Hartle-Hawking no-boundary proposal in dRGT massive gravity: Making inflation exponentially more probable

Understand

It is known that the no-boundary proposal in the traditional Einstein gravity does not prefer inflation, that is, the probability of realizing a large number of e-folds is exponentially suppressed.

• This situation may be changed drastically in a class of nonlinear massive gravity theories recently proposed by deRham, Gabadadze and Tolley, called dRGT massive gravity.
• We show that the contribution from the massive gravity sector can enhance the probability of a large number of e-folds substantially for a sufficiently large mass parameter mg comparable to the Hubble parameter during inflation, say $m_g \gtrsim 10^{12}$ GeV.
• We illustrate possible models to trigger such a large mass parameter in the early universe while it is negligibly small in the present universe.