Alladi Ramakrishnan Hall

Exorcising ghosts in Induced Gravity

Gaurav Narain

KITPC, Beijing

Unitarity of scale-invariant coupled theory of higher-derivative gravity and matter is considered. A scalar field coupled with dirac fermion is taken as matter sector.
The problem is investigated along the ideas of induced gravity where the Einstein-Hilbert term is generated via dynamical symmetry breaking of scale-invariance.The renormalisation group flows are computed in $4-\ep$ dimensional regularisation scheme, and one-loop RG improved effective potential of scalar is calculated. Scalar field develops a new minimum in the quantum theory via Coleman-Weinberg procedure and in turn induces Newton's constant and masses in the matter sector. The spin-2 problematic ghost and the spin-0 mode of the metric fluctuation gets a mass in the broken phase of theory. The energy-dependence of VeV in the RG improved scenario implies a running for the induced Newton's constant and masses. This sets up platform to ask the meaningful question whether it is possible to evade the problematic spin-2 ghost by keeping its
mass always above the running energy scale? In broken phase it is seen that this question can be satisfactorily answered for a large domain of coupling parameter space, where the
spin-2 ghost becomes innocuous.