diff --git a/papers/Report/index.tex b/papers/Report/index.tex
index d6e1512..812d68e 100644
--- a/papers/Report/index.tex
+++ b/papers/Report/index.tex
@@ -409,7 +409,7 @@ defeat the point.
 It is useful to express the above in terms of an effective Hamiltonian
 \begin{equation}
   \label{eq:26}
-  H_{\eff}[H](t)\equiv \frac{1}{-\iu t} \log[U_{t}[H]].
+  H_{\eff}[H](t)\equiv \frac{1}{-\iu t} \log[\mathcal{U}_{t}[H]].
 \end{equation}
 This Hamiltonian, similar to the Floquet Hamiltonian, has a spectrum
 limited by the branch cut of the complex logarithm, which however has