  At finite hyperconductivity and finite fermionic density the flux lines of
long range hypermagnetic fields may not have a topologically trivial structure.
The combined evolution of the chemical potentials and of pseudoscalar fields
(like the axial Higgs), possibly present for temperatures in the TeV range, can
twist the hypercharge flux lines, producing, ultimately, hypermagnetic knots
(HK). The dynamical features of the HK depend upon the various particle physics
parameters of the model (pseudoscalar masses and couplings, strength of the
electroweak phase transition, hyperconductivity of the plasma) and upon the
magnitude of the primordial flux sitting in topologically trivial
configurations of the hypermagnetic field. We study different cosmological
scenarios where HK can be generated. We argue that the fermionic number sitting
in HK can be released producing a seed for the Baryon Asymmetry of the Universe
(BAU) provided the typical scale of the knot is larger than the diffusivity
length scale. We derive constraints on the primordial hypermagnetic flux
required by our mechanism and we provide a measure of the parity breaking by
connecting the degree of knottedness of the flux lines to the BAU. We rule out
the ordinary axion as a possible candidate for production (around temperatures
of the order of the GeV) of {\em magnetic} knots since the produced {\em
electromagnetic} helicity is negligible (for cosmological standard) if the
initial amplitude of the axion oscillations is of the order of the Peccei-Quinn
breaking scale.
