Corrections from low momentum physics to heavy quark symmetry relations for $B\to \mathrm{De}{\overline{\nu }}_e$ and $B\to D^{*}e{\overline{\nu }}_e$ decay

Heavy quark symmetry relations for $B\to \mathrm{De}{\overline{\nu }}_e$ and $B\to D^{*}e{\overline{\nu }}_e$ form factors receive corrections suppressed by powers of the charm quark mass. For small up and down quark masses the leading corrections of order ${\left(\frac{1}{m_c}\right)}^{n+2\mathrm{}}$, $n=0, 1, 2, \dots$, have a nonanalytic dependence on the light quark masses of the form $\ln m_{\pi }^2$ for $n=0\mathrm{}$ and ${\left(\frac{1}{m_{\pi }}\right)}^n$ for $n=1, 2, \dots$. These corrections arise from very low momentum physics (i.e., well below the chiral-symmetry-breaking scale) and are computed using chiral perturbation theory. They are typically of the order of a few percent.