Search

In this thesis we present four main results: • The computation of the matching coefficients for a complete set of 4-quark operators between the continuum HQET and Lattice HQET. This result extends and completes a preceding computation of the matching coefficients relevant for the B⁰ - B̄;⁰ mixing (and corrects a mistake in the latter). • The Lattice evaluation of the coupling g_B*Bπ, which is related to the form factor of zero momentum transfer of the axial current between B*- and B-states. Moreover we show how this coupling constant is also related to the coupling g between heavy mesons and low-momentum pions that appears the effect heavy meson chiral Lagranigan. We find the value g = 0.42(4)(8). Besides its theoretical interest, the phenomenological implications of such a determination are discussed. • The lattice evaluation of the matrix elements of the four-quark operators which contribute to the lifetimes of B-mesons and the Λb-baryon. We find that the spectator effects are larger than naively expected and are in part responsible for the discrepancy between the O(1/m²_b) theoretical prediction and experimental measurement of the ratio of lifetimes τ(Λb)/τ(B⁰). In fact for this ratio we obtain the value 0.93(1)(2). • A re-evaluation of the B_B parameter relevant for the B⁰ - B̄;⁰ mixing, using our correct result for the matching coefficients. We obtain B_B = 0.96(3).

We present the new framework based on BFKL and DGLAP evolution equations in which the leading in(Q(_2)) and in(l/x) terms are treated on equal footing. We introduce a pair of coupled integro-difFerential equations for the quark singlet and the unintegrated gluon distribution. The observable structure functions are calculated using high energy factorisation approach. We also include the sub-leading in (l/x) effects via consistency constraint. We argue that the use of this constraint leads to more stable solution to the Pomeron intercept than that based on the NLO calculation of the BFKL equation alone and generates resummation to all orders of the major part of the subleading in (l/x) effects. The global fit to all available deep inelastic data is performed using a simple parametrisation of the non-perturbative region. We also present the results for the longitudinal structure function and the charm component of the F(_2) structure function. Next; we extend this approach to the low Q(^2) domain. At small distances we use the perturbative approach based on the unified BFKL/DGLAP equations and for large distances we use Vector Meson Dominance Model and, for the higher mass qq states, the additive quark approach. We show the results for the total cross section and for the ratio of the longitudinal and transverse structure functions. Finally, we calculate the dijet production and consider the decorrelation effects in the azimuthal distributions caused by the diffusion in the transverse momentum k(_r) of the exchanged gluon. Using the gluon distribution which is fixed by the fit to the DIS data we are able to make absolute predictions. We show the results for the dF(_r)/dɸ, the total cross section and also the distributions in Q(^2) as well as in the longitudinal momentum fraction of the gluon. Our theoretical predictions are confronted with the measurements made using ZEUS detector at HERA.