γ-duality in the EPRL spinfoam model determines the relation between parity-even and parity-odd terms in an effective gravity theory, allowing the Barbero-Immirzi parameter to be measured from inflationary tensor observables.
Birefringent Gravitational Waves and the Consistency Check of Inflation
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abstract
In this work we show that the gravitational Chern-Simons term, aside from being a key ingredient in inflationary baryogenesis, modifies super-horizon gravitational waves produced during inflation. We compute the super-Hubble gravitational power spectrum in the slow-roll approximation and show that its overall amplitude is modified while its spectral index remains unchanged (at leading order in the slow-roll parameters). Then, we calculate the correction to the tensor to scalar ratio, T/S. We find a correction of T/S which is dependent on $\cal{N}$ (more precisely quadratic in ${\cal N}$), the parameter characterizing the amplitude of the Chern-Simons terms. In a stringy embedding of the leptogenesis mechanism, $\cal{N}$ is the ratio between the Planck scale and the fundamental string scale. Thus, in principle, we provide a direct probe of leptogenesis due to stringy dynamics in the Cosmic Microwave Background (CMB). However, we demonstrate that the corresponding correction of T/S is in fact very small and not observable in the regime where our calculations are valid. To obtain a sizable effect, we argue that a non-linear calculation is necessary.
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One-loop integration of a heavy fermion with inflaton-dependent mass in axion inflation generates localized gauge-field production and a detectable chiral gravitational-wave signal in the deci-hertz range.
Coupling Chern-Simons gravity to a spectator field in multi-field inflation generates distinctive parity-odd scalar-tensor bispectra with perturbativity bounds on the couplings.
Fuzzy dark matter induces frequency-dependent amplitude birefringence in gravitational waves with periodic time modulation set by the scalar mass, but no velocity birefringence.
citing papers explorer
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Spinfoams, $\gamma$-duality and parity violation in primordial gravitational waves
γ-duality in the EPRL spinfoam model determines the relation between parity-even and parity-odd terms in an effective gravity theory, allowing the Barbero-Immirzi parameter to be measured from inflationary tensor observables.
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Axion Inflation from Heavy-Fermion One-Loop Effects
One-loop integration of a heavy fermion with inflaton-dependent mass in axion inflation generates localized gauge-field production and a detectable chiral gravitational-wave signal in the deci-hertz range.
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Chern-Simons gravitational term coupled to a spectator field
Coupling Chern-Simons gravity to a spectator field in multi-field inflation generates distinctive parity-odd scalar-tensor bispectra with perturbativity bounds on the couplings.
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Gravitational Wave Birefringence from Fuzzy Dark Matter
Fuzzy dark matter induces frequency-dependent amplitude birefringence in gravitational waves with periodic time modulation set by the scalar mass, but no velocity birefringence.