The color dipole picture and the ratio of R(W2,Q2)=σL/σTR(W2,Q2)=σL/σT

The transverse size of qq¯ fluctuations of the longitudinal photon is reduced relative to the transverse size of qq¯ fluctuations of the transverse photon. This implies R(W2,Q2)=0.375R(W2,Q2)=0.375 or, equivalently, FL/F2=0.27FL/F2=0.27 at x≪0.1x≪0.1 and Q2Q2 sufficiently large, while R(W2,Q2)=0.5R(W2,Q2)=0.5, if this effect is not taken into account. Forthcoming experimental data from HERA will allow to test this prediction.