Every Poincaré gauge theory is conformal: a compelling case for dynamical vector torsion

Kavli Affiliate: Anthony Lasenby

| First 5 Authors: Will Barker, Michael Hobson, Anthony Lasenby, Yun-Cherng Lin, Zhiyuan Wei

| Summary:

The Poincar’e gauge theory (PGT) of gravity provides a viable formulation of
general relativity (Einstein-Cartan theory), and a popular model-building
framework for modified gravity with torsion. Notoriously, however, the PGT
terms which propagate vector torsion lead to strongly-coupled ghosts: the
modern view is that only scalar torsion can propagate. To fix this, we revisit
the concept of embedding explicit mass scales in scale-invariant theories,
showing how the Klein-Gordon theory naturally leads to a slowly-rolling
inflaton. We then show that the unique scale-invariant embedding of PGT leads
to two new terms, one of which is the Maxwell term for vector torsion. We
provide the full spectrum of quantum particles in the resulting theory. Our
result means that every PGT is conformal and – after a two-decade hiatus –
vector torsion is back on the menu.

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