Jump to content

Stress energy tensor transformation

Featured Replies

Show that if you add a total derivative to the Lagrangian density \( L \to L + \partial_\mu X^\mu \), the energy momentum tensor changes as \( T^{\mu\nu} \to T^{\mu\nu}+\partial_\alpha B^{\alpha\mu\nu}\) with \( B^{\alpha\mu\nu}=-B^{\mu\alpha\nu}\). The Lagrangian can depend on higher order derivatives of the field.
 
Attempted Solution:
 
So we have \( T_{\mu\nu}=\frac{\partial L}{\partial(\partial_\mu \phi)}\partial_\nu \phi-g_{\mu\nu}L\), where \( \phi\) is the field that the Lagrangian depends on. If we do the given change on the Lagrangian, the change in \( T_{\mu\nu}\) would be \( \frac{\partial (\partial_\alpha X^\alpha)}{\partial(\partial_\mu \phi)}\partial_\nu \phi-g_{\mu\nu}\partial_\alpha X^\alpha =\partial_\alpha \frac{\partial  X^\alpha}{\partial(\partial_\mu \phi)}\partial_\nu \phi-g_{\mu\nu}\partial_\alpha X^\alpha\). From here I thought of using this: \( g_{\mu\nu}\partial_\alpha X^\alpha=g_{\mu\nu}\partial_\alpha \phi \frac{\partial X^\alpha}{\partial \phi}\) But I don't really know what to do from here. Mainly I don't know how to get rid of that \(g_{\mu\nu}\). Also I am not sure if what I did so far is correct. Can someone help me?

Archived

This topic is now archived and is closed to further replies.

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.

Configure browser push notifications

Chrome (Android)
  1. Tap the lock icon next to the address bar.
  2. Tap Permissions → Notifications.
  3. Adjust your preference.
Chrome (Desktop)
  1. Click the padlock icon in the address bar.
  2. Select Site settings.
  3. Find Notifications and adjust your preference.