  We assume the t-t'-J model to describe the CuO_2 planes of hole-doped
cuprates and we adapt the spin-charge gauge approach, previously developed for
the t-J model, to describe the holes in terms of a spinless fermion carrying
the charge (holon) and a neutral boson carrying spin 1/2 (spinon), coupled by a
slave-particle gauge field. In this framework we consider the effects of a
finite density of incoherent holon pairs in the normal state. Below a crossover
temperature, identified as the experimental "upper pseudogap", the scattering
of the "quanta" of the phase of the holon-pair field against holons reproduces
the phenomenology of Fermi arcs coexisting with gap in the antinodal region. We
thus obtain a microscopic derivation of the main features of the hole spectra
due to pseudogap. This result is obtained through a holon Green function which
follows naturally from the formalism and analytically interpolates between a
Fermi liquid-like and a d-wave superconductor behavior as the coherence length
of the holon pair order parameter increases. By inserting the gauge coupling
with the spinon we construct explicitly the hole Green function and calculate
its spectral weight and the corresponding density of states. So we prove that
the formation of holon pairs induces a depletion of states on the hole Fermi
surface. We compare our results with ARPES and tunneling experimental data. In
our approach the hole preserves a finite Fermi surface until the
superconducting transition, where it reduces to four nodes. Therefore we
propose that the gap seen in the normal phase of cuprates is due to the thermal
broadening of the SC-like peaks masking the Fermi-liquid peak. The Fermi arcs
then correspond to the region of the Fermi surface where the Fermi-liquid peak
is unmasked.
