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Exact Solutions and Scalar Fields in Gravity - Instituto Avanzado de ...

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258 EXACT SOLUTIONS AND SCALAR FIELDS IN GRAVITY<br />

Although connected with entropy production, this configuration is characterized<br />

by an equilibrium distribution function of the gas particles.<br />

Macroscopically, this evolution is connected with a smooth transition<br />

from a “symmetry” condition (where is a “projector-<br />

conformal timelike Kill<strong>in</strong>g vector” [7]) dur<strong>in</strong>g the <strong>de</strong> Sitter stage to the<br />

conformal symmetry as the FLRW dynamics is approached.<br />

Mapp<strong>in</strong>g the non-equilibrium contributions onto an effective<br />

refraction <strong>in</strong><strong>de</strong>x of the cosmic matter, the <strong>de</strong>flationary transition<br />

appears as the manifestation of a timelike conformal symmetry of an<br />

optical metric <strong>in</strong> which the refraction <strong>in</strong><strong>de</strong>x<br />

changes smoothly from a very large value <strong>in</strong> the <strong>de</strong> Sitter period to<br />

unity <strong>in</strong> the FRLW phase. The <strong>de</strong>flationary gas dynamics may alternatively<br />

be <strong>in</strong>terpreted as a production process of relativistic particles out<br />

of a <strong>de</strong>cay<strong>in</strong>g vacuum. Furthermore, there exists an equivalent scalar<br />

field <strong>de</strong>scription with an exponential type potential which generates the<br />

same <strong>de</strong>flationary scenario as the self-<strong>in</strong>teract<strong>in</strong>g gas mo<strong>de</strong>l.<br />

Acknowledgments<br />

This work was supported by the Deutsche Forschungsgeme<strong>in</strong>schaft.<br />

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