Wednesday, January 14, 2026 at 4:00 pm

JILA auditorium

Andrew Hamilton , CU Boulder

"String Theory Reborn"

Abstract:

String theory offers a viable theory of quantum gravity, with spin 2 gravitons encoded in closed strings. But the failure to find evidence for supersymmetry at the LHC has left string theory in an uncertain state. A solution to the problem is in plain sight: revert to classic nonsupersymmetric, bosonic string theory, reenvisaged as a theory of all the forces, not just the strong force. The classic theory correctly reproduces the Brauer-Weyl (1935) algebraic relation between fermions and bosons seen in the standard model, whereas supersymmetry does not. Sages rejected the classic theory on the grounds that (1) it does not admit fermions, and (2) its ground state is tachyonic. But rejection (1) assumes that fermions are strings, wheres the fermions of bosonic string theory are the endpoints of strings, and are not themselves strings; in modern parlance, the fermions are excitations of the D- brane boundary of strings. As to rejection (2), the properties of the tachyon are precisely those of a Higgs field: it is a multiplet of the unbroken symmetry; the "vacuum" state where the Higgs field vanishes identically is tachyonically unstable; and it has spin zero. The gauge group of bosonic string theory is tightly constrained. I show that a 26-dimensional bosonic string theory that fits the standard model emerges without contrivance. Unburdened by supersymmetry, bosonic string theory has the potential to bring string theory back into the realm of testable physics accessible to present-day observation and experiment.

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