in EMSFT (or more generally written as just self-field theory SFT) strings are condensates of subquantum particles; what i mean is that at the edges of the universe where the temperature is close to zero, or alternatively where energy levels are close to zero (no motion whatsoever) then photons become 'frozen'. in this state the photon streams of SFT become like a crystal of positive and negative charges that occur either in a planar form or as 'strings' (one dimensional).
i know i've written on this somewhere, and i'll dig up a web reference to it over the next day or so; you're welcome to investigate
www.unifiedphysics.com for other writings on the photon 'chemistry' that appears to solve how nuclear physics works. in NSFT (nuclear self-field theory) we find that by using different photonic compounds other than the 'ordinary photon' we can come up with modified systems of equations based on Maxwell's equations but that sustain so-called 'confined' motions of quarks. this is going off-topic, but i am using it to show that the photon CAN be shown from a number of different theoretical view-points to sustain a substructure. the substructure taht fits the evidence is one that like the hydrogen atom has two oppositely charged particles but unlike the hydrogen atom the masses opf teh two subphotonic particles are EQUAL so that the allowed energy levels are NOT quantum but rather continuous. see the photon chemistry paper at
www.unifiedphysics.com .
more later