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Renormalization of the spin-wave spectrum is discussed in a cubic ferromagnetwith dipolar forces at $T_C\gg T\ge0$. First 1/S-corrections are considered indetail to the bare spectrum $\epsilon_{\bf k} = \sqrt{Dk^2 (Dk^2 +S\omega_0\sin^2\theta_{\bf k})}$, where $D$ is the spin-wave stiffness,$\theta_{\bf k}$ is the angle between $\bf k$ and the magnetization and$\omega_0$ is the characteristic dipolar energy. In accordance with previousresults we obtain the thermal renormalization of constants $D$ and $\omega_0$in the expression for the bare spectrum. Besides, a number of previouslyunknown features are revealed. We observe terms which depend on azimuthal angleof the momentum $\bf k$. It is obtained an isotropic term proportional to $k$which makes the spectrum linear rather than quadratic when $\sin\theta_{\bfk}=0$ and $k \ll \omega_0/D$. In particular a spin-wave gap proportional to$\sin\theta_{\bf k}$ is observed. Essentially, thermal contribution from theHartree-Fock diagram to the isotropic correction as well as to the spin-wavegap are proportional to the demagnetizing factor in the direction of domainmagnetization. This nontrivial behavior is attributed to the long-range natureof the dipolar interaction. It is shown that the gap screens infraredsingularities of the first 1/S-corrections to the spin-wave stiffness andlongitudinal dynamical spin susceptibility (LDSS) obtained before. Wedemonstrate that higher order 1/S-corrections to these quantities are small at$T\ll\omega_0$. However the analysis of the entire perturbation series is stillrequired to derive the spectrum and LDSS when $T\gg\omega_0$.Comment: 11 pages, 1 figur

Renormalization of the spin-wave spectrum in three-dimensional ferromagnets with dipolar interaction