We assume the space-time foam picture in which the vacuum is filled with a gas of virtual wormholes. It is shown that virtual wormholes form a finite (of the Planckian order) value of the energy density of zero-point fluctuations. However such a huge value is compensated by the contribution of virtual wormholes to the mean curvature and the observed value of the cosmological constant is close to zero. A nonvanishing value appears due to the polarization of vacuum in external classical fields. In the early Universe some virtual wormholes may form actual ones. We show that in the case of actual wormholes vacuum polarization effects are negligible while their contribution to the mean curvature is apt to form the observed dark energy phenomenon. Using the contribution of wormholes to dark matter and dark energy we find estimates for characteristic parameters of the gas of wormholes. 1. Introduction As is well known modern astrophysics (and, even more generally, theoretical physics) faces two key problems. Those are the nature of dark matter and dark energy. Recall that more than 90% of matter of the Universe has a nonbaryonic dark (to say, mysterious) form, while lab experiments still show no evidence for the existence of such matter. Both dark components are intrinsically incorporated in the most successful CDM (Lambda cold dark matter) model which reproduces correctly properties of the Universe at very large scales (e.g., see [1] and references therein). We point out that CDM predicts also the presence of cusps in centers of galaxies [2] and a too large number of galaxy satellites. Therefore other models are proposed, for example, like axions [3], which may avoid these. To be successful such models should involve a periodic self-interaction and therefore require a fine tuning, while in general the presence of standard nonbaryonic particles cannot solve the problem of cusps. Indeed, if we admit the existence of a self-interaction in the dark matter component, or some coupling to baryonic matter (which should be sufficiently strong to remove cusps), then we completely change properties of the dark matter component at the moment of recombination and destroy all successful predictions at very large scales. Recall that both warm and self-interacting dark matter candidates are rejected by the observing spectrum [1]. In other words, the two key observational phenomena (cores of dark matter in centers of galaxies [4–6] and spectrum) give a very narrow gap for dark matter particles which seems to require attracting some exotic objects in addition to standard
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