  After the recent high precision determinations of $V_{us}$ and $V_{ud}$, the
first row of the CKM matrix shows more than $4\sigma$ deviation from unitarity.
Two possible scenarios beyond the Standard Model can be investigated in order
to fill the gap. If a 4th quark $b'$ participates in the mixing, with $\vert
V_{ub'} \vert \sim0.04$, then its mass should be no more than 6 TeV or so. A
different solution can come from the introduction of the gauge horizontal
family symmetry acting between the lepton families and spontaneously broken at
the scale of about 6 TeV. Since the gauge bosons of this symmetry contribute to
muon decay in positive interference with Standard Model, the Fermi constant is
slightly smaller than the muon decay constant so that unitarity is recovered.
Also the neutron lifetime problem, that is about $4\sigma$ discrepancy between
the neutron lifetimes measured in beam and trap experiments, is discussed in
the light of the these determinations of the CKM matrix elements.
