I would like to have a group of people who have the ability to manipulate other's brain waves so the user could force a target to feel a certain emotion, such as joy, fear, or nausea. This ability would have to work on those who do not have any other functions in their brain to receive the manipulation, and this ability should not lead to the situation with those with this ability would be able to read other's mind.
Assume both groups of brains are human for the sake of the question.
Firstly, I'd like to point the fact that all I'm gonna mention is speculation, my points may be completely shut down by basic physics and biology.
The first thing I think about after beign presented with your scenario is electricity. The human brain uses electricity to "transport commands" through your body, therefore, it's possible that beigns with especific electric abilities would be able to generate, alter or remove emotions and feelings (although feelings are more related to chemicals than electricity).
The usage of electricity would not result in extracting informations (mind reading), as it would basically be a one way discharge.
It's important to notice that this would most likely result in very close-range possibilities, limiting the range of the electrical being's powers to melee range.
Sure. It can be done now, in crude form. Electrical stimulation of some parts of the brain can caused hallucinations (although the subject is usually aware what they're experiencing isn't real), and in monkeys they've been able to artificially create disgust and friendliness.
Use Drugs Instead
Instead of messing with their brains by trying to mess with brain waves, this can easily be done with drugs. Depends on how you want to deal with administering the drugs but even discretely spaying it in the air as they walk by can be enough to completely override their emotional state if the correct drug is used. There is a reason why drugs are used much more readily deal with psychological conditions over electro-therapy.
There are drugs that make you high, ones that makes you depressed, ones that completely destroy your sense of reality and ones that knock you out. It is why so many drugs are controlled substances in most countries. And part of the reason why some drugs are so addictive.
Drugs also do not allow mind reading so your concern of that can be eliminated.
Yes. We know from studies of people with traumatic brain injuries that emotions happen in one part of the brain, but are experienced in another part of the brain. You would expect stimulating one part of the brain would create the emotions, while stimulating the other would create the experience of the emotions without the reality.
The ability to insert emotional content directly into a person's brain by firing neurons via some sort of electrical field stimulation is both biologically explainable and within the bounds of physics, but the exact technique will require some handwavium at this point.
