Ways of producing light through neutral particles My question is whether light can be produced in some way through neutral particles?
Like usually I hear about light being produced by oscillating charged particles. Can it be produced by neutral particles by any means, and not involving charged particles? I've heard light being produced by smashing neutral with charged particles, but can it be produced by decay of only neutral particles, without getting smashed by charged particles?
Is it theoretically possible to produce light by neutral particles? I mean possible according to conservation laws, satisfying conservation of lepton number, and all other laws?
 A: A neutral particle can decay to a charged particle/antiparticle pair, which can then annihilate to two photons. For example, the Higgs boson can decay to two photons in this way.
However, in the Standard Model of particle physics, photons directly couple only to charged particles.
In some extensions of the Standard Model, photons couple directly to the neutral Higgs and simultaneously to the neutral $Z$ boson, without any charged particles involved.
In quantum gravity theories, photons also couple directly to gravitons, which are neutral. Rapidly expanding spacetime can theoretically create photons without first creating charged particles.
A: If particles with dipoles, quadrupoles etc and other types of form-factors are included in the definition of a neutral particle, i.e. the neutral particle is defined as one without the monopole form-factor, then there are many channels for producing light.
Indeed, it is well-known that an accelerating charged particle, a monopole, will produce light. However a particle that is netural, but has electric/magnetic dipole, will also produce radiation, as shown, amongst others, by Ellis. 
In fact even if particle produced no electromagnetic fields when stationary, but has non-trivial configurations of charges and currents, the so-called non-radiating configuration, it will still produce light when accelerated.
The prescription I gave is very broad, so whilst it is possible that some symmetry and conservation laws will forbid some form-factors for a specific case, e.g. electric dipole is incompatible with inversion symmetry, I don't think all of them can be ruled out without in-depth scrutiny. 
Note than in almost all cases, radiation produced by these high-order form-factors (i.e. not monopoles) will have a more complex distribution, e.g. emitted light may have non-zero orbital angular momentum etc., as a result emission will be very ineffective, but that may not be a show-stopper.

I mostly work with classical electromagnetism, but the discussion on multipole form-factors has been extended to quantum electrodynamics as well, eg.
https://inis.iaea.org/search/search.aspx?orig_q=RN:6191347
https://books.google.co.uk/books?hl=en&lr=&id=zTwVDAAAQBAJ&oi=fnd&pg=PR9&dq=multipole+expansion+in+classicla+and+quantum+theory+of+radiation&ots=hnG1fAwKhO&sig=ZyuXCBjuCh4GiocAr8Cp92EFVf0&redir_esc=y#v=onepage&q=multipole%20expansion%20in%20classicla%20and%20quantum%20theory%20of%20radiation&f=false
