The University of Florida Astrophysics Seminar is held on Wednesdays at 2:00pm. During the Spring 2024 semester, seminars will be held in-person in NPB 2165. Seminars may also be broadcast over Zoom, and recorded.

Spring 2024 Schedule

February 28th: Pawel Jung (University of Central Florida)

Title: New Frontiers in Multimode Nonlinear Optics: Fundamental Aspects and Applications

Abstract:

In this talk, I will discuss future directions in my research on fundamental aspects of multimode nonlinear dynamics of light and their promise for a variety of applications ranging from light generation and control to light-based sensing. By exploiting concepts from nonlinear optics, topological photonics, and non-Hermitian physics, I explore new possibilities for sensing, optical switching, high-power light sources, and new regimes of light-matter interaction. Firstly, I delve into a novel type of soliton molecules, where light pulses and beams bind together with positive and negative effective masses. By invoking an analogy with mechanical systems, I will show how this system violates the action-reaction principle, thus paving the way for advanced optical sensing schemes. Next, I turn to the exciting realm of programmable topological platforms. By utilizing soft matter materials, we can manipulate light in unconventional ways, leading to robust photonic systems and new insights into the interaction between topological states. My research further ventures into optical thermodynamics, extending the theory to the strong nonlinear regime. This allows us to observe phase transitions in complex optical systems, analogous to the solidification and liquefaction of water. Finally, I discuss future directions in harnessing the interplay between topology, non-Hermicity, and nonlinearity. This opens doors to maximizing topological currents and exploring novel photonic states.

February 21st: Junxin Chen (MIT)

Title: Beyond the Standard Quantum Limit

Abstract:

Measurement of a mechanical oscillator inevitably perturbs it. The tradeoff between the accuracy of the measurement and the perturbation gives the standard quantum limit (SQL), which restricts the measurement sensitivity of gravitational wave detectors. In this talk, I will introduce the techniques to overcome the SQL, and the path I would like to take to improve measurement sensitivity further. In addition, I would like to introduce my plans of searching for vector dark matter and preparing the 40-kg LIGO testmass into quantum states.

February 7th: Kevin Huffenberger (Florida State University)

Title: Physics from the Cosmic Microwave Background and the road to CMB-S4

Abstract:

The Cosmic Microwave Background (CMB), the radiation afterglow of the Big Bang, provides us with both a snapshot of the early Universe and a backlight that illuminates all the later-developing structure. The statistics of this light provide avenues to detect beyond-the-standard-model physics from inflationary gravitational waves or light relic particles. The growth of large-scale structure, measured by gravitational lensing of the CMB, provides information on the mass of neutrinos and on dark energy. Both the intensity and the polarization of the microwave light are crucial. Electron scattering of CMB photons allows us to find distant galaxy clusters via their gas content. With good time resolution, CMB surveys can identify and measure variable and transient objects from flaring stars to gamma-ray bursts to supermassive black holes in active galactic nuclei, and can play a role in multimessenger astronomy. I will briefly tour ground-based experimental efforts at the South Pole and in Chile, including the South Pole Observatory, Atacama Cosmology Telescope, Simons Observatory, and their successor, CMB-S4, a project well-regarded both by the Decadal Survey of Astronomy and Astrophysics and by the Snowmass and P5 planning exercises for high-energy physics.

January 10: Karl van Bibber (UC Berkeley)

Title: Axion Haloscopes

Abstract:

Several axion haloscopes, using the mechanism invented by Pierre Sikivie, are in operation and planned. Some of these will be described.

Fall 2023 Schedule

September 6: Siyao Xu (University of Florida)

Title: Mirror diffusion of cosmic rays in MHD turbulence

Abstract:

Diffusion of cosmic rays (CRs) in magnetized and turbulent astrophysical media is a long-standing and challenging problem. The recent explosive interest in understanding CR diffusion arises from its close connection to other cosmic messengers and broad astrophysical impacts as revealed by observations and simulations with their ever-increasing capabilities. However, the existing CR diffusion theories in general face severe difficulties when explaining new-generation CR observations. This tension necessitates exploration of new CR diffusion mechanisms. I will talk about the new mirror diffusion of CRs. In our recent numerical study (Zhang Chao & Xu), we find that the mirror diffusion strongly enhances the confinement of CRs in space, and CRs stochastically undergo slow mirror diffusion within a small region and fast scattering diffusion over a large distance, resulting in a Lévy-flight-like propagation. This finding is different from the normal diffusion of CRs studied for decades. I will also briefly talk about its implications on astrophysics and space physics.

Zoom recording

October 11: Robert Brandenberger (McGill University)

Title: Searching for Cosmic Strings in New Observational Windows

Abstract:

Cosmic string solutions exist in a wide class of theories beyond the Standard Model (BSM) of particle physics. If Nature is described by such a theory, then a network of strings will form in the early universe and persist to the present time. Thus, searching for cosmic strings in the sky is a way to probe BSM complementary to accelerator searches. I will discuss searches for cosmic strings in new observational windows, in particular in 21-cm surveys. In addition, cosmic strings may explain the origin and abundance of high redshift supermassive black holes and galaxies.

October 18:

Title: TBD

Abstract:

TBD

October 25: Marek Szczepanczyk (University of Florida)

Title: Searching for exceptional gravitational-wave sources in the LIGO/Virgo/KAGRA observing runs

Abstract:

Multi-messenger Gravitational-Wave Astrophysics is an exciting venue for discovery. The gravitational-wave observations by LIGO/Virgo/KAGRA challenge our understanding of the Universe and allow testing theories at an unprecedented level. In particular, the discovery of gravitational waves from exceptional astrophysical sources plays a key role in this endeavor of exploring the Universe. Examples of exceptional sources are compact binary mergers with unique source properties or sources generating non-deterministic gravitational-wave signals, such as core-collapse supernovae. I will explain the model-independent searches that are suitable for making discoveries. I will talk about example detections during the previous observing runs of LIGO/Virgo/KAGRA. I will discuss the status of the ongoing fourth observing run that started around half a year ago and alerted the scientific community in real-time with around 50 gravitational-wave candidates.

November 1: TBD

Title: TBD

Abstract:

TBD

November 8: TBD

Title: TBD

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TBD

November 17: Christopher Pope (Texas A&M University)

Title: Mass And Force Relations For Dyonic Einstein-Maxwell-Dilaton Black Holes

Abstract:

We investigate various properties of extremal dyonic static black holes in Einstein-Maxwell-Dilaton theory. Using the fact that the long-range force between two identical extremal black holes always vanishes, we obtain a simple first-order ordinary differential equation for the black hole mass in terms of its electric and magnetic charges. Although this equation appears not to be solvable explicitly for general values of the strength a of the dilatonic coupling to the Maxwell field, it nevertheless provides a powerful way of characterising the black hole mass and the scalar charge. We make use of these expressions to derive general results about the long-range force between two non-identical extremal black holes. In particular, we argue that the force is repulsive whenever a>1 and attractive whenever a<1 (it vanishes in the intermediate BPS case a=1). The sign of the force is also correlated with the sign of the binding energy between extremal black holes, as well as with the convexity or concavity of the surface characterizing the extremal mass as a function of the charges. We extend our results also to a class of Einstein-Maxwell-Dilaton-Axion theories. Our work is motivated in part by the Repulsive Force Conjecture and the question of whether long range forces between non-identical states can shed new light on the Swampland.

November 29: Zsuzsa Marka (Columbia University)

Title: Machine Learning to Boost Multimessenger Astrophysics

Abstract:

Exploration of the Universe through combining information from a multitude of cosmic messengers (electromagnetic radiation, gravitational-waves, neutrinos) is an emerging field enabled by giant leaps in building large-scale detectors. Connecting different kinds of observations of the same astrophysical event must be done near real-time, requiring prompt analysis of disparate data streams. We gain attuned information on the time and localization of a cataclysmic event, its energetics, and other observable properties, only accessible through multimessenger analytics. Gravitational-wave detections and open public alerts enabled prompt multimessenger studies for the global community. There is an ongoing effort within LIGO-Virgo-KAGRA to assimilate and invent machine learning techniques that will allow faster and more confident detections. Better characterized detections of more gravitational-wave events thereby will expand multimessenger science. Pioneering machine learning efforts at Columbia target two critical topics: trailblazing the frontiers of more efficient methods for gravitational-wave discovery and increasing detector sensitivity through terrestrial transients’ identification and elimination. I will highlight specific examples of investigations on the intersection of Data Science, Astrophysics, and Instrumentation that are spearheaded by the Columbia Experimental Gravity group.

December 6: Kevin Kuns (MIT)

Title: Cosmic Explorer: Science and Design of a Next Generation Gravitational Wave Observatory

Abstract:

Cosmic Explorer is the concept for a next generation gravitational wave observatory to be built in the United States which, along with the European Einstein Telescope, will significantly improve on the success of today's gravitational wave detectors starting in the mid-2030s. Cosmic Explorer would consist of two laser interferometers, one 40 km long and one 20 km long, improving on the design of the 4 km long LIGO detectors but with an order of magnitude increase in sensitivity and an optical design chosen to target astrophysical sources of interest. Among its vast potential, the observatory could study the remnants of the first stars and the formation of supermassive black holes and galaxies by detecting sources up to redshifts of 100, make precision tests of general relativity, investigate the nature of dark energy and dark matter, study the neutron star equation of state, probe new phases of matter not accessible to colliders, and study heavy element nucleosynthesis. The design is relatively low risk by largely scaling up the proven design of the LIGO interferometers along with some technological improvements to further reduce the dominant noise sources arising from quantum mechanics, thermodynamics, and geophysics.

Spring 2023 Schedule

January 18: Special Astrophysics Colloquium at 1pm by Mark Avara (Cambridge)

Title: Simulations of Accreting Black Hole Binaries: High Fidelity for the Big-Data Era

Abstract:

While several promising candidate supermassive black hole binaries have been identified, more realistic physical modeling of these systems will be necessary to confirm their identity and perform robust searches in the era of big-data astronomy. Unfortunately, the large range of temporal and physical scales and wide parameter space have historically made their modeling prohibitive when performed via full 3D general relativistic magnetohydrodynamic simulations (3D-GRMHD). I will first demonstrate the necessity of this type of modeling, despite its complexity and computational expense, and then briefly describe a new tool we have built to aid in the effort. I will present our recent 3D-GRMHD simulations which extend longer in duration than comparable prior models and achieve higher resolution and global realism, made possible by using our new multi-domain/multi-physics code, PatchworkMHD. With these improvements we have found unexpected 3D hydrodynamical and magnetic behavior that is guiding us towards unique binary observational signatures. In upcoming surveys like Vera Rubin Observatory’s LSST these unique signatures will be key to confirming the identity of binary black hole systems and secure them as a corner-stone of multi-messenger astrophysics.

January 19: Special Astrophysics Seminar at 2pm by Mark Avara (Cambridge)

Title: Magnetic Field Evolution in Binaries Revealed By the Multi-Patch Approach

Abstract:

Magnetic field evolution and the role of dynamically important large-scale field structures have increasingly taken center-stage when interpreting observations of single black hole accretion, including direct imaging by the Event Horizon Telescope. However, the added complexity of magnetohydrodynamic evolution in accreting binaries has left analogous magnetically-dominated behavior almost entirely unexplored. In this seminar I will describe how we developed the multi-patch code PatchworkMHD and why it is ideal for tackling this hard problem. Along the way I will review some fundamentals of highly magnetized (especially magnetically arrested disk, “MAD”) accretion onto single black holes, and what behavior might be revealed by the first highly magnetized binary simulations.

February 1: Special Astrophysics Colloquium at 1pm by Tonima Ananna (Dartmouth College)

Title: AGN lifecycles: What we know so far and where we are going

Abstract:

Supermassive black holes (SMBH) at the centers of galaxies become active when they devour matter from around them at a high rate. Much is still unknown about how matter around Active Galactic Nuclei (AGN) is regulated. The pure unified model posits that the differences in the observed signatures from AGN occur only due to differences in observers’ viewing angles. The receding torus model offers an explanation for the observed decrease in obscured AGN fraction with luminosity (i.e., the dust sublimation radius is higher for more luminous AGN, making them unobscured in many more viewing angles). I present my most recent work, which finds that matter around AGN is more definitively regulated by feeding rate (also known as Eddington ratio) rather than luminosity. This calls for a revision of the well-established Unified model and offers a clear path toward exploring AGN lifecycles using current and future missions.

February 2: Special Astrophysics Seminar at 2pm by Tonima Ananna (Dartmouth College)

Title: Constraining the Feeding Rate Distribution of AGN

Abstract:

My most recent projects focus on constraining the feeding rate distribution function of Active Galactic Nuclei (AGN). I will discuss the ways we accounted for uncertainties in mass measurements for this work, which can be significant, and how we constructed and tested our algorithm using simulated catalogs. I will discuss the improvements made over previous works, the various observational and theoretical constraints our model had to satisfy, and the significance of the results.

February 6: Special Astrophysics Colloquium at 1pm by J.J. Zanazzi (UC Berkeley)

Title: Are Planetary Systems Coplanar?

Abstract:

Because planets are thought to form in flat disks of gas and dust around young stars, planetary systems should have nearly coplanar orbits, with the host star spinning in the same direction as the planets’ orbits. Although most planetary systems appear to be coplanar, new observations have uncovered planetary systems with large mutual inclinations, stars spinning in the opposite direction as the orbits of surrounding planets, and planet-forming disks with large misalignments between neighboring rings. In this talk, we discuss how the dynamics of planets forming in disks can generate misaligned planetary systems. Secular resonances can excite large tilts between two planets forming within a disk cavity, and misalign the host star’s spin direction when a disk has an inclined binary companion. Disks orbiting two stars on an eccentric orbit can also be driven into a 90 degree misalignment with the binary orbital plane, due to dissipation from viscous disk warping torques. We discuss detected protoplanetary and planetary systems which validate predictions made by these dynamical theories, as well as ongoing work to explain the remaining observational puzzles.

February 7: Special Astrophysics Seminar at 2pm by J.J. Zanazzi (UC Berkeley)

Title: Tidal Circularization of Binaries by Resonance Locking

Abstract:

Although tidal dissipation in binary stars has been studied for over a century, theoretical predictions have yet to match the observed properties of binary populations. This work quantitatively examines the recent proposal of tidal circularization by resonance locking, where tidal dissipation arises from resonances between the star's natural oscillation frequencies and harmonics of the orbital frequency, and where resonances are "locked" for an extended period of time due to concurrent stellar evolution. We focus on tidal resonances with axi-symmetric gravity modes, and examine binaries with primary masses from one to two solar masses. We find that orbital evolution via resonance locking occurs primarily during the star's pre-main-sequence phase, with the main-sequence phase contributing negligibly. Resonance locking, ignoring nonlinearity, can circularize binaries with peri-center distances out to ∼10 stellar radii, corresponding to circular periods of ∼4-6 days. However, we find resonantly excited gravity modes will become nonlinear in stellar cores, which prevents them from reaching their full, linear amplitudes. We estimate that such a "saturated resonance lock" reduces the circularization period by about a third, but resonance locking remains much more effective than the cumulative actions of equilibrium tides. We briefly discuss a companion paper, where recent binary data is compared against theory.

February 8: Special Astrophysics Colloquium at 1pm by Siyao Xu (Institute for Advanced Study)

Title: Turbulence and cosmic accelerators

Abstract:

Turbulence is the most ubiquitous phenomenon shaping diverse processes across all length scales in the universe. Despite its ubiquity and importance, there exists a gap between the ever-improved understanding on turbulence and its application to understanding the extreme universe. I will discuss my efforts in bridging this gap by addressing (1) how turbulence connects the microscopic physics and macroscopic astronomical observations; and (2) how turbulence affects the multi-messenger astronomy and switches on cosmic fireworks. By using shock acceleration as an example, I will illustrate how I use the turbulence toolbox to understand the most energetic events in the universe. In the era of multi-messenger astronomy, the turbulence toolbox provides us a new vision of the extreme universe.

February 9: Special Astrophysics Seminar at 2pm by Siyao Xu (Institute for Advanced Study)

Title: Turbulence and star formation

Abstract:

Turbulence is an essential part of current paradigm of star formation. My research reveals a number of key impacts of turbulence that have been overlooked. (1) A significant deviation from the widely accepted Kolmogorov turbulence spectrum is found from observations of pulsars. It reveals the importance of compressible turbulence in making stars. (2) The breakdown of flux freezing by turbulence is found to be a promising solution to the long-standing magnetic flux problem of star formation. This prediction is recently tested and found to have important implications for the first star formation. (3) Turbulence is imprinted into motions of young stars, which is recently confirmed by Gaia observations. This entails far-reaching implications, including binary formation, eccentricity distribution of wide binaries, and formation channels of merging compact binaries.

February 15: Regular Astrophysics Seminar at 2pm by Andrei Nomerotski (Brookhaven National Laboratory)

Title: Quantum-Assisted Optical Interferometry for Precision Astrometry

Abstract:

The highest resolutions in astronomical imaging are achieved through interferometry, the process of combining wave information from multiple separate telescopes/apertures. We review the standard techniques of single-photon amplitude (Michelson) interferometry and two-photon (Hanbury Brown & Twiss) intensity interferometry, and then visit recent ideas for how they can be improved in the optical through the use of quantum networking and entanglement distribution. A proposed new technique of two-photon amplitude interferometry is described, with particular application for precision astrometry. First bench-top results will be shown and basic instrument requirements discussed, along with future improvements for detector systems and quantum methods.

February 22: Special CMS Seminar at 2pm by Yoav Afik (CERN)

Title: Searching for New Phenomena in Final States with Two Leptons and b-tagged Jets

Abstract:

One of the fundamental predictions of the Standard Model is Lepton Flavor Universality. Any deviation from this prediction would indicate the existence of physics beyond the Standard Model. If Lepton Flavor Universality is indeed violated in nature, physics beyond the Standard Model may mediate interactions involving a pair of quarks and a pair of leptons, which can be modeled by a four-fermion contact-interaction. Some of these models motivate a search in novel final states, that have only been recently started to be tested at the LHC, including two opposite-sign leptons (electrons or muons) with large invariant mass and $b$-tagged jet selections. This unique signature allows an enhanced sensitivity to a variety of contact-interactions, well beyond the limits which currently exist in the literature. In this talk, I will discuss the relevant models for these signatures, the past and the ongoing searches at the LHC.

March 1: Special CMS Seminar at 2pm by Yuta Takahashi (UCSB) at 2pm

Title: Solving the puzzle of particle flavour using the CMS experiment

Abstract:

One of the key conundrums in particle physics is the three-generation structure of the fermions and its vastly different mass spectrums. A currently unknown physics interaction at the beginning of the Universe, i.e. at a high energy scale, which acted differently depending on the fermion flavor, could have shaped the “flavor structure” we see today. The discovery of such an interaction is the ultimate goal of my research and is currently one of the top priorities in particle physics, given hints of Lepton Flavor Universality (LFU) violations reported by muon g-2 and B-physics experiments. In this seminar, I will review my past/on-going/future research projects to tackle this conundrum uniquely at the CMS experiment. I have been using and will use the tau lepton as my primary tool. I will also share my future prospects towards HL-LHC (>2027); particular focus is on the development of a new scheme to select hadronically decaying tau-leptons right at the first stage of the trigger by exploiting CMS’s capability during HL-HLC for the fast reconstruction of track trajectories, called the track-trigger. At the end of the colloquium, I will briefly share my vision towards future collider experiments.

March 22: Evan Hall

Title: TBD

Abstract:

TBD

March 29: Johannes Eichholz

Title: TBD

Abstract:

TBD

May 3: Luc Blanchet (Institut d'Astrophysique de Paris)

Title: Gravitational-wave phasing of compact binaries to 4.5PN order beyond the Einstein quadrupole formula

Abstract:

Post-Newtonian theory plays an important role for the data analysis of gravitational waves generated by compact binary systems. In this talk, after some general review of the field, we describe the recent calculation of gravitational waves emitted by spinless compact binaries through the fourth-and-a-half post-Newtonian (4.5PN) order beyond quadrupole radiation. Rough numerical estimates for the contribution of each PN order are provided for typical systems observed by current and future gravitational wave detectors. Comparaisons with other methods are emphasized.

May 24: Jake Lange (UT Austin)

Title: On the Importance of Expanding and Improving Numerical Relativity Simulations

Abstract:

Since the original breakthrough of the numerical relativity (NR) evolution codes, multiple research groups have been able to solve Einstein’s equations numerically on supercomputers to simulate merging binary black hole gravitational wave sources. While these NR simulations can be directly compared to the data using special configurations parameter estimation codes, these waveforms are mostly used to calibrate and verify the accuracy semi-analytical gravitational wave models. These models are in turn used for production level parameter estimation analyses of gravitational wave detections from the LIGO-Virgo-KAGRA Collaboration. Because of this, it is essential not only to expand our current NR simulation grid into more exotic parts of parameter space (i.e. more unequal mass ratios, more extreme precessing spins, inclusion of eccentricity) but also to improve the accuracy of our current simulations as we prepare for next generation detectors. For the former, I present a novel algorithm that suggests new NR simulation placement based off of the interpolated likelihood as well as the error to that interpolated likelihood when directly comparing the NR waveforms to a real event. This allows the placement of new simulations to be in relevant parts of parameter space (high likelihood) as well as in sparse parts of parameter space for the existing grid (high error in interpolated likelihood). For the latter, I present parameter estimation results investigating the effects of waveform systematics due to NR resolution. With our current expected signal-to-noise ratios (SNR) for signals from our current ground-based detectors, the resolutions used to generate the current catalogs of NR simulations are considered large enough to be indistinguishable from an infinite resolution simulation (i.e. statistical errors dominate). As our current and next generation detectors increase our sensitivity, the systematic errors due to our finite resolution becomes more important. Following up from a previous mismatch study by Ferguson et. al. comparing different resolutions for a given simulation using different detectors, I present preliminary work that quantifies the impact of resolution error by injecting these different resolution simulations at different SNRs based off the criteria investigated in Ferguson et. al.

Other Events

Students may receive credit for attending the Astrophysics Seminar by registering for PHY 6391.