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spaghetti3451
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Homework Statement
Given the Lagrangian ##\mathcal{L} = \frac{1}{2}(\partial_{\mu}\Phi)^{2}+\frac{1}{2}\Phi^{2}-\frac{1}{2}\Phi^{3}+\frac{\alpha}{8}\Phi^{4}##, where ##\Phi=\Phi(x)##, find the equation of motion of the system. Assume that the field ##\Phi## is spherically symmetric, i.e. ##\Phi = \Phi(r)##.
Homework Equations
The Euler-Lagrange equation of motion for a scalar field
The Attempt at a Solution
##S = \int d^{4}x \bigg(\frac{1}{2}(\partial_{\mu}\Phi)^{2}+\frac{1}{2}\Phi^{2}-\frac{1}{2}\Phi^{3}+\frac{\alpha}{8}\Phi^{4}\bigg)##
The spherical volume element in ##4-##dimensional Euclidean space is ##d^{4}x = r^{3}\ \text{sin}^{2}(\phi_{1})\ \text{sin}(\phi_{2})\ dr\ d\phi_{1}\ d\phi_{2}\ d\phi_{3}##.
Therefore, ##S = \int d^{4}x \bigg(\frac{1}{2}(\partial_{\mu}\Phi)^{2}+\frac{1}{2}\Phi^{2}-\frac{1}{2}\Phi^{3}+\frac{\alpha}{8}\Phi^{4}\bigg)##
##=\int_{0}^{2\pi}d\phi_{3}\ \int_{0}^{\pi}d\phi_{2}\ \text{sin}(\phi_{2}) \int_{0}^{\pi}d\phi_{1}\ \text{sin}^{2}(\phi_{1}) \int_{0}^{r}r'^{3}\ dr'\ \bigg(\frac{1}{2}(\partial_{r'}\Phi)^{2}+\frac{1}{2}\Phi^{2}-\frac{1}{2}\Phi^{3}+\frac{\alpha}{8}\Phi^{4}\bigg)##
##=(2\pi)(2)\bigg(\frac{\pi}{2}\bigg)\int_{0}^{r}r'^{3}\ dr'\ \bigg(\frac{1}{2}(\partial_{r'}\Phi)^{2}+\frac{1}{2}\Phi^{2}-\frac{1}{2}\Phi^{3}+\frac{\alpha}{8}\Phi^{4}\bigg)##.
Am I correct so far?