ar X iv : h ep - p h / 98 02 38 6 v 1 2 1 Fe b 19 98 QCD Predictions for g p 1 at Small x Incorporating Double
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چکیده
The proton spin dependent structure function g p 1 is analysed using the unified scheme incorporating both Altarelli-Parisi evolution and the double ln 2 (1/x) effects at low x. The latter are found to be very important in the region of x which can possibly be probed at HERA. Predictions for the polarized gluon distribution ∆G(x) at low x are also given. It has recently been pointed out that the spin dependent structure function g 1 at low x is dominated by the double logarithmic ln 2 (1/x) contributions i.e. by those terms of the perturbative expansion which correspond to the powers of ln 2 (1/x) at each order of the expansion [1, 2]. Those contributions go beyond the LO or NLO order QCD evolution of polarised parton densities [3] and in order to take them into account one has to include the resummed double ln 2 (1/x) terms in the coefficient and splitting functions [4]. In ref. [5] we have developed an alternative approach based on unitegrated distributions which for simplicity was formulated for the non-singlet distributions. In this note we wish to present the preliminary results for the singlet structure functions concentrating on the proton polarized structure function g p 1 (x, Q 2). Our main aim is to study g p 1 (x, Q 2) in the region of the small values of x which can possibly be probed at HERA [6] and confront obtained results with those obtained from the LO Altarelli-Parisi evolution. We will also show similar results for the polarised gluon distribution ∆G(x, Q 2). The dominant contribution to the double ln 2 (1/x) resummation comes from the ladder diagrams with quark and gluon exchanges along the ladder. In what follows we
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تاریخ انتشار 1998