Seminars And Colloquia This Week

Ultralight axion-like particles, an excellent candidate for dark matter, can mediate a long-range macroscopic force with monopole-monopole and monopole-dipole interactions between the planets and the Sun. The presence of these long-range potentials affects the perihelion precession of planets, gravitational light bending and Shapiro time delay. From the precision studies of these tests of gravity, we obtain new constraints on the macroscopic forces. The bound is three orders of magnitude stronger than the Eot-Wash experiment. The ultralight scalar and vector dark matter also influence active-sterile neutrino oscillation in the supernova core which is one of the solutions to explain the longstanding problem of the pulsar kick. The signal from the asymmetric emission of neutrinos in the presence of an ultralight dark matter background can be probed by future gravitational wave detectors. The effects of ultralight dark matter in explaining pulsar kick are equivalent to the Lorentz and CPT invariance violation in the theory and we obtain an equivalent bounds on these parameters. 

In some theories beyond the Standard Model, new force mediating bosons appear as explanations for dark matter. If such forces exist, they are necessarily weak to be so far undetected. It is then desirable to search for these particles with neutrons, which have the benefit of electric neutrality and small polarizability, significantly reducing experimental false effects from stray electric fields. In this talk, I will discuss how one can utilize the localization of neutrons along a curved surface, a phenomenon called the "neutron whispering gallery effect," to search for these new forces; and the measurements of this effect made at the Institut Laue Langevin will be described.

The whispering gallery effect is also predicted to exist with anti-atoms, and an experiment with this effect could support recent campaigns to measure the gravitational acceleration of anti-matter. The methodology of such an experiment will be explained and preliminary results of a recent proof of principle experiment with the neutron whispering gallery will be shared.

Machine learning is now a part of physics for the foreseeable future, but many deep learning tools, architectures, and algorithms are imported from industry to physics with minimal modifications. Does physics really need all of these fancy techniques, or does “dumb” machine learning with the simplest possible neural networks suffice? I will argue that the needs for interpretability and uncertainty quantification in physics applications of machine learning mitigate toward the use of simpler tools with more predictable performance. I will give several examples illustrating how tools imported from physics may be used to better understand the training dynamics of fully-connected networks, and conversely, how the topology and geometry of collider physics data may be used as a testbed for theories of machine learning relevant for data “in the wild”.

 

The quantum laws governing atoms and other tiny objects seem to defy common sense, and information encoded in quantum systems has weird properties that baffle our feeble human minds. John Preskill will explain why he loves quantum entanglement, the elusive feature making quantum information fundamentally different from information in the macroscopic world. By exploiting quantum entanglement, quantum computers should be able to solve otherwise intractable problems, with far-reaching applications to cryptology, materials, and fundamental physical science. Preskill is less weird than a quantum computer, and easier to understand.

Inspired by the work of Hermann von Helmholtz, William Thomson proposed in 1867 that atoms could be vortices in the aether. While subsequent experiments put this proposal out of business, the concept of topological solitons as fundamental building blocks or artificial atoms remains enticing. Recent developments since the 1960s have revealed ample evidence that nature offers updated versions of the aether concept. In the realm of quantum magnets, the aether manifests as the vector field of magnetic moments, whose topological solitons can be seen as emergent mesoscale atoms. Analogous to real atoms, these solitons organize into periodic arrays or crystals governed by principles of symmetry, anisotropy, and competing microscopic interactions. These magnetic textures generate an effective magnetic field, coupled to the orbital degrees of freedom of conduction electrons, capable of reaching astronomical magnitudes. We will explore how these topological magnetic structures manifest in real materials and how the quantum mechanical nature of spins can give rise to more intricate skyrmion textures than those observed thus far.