Seminars And Colloquia This Week

Gravitational-wave (GW) memory effects are the permanent changes in asymptotically flat spacetime that persist after the passage of a wave. Three types of memory effects have been well studied: displacement memory (permanent change in the relative positions of comoving test masses), spin memory, and center-of-mass memory (both related to permanent change in separation for test masses with initial relative velocities). The evolution equations in the asymptotic region of spacetime predict a hierarchy of persistent effects that have recently been called “higher memory effects”, with the well-known memory effects being the leading and subleading contributions. The higher memory effects provide new GW observables that are determined by a set of temporal moments of the gravitational radiation from an isolated source. These effects can deepen our understanding of asymptotically flat spacetimes and how information about source dynamics is encoded in gravitational waves. This talk explores three key aspects of higher memory effects in the context of gravity. First, we present the contribution from the moments of the News to the GW strain in terms of the source multipole moments. Second, within the post-Newtonian framework, we demonstrate how these moments contribute to the terms in the radiative multipole moments of the strain. Third, we discuss the prospects for detecting these effects up to the second order. Lastly, the talk will also explore analogous hierarchies of persistent effects in other gauge theories, including electromagnetism and classical Yang-Mills theory.

The Super BigBite Spectrometer (SBS) program at Jefferson Lab aims to measure nucleon electromagnetic form factors (EMFFs) at high momentum transfers. The GEn-RP experiment, the third in the SBS experiment series, concluded data taking in May 2024. This experiment is focused on measuring the neutron EMFF ratio GnE/GnM through recoil polarimetry at a Q2 = 4.5 (GeV/c)². Two polarimetry techniques have been used in this experiment: charge-exchange np→pn with a passive Fe analyzer, and conventional np→np scattering with an active CH analyzer. The results of this experiment will serve to optimize future even higher Q2 experiments aimed at measuring GnE/GnM. An overview of the experiment and post- experiment data analysis efforts will be presented.

Baryon number violation is our most sensitive probe of physics beyond the Standard Model. Its realization through heavy new particles can be conveniently encoded in higher dimensional operators that allow for a model-agnostic analysis. The unparalleled sensitivity of nuclear decays to baryon number violation makes it possible to probe effective operators of very high mass dimensions, far beyond the commonly discussed dimension-six operators. To facilitate studies of this ginormous and scarcely explored testable operator landscape we provide the exhaustive set of UV completions for baryon number-violating operators in vRSMEFT up to mass dimension 15, which corresponds roughly to the border of sensitivity. In addition, we will also include operators involving derivatives, which are usually ignored in phenomenological analyses since they are generically suppressed compared to non-derivative operators. We will study exceptions to this statement and explore scenarios in which derivative operators are important.

Motivated by remarkable properties of superfluid edge dislocations in solid Helium-4—responsible for the unique supertransoprt-through-solid and “syringe” effects, 

we reveal a broad class of quantum systems—boundaries in phase separated lattice states, magnetic domain walls, and ensembles of Luttinger liquids—that can be classified as transverse quantum fluids.  

Transverse quantum fluids provide us with a striking demonstration of conditional character of many dogmas associated with superfluidity, such as the necessity of elementary excitations, in general, 

and the ones obeying Landau criterion in particular, as well as the absence of long-range order in one-dimensional quantum superfluids.

Hydrogen will play an important role as the cleanest energy source in the future. How to produce, transport, and store hydrogen is an important issue. Meanwhile, hydrogen is also an ideal coolant for cooling the high temperature superconductor for power transmission and storage, and also for superfast transit for people and goods. In this presentation, I will discuss the development of efficient catalysts for hydrogen production through water electrolysis, transport and storage, and superfast vehicles traveling at about 400 miles per hour with absolute flexibility and safety.

Ultrahigh thermal conductivity has been constantly pursued for many applications. Diamond has the highest thermal conductivity but is an insulator, silicon and GaAs are good semiconductors used for our daily life but the thermal conductivity is too low, the band gap is not large enough nor the carrier mobility. Boron arsenide was theoretically predicted to have a unique combination of thermal conductivity close to that of diamond, a band gap as large as 2 eV, and equally high mobility in both electrons and holes. In this talk, I will present our progress on boron arsenide single crystals.

On December 25, 2021, the James Webb Space Telescope was launched from Earth towards its ultimate destination at the L2 Lagrange Point, 1.5 million kilometers away from Earth. The culmination of decades of planning, construction, execution, and transport all came down to a critical few minutes, which led to our newest flagship observatory in space. Science operations began in July of 2022, with the past 2+ years bringing about a number of scientific revolutions: both expected, such as the discovery of a number of record-breaking galaxies and other cosmic objects, and unexpected, such as new features in star and planet-formation, and big surprises about the earliest supermassive black holes in our Universe. Come learn what we've discovered and how it's altered our cosmic perspective, and explore what's inside the speaker's first National Geographic book, Infinite Cosmos: Visions from the James Webb Space Telescope.