Mechanism of Halogenation of Alkene In the above reaction, we use a non-polar compound (such as CCl$_4$) as a solvent. Then, why does the Br$_2$ polarise on attack by the alkene, even though a non-polar solvent does not encourage polarisation of a compound. Is the mutual polarisation enough for the reaction to occur. 

Further, in different books the mechanism is either explained by the above mechanism or by the Molecular Orbital Theory (the alkene's filled $\pi$ orbital (HOMO) will interact with bromine's empty $\sigma$* to give the product).

Which one of these is the more popular and/or the officially accepted explanation.
Alkene double bond is an area of high electron density and hence high (partial) negative charge. Bromine molecule, approaching double bond, shifts its electrons of covalent bond towards farther Br atom, it becomes polarized and an induced dipole. 

That's the simplest explanation in terms of electron movement I would use.