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We propose a mechanism for solving the horizon and entropy problems ofstandard cosmology which does not make use of cosmological inflation. Crucialingredients of our scenario are brane gases, extra dimensions, and a confiningpotential due to string gas effects which becomes dominant at string-scalebrane separations. The initial conditions are taken to be a statisticallyhomogeneous and isotropic hot brane gas in a space in which all spatialdimensions are of string scale. The extra dimensions which end up as theinternal ones are orbifolded. The hot brane gas leads to an initial phase(Phase 1) of isotropic expansion. Once the bulk energy density has decreasedsufficiently, a weak confining potential between the two orbifold fixed planesbegins to dominate, leading to a contraction of the extra spatial dimensions(Phase 2). String modes which contain momentum about the dimensionsperpendicular to the orbifold fixed planes provide a repulsive potential whichprevents the two orbifold fixed planes from colliding. The radii of the extradimensions stabilize, and thereafter our three spatial dimensions expand as instandard cosmology. The energy density after the stabilization of the extradimensions is of string scale, whereas the spatial volume has greatly increasedduring Phases 1 and 2, thus leading to a non-inflationary solution of thehorizon and entropy problems.Comment: 7 pages, no figures, small error in Section IV correcte

The confining heterotic brane gas: a non-inflationary solution to the entropy and horizon problems of standard cosmology