add brief for particle physics

theory/particle physics/index.md

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 ## Astro Particle Physics
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+This captivating field serves as an interdisciplinary bridge between astronomy and particle physics, exploring the high-energy particles and cosmic phenomena that originate from distant celestial sources. [Astro particle physics](#astro-particle-physics) investigates [cosmic rays](./cosmic%20rays.html), [neutrinos](./neutrinos.html), and high-energy photons originating from astrophysical phenomena like [supernovae](../energetic%20sources/supernovae.html), [black holes](../special%20stars/black%20holes.html), and [active galactic nuclei](../energetic%20sources/AGNs.html). By studying these particles and their interactions, scientists gain insights into the extreme environments and cosmic events that produce them. This fascinating field enables us to unravel the mysteries surrounding the universe's most energetic processes, shedding light on the universe's evolution, the nature of dark matter, and the high-energy universe.