The Barbero-Immirzi Parameter as a Scalar Field: K-Inflation from Loop Quantum Gravity?

Details The Barbero-Immirzi Parameter as a Scalar Field: K-Inflation from Loop Quantum Gravity? The Barbero-Immirzi Parameter as a Scalar Field: K-Inflation from Loop Quantum Gravity?

2008-07-16

arxiv.org/abs/0807.2652v2

Phys.Rev.D78:064070,2008

Astronomy and Astrophysics

Astrophysics

General Relativity and Quantum Cosmology

Phys. Rev. D78, 064070 (2008)

Scientific paper

10.1103/PhysRevD.78.064070

We consider a loop-quantum gravity inspired modification of general relativity, where the Holst action is generalized by making the Barbero-Immirzi (BI) parameter a scalar field, whose value could be dynamically determined. The modified theory leads to a non-zero torsion tensor that corrects the field equations through quadratic first-derivatives of the BI field. Such a correction is equivalent to general relativity in the presence of a scalar field with non-trivial kinetic energy. This stress-energy of this field is automatically covariantly conserved by its own dynamical equations of motion, thus satisfying the strong equivalence principle. Every general relativistic solution remains a solution to the modified theory for any constant value of the BI field. For arbitrary time-varying BI fields, a study of cosmological solutions reduces the scalar field stress-energy to that of a pressureless perfect fluid in a comoving reference frame, forcing the scale factor dynamics to be equivalent to those of a stiff equation of state. Upon ultraviolet completion, this model could provide a natural mechanism for k-inflation, where the role of the inflaton is played by the BI field and inflation is driven by its non-trivial kinetic energy instead of a potential.

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