is presented for dissipationless energy transfer in cell microtubules due to quantum coherent states. The model is based on conjectured (hydrated) ferroelectric properties of microtubular arrangements. Ferroelectricity is essential in providing the necessary isolation against thermal losses in thin interior regions, full of ordered water, near the tubulin dimer walls of the microtubule. These play the role of cavity regions, which are similar to electromagnetic cavities of quantum optics. As a result, the formation of (macroscopic) quantum coherent states of electric dipoles on the tubulin dimers may occur. Some experiments, inspired by quantum optics, are suggested for the falsification of this scenario.Comment: 7 pages LATEX. Invited talk at the 2000 International Conference on Mathematics and Engineering Techniques in Medicine and Biological Sciences, Monte Carlo Resort, Las Vegas (USA), June 26-29 2000, published in the proceeding

Dark Energy as an off-shell Tachyon Background in four-dimensional Strings

We consider a time-dependent bosonic string in graviton, dilaton and tachyon backgrounds, for which it was already shown that conformal invariance is respected to all orders in alpha' and in any space-time dimension. Assuming that the tachyon is off-shell, we show in this note that the specific time-homogeneity of the corresponding space time effective action leads to a power-law expanding Universe, that can be accelerating or decelerating, depending on the range of parameter space considered. We interpret this result as dark energy. We arrive at this result without requiring the knowledge of the structure of the string effective action, which is not known to all orders in alpha'. Moreover, in our approach, the background configurations are consistent in a four-dimensional space time, without any need for extra dimensions.Comment: 10 pages, typos correcte

Potentials between D-Branes in a Supersymmetric Model of Space-Time Foam

We study a supersymmetric model of space-time foam with two stacks each of eight D8-branes with equal string tensions, separated by a single bulk dimension containing D0-brane particles that represent quantum fluctuations. The ground-state configuration with static D-branes has zero vacuum energy, but, when they move, the interactions among the D-branes and D-particles due to the exchanges of strings result in a non-trivial, positive vacuum energy. We calculate its explicit form in the limits of small velocities and large or small separations between the D-branes and/or the D-particles. This non-trivial vacuum energy appears as a central charge deficit in the non-critical stringy $\sigma$ model describing perturbative string excitations on a moving D-brane. These calculations enable us to characterise the ground state of the D-brane/D-particle system, and provide a framework for discussing brany inflation and the possibility of residual Dark Energy in the present-day Universe.Comment: 26 pages Latex, four eps figures incorporated, minor typos corrected, no effects on conclusion

High-Energy QCD as a Topological Field Theory

We propose an identification of the conformal field theory underlying Lipatov's spin-chain model of high-energy scattering in perturbative QCD. It is a twisted N=2 supersymmetric topological field theory, which arises as the limiting case of the SL(2,R)/U(1) non-linear sigma model that also plays a role in describing the Quantum Hall effect and black holes in string theory. The doubly-infinite set of non-trivial integrals of motion of the high-energy spin-chain model displayed by Faddeev and Korchemsky are identified as the Cartan subalgebra of a W_{\infty} \otimes W_{\infty} bosonic sub-symmetry possessed by this topological theory. The renormalization group and an analysis of instanton perturbations yield some understanding why this particular topological spin-chain model emerges in the high-energy limit, and provide a new estimate of the asymptotic behaviour of multi-Reggeized-gluon exchange.Comment: 24 pages LATEX, one eps figure incorporate