Yes, it is possible for certain particles to exist as both matter and antimatter. These types of particles are called "Majorana particles," named after the physicist Ettore Majorana who first proposed their existence in 1937.
In particle physics, matter particles are typically associated with the presence of electric charge, while their corresponding antimatter particles have opposite charge. For example, an electron is a matter particle with a negative charge, and its antimatter counterpart is the positron, which has the same mass as the electron but a positive charge.
However, Majorana particles are unique because they are their own antiparticles. In other words, a Majorana particle would have properties of both matter and antimatter within itself. These particles have not yet been observed directly, but they are predicted to exist in certain theories, such as in the context of neutrinos.
Neutrinos are elementary particles that have extremely low mass and interact weakly with other particles. According to some theories, neutrinos could be Majorana particles. If this is true, it would imply that neutrinos can simultaneously exist as both matter and antimatter.
It is important to note that the existence of Majorana particles and Majorana neutrinos is still an open question in physics, and ongoing experiments and research are actively investigating this possibility. Confirmation of their existence would have significant implications for our understanding of particle physics and the fundamental nature of matter and antimatter.