simplify formula

roam/data/d6/e44fbc-975b-463d-87f9-878d50758b55/index.tex

@@ -379,8 +379,7 @@ Altogether we arrive at
   \label{eq:28}
   \dot{\tilde{c}}_{m} = -\iu\bqty{∑_{n}V^{0}_{mn} \tilde{c}_n +
     \frac{\eu^{\iu ω_{m}^{0}t}}{\sqrt{ω_{m}^{0}}}
-    \pqty{
-      g_{m,+}^\ast b_{\inputf,+}^{m}(t) + g_{m,-}^\ast b_{\inputf,-}^{m}(t)}} - η_{m}\tilde{c}_{m}(t).
+    ∑_{σ=\pm}g_{m,σ}^\ast b_{\inputf,+}^{m}(t)} - η_{m}\tilde{c}_{m}(t).
 \end{equation}
 The usual situation is that \(b^{m}_{\inputf, -} = 0\) and we can
 restrict ourselves to the coupling to the right-moving input field.