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Abstract:
In this presentation I am going to show our recent work on the graviton-photon and axion-photon mixing systems in the presence of the stochastic magnetic field background. Two mixing systems share similar dynamics and properties. We adopt a robust perturbative approach and find that the conversion probability from graviton/axion to photon can be resonantly enhanced in monochromatic, multi-chromatic and truncated scale invariant spectrum models of stochastic magnetic field fluctuations. Including decoherence from cosmic expansion, we find that conversion probabilities for stochastic magnetic fields are remarkably different than results predicted from existing magnetic domain-like models in a wide range of magnetic strengths and coherence lengths. In particular, we consider axion-like-particle (ALP)-photon oscillation within our model and explore its effect on two anomalous radio signals: radio excess detected by ARCADE2 and twice-deeper 21cm absorption trough by EDGES. We show that proper abundance of photon injection from ALP resonant conversion can naturally give a simultaneous explanation on the radio excess between 0.4-10GHz and 21cm absorption at 78MHz. Our model predicts a new power-law scaling of radio spectrum above 0.5GHz and an additional absorption trough below 30MHz, which could be cross-detected in upcoming experiments. Such a joint analysis of radio excess and 21cm absorption provides a novel probe into the properties of the dark sector and primordial magnetogenesis.
Biography:
Dr. Qingyu Gan is a Postdoctoral Fellow in the Scuola Superiore Meridionale in Italy. He obtained his Ph.D. in Theoretical Physics from Sichuan University in China in 2022, where his dissertation focused on the black hole physics in a scalar cloud or in Modified gravity. Dr. Gan's current research centered on the multimessage physics involving radio signal, gravitational waves and dark sector. He investigates the particle mixing phenomena in the presence of the stochastic primordial magnetic field and its implications on dark age cosmology. His work contributes to understanding the observational signatures of axion-like particles in CMB and 21cm data. He is also involved in projects related to GW physics across a broad frequency region, including nHz GW from dark phase transition, mHz GW from the sound speed resonance of inflaton and GHz GW from interaction with microwave radiation. Dr. Gan has published several papers in high-IF journals such as Physical Review D, Physical Letter B and Journal of Cosmology and Astroparticle Physics.
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