What fundamental particles do most Grand Unified and Inflationary theories predict existed before the Inflationary period? Basically, what do we expect the family of particles existing during the Grand Unification epoch to look like? It is my understanding that before electroweak symmetry breaking, particles had no mass. Some sources also say they had no electric charge. Would there still be 3 generations of leptons and quarks then? Are electrons and neutrinos even distinguishable? I know that photons and WZ bosons recombine into electroweak bosons, but before inflation do those recombine with gluons? Is that what XY bosons are? Where can I find a straightforward answer to what a non-symmetry broken standard model looks like, as a lot of what I see seems contradictory?
Particle Physics – What Particles Existed Before Cosmological Inflation?
cosmological-inflationelementary-particlesgrand-unificationmagnetic-monopolesparticle-physics
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I think you have understood it almost well.
The masses do not change, they are what they are; at least at colliders. At high energy, it is true that the impact of masses and, more generally, of any soft term, becomes negligible. The theory for $E\gg v$ becomes very well described by a theory that respects the whole symmetry group.
Notice that to do so consistently in a theory of massive spin $-1$, you have to introduce the Higgs field as well at energies above the symmetry breaking scale. For the early universe, the story is slightly different because you are not in the Fock-like vacuum, and there are actual phase transitions (controlled by temperature and pressure) back to the symmetric phase where in fact the gauge bosons are massless (except perhaps for a thermal mass, not sure about it).
EDIT
I'd like to edit a little further about the common misconception that above the symmetry breaking scale gauge bosons become massless. I am going to give you an explicit calculation for a simple toy mode: a $U(1)$ broken spontaneously by a charged Higgs field $\phi$ that picks vev $\langle\phi\rangle=v$. In this theory we also add two dirac fields $\psi$ and $\Psi$ with $m_\psi\ll m_\Psi$. In fact, I will take the limit $m_\psi\rightarrow 0$ in the following just for simplicity of the formulae. Let's imagine now to have a $\psi^{+}$ $\psi^-$ machine and increase the energy in the center of mass so that we can produce on-shell $\Psi^{+}$ $\Psi^{-}$ pairs via the exchange in s-channel of the massive gauge boson $A_\mu$. In the limit of $m_\psi\rightarrow 0$ the total cross-section for $\psi^-\psi^+\rightarrow \Psi^-\Psi^+$ is given (at tree-level) by $$ \sigma_{tot}(E)=\frac{16\alpha^2 \pi}{3(4E^2-M^2)^2}\sqrt{1-\frac{m_\Psi^2}{E^2}}\left(E^2+\frac{1}{2}m_\Psi^2\right) $$ where $M=gv$, the $A_\mu$-mass, is given in terms of the $U(1)$ charge $g$ of the Higgs field. In this formula $\alpha=q^2/(4\pi)$ where $\pm q$ are the charges of $\psi$ and $\Psi$. Let's increase the energy of the scattering $E$, well passed all mass scales in the problem, including $M$ $$ \sigma_{tot}(E\gg m_{i})=\frac{\pi\alpha^2}{3E^2}\left(1+\frac{M^2}{2E^2}+O(m_i^2/E^4)\right) $$ Now, the leading term in this formula is what you would get for a massless gauge boson, and as you can see it gets correction from the masses which are more irrelevant as $m_i/E$ is taken smaller and smaller by incrising the energy of the scattering. Now, this is a toy model but it shows the point: even for a realistic situation, say with a GUT group like $SU(5)$, if you scatter multiplets of $SU(5)$ at energy well above the unification scale, the masses of the gauge bosons will correct the result obtained by scattering massless gauge bosons only by $M/E$ to some power.
Best Answer
I think your question is about electroweak symmetry breaking and GUT symmetry breaking, and not inflation as such.
Here's a list of the fundamentally different particles in the Standard Model. There's one line for each family of particles that are related by Standard Model symmetries.
The fields after EWSB are the same; they are just "reinterpreted". As an analogy, if you have a wooden board that you initially covered with Cartesian coordinates, and the Texas sharpshooter of legend shoots a hole in the board, you may wish to switch to polar coordinates centered on the location of the hole, since they better respect the symmetry of the modified board. But the number of coordinates (2) is unchanged. If you had foreknowledge of where the hole would appear, then you could use the polar coordinates from the beginning. Presentations of the Standard Model tend to do that, which is why you'll sometimes hear that there are Higgs fields with different electric charges, even though those fields only make sense before EWSB and electric charge only makes sense after.
Post-EWSB, the up-type quarks are half of the SU(2)- and SU(3)-charged family of fermions coupled with one of the 6-d.o.f. families via the Higgs field, and the down-type quarks are the other half coupled with the other 6-d.o.f. family. The electrons and neutrinos work the same way if the uncharged fermions exist. If they don't exist then the neutrinos are just one half of the SU(2)-only family, not Higgs-coupled to anything.
The idea of grand unified theories is that something similar to EWSB happened at higher energy, leaving 12 massless bosons in three families (the U(1), SU(2) and SU(3) bosons), and some massive bosons like the W and Z, but much heavier, which are called X and sometimes Y.
One popular GUT is SU(5), which has a single SU(5) force with 24 gauge bosons / 48 d.o.f. (in general, SU(n) has $n^2-1$ gauge bosons). Instead of 5×3 charged fermion families, there are just 2×3 (while the uncharged fermions, if present, are still in their own 3 families).
Another popular GUT is SO(10), which has $10(10-1)/2=45$ bosons / 90 d.o.f., but has the advantage that all of the fermions in each generation, including the uncharged ones, are in a single family.
The SU(2) charged halves of the electrons and neutrinos are aspects of the same thing pre-EWSB. The SU(2)-uncharged halves are different even pre-EWSB because they have different U(1) charges. The "halves" are not really associated with each other the way they are post-EWSB, although the Higgs coupling does exist. Pre SO(10)-symmetry breaking, they would all be aspects of the same thing, except that there are still 3 generations and they could be made of different mixes of generations. In other GUTs like SU(5), they may be different even before the GUT symmetry breaking.
Technically yes, but technically they have no mass even after EWSB.
The particles that "gain mass" from EWSB never behave like light propagating freely in a vacuum, which is what most people imagine when they imagine a massless particle. Post-EWSB, they're prevented from doing that by their coupling to the vacuum Higgs field. Pre-EWSB, they're preventing from doing it by couplings to the soup of other particles that are present.
No one understands the reason for the 3 copies of the fermion fields. In most theories they are just added by fiat. There could be fermions that don't come in three copies; no one knows.