Scattering amplitudes mediated by graviton exchange display Infra-Red(IR) singularities in the forward limit. This obstructs standard application of positivity bounds based on twice subtracted dispersion relations. Such divergences can be cancelled only if the Ultra-Violet(UV) limit of the scattering amplitude behaves in a specific way, which implies a very non-trivial connection between the UV and IR behaviors of the amplitude. The research team and the speaker show that this relation can be expressed in terms of an integral transform, obtaining analytic results when t log s→0. Carefully applying this limit to dispersion relations, they find that infinite arc integrals, which are usually taken to vanish, can give a non-trivial contribution in the presence of gravity, unlike in the case of finite negative t. This implies that gravitational positivity bounds cannot be trusted unless the size of this contribution is estimated in some way, which implies assumptions on the UV completion of gravitational interactions. They discuss the relevance of these findings in the particular case of Quantum ElectroDynamics(QED) coupled to gravity.
頻道：(網上講授)Zoom ID:421-480-1692 ← cosmology
講者：Anna Tokareva(Imperial College, London)
“Copernicus Webinar and Colloquium Series”: To promote scientific discussions during this pandemic, they are organizing an online seminar series, i.e. Copernicus Webinar Series, seeking the most outstanding speakers to introduce innovative ideas and important progress in the field of gravity and cosmology. This series is named after the famous Polish Astronomer, Nicolaus Copernicus, whose discovery eventually marked the dawn of modern science.