How many new particles do we need?

The Standard Model of particle physics (SM) and Einstein general relativity are extremely successful in describing almost all phenomena observed in Nature so far, spanning distances from a fraction of Fermi to thousands of megaparsec (Mpc). In this review article, the author deliberates on the question formulated in the title, given that the SM does not allow neutrino oscillations, does not have a candidate for dark matter in the Universe, and does not explain the observed cosmological dominance of matter over antimatter.

The author thanks his collaborators Takehiko Asaka, Fedor Bezrukov, Steve Blanchet, Alexey Boyarsky, Laurent Canetti, Marco Drewes, Shintaro Eijima, Juan Garcia-Bellido, Dmitry Gorbunov, Georgios Karananas, Juraj Klaric, Mikko Laine, Javier Rubio, Oleg Ruchayskiy, Andrey Shkerin, Inar Timiryasov, Sebastian Zell, and Daniel Zenhausern, with whom these ideas were developed over the last 20 years.

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