Temperature dependence of the nodal Fermi velocity in layered cuprates

We explain recently observed linear temperature dependence of the nodal Fermi velocity $v_F(T)$ in near-optimally doped cuprates. We argue that it originates from electron-electron interaction, and is a fundamental property of an arbitrary 2D Fermi liquid. We consider a spin-fermion model with the same parameters as in earlier studies, and show that the T term is about 30% at 300K, in agreement with the data. We show that the sub-leading term in $v_F (T)$isaregular(andsmall)$T^2$correction\mathrm{.}Wealsoshowthatata$2k_F$ quantum-critical point, temperature corrections to the dispersion are singular.