Dr. Maxim Pospelov, University of Minnesota

Dark Matter snooker

Despite enormous experimental investment in searches of particle dark matter, certain well-motivated corners of parameter space remain to be elusive “blind spots” for direct detection. In my talk I will address two of such exceptions: light particles that simply do not have enough kinetic energy to detect, and strongly-interacting particles that quickly thermalize and also become sub-threshold for direct detection. I show that both blind spots can be probed through double collisions of Dark matter – first with some energetic Standard model particles (solar electrons, cosmic rays, particles in a beam, neutrons in nuclear reactors etc) that bring DM to energies above thresholds followed by the scattering inside a detector. This way, I derive novel constraints on light dark matter, as well as strongly-interacting dark matter models, using existing dark matter and neutrino experiments. 

Dr. Maxim Pospelov, University of Minnesota

New developments in EDM theory

Over the last 10 years there has been a large progress in experiments testing the coupling of electron spin to electric field. These experiments are often referred to as “electron dipole moment experiments” (or EDMs). In my talk I will show how the Standard Model CP-violation leads to the coupling of electron spin to the electric field, and argue that the most important mechanism is related to the spin interaction with the nucleus. I will finish the talk with some comments on lattice attempts to calculate neutron EDM induced by theta QCD.

Prof. Debayan Mitra, Indiana University Bloomington

Molecular Advantage for Quantum Science Applications

In recent years, cold and ultracold molecules have emerged as a mature platform for quantum simulation, computation, chemistry and precision measurements. Molecules provide unique features and challenges compared to their atomic analogs. In this talk, I will discuss two avenues where molecular advantage plays a key role. First, I will discuss how the molecules CaH and CaD can be used as a vehicle to produce ultracold and trapped hydrogen and deuterium atoms for precision measurement. I will discuss the process of formation of the molecules CaH and CaD and our latest efforts towards laser cooling it. Second, I will talk about the planned pathway to building a quantum gas microscope of laser cooled fermionic molecules with tunable long-range interactions. I will describe how the molecule MgF possesses many of the properties favorable to both laser cooling and single-site imaging. I will also discuss some of the challenges posed by this new class of molecules with UV transitions.

Dr. Daniil Antonenko, Yale University

Exotic Magnetism and Vestigial Nematicity in MPX3 Materials and Bey

MPX3 materials consist of stacked honeycomb layers and host a variety of zigzag and Néel magnetic orders. I will explain how quantum fluctuations determine magnetic ordering through the order-by-disorder mechanism and modify the spin-wave spectrum by gapping pseudo-Goldstone modes. Next, I will describe how theory predicts and experiment supports the existence of a vestigial Potts-nematic phase at the onset of the magnetic order. In the second part of my talk, I will discuss recent advances, including topological phenomena in altermagnets and p-wave magnets.

Dr. Rebecca Larson, Rochester Institute of Technology

Advancements in Exploring the Early Universe: Unlocking the Mysteries of Galaxies During the Reionization Era

The history of galaxies in the early Universe remains substantially unknown. The mystery surrounding these galaxies is primarily a result of the epoch in which they existed. During the epoch of reionization (z>6), the Universe experienced its last major phase change, where the neutral gas permeating the intergalactic medium [IGM] became ionized. Light emitted from early galaxies was often blocked by this neutral gas (or “cosmic fog”), preventing restframe ultraviolet [UV] spectroscopic studies of this epoch except for faint traces of light detectable in the near-infrared [NIR] from the brightest sources. Before 2022, the high-redshift field was restricted due to limited ground- and space-based instrumentation probing NIR wavelengths and beyond. Much of what we learned spectroscopically about these galaxies during this time came from a handful of bright UV metal emission lines or far-infrared [FIR] emission (generally with only 1-2 lines detected in individual galaxies). These data only came after fighting for hours using the most massive telescopes on the ground and in space. Since the advent of JWST, the high-redshift field has exploded with new science probing wavelengths and redshifts previously inaccessible. Using the advanced spectroscopic NIR capabilities of the JWST, we have found increasingly distant galaxies and characterized these sources within the heart of the epoch of reionization [EoR] for the first time. In this talk, I will discuss the state of the high-redshift field before and after the launch of JWST – highlighting our work from the Cosmic Evolution and Early Release Science [CEERS] survey, among other key early release science [ERS] & Cycle 1-3 programs. These new data have led to the discovery of an unexpected abundance of bright galaxies and active galactic nuclei [AGN] in the EoR, providing insights into the roles that the nature of these early galaxies and the nurturing from their environments played in the reionization of the Universe.

Prof. Gregory A. Fiete, Northeastern University

Nonlinear optical probing and control of magnetic and electronic quantum geometry

Illuminating a material with light can reveal both interesting aspects of electronic and lattice degrees of freedom, as well as drive phase and topological transitions in the material itself. In this talk, I will focus on three distinct responses of a material to light: (1) Nonlinear phononic control of magnetism in bilayer CrI , MnBi Te , and MnSb Te. (2) The non-linear photogalvanic response of Weyl semimetals with tilted cones and chiral charge up to 4 (the largest allowed in a lattice model), as well as the topological superconductor candidate 4Hb-TaS , and (3) The coupling of phonons to electronic degrees of freedom to produce chiral phonons with large g factors of order 1, which can be measured with Raman scattering.  I will discuss how these nonlinear responses are related to the underlying quantum geometry of the Bloch states and present a perspective on interesting frontiers in out-of-equilibrium quantum materials.

Nazar Budaiev, University of Florida

Multiwavelength mysteries in the most star-forming cloud in the Galactic Center

The high-density, turbulent, and overall extreme environment of the Central Molecular Zone (CMZ) provides a unique laboratory for studying disk-scale star formation under conditions similar to those at cosmic noon. Despite the importance of the region – ranging from the formation history of stars like our Sun to informing our understanding of other galaxies, many key properties of the CMZ, such as the relatively low star formation rate, remain unexplained.

The CMZ forms ~10% of all stars in the Galaxy, half of which are born in a single cloud: Sagittarius B2. We present a multi-wavelength overview of Sgr B2, the most massive molecular cloud in the CMZ. Combining observations from ALMA, VLA, and JWST, we construct a holistic picture of star forming processes in the cloud. We find a large-scale asymmetry in star formation across the cloud, with a sharp edge facing the epicenter of its orbit around the Galactic center. This asymmetry highlights that, even in high-pressure environments, feedback has escape valves. We examine different stages of star formation and their interactions within the cloud – from the collapsing dust cores observed with ALMA, to highly pressurized HII regions detected by VLA, to accreting stars revealed with JWST.

Prof. Felix Ringer, Stony Brook University

From Qubits to Quarks: Quantum Computing Meets Nuclear Physics

The strong force in nature, described by the theory of quantum chromodynamics (QCD), governs the interaction of quarks and gluons, which constitute the main building blocks of the visible universe. Since its development over five decades ago, various fundamental questions have remained unanswered despite significant theoretical and experimental efforts: How do the dynamics of quarks and gluons give rise to emergent structures such as nucleons and nuclei? What is the phase diagram of nuclear matter, and what are the real-time and non-equilibrium dynamics at collider experiments and in the early universe? While significant progress has been made on the theory side using perturbative techniques and lattice QCD, the answers to some of the most challenging questions are expected to be beyond the capabilities of classical computing. Advances in quantum computing coupled with the development of innovative algorithms motivate the exploration of quantum simulations to address these questions. In this talk, I will discuss recent progress toward quantum simulations for fundamental particle and nuclear physics, covering both discrete (qubit) and continuous variable (qumode) approaches.

Prof. Hal Haggard, Bard College

Falling Cats, Tunneling of Quantum Geometries, and Quantum Gravity

After his departure, a legend began to build about Maxwell’s time at Trinity College, Cambridge. The story went that he would toss cats from school windows to watch them land upright on their padded paws. (This was not so.) I will describe the true fascination that Maxwell, and many physicists after him, have had with falling cats. Indeed, a falling cat is a remarkably accessible example of a gauge theory and turns out to be mathematically identical to a model of the simplest grain of space used in loop quantum gravity. Insights garnered from this model are allowing us to create detailed pictures of the tunneling of quantum geometry in quantum gravity. This new realm of application for quantum tunneling is unexpected and rich, already lending new perspectives on quantum gravity. I aim to build upon these simpler models to describe the late stages of the evaporation of black holes and the possibility of their quantum metamorphosis into white holes.

Dr. Serhii Kryhin, Harvard University

Linear-in-temperature conductance and collective mode cyclotron resonances in electron hydrodynamics

Linear temperature dependence of transport coefficients in metals is habitually viewed as a signature of non-Fermi-liquid physics, whereas the hallmark of Fermi-liquid physics is a T^2 conductivity scaling. In contrast to this common lore, this talk will argue that 2D electron fluids with simple Fermi surfaces feature conductivity that scales linearly with temperature. The T-linear scaling originates from the propagation of long-lived excitations of the 2D Fermi surface. At low frequencies, these excitations generate multiple viscous modes that propagate over large distances, leading to power-law cascades in both wavenumber and frequency space and giving rise to exotic tomographic hydrodynamics. The linear T dependence, predicted to occur in a wide range of temperatures, provides a smoking gun for nonclassical hydrodynamics, which is supported by linear T dependence of conductance recently measured in 2D electron fluids. This talk will further discuss the potential for probing these modes through cyclotron resonance experiments, where resonances at multiple cyclotron frequencies excite high-order angular harmonics of the Fermi surface, allowing for the observation of their dynamics. Due to Kohn’s theorem, accessing these higher-order cyclotron resonances requires spatially modulated excitations with nonzero wavenumbers or non-parabolic band dispersion.

1. https://arxiv.org/abs/2112.05076
2. https://arxiv.org/abs/2305.02883
3. https://arxiv.org/abs/2310.08556
4. https://arxiv.org/abs/2308.06056

Jeffrey McKaig, George Mason University

Why Are Optical Coronal Lines Faint in Active Galactic Nuclei?

Forbidden collisionally excited optical atomic transitions from high ionization potential (IP~54eV) ions (e.g., Ne4+, Fe10+, Ar10+), are known as optical coronal lines (CLs). The spectral energy distribution (SED) of active galactic nuclei (AGN) typically extends to hundreds of electron volts and above, which should be able to produce such highly ionized gas. However, optical CLs are often not detected in AGN using large scale optical surveys such as the SDSS. In this talk I will present recent photoionization calculations with the Cloudy spectral synthesis code which determine possible reasons for the rarity of these optical CLs. I will report on the observability of optical CLs given the dust content and metallicity of the gas, as well as the ionizing slope of the incident AGN SED. Our main conclusions are (1) dust reduces the strength of most CLs by ~three orders of magnitude, primarily as a result of depletion of metals onto the dust grains. (2) In contrast to the CLs, the more widely observed lower IP optical lines such as [O III] 5007A, are less affected by depletion and some are actually enhanced in dusty gas. (3) In dustless gas many optical CLs become detectable, and are particularly strong for a hard ionizing SED. This implies that prominent CL emission likely originates in dustless gas. I will also present recent work our group has conducted which indeed suggests dust is being destroyed in objects with CL emission and may indicate an important stage in AGN host-galaxy evolution.

Dr. Todd J. Martinez, Department of Chemistry and The PULSE Institute, Stanford University

Discovering Chemistry and Photochemistry From First Principles Molecular Dynamics

Novel computational architectures and methodologies are revolutionizing diverse areas ranging from video gaming to advertising and espionage. In this talk, I will discuss how these tools and ideas can be exploited in the context of theoretical and computational chemistry. I will show how the resulting advances in the efficiency of quantum chemistry can be harnessed to progress from traditional “hypothesis-driven” methods for using electronic structure and first principles molecular dynamics to a “discovery-driven” mode where the computer is tasked with discovering chemical reaction networks. We apply this reaction discovery method to methane pyrolysis, as an example where direct comparison to experimental results is possible. I show that the first principles method with no experimental input produces predictions in agreement with experiments and as good as bespoke models parameterized to experimental data. I then discuss the extension of these ideas to photochemical reactions involving electronic excited states. Finally, I describe our recent efforts to make computational chemistry tools broadly accessible for both education and research purposes.

UConn Particles, Astrophysics, and Nuclei Seminar Series.

Dr. Neill Warrington, MIT (Title and abstract forthcoming)

Contact: Prof. Gerald Dunne

Dr. Jacob Pettine​, MIT

Tuning the properties of quantum materials through nanostructured symmetries

Fine-tuning interactions and quantum phenomena in materials has been a longstanding challenge, with recent advances in stacked and twisted van der Waals crystals as well as light-driven transient phases. Yet intrinsic lattice symmetries still fundamentally constrain the phases that can be accessed in these systems. The ability to further design these symmetries therefore represents an exciting frontier for controlling both the static properties and ultrafast responses of quantum materials. Although directly engineering the atomic lattice remains a significant challenge, we can nevertheless nudge the symmetries of a material through high-precision nanostructuring, despite the apparent disparity in spatial scales. In this talk, I will discuss recent progress in this direction, including tuning electronic structure via two-dimensional superlattice strain on ultra-fine lithographic arrays and the direct patterning of thin crystals to induce symmetry-tailored dynamical strain fields through ultrafast nano-acoustic modes. Special attention will be given to the photocurrent responses that emerge in centrosymmetric materials such as graphene when patterned with symmetry-broken metasurfaces. These hybrid systems enable nearly arbitrary control over nanoscale vectorial current and provide a novel local probe of electronic anisotropy. Upon ultrafast excitation, they also act as efficient sources of tunable terahertz vector radiation, simultaneously probing the collective material dynamics.

1. Pettine, J. et al. Light-driven nanoscale vectorial currents. Nature 626, 984 (2024)
2. Pettine, J. et al. Ultrafast terahertz emission from emerging symmetry-broken materials. Light Sci. Appl. 12, 133 (2023)