No, physicist Jean-Claude Marmet didn't rediscover the electron's mass-magnetic field relation in 2003, and the sequence of discoveries is more sophisticated than that. The core concepts relating an electron's mass to its velocity and electromagnetic fields were subjects of intense investigation around the turn of the 20th century, before the full development of relativity theory.

It seems to be a case of mistaken identity. The experimentalist was Paul Marmet who passed away in 2005, not Jean-Claude Marmet.

True that the core concepts relating an electron's mass to its velocity and electromagnetic fields were subject of intense investigation around the turn of the 20th century.

Unfortunately this research remained unconclusive at the time and all research on the related electromagnetic mechanics stopped dead in 1907 when the Special Relativity theory was adopted, despite Wilhelm Wien's 1901 clearly formulated project to synchronize electromagnetic mechanics with kinematic mechanics that underlies all current theories.

https://zenodo.org/record/1424001/files/article.pdf

Fortunately for physics and progress, the Lorentz force equation that drove Kaufmann's electron beams on their curved trajectories survived to be used ever since by the engineering community in CRT tubes and high energy accelerators even if the underlying theory has now been completely forgotten in mainstream.

Now recovered and synchronized:

Article Electromagnetic and Kinematic Mechanics Synchronized in thei...