Transient Parity Violation during Inflation: Implications for PTA Gravitational Waves
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arXiv
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| Natura: | Preprint |
| Pubblicazione: |
2026
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| _version_ | 1866913072630726656 |
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| author | Tasinato, Gianmassimo |
| author_facet | Tasinato, Gianmassimo |
| contents | We investigate the consequences of a transient phase of enhanced parity violation during inflation. Modeling this phase through a time-localized Chern--Simons-like coupling, we show that it amplifies primordial gravitational waves at small scales, producing a robust spectral shape with a blue growth of effective slope $n_T \simeq 2$, largely insensitive to microscopic details. This prediction lies in the range explored by recent pulsar timing array (PTA) analyses under cosmological power-law interpretations, while differing from the canonical supermassive black hole binary expectation. Our framework thus provides a predictive cosmological template to benchmark astrophysical versus primordial origins of the signal, consistent with cosmic microwave background bounds. The signal also exhibits large linear polarization and non-trivial Stokes correlations, corresponding to an almost maximally phase-coherent helicity state. Such features are difficult to realize in classical stochastic backgrounds, and their detection would provide circumstantial evidence for a primordial, coherently generated origin of the gravitational-wave background. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_26513 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Transient Parity Violation during Inflation: Implications for PTA Gravitational Waves Tasinato, Gianmassimo Cosmology and Nongalactic Astrophysics High Energy Physics - Theory We investigate the consequences of a transient phase of enhanced parity violation during inflation. Modeling this phase through a time-localized Chern--Simons-like coupling, we show that it amplifies primordial gravitational waves at small scales, producing a robust spectral shape with a blue growth of effective slope $n_T \simeq 2$, largely insensitive to microscopic details. This prediction lies in the range explored by recent pulsar timing array (PTA) analyses under cosmological power-law interpretations, while differing from the canonical supermassive black hole binary expectation. Our framework thus provides a predictive cosmological template to benchmark astrophysical versus primordial origins of the signal, consistent with cosmic microwave background bounds. The signal also exhibits large linear polarization and non-trivial Stokes correlations, corresponding to an almost maximally phase-coherent helicity state. Such features are difficult to realize in classical stochastic backgrounds, and their detection would provide circumstantial evidence for a primordial, coherently generated origin of the gravitational-wave background. |
| title | Transient Parity Violation during Inflation: Implications for PTA Gravitational Waves |
| topic | Cosmology and Nongalactic Astrophysics High Energy Physics - Theory |
| url | https://arxiv.org/abs/2604.26513 |