The graviton is an elementry hypothetical particle. Right now many scientists support the existance, however some do not. It is proposed by multiple theories of quantum gravity and by the sting theory, along with others. It would also make sense that there is another force carrier since the other 3 fundamental forces have force carriers. Electromagnitism is carried by photons, the weak force is carried by W and Z bosons, the strong force is carried by gluons, so it would make sense that the graviton would be the carrier of gravity and the gravitational field. The graviton is one of the particles that is going to be looked for at the new particle accelerator in Switzerland. The thoughts behind the graviton seem to be solid, however, there are some flaws. For one, it would just be confusing, strange, and different. Another problem with the idea is gravitons are thought to be identical to their antiparticles and antigravity is very questionable.

               Gravitons would be: 

• Uncharged and massless
• Have a spin of 2 making it a boson
• Thought to interact with leptons and quarks
• Thought to be always attractive, work over any distance, and come in unlimited numbers
• Would travel at the speed of light 

Sources

http://en.wikipedia.org/wiki/Graviton

http://www.bbc.co.uk/radio4/history/inourtime/inourtime_20051124.shtml

http://www.britannica.com/EBchecked/topic/242507/graviton

http://physics.about.com/od/glossary/g/graviton.htm

http://scienceworld.wolfram.com/physics/Graviton.html

http://www.123exp-science.com/t/01554057973/