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Since neutrinos interact with the Higgs field, that means it can lose weak hypercharge to the Higgs field and thus flip chirality? (LH: $T_3 = +\frac{1}{2}, Y_w = -1$ RH: $T_3 = 0, Y_w = 0$)

(Or, it can obtain mass via the Majorana equation, but the presence of its weak hypercharge still enables chirality switching?)

Chirality switching has never been observed in neutrinos.

If so, what's the mechanism (higgs?) and is the time taken to flip its chirality also $∼1/E$ ?

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  • $\begingroup$ Neutrinos don't interact with the Higgs field. They are massless in the Standard Model. They get mass by some other mechanism. I hope the experts would clarify. Also, if a left neutrino changes chirality, it becomes a pretty much undetectable particle of dark matter. $\endgroup$ – safesphere Nov 25 '17 at 18:05
  • $\begingroup$ @safesphere: In the old Standard Model, neutrinos don't interact with the Higgs boson and don't have mass. We know this is incorrect. There are a number of revisions proposed to the Standard Model that account for neutrino mass. Why do you claim neutrinos don't interact with the Higgs field in these revisions? Do you have some reference for this? $\endgroup$ – Peter Shor Nov 25 '17 at 18:48
  • $\begingroup$ @PeterShor See "Standard Model" in Wikipedia, "The model does not contain any viable dark matter particle that possesses all of the required properties deduced from observational cosmology. It also does not incorporate neutrino oscillations and their non-zero masses." I've no idea why neutrinos don't interact with the Higgs field, but apparently they don't. I hope the experts will clarify. See this from the same Wiki: en.m.wikipedia.org/wiki/… $\endgroup$ – safesphere Nov 25 '17 at 18:57
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    $\begingroup$ @safesphere: actually a chiral flip would turn active neutrinos into sterile neutrinos (undetectable dark matter as you put it) only if they are Dirac in nature. If neutrinos are Majorana in nature, as is highly suspected, a chiral flip would transform a neutrino into an antineutrino and vice versa. $\endgroup$ – enumaris Nov 25 '17 at 19:18
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    $\begingroup$ @safesphere well if the neutrino gets its mass via the Dirac mechanism, then it will only have Yukawa interactions with the neutral component of the Higgs doublet, so its sterile...? The question is why will neutrinos not couple to the higgs field though, it clearly has a weak hypercharge. $\endgroup$ – Lagrangian Nov 25 '17 at 20:11
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In fact, in the presence of matter (and, importantly, anisotropies in the background matter field), neutrinos can change Chirality. This fact can be derived from careful analysis of the Quantum Kinetic Equations, see: [1] and [2]

Due to the nature of this Chiral flipping, the amplitude to get such a flip is suppressed from the usual weak-couplings (of neutrinos on matter) by another order of $m_\nu/E_\nu$ and so it seems difficult to get a significant effect.

There has been some explorations of whether this Chiral flipping occurs in astrophysical environments, but it seems that one needs either an unrealistically large neutrino rest mass to get this to happen, and/or an extremely flat electron-fraction profile that hovers near $Y_e\approx 1/3$ (the resonance condition for such an effect). See for example: [3] , [4] , [5] , [6]

In addition to this kinetic effect (caused by scatterings), one can also obtain Chiral flipping due to the (extremely small, but present) magnetic moment of neutrinos. Large magnetic fields can perhaps also give rise to this effect. See, for example: [7] , [8]

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    $\begingroup$ These are just ideas with no experimental proof, correct? $\endgroup$ – safesphere Nov 25 '17 at 19:02
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    $\begingroup$ Well, I wouldn't relegate them to "just ideas"; they are based on the physical equations, i.e. they can be derived as implications of the quantum kinetic equations. But you are right in that this chiral flipping has not been observed experimentally. $\endgroup$ – enumaris Nov 25 '17 at 19:13

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