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CÁLCULO DEL ESCALAR DE CURVATURA

Dada la trimétrica $ds^2=e^{-U+V}dx^2+e^{-U-V}dy^2+e^{-M}d\mu ^2,$ se procede a obtener los símbolos de Christoffel, dados por la siguiente ecuación

\begin{displaymath}
\Gamma _{ij}^k=\frac 12g^{ks}\left( g_{js,i}+g_{si,j}-g_{ij,s}\right)
\end{displaymath} (A.1)

De los 27 $\Gamma _{ij}^k$, aquellos que son diferentes de cero son
$\displaystyle \Gamma _{13}^1$ $\textstyle =$ $\displaystyle -\frac 12U^{\prime }+\frac 12V^{\prime }$  
$\displaystyle \Gamma _{31}^1$ $\textstyle =$ $\displaystyle -\frac 12U^{\prime }+\frac 12V^{\prime }$  
$\displaystyle \Gamma _{23}^2$ $\textstyle =$ $\displaystyle -\frac 12U^{\prime }-\frac 12V^{\prime }$  
$\displaystyle \Gamma _{32}^2$ $\textstyle =$ $\displaystyle -\frac 12U^{\prime }-\frac 12V^{\prime }$ (A.2)
$\displaystyle \Gamma _{11}^3$ $\textstyle =$ $\displaystyle \frac 12\left( U^{\prime }-V^{\prime }\right) e^{M-U+V}$  
$\displaystyle \Gamma _{22}^3$ $\textstyle =$ $\displaystyle \frac 12\left( U^{\prime }+V^{\prime }\right) e^{M-U-V}$  
$\displaystyle \Gamma _{33}^3$ $\textstyle =$ $\displaystyle -\frac 12M^{\prime }$  
       
       

Con lo anterior se puede encontrar el tensor de Riemann mediante la expresión
\begin{displaymath}
R_{\beta \gamma \delta }^\alpha =\Gamma _{\beta \delta ,\ga...
...mu -\Gamma _{\mu \delta }^\alpha \Gamma _{\beta \gamma
}^\mu
\end{displaymath} (A.3)

Las componentes diferentes de cero son las siguientes
$\displaystyle R_{212}^1$ $\textstyle =$ $\displaystyle \frac 14\left( -U^{\prime }+V^{\prime }\right) \left( U^{\prime
}+V^{\prime }\right) e^{M-U-V}$  
$\displaystyle R_{221}^1$ $\textstyle =$ $\displaystyle -\frac 14\left( -U^{\prime }+V^{\prime }\right) \left(
U^{\prime }+V^{\prime }\right) e^{M-U-V}$  
$\displaystyle R_{313}^1$ $\textstyle =$ $\displaystyle \frac 12U^{\prime \prime }-\frac 12V^{\prime \prime }-\frac
14(U^...
...14(V^{\prime
})^2+\frac 14M^{\prime }U^{\prime }-\frac 14M^{\prime }V^{\prime }$  
$\displaystyle R_{331}^1$ $\textstyle =$ $\displaystyle -\frac 12U^{\prime \prime }+\frac 12V^{\prime \prime }+\frac
14(U...
...14(V^{\prime
})^2-\frac 14M^{\prime }U^{\prime }+\frac 14M^{\prime }V^{\prime }$  
$\displaystyle R_{112}^2$ $\textstyle =$ $\displaystyle \frac 14\left( U^{\prime }+V^{\prime }\right) \left( U^{\prime
}-V^{\prime }\right) e^{M-U+V}$  
$\displaystyle R_{121}^2$ $\textstyle =$ $\displaystyle -\frac 14\left( U^{\prime }+V^{\prime }\right) \left( U^{\prime
}-V^{\prime }\right) e^{M-U+V}$  
$\displaystyle R_{323}^2$ $\textstyle =$ $\displaystyle \frac 12U^{\prime \prime }+\frac 12V^{\prime \prime }-\frac
14(U^...
...14(V^{\prime
})^2+\frac 14U^{\prime }M^{\prime }+\frac 14V^{\prime }M^{\prime }$ (A.4)
$\displaystyle R_{332}^2$ $\textstyle =$ $\displaystyle -\frac 12U^{\prime \prime }-\frac 12V^{\prime \prime }+\frac
14(U...
...14(V^{\prime
})^2-\frac 14U^{\prime }M^{\prime }-\frac 14V^{\prime }M^{\prime }$  
$\displaystyle R_{113}^3$ $\textstyle =$ $\displaystyle \frac 14e^{M-U+V}\left( -U^{\prime }M^{\prime }+V^{\prime
}M^{\pr...
...{\prime \prime }+(U^{\prime
})^2-2U^{\prime }V^{\prime }+(V^{\prime })^2\right)$  
$\displaystyle R_{131}^3$ $\textstyle =$ $\displaystyle -\frac 14e^{M-U+V}\left( -U^{\prime }M^{\prime }+V^{\prime
}M^{\p...
...{\prime \prime }+(U^{\prime
})^2-2U^{\prime }V^{\prime }+(V^{\prime })^2\right)$  
$\displaystyle R_{223}^3$ $\textstyle =$ $\displaystyle \frac 14e^{M-U-V}\left( -U^{\prime }M^{\prime }-V^{\prime
}M^{\pr...
...{\prime \prime }+(U^{\prime
})^2+2U^{\prime }V^{\prime }+(V^{\prime })^2\right)$  
$\displaystyle R_{232}^3$ $\textstyle =$ $\displaystyle -\frac 14e^{M-U-V}\left( -U^{\prime }M^{\prime }-V^{\prime
}M^{\p...
...{\prime \prime }+(U^{\prime
})^2+2U^{\prime }V^{\prime }+(V^{\prime })^2\right)$  

Con lo anterior se calcula el tensor de Ricci, que se encuentra contrayendo el tensor de Riemann, esto es
\begin{displaymath}
R_{\mu \nu }=R_{\mu \alpha \nu }^\alpha
\end{displaymath} (A.5)

esta ecuación da el siguiente resultado
$\displaystyle R_{11}$ $\textstyle =$ $\displaystyle \frac 14e^{M-U+V}\left( -2(U^{\prime })^2+2U^{\prime \prime
}-2V^...
... }+2U^{\prime }V^{\prime }+U^{\prime }M^{\prime
}-V^{\prime }M^{\prime }\right)$  
$\displaystyle R_{22}$ $\textstyle =$ $\displaystyle \frac 14e^{M-U-V}\left( -2(U^{\prime })^2+2U^{\prime \prime
}+2V^...
... }-2U^{\prime }V^{\prime }+U^{\prime }M^{\prime
}+V^{\prime }M^{\prime }\right)$ (A.6)
$\displaystyle R_{33}$ $\textstyle =$ $\displaystyle U^{\prime \prime }-\frac 12(U^{\prime })^2-\frac 12(V^{\prime
})^2+\frac 12U^{\prime }M^{\prime }$  

Finalmente, el escalar de curvatura está dado por
$\displaystyle R$ $\textstyle =$ $\displaystyle g^{\mu \nu }R_{\mu \nu }$  
$\displaystyle R$ $\textstyle =$ $\displaystyle \frac 12e^M\left( -3(U^{\prime })^2+4U^{\prime \prime }+2U^{\prime
}M^{\prime }-(V^{\prime })^2\right)$ (A.7)


next up previous contents
Next: Sobre este documento... Up: tglo Previous: Bibliografía   Índice General
enrique pazos 2000-09-27