Is there a study or a test article for tachyons? Or was it denied?

Try Google.

Originally a tachyon referred to particles which always travel much faster than light, and cannot 'slow down' to the speed of light.
These particles violate causality and travel backwards in time; a very non-physical situation.

Recently the term 'tachyonic' has been applied to fields

"Although the notion of a tachyonic imaginary mass might seem troubling because there is no classical interpretation of an imaginary mass, the mass is not quantized. Rather, the scalar field is; even for tachyonic quantum fields, the field operators at spacelike separated points still commute (or anticommute), thus preserving causality. Therefore, information still does not propagate faster than light,^[8] and solutions grow exponentially, but not superluminally (there is no violation of causality).

The "imaginary mass" really means that the system becomes unstable. The zero value field is at a local maximum rather than a local minimum of its potential energy, much like a ball at the top of a hill. A very small impulse (which will always happen due to quantum fluctuations) will lead the field to roll down with exponentially increasing amplitudes toward the local minimum. In this way, tachyon condensation drives a physical system that has reached a local limit and might naively be expected to produce physical tachyons, to an alternative stable state where no physical tachyons exist. Once the tachyonic field reaches the minimum of the potential, its quanta are not tachyons any more but rather are ordinary particles with a positive mass-squared, such as the Higgs boson."

From      Tachyonic field - Wikipedia

IOW, the scalar Higgs field is one such field.

2 hours ago, mathematic said:

Try Google.

Are tachyon questions off-limits here?

10 hours ago, zapatos said:

Are tachyon questions off-limits here?

!

Moderator Note

No, but the question was about articles on tachyons, and a search engine should be the first option for that.