Seminar detail: Sommerfeld Enhancement from Unstable Final-state Particles in Dark Matter Annihilation

Date&Time	Mon Jun 08 2026 (13:00 - 14:00)
Speaker	Takumu Yamanaka
Affiliation	Osaka University
Title	Sommerfeld Enhancement from Unstable Final-state Particles in Dark Matter Annihilation
Abstract	Dark matter (DM) is one of the most compelling mysteries in modern physics, yet its fundamental nature remains unknown. The annihilation cross section of DM plays a central role in determining its thermal relic abundance. When attractive long-range forces are present, quantum mechanical distortion of the two-body wave function can significantly amplify the annihilation cross section — an effect known as the Sommerfeld enhancement. While previous studies of this effect have focused on long-range forces between the initial-state DM particles, we instead consider long-range forces acting between the unstable annihilation products in the final states. We develop a consistent framework for this process by incorporating the decay widths of the unstable final-state particles into the Schrödinger equation, and show that bound-state resonances among them can lead to a significant enhancement. Our results enable more precise calculations of the dark matter relic abundance in the framework of forbidden dark matter scenario in which DM annihilates into heavier particles.
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