arXiv subjects

K. Behrndt

Publications and source records attributed to K. Behrndt.

22 records · Page 2Linked to original sources

arXiv1993

Cosmological String Solutions in 4 Dimensions from 5d Black Holes

We obtain cosmological four dimensional solutions of the low energy effective string theory by reducing a five dimensional black hole, and black hole--de Sitter solution of Einstein gravity down to four dimensions. The appearance of a cosmological constant in the five dimensional Einstein--Hilbert action produces a special dilaton potential in the four dimensional effective string action. Cosmological scenarios implemented by our solutions are discussed.

hep-th↗

arXiv1993

A Monopole Solution in open String Theory

We investigate a solution of the Weyl invariance conditions in open string theory in 4 dimensions. In the closed string sector this solution is a combination of the SU(2) Wess--Zumino--Witten model and a Liouville theory. The investigation is carried out in the $σ$ model approach where we have coupled all massless modes (especially an abelian gauge field via the boundary) and tachyon fields. Neglecting all higher derivatives in the field strength we get an exact result which can be interpreted as a monopole configuration living in non--trivial space time. The masses of both tachyon fields are quantized by $c_{wzw}$ and vanish for $c_{wzw} = 1$.

hep-th↗

arXiv1992

The Tachyon in a Linear Expanding Universe

We investigate the tachyon coupling in a static Robertson--Walker like metric background. For a tachyon and dilaton field which are only time dependent one can rewrite this model as a SU(2) Wess--Zumino--Witten model and a scalar Feigin--Fuchs theory. In this case the restriction to a real exponential tachyon field fixes the level $k$ of the Wess--Zumino--Witten model. For a spatially dependent tachyon the world radius and the dilaton are quantized in terms of $k$ and the tachyon by two integers, i.e. one has a discrete set of fields. The spatial part of the tachyon is given by Chebyshev polynomials of the second kind. An investigation of the tachyon mass shows that the tachyon is massless for $k=1$.

hep-th↗

arXiv1992

Non-Critical Strings in Robertson-Walker Space Time

I consider a D+1 dimensional nonlinear $σ$ model based on a possible interpretation of the Liouville field as a physical time. The Weyl invariance of this theory gives us restrictions for the background fields and the parameters of the theory, e.g.\ for trivial background one obtains the known regions for the dimension of the space-time ($\leq$1 or $\geq$25). For a Robertson-Walker space time a special solution of these equations is discussed.

hep-th↗