Speaker
Description
Some of the most pressing open questions in modern physics, such as dark matter, dark energy, and the Hubble tension, point towards the gravitational sector, making it natural to explore alternative formulations of gravity rather than only modifying the Standard Model matter sector. Both General Relativity and the Standard Model admit formulations in terms of fields of fixed mass and spin. From this perspective, gravity is mediated by spin-2 fields, yet theories with multiple interacting spin-2 fields remain far less understood than their lower-spin counterparts, where, for instance, Yang–Mills theory is essentially the unique theory of interacting spin-1 fields. The central obstacle to consistent spin-2 interactions is the generic appearance of ghosts, pathological modes with negative kinetic energy. In this talk, I will introduce multi-gravity, explain its theoretical and phenomenological interest, and outline how the requirement of ghost-freedom singles out a unique interaction.