Schedule: Fall Term 2025-26

The seminars are taking place on Zoom every second Tuesday at 11 am (all times in US Eastern Time Zone).

The Seminar Series on String Phenomenology is currently in session!

Dec 9th 2025: 

• 11:00: "Superstring Phases in the Early Universe and Gravitational Waves", Noelia Sánchez González , Oxford University

Abstract: When moduli roll in the early universe, all physical scales - including string tensions - simultaneously evolve. In this talk, we will see how the dynamics of cosmic strings with time-varying tensions can produce cosmic string loop trackers in which most of the energy density of the universe lies in the form of string loops. This solution can exist as an attractor until the rolling modulus reaches its minimum, when the loops ultimately decay through gravitational wave emission. We will also see the resulting spectrum for this scenario, which peaks in the GHz regime today. Its amplitude is diluted by any subsequent matter-dominated epochs, and thus the potential observability of the signal crucially depends on the duration of the moduli-dominated epoch that follows once the moduli settle down and oscillate about their minimum.

• 11:30: "The String Theory Photoverse",  Jonathan Steiner, University of Heidelberg

Abstract: String theory compactifications typically feature numerous U(1) factors, implying the presence of many hidden photons in the low-energy EFT. One may call this the “string photoverse”. In this talk I will argue that, generically, these hidden photons are massless and do not couple to any light dark current such that, naively, kinetic mixing with the Standard Model is unobservable. Thus, from gauge symmetry, one expects the leading interactions of these “superhidden photons” with the standard model to be dimension-6 dipole operators that couple them to quarks or leptons and the Higgs field. I will estimate these couplings by dimensionally reducing the fermionic action of 7-branes realizing the Standard Model and discuss the resulting constraints on the compactification volume/string scale. Finally, I will comment on the “photinoverse”—the collection of hidden-photon superpartners—and its potential phenomenological implication.