  We theoretically discuss dynamical properties of spin-1/2 Heisenberg
antiferromagnet on the triangular lattice in magnetic field $\bf H$. We use the
recently proposed bond-operator theory which operates with quantum states of
the whole magnetic unit cell containing three spins. This technique describes
accurately short-range spin correlations and provides a quantitative
description of elementary excitations which appear in other approaches as bound
states of conventional low-energy quasiparticles (e.g., magnons). In
quantitative agreement with previous numerical and analytical findings, we
observe four phases with coplanar spin arrangements upon the field increasing:
the three-sublattice Y-phase, the collinear "up-up-down" (UUD) state, the
non-collinear V-phase, and the collinear fully polarized (FP) state. We
demonstrate that apart from magnons there are spin-0 elementary excitations in
the UUD state one of which is long lived and its spectrum lies below magnon
branches. This mode originates from a high-energy quasiparticle at $H=0$ and it
produces anomalies only in the longitudinal spin correlator. In the V-phase, we
obtain multiple short-wavelength spin excitations which have no counterparts in
the semiclassical spin-wave theory. We demonstrate a highly nontrivial field
evolution of quasiparticles spectra on the way from one collinear state (UUD)
to another one (FP) via the non-collinear V-phase (in which the longitudinal
and the transverse channels are mixed). In particular, some parts of the spin-0
branch in the UUD state become parts of the spin-1 (magnon) branch in the FP
phase whereas some parts of one magnon branch turn into parts of spin-2 branch.
Such evolution would be very difficult to find by any conventional analytical
approach. Our results are in good agreement with neutron experimental data
obtained recently in $\rm Ba_3CoSb_2O_9$, $\rm KYbSe_2$, and $\rm CsYbSe_2$.
