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### Event Number 3448

**Theory Seminar (High Energy/Cosmology)****Stueckelberg U(1)'s and Axions in String Theory****Time:**3:00 pm**Place:**5280 Chamberlin Hall**Speaker:**Fang Ye, University of Wisconsin-Madison**Abstract:**In this talk, we will discuss several interesting scenarios in which U(1) gauge fields couple to axions through the Stueckelberg mechanism from a string theory perspective. We will first introduce the milli-charged dark matter scenario in which a small electric charge carried by the dark matter particles arise exclusively through kinetic mixing of the photon with some extra massless U(1)'s. We discuss how this apparent contradiction with the "folk theorem" of quantum gravity (that forbids the existence of non-quantized charges) can be resolved when embedded in string theory. Then we will discuss a related scenario - "Stueckelberg Portal" - in which the sizable interactions between Standard Model (SM) and the hidden sectors through heavy Z' bosons arise from a large U(1) mass mixing induced by the Stueckelberg mechanism. Such models present many interesting phenomenological features (e.g. SUSY mediation, hidden valley, no chiral exotics, etc), and are simple and generic in top-down models. We will see how the Stueckelberg Portal can naturally be implemented in string theory. An explicit intersecting D-brane model will be presented. Finally, we will briefly mention some ongoing work on realizing super-Planckian axion decay constants in string theory.**Host:**Ran Lu- Add this event to your calendar