# DIS at low x

# DIS at low x

This chapter is concerned with physics at low values of Bjorken *x*, below 0.01, where the q-qbar sea and gluon are the dominant partons and increasing rapidly as x decreases. It starts with an overview of the approaches considered and their regions of validity in the ln(1/x)-ln(Q^{2} ) plane. Then follows an account of the ‘standard’ approaches: DGLAP equations at low *x* and the Regge approach to total cross-sections. The hard and soft Pomerons are introduced and explained, followed by the BFKL equation. Angular ordering of gluon radiation and the CCFM approach to DIS comes next. These aforementioned approaches are linear and lead to an undamped increasing structure function as *x* decreases, which will violate unitarity eventually. This problem and how non-linear effects ameliorate it are covered next. The last section gives a comparison of the low-*x* approaches with structure-function data and outlines the need for precision measurements of other observables.

*Keywords:*
low x, DGLAP equations, BFKL equation, Regge approach, soft Pomeron, angular ordering, CCFM, non-linear effects, unitarity

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