Alexandru Proca (16 October 1897 – 13 December 1955) was a Romanian physicist who studied and worked in France.

He carried out Ph.D. studies in theoretical physics under the supervision of Nobel laureate Louis de Broglie.

In 1933 he defended successfully his Ph.D. thesis entitled "On the relativistic theory of Dirac's electron" in front of an examination committee chaired by the Nobel laureate Jean Perrin.

In 1943 he made a brief stay in Portugal, where (replacing Guido Beck) he guided the seminar on Theoretical Physics, organized by Ruy Luís Gomes at the Center for Mathematical Studies at the University of Porto.

From 1943 to 1945 he was in the United Kingdom, at the invitation of the Royal Society and the British Admiralty, in order to assist in the war effort.

[1] In 1929, Proca became the editor of the influential physics journal Les Annales de l'Institut Henri Poincaré.

Then, in 1934, he spent an entire year with Erwin Schrödinger in Berlin, and visited for a few months with Nobel laureate Niels Bohr in Copenhagen where he also met Werner Heisenberg and George Gamow.

[3][4] Proca came to be known as one of the most influential Romanian theoretical physicists of the last century,[5] having developed the vector meson theory of nuclear forces in 1936, ahead of the first reports of Hideki Yukawa, who employed Proca's equations for the vectorial mesonic field as a starting point.

Pions being the lightest mesons play a key role in explaining the properties of the strong nuclear forces in their lower energy range.

The spin-1 vector mesons considered by Proca in 1936—1941 have an odd parity, are involved in electroweak interactions, and have been observed in high-energy experiments only after 1960, whereas the pions predicted by Yukawa's theory were experimentally observed by Carl Anderson in 1937 with masses quite close in value to the 100 MeV predicted by Yukawa's theory of pi-mesons published in 1935; the latter theory considered only the massive scalar field as the cause of the nuclear forces, such as those that would be expected to be found in the field of a pi-meson.

In the range of higher masses, vector mesons include also charm and bottom quarks in their structure.