  Higgs bosons - the amplitude modes - have been experimentally investigated in
condensed matter for many years. An example is superfluid $^3$He-B, where the
broken symmetry leads to 4 Goldstone modes and at least 14 Higgs modes, which
are characterized by angular momentum quantum number $J$ and parity. Based on
the relation $E_{J+}^2+E_{J-}^2=4\Delta^2$ for the energy spectrum of these
modes, Yoichiro Nambu proposed the general sum rule, which relates masses of
Higgs bosons and masses of fermions. If this rule is applicable to Standard
Model, one may expect that the observed Higgs boson with mass $M_{{\rm
H}1}=125$ GeV has a Nambu partner -- the second Higgs boson with mass $M_{{\rm
H}2}=325$ GeV. Together they satisfy the Nambu relation $M_{{\rm H}1}^2 +
M_{{\rm H}2}^2 = 4 M_{\rm top}^2$, where $M_{\rm top}$ is the top quark mass.
Also the properties of the Higgs modes in superfluid $^3$He-A, where the
symmetry breaking is similar to that of the Standard Model, suggest the
possible existence of two electrically charged Higgs particles with masses
$M_{{\rm H}+}=M_{{\rm H}-}\sim 245$ GeV, which together obey the Nambu rule
$M_{{\rm H}+}^2 + M_{{\rm H}-}^2 = 4 M_{\rm top}^2$. A certain excess of events
at 325 GeV and at 245 GeV has been reported in 2011, though not confirmed in
2012 experiments. Besides, we consider the particular relativistic model of top
- quark condensation that suggests the possibility that two twice degenerated
Higgs bosons contribute to the Nambu sum rule. This gives the mass around 210
GeV for the Nambu partner of the 125 GeV Higgs boson. We also discuss the other
possible lessons from the condensed matter to Standard Model, such as hidden
symmetry, where light Higgs emerges as quasi Nambu-Goldstone mode, and the role
of broken time reversal symmetry.
