Symmetry and conserved quantitiy : Noether's theorem
imported>Pythagoras0님의 2013년 4월 1일 (월) 04:13 판
introduction
- fields
- the condition for the extreme of a functional leads to Euler-Lagrange equation
- invariance of functional imposes another constraint
- Noether's theorem : extreme+invariance -> conservation law
- 틀:수학노트
field theoretic formulation
- \(\alpha_{s}\) continuous symmetry with parameter s
- current \(j(x)=(j^0(x),j^1(x),j^2(x),j^3(x))\)
\[j^{\mu}(x)= \frac{\partial \mathcal{L}}{\partial ( \partial_\mu \phi )}\left(\frac{\partial\alpha_{s}(\phi)}{\partial s} \right) \]
- obeys the continuity equation
\[\partial_{\mu} j^{\mu}=\sum_{\mu=0}^{3}\frac{\partial j^{\mu}}{\partial x^{\mu}}=0\]
- \(j^{0}(x)\) density of some abstract fluid
- Put $rho:=j_0$ and \(\mathbf{J}=(j_x,j_y,j_z)\) velocity of this abstract fluid at each space time point
- conserved charge
\[Q(t)=\int_V \rho \,d^3 x\] \[\frac{dQ}{dt}=0\]
history