Dark matter: Will Special Relativity hold? Part 1:
It’s been said that dark matter makes up about 26 % of the universe. The restart of LHC would be dealing with the existence of dark matter also. Consider a situation that the results are positive, i.e there is dark matter?
Would it demands any revisions for theories which currently we use?
For example, Special Relativity, in which Einstein establishes that velocity of light in vacuum (will it be still valid to use the word vacuum? Well I am not quite certain) is a constant(=3x$10^8 ms^{-1}$, I hope this fact doesn’t need any revision other than redefining “vacuum”) and is the highest attainable velocity.
$$c=1/(ε_0μ_0)^{1/2}$$
Where the symbols have their usual meaning. Then $ε_0$&$μ_0$ are the values of permittivity and permeability of free space (as we say today) should be the values for dark matter? 
The question:
    Do we have to revise any theory? If yes, what would be its aftereffects? And are we capable of revising them and coming up with more accurate theories?
Part 2:
    Consider a situation where we have absolute vacuum (i.e. nothing including dark matter is present), what would be the values of $ε_0$&$μ_0$? From their definition, I think they should be zero, which in turn shows that radiation has an infinite velocity in absolute vacuum, is it possible?
 A: The permittivity and permeability of free space are non-zero in 'absolute vacuum' and they will be unaffected by dark matter which interacts extremely weakly (if at all) with the EM force. We might need to modify gravity to account for dark matter (hopefully not) but that's all.
A: On average the density of dark matter in the universe is about the same as two hydrogen atoms per cubic metre. That's about 0.00000000000000000000001% of the density of air (a factor of $10^{-25}$). So even if it did interact with light, the effect of the relative permittivity and permeability would be negligable.
But dark matter doesn't interact strongly with light - if it did it wouldn't be dark! For example a popular model of dark matter is particles that only interact via the weak and gravitational forces, and light only interacts strongly via the electromagnetic force.
Dark matter does interact with light via the gravitational force. We see this in lensing experiments such as the Bullet Cluster. However we describe this interaction as being due to the curvature of spacetime rather than due to any change in its dielectric properties.
