The impact of beamstrahlung on precision measurements at CLIC

We review two commonly used approximate treatments of beamstrahlung at lepton colliders. We discuss the applicability of those approximations and show that they are bound to fail at very high energy $e^+e^-$ colliders such as CLIC. We model the beamstrahlung effects at CLIC by an exact numerical solution to the evolution equation for beamstrahlung and compare to the two approximations. We also discuss the impact of beamstrahlung on precision measurements of new physics parameters. As an illustration we consider Kaluza-Klein lepton production in Universal Extra Dimensions and study the deterioration of the endpoint lepton energy spectrum caused by beamstrahlung.