According to our current understanding of quantum physics, there are several subatomic particles that have been predicted by theoretical frameworks but have not yet been observed experimentally. These predicted particles are often extensions or modifications of the standard model of particle physics and arise from various theoretical considerations.
Here are a few examples:
Supersymmetric particles: Supersymmetry is a theoretical framework that proposes a symmetry between fermions (particles with half-integer spin) and bosons (particles with integer spin). It predicts the existence of "superpartners" for every known particle in the standard model. These superpartners have not been observed yet, and their discovery would provide a solution to certain theoretical and observational puzzles.
Axions: Axions are hypothetical particles that arise in theories attempting to explain why the strong nuclear force (described by quantum chromodynamics) appears to violate certain symmetry principles. Axions are extremely light and weakly interacting, making them challenging to detect. They have been proposed as a possible explanation for dark matter.
Sterile neutrinos: Neutrinos are neutral, weakly interacting particles that exist in three known flavors: electron neutrinos, muon neutrinos, and tau neutrinos. Sterile neutrinos are additional neutrino flavors that do not participate in the weak interaction. They are hypothesized to explain phenomena like neutrino oscillations and the observed neutrino masses.
Gravitons: In the framework of quantum gravity, it is expected that the gravitational force is mediated by a hypothetical particle called the graviton. The graviton is the quantized version of the gravitational field and is thought to play a role in unifying quantum mechanics with general relativity. However, experimental confirmation of gravitons has not yet been achieved.
It is worth noting that while these particles are predicted by various theoretical frameworks, their existence is still speculative until experimental evidence confirms them. Scientists are actively searching for these particles using high-energy particle accelerators, underground detectors, and other experimental techniques. The discovery or non-discovery of these particles will help shape our understanding of the fundamental building blocks of the universe and the laws that govern them.