Masato Nagatsuka, KEK, the High Energy Accelerator Research Organization, Japan

Search for bound state formation in DD* and BB* channels using lattice QCD with a relativistic heavy quark action

A color-singlet combination of two heavy quarks and two light antiquarks is an attractive object in search for exotic hadrons. In particular, the doubly charmed tetraquark has been observed by LHCb and the doubly bottomed tetraquark is expected to have a deeply bound state. In this seminar, we address a scenario that the BB* channel has a shallow bound state based on our latest lattice simulations to explore the phase shifts of DD and BB* scattering. For this purpose, 2+1 flavor PACS-CS gauge ensembles with pion masses 295, 411 and 569 MeV are utilized and a relativistic heavy quark action is adopted for the charm and bottom quarks.

We are hosting weekly shows, open to anyone who is interested in learning a bit about our universe in our newly-remodeled planetarium! Space is limited, so make sure to reserve a space through our Marketplace page: http://tiny.cc/uconn_planetarium

Dr. Daniel Kaplan, Rutgers University

Quantum geometry in nonlinear response

The question of electronic transport in solids has been actively reexamined in light of quantum geometry, that is the effects of band topology and wavefunction structure on electronic properties.

In linear response, these signatures are most famously connected with the Berry curvature which is associated with an anomalous Hall effect. Here, I will show a panoply of responses that emerges at nonlinear order, entirely defined by quantum geometric properties of electronic wavefunctions. I will present the general theory of nonlinear response and photoconductivity, focusing on second order effects, and specifically current rectification and second harmonic generation. Related to Moir’e materials, I will discuss a dc current generated by higher momentum correlations of the electronic wavefunction, which is strongly enhanced by flat band to flat band transitions. I will also present a unique nonlinear current, directly related to the dipole of the quantum metric, which sets on when time-reversal symmetry (TRS) is broken. This current dominates transport in scenario where the Berry curvature is strictly zero (by symmetry), such as in PT-symmetric systems or recently investigated altermagnets. This current also serves as a probe of crystal symmetries and the magnetic order of the system; I will present recent experiments on the magnetic topological insulator (and candidate axionic insulator) MnBi2Te4 which have uncovered this novel nonlinear transport effect. I will conclude with a general overview of quantum geometry in nonlinear signals, showing applications to polarization generation (in non-polar media), symmetry breaking in superconductors and light-induced sliding ferroelectricity.

Micah Banschick, University of Connecticut

Stochastic Methods for Binary Supermassive Black Holes

Binary supermassive black holes, surrounded by circumbinary accretion disks, produce complex and variable light curves that encode valuable astrophysical information. Traditional deterministic models often struggle to capture the chaotic and stochastic nature of these systems. In this talk, I will present a stochastic modeling approach to analyze the luminosity variations produced in binary systems. By applying these methods to both synthetic and observational data, the methods will extract key physical parameters such as black hole masses, orbital separations, and disk density distributions.

Prof. Ronald Garcia Ruiz, MIT

Radioactive Molecules are Dying to Reveal New Physics

Rapid progress in the experimental control and interrogation of molecules is enabling new opportunities for investigating the fundamental laws of our universe. In particular, molecules containing heavy, octupole-deformed nuclei, such as radium, offer enhanced sensitivity for measuring yet-to-be-discovered parity and time-reversal violating nuclear properties. In this colloquium, I will present recent highlights and perspectives from laser spectroscopy experiments on these species, as well as discuss the relevance of these experiments in addressing open problems in nuclear and particle physics.

Prof. Philip Mannheim, Department of Physics, University of Connecticut

Not one but two renormalizable theories of gravity

Second-order-derivative plus fourth-order-derivative gravity is the ultraviolet completion of second-order-derivative quantum Einstein gravity. While it achieves renormalizability through states of negative Dirac norm, the unitarity violation that this would entail can be postponed to Planck energies. As we show in this paper the theory has a different problem, one that occurs at all energy scales, namely that the Dirac norm of the vacuum of the theory is not finite. To establish this we present a procedure for determining the norm of the vacuum in any quantum field theory. With the Dirac norm of the vacuum of the second-order-derivative plus fourth-order-derivative theory not being finite, the Feynman rules that are used to establish renormalizability are not valid, as is the assumption that the theory can be used as an effective theory at energies well below the Planck scale. This lack of finiteness is also manifested in the fact that the Minkowski path integral for the theory is divergent. Because the vacuum Dirac norm is not finite, the Hamiltonian of the theory is not Hermitian. However, it turns out to be CPT symmetric. And when one continues the theory into the complex plane and uses the CPT symmetry inner product, viz. the overlap of the left-eigenstate of the Hamiltonian with its right-eigenstate, one then finds that for the vacuum this norm is both finite and positive, the Feynman rules now are valid, the Minkowski path integral now is well behaved, and the theory now can serve as a low energy effective theory. Consequently, the theory can now be offered as a fully consistent, unitary and renormalizable theory of quantum gravity. By analogous reasoning a pure fourth-order derivative theory is a fully consistent quantum gravity theory in its own right.

P. D. Mannheim, arXiv:2301.13029, Classical and Quantum Gravity 40, 205007 (2023); arXiv:2303.10827, Int. J. Mod. Phys. D 32, 2350096 (2023).

We are hosting weekly shows, open to anyone who is interested in learning a bit about our universe in our newly-remodeled planetarium! Space is limited, so make sure to reserve a space through our Marketplace page: http://tiny.cc/uconn_planetarium

APS March meeting talks rehearsal

Dr. Jesus Perez Rios, Department of Physics and Astronomy, Stony Brook University

The three-body problem in chemical physics

The three-body problem, such as three bodies interacting through gravity, is paramount in fundamental and mathematical physics. It is well-known that it has no closed solution, and the dynamics is chaotic. The equivalent problem in chemical physics is a termolecular reaction (or third-order reaction) in which three bodies (chemicals) collide, yielding a bound state between two bodies while the third one gets the excess kinetic energy. Termolecular reactions are essential to many chemical and physical systems, from ultracold atoms, determining the system’s stability, to plasma physics, explaining the recombination dynamics. In this talk, we will present our methodology for treating termolecular reactions and its application to several intriguing scenarios: cold chemistry, atmospheric physics, and geochemistry. Within cold chemistry, we will present the current understanding of ion-atom-atom recombination reactions essential to understanding the stability of cold ions in ion-atom hybrid traps. On the atmospheric physics front, we will present our results on the ozone formation reaction, one of the most relevant reactions in atmospheric physics. Regarding geochemistry, we will discuss our latest results on the sulfur cycle reactions essential to understanding the great oxygenation event, that moment in the history of our planet when the living organism transitioned from anaerobic to aerobic. Finally, we will present some of our efforts toward the theoretical understanding of cluster physics, solvation chemistry, and nucleation dynamics.

Prof. Dr. Ralf S. Klessen, Universität Heidelberg

The First Stars: Formation, Properties, and Impact

The first generation of stars, often called Population III (or Pop III), form from metal-free primordial gas at redshifts z ~ 30 and below. They dominate the cosmic star formation history until z ~ 20-15, at which point the formation of metal-enriched Pop II stars takes over. I review current theoretical models for the formation, properties and impact of Pop III stars, and discuss observational constraints. I argue that primordial gas is highly susceptible to fragmentation and Pop III stars form as members of small clusters with a logarithmically flat mass function. Feedback from massive Pop III stars plays a central role in regulating subsequent star formation, but major uncertainties remain regarding its immediate impact. Direct observations of Pop III stars in the early Universe remain extremely challenging, whereas stellar archeological surveys allow us to constrain both the low-mass and the high-mass ends of the Pop III mass distribution. Observations suggest that most massive Pop III stars end their lives as core-collapse supernovae rather than as pair-instability supernovae. I also speculate about the formation of supermassive stars, which under very specific circumstances can get as massive as several 100.000 solar masses and can become the seeds of the supermassive black holes observed in the high-redshift universe.