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For several processes at colliding beams, macroscopically large impactparameters give an essential contribution to the standard cross section. Theseimpact parameters may be much larger than the transverse sizes of the collidingbunches. In that case, the standard calculations have to be essentially modify.The corresponding formulae for such a beam-size effect were given twenty yearsago without taking into account correlations of particle coordinates in thebeams. In the present paper we derive formulae which necessary to take intoaccount quantitatively the effect of particle correlations in the spectrum ofbremsstrahlung as well as in pair production. Besides, we consider criticallyrecent papers of Baier and Katkov [Phys. Rev. D {\bf 66}, 053009 (2002) andhep-ph/0305304] in which it was calculated a new additional ``subtractionterm'' related to the coherent contribution into beam-size effect. We show thatthis result is groundless and point out the origin of the mistake.Comment: 19 LaTeX pages, 3 eps Fig

Beam-size effect at colliders and correlations of particles in a beam