Knotted Cosmic Strings in the Early Universe

When a U(1) symmetry is spontaneously broken in a quantum field theory, solitons known as cosmic strings appear. In models addressing open problems of the Standard Model — such as dark matter and neutrino masses — cosmic strings often arise and play important roles in the early universe. In this talk I show that, in well-studied beyond-Standard-Model setups featuring a QCD axion and a gauged B−L symmetry, there exist new soliton solutions called knotted solitons composed of two types of cosmic strings. Their impact on the early universe and the prospects for verification via gravitational waves are discussed.