Negative Mass?

Can negative mass exist? If it actually did not violate some laws of physics, such as the law of conservation of energy, could it be possible for it to exist in the universe? In addition, could dark matter possess the properties of negative mass, as if dark matter would not exist, probably, particles would not have formed? If dark matter particles would exist, could they be the ones that hold the particles, and with it, the universe together, as they interact with positive masses? If so, would atoms and particles exist (as they do) If you had 2 objects, 1 with negative mass and the other with positive, (eg: 2kg, -5kg) would they exert unequal forces on each other to make them attract and repel? Would negative or positive mass difference (eg: 2kg and -5kg, not 2kg and -2kg) only affect forces exerted between particles at low scale, allowing larger structures to form, such as atoms, molecules, and with them, life?Then, if something with negative mass did exist, would it be formed by particles, if so, how would they work, how would their structure be? Why don�t they work as normal particles? Why would they exist?
- James (age 12)
London, Great Britain, United Kingdom

Check this old answer and see if you need a follow-up:

https://van.physics.illinois.edu/qa/listing.php?id=30183&t=negative-mass-via-higgs

https://van.physics.illinois.edu/qa/listing.php?id=30183&t=negative-mass-via-higgs

Mike W.

(published on 02/13/2017)