Abstract: Although chaotic dynamics limits our ability to predict individual trajectories, it may still be possible to make accurate statistical predictions. The Newtonian three-body problem offers a fascinating setting in which to explore this distinction, combining a rich history, fundamental questions in dynamical systems, and considerable astrophysical importance. In this colloquium, I will present a novel statistical theory that expresses predictions in terms of phase-space flux. Validated against extensive numerical simulations, this flux-based theory provides the most accurate statistical predictions to date for the three-body problem. I will also describe a novel dynamical reduction, introducing dynamical variables that significantly simplify the formulation of the problem. Finally, I will show how a related flux-based theory successfully predicts statistical properties of another paradigmatic chaotic system—the double pendulum—including its mean flip rate.

Abstract: Gamma-ray bursts (GRBs) are the strongest explosions in the Universe, and are powered by initially ultra-relativistic jets. The angular profile of GRB jets encodes important information about their launching and propagation near the central source, and can be probed through their afterglow emission. Detailed analysis of the multiwavelength afterglow light curves of recent GRBs shows evidence of an extended angular structure beyond the jet’s narrow core. The afterglow emission is determined by the jet angular structure, our viewing angle, and the magnetic field structure behind the shock, often leading to degeneracies when considering the light curves and broadband spectrum alone. Such degeneracies can be lifted with joint modeling of the afterglow light curves and polarization, which is expected for synchrotron radiation. In this talk I will explain the origin of polarized emission in GRB afterglows, and expand our basic intuition to the regime of structured jets. Finally, I will show the potential and implications such models have for energetic GRBs and orphan afterglow candidates.

Abstract: Zoom link: https://us02web.zoom.us/j/87804260494?pwd=aQITIeL97YNDWfnsKcyxjnVcLq8KzJ.1

Abstract:
Self-compensated comagnetometers, employing overlapping samples of spin-polarized alkali and noble gases (for example K-3He) are promising sensors for exotic beyond-the-standard-model fields and high-precision metrology such as rotation sensing. In the context of these experimental platforms, we demonstrate dynamical control of the effective spin-spin interaction between alakali metals and noble gas via parametric modulation. We show that the periodic modulation of the direction of the electron spin polarization with respect to the nuclear polarization leads to a Floquet induced renormalization of the spin-exchange coupling. This effect enables continuous tuning and suppression of the effective interaction strength without altering the intrinsic properties of the system. We develop a theoretical model that supports the experimental measurements. The results establish a general mechanism for controlling interaction strengths in hybrid atomic systems and provide new opportunities for precision measurements and quantum memories.

Abstract: 2D materials, and in particular transition-metal dichalcogenides (TMDs) are elastic materials that can sustain high strain. The effects of uniform (uniaxial) strain and non-uniform strain have been investigated in the last decade. In this talk I will present recent studies done in our lab which reveal new phenomena that were not observed (or at least not understood) with different strain engineering methods. In the first part I will present new results of the photoluminescence from uniaxially strained TMDs where we observe fluctuating intensities as a function of strain for low strain magnitudes (<0.2%). By combining k-space imaging with the strain, we find that both the choice of substrate and the curvature define the intensity of the emission [1].

In the second part we will present recent results that resolve a long-standing debate between funneling of excitons under non-uniform strain and exciton-to-trion conversion due to limited funneling [2]. We show that by suspending monolayers on top of large holes, and by choosing the right configuration of substrate, funneling can be reached for micron-size regions while avoiding exciton-to-trion conversion that was observed in previous works [3].

[1] L. Grimberg, S. Kostyukovets, N. Basu, and M. G. Harats, Angular Emission Properties of Strained Transition-Metal Dichalcogenides in the Low Strain Regime, ACS Appl. Mater. Interfaces 18, 29337 (2026).
[2] M. G. Harats and K. I. Bolotin, Limits of funneling efficiency in non-uniformly strained 2D semiconductors, 2d Mater. 8, 015010 (2021).
[3] M. G. Harats, J. N. Kirchhof, M. Qiao, K. Greben, and K. I. Bolotin, Dynamics and efficient conversion of excitons to trions in non-uniformly strained monolayer WS2, Nature Photonics 14, 324 (2020).

Abstract: The dark photon is a well-motivated ultralight dark-matter candidate that may couple to the Standard Model through kinetic mixing. We search for dark-photon dark matter in the mass range 4 × 10⁻¹² – 2 × 10⁻⁹ eV (1-500kHz) using a three-axis magnetometer inside a large conductive shielded room. We set new laboratory limits on the kinetic-mixing parameter, improving upon previous laboratory bounds by up to two orders of magnitude. Our search exploits a geometry-defined null response along one axis as a noise reference to implement a subtraction procedure, lowering noise and enhancing sensitivity. These results establish the strongest laboratory constraints in this mass range and illustrate how null-axis magnetometry can broaden terrestrial searches for ultralight vector dark matter.

Abstract: TBA

Abstract: TBA