Johan Bijnens, Ilaria Jemos Vector Formfactors in Hard Pion Chiral Perturbation Theory Abstract We use three-flavour hard pion Chiral Perturbation Theory (HPChPT) in both the heavy meson and a relativistic formulation to calculate the chiral logarithms $m^2\log(m^2/\mu^2)$ contributing to the formfactors of the $B_{(s)}\rightarrow \pi,K,\eta$ and $D_{(s)}\rightarrow \pi,K,\eta$ transitions at momentum transfer $q^2$ away from the endpoint $q^2_\mathrm{max}=(m_B-m_M)^2$. We compare our results with CLEO $D\to\pi$ and $D\to K$ data. We also calculate the Isgur-Wise function of the $B_{(s)}\rightarrow D_{(s)}$ semileptonic decay away from the endpoint and the chiral logarithms for the pion and kaon electromagnetic formfactor. In two-flavour HPChPT we calculate the chiral logarithms for the pion vector and the scalar formfactors at $s\gg m_\pi^2$. This allows us to test hard pion ChPT using the existing two-loop calculations for these quantities. LU TP 10-27