Events at Physics |
Events on Monday, October 12th, 2026
- Theory Seminar (High Energy/Cosmology)
- Aspects of Cosmology of Dark Particles & Dark Sectors
- Time: 11:30 am - 1:00 pm
- Place: Chamberlin 5280
- Speaker: Anshuman Maharana, Harish-Chandra Research Institute
- Abstract: Dark particles and sectors are ubiquitous in Beyond the Standard Model (BSM) model building and string compactifications. It is important to develop a systematic understanding of their implications of cosmology. In this talk, we will take steps in this direction by looking at various cosmological implications of moduli, (dark) monopoles and dark relics. We will also discuss a universal aspect of dark sector cosmology -- the cosmic gravitational wave background (the gravitational analogue of the cosmic microwave background.)
- Host: Gary Shiu
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Parity-Time Symmetry of Plasma Waves
- Time: 12:00 pm - 1:00 pm
- Place: 2241 Chamberlin Hall
- Speaker: Hong Qin, University of Wisconsin-Madison
- Abstract: The susceptibility tensor of a homogeneous collisionless magnetized plasma possesses parity-time (PT) symmetry. For a stationary gyrotropic equilibrium, with the wave vector $\mathbf{k}$ and the equilibrium magnetic field $\mathbf{B}_0$ in the x-z plane, the kinetic response satisfies $\chi(\omega^,\mathbf{k})=R\chi(\omega,\mathbf{k})^R$, where $R=\operatorname{diag}(1,-1,1)$. We show that the susceptibility PT-symmetry is a reduced-response-space manifestation of PT symmetry of the underpinning kinetic system. We identify parity P and time reversal T on the complete electromagnetic kinetic eigenmode space and show that the Hamiltonian operator $\mathcal{H}_{\mathrm{VM}}$ of the linearized Vlasov--Maxwell system is PT-symmetric, satisfying $PT\mathcal{H}_{\mathrm{VM}}(PT)^{-1}=\mathcal{H}_{\mathrm{VM}}$. The corresponding PT symmetry of the homogeneous magnetized Vlasov--Poisson eigenproblem is also established. Many kinetic instabilities associated with nonmonotonic distributions, rings, loss cones, and resonant energetic-particle populations are fundamentally spontaneous PT-symmetry breaking, which is achieved through and only through Krein collisions. Three examples demonstrate distinct utilities of this analysis. Definite-sign cyclotron residues protect thermal Bernstein modes from spontaneous PT-symmetry breaking. The nonmonotonic Dory--Guest--Harris distribution permits sign-indefinite residues and Krein collisions, for which we derive an analytical instability threshold and growth rate. The recently discovered mode-pole resonance instability provides a distinct realization of spontaneous PT-symmetry breaking and illustrates how PT symmetry can guide the discovery of kinetic instabilities with applications to fusion energy. These results establish PT symmetry as a structural principle of plasma waves and instabilities and open new directions for studying spectral topology in kinetic plasmas.
- Host: Vladimir Zhdankin