Birefringent Gravitational Waves and the Consistency Check of Inflation

By S. Alexander, Jérôme Martin. 2004

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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 N (more precisely quadratic in N), the parameter characterizing the amplitude of the Chern-Simons terms. In a stringy embedding of the leptogenesis mechanism, 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.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics, Oceanography

View Paper: https://www.semanticscholar.org/paper/38a597b8308d9e024f5c200d6fe74617d6a6c1c9

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Citations in the corpus

On graviton non-gaussianities during inflation (2011, background): “This arises from terms in the effective action of the form ∫ f(φ)WW̃ [26, 27].”
The Quest for B Modes from Inflationary Gravitational Waves (2015, background): “The chirality of the GW background may also be connected to the cosmic baryon asymmetry (Alexander, Peskin & Sheikh-Jabbari 2006; Alexander & Martin 2005; Alexander & Gates 2006).”
Perturbations in Chromo-Natural Inflation (2013, background): “In fairness, we should mention that chiral gravitational waves are not unique to this scenario, and have been noticed in related contexts [61, 62].”
Chern-Simons Modified General Relativity (2009, methodology): “Assuming further that time derivatives of the CS scalar do not scale with H, one finds that the above equation reduces to [29,33]”