  Composite particles generated by an unknown strong dynamics can be
responsible for the ElectroWeak Symmetry Breaking (EWSB) and can substitute the
Standard Model (SM) Higgs boson in keeping perturbative unitarity in the
longitudinal WW scattering up to a cut-off \Lambda\approx 4\pi v. These new
states can be sufficiently light to be observed at the Large Hadron Collider
(LHC) and they can even be the first manifestation of new physics at the LHC.
Their couplings among themselves and with the SM particles, can be described
using reasonable effective Lagrangians and Chiral Perturbation Theory. In the
first part of this thesis different possibilities for a strongly interacting
EWSB are discussed in details with particular attention to the roles of
unitarity in the longitudinal WW scattering and of ElectroWeak Precision Tests
(EWPT). Higgsless models with composite vectors and scalars, based on the
SU(2)_{L}\times SU(2)_{R}/SU(2)_{L+R} custodial symmetry, are discussed in the
context of ElectroWeak Chiral Lagrangians and the phenomenology of the pair
productions is studied for the high energy and high luminosity phase of the
LHC. In the second part of the thesis the possible signals of single particle
production at the early LHC, with 7 TeV of center of mass energy and 1-5
fb^{-1} of integrated luminosity, are treated with a phenomenological
Lagrangian approach. The final states containing at least one photon emerge as
the most promising channels for an early discovery already with tens of inverse
picobarns of integrated luminosity. Finally, in the last part of this work, the
role of a composite iso-singlet vector in Dark Matter models is discussed and
the related LHC phenomenology is studied, giving particular attention to the
Z\gamma final state.
