424 research outputs found
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
Existence Theorems for Hairy Black Holes in su(N) Einstein-Yang-Mills theories
We establish the existence of hairy black holes in su(N) Einstein-Yang-Mills
theories, described by N-1 parameters, corresponding to the nodes of the gauge
field functions.Comment: 64 pages, latex2e, minor changes on the nature of the parameters,
version to appear in J. Math. Phy
Instability of hairy black holes in spontaneously-broken Einstein-Yang-Mills-Higgs systems
The stability of a new class of hairy black hole solutions in the coupled
system of Einstein-Yang-Mills-Higgs is examined, generalising a method
suggested by Brodbeck and Straumann and collaborators, and Volkov and Gal'tsov.
The method maps the algebraic system of linearised radial perturbations of the
various field modes around the black hole solution into a coupled system of
radial equations of Schr\"odinger type. No detailed knowledge of the black hole
solution is required, except from the fact that the boundary conditions at the
physical space-time boundaries (horizons) must be such so as to guarantee the
{\it finiteness} of the various expressions involved. In this way, it is
demonstrated that the above Schr\"odinger equations have bound states, which
implies the instability of the associated black hole solution.Comment: 8 pages, LATE
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
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
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
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