From Turbulence to Reconnection to Particle Acceleration: Connecting the Dots

November 28, 2023

Luca Comisso, Columbia University

Abstract: Plasma turbulence, magnetic reconnection, and particle acceleration underpin and drive a multitude of plasma phenomena across a wide spectrum of environments. It comes as no surprise therefore that they constitute three vibrant research areas at the frontier of modern astrophysics. Originally, these three paradigms were treated as distinct plasma processes. However, with the rapid advances in computing, observations and theory, they are converging towards an interconnected and entangled domain. This ongoing progress holds the potential for solving long-standing problems in several areas of plasma astrophysics ranging from the thermal disequilibration of ions and electrons in collisionless accretion flows to the genesis of the most energetic particles in the Universe. In this talk, using a powerful combination of first-principles plasma kinetic simulations and analytical modeling, I will highlight novel insights arising from my research in plasma self-organization regulated by the mutual interplay of turbulence and magnetic reconnection, and the underlying physical principles that link these processes to the acceleration of particles to high energies.

Bubbles at the Interface

November 14, 2023

Lydia Bourouiba, MIT

Abstract: Bubbles are ubiquitous in industrial and environmental processes and have an important impact on a wide range of systems. They can be beneficial in mixing bulk water, they contribute significantly to the planetary-scale transfer of chemical  compounds from water bodies to the atmosphere and they are key in a range of industrial foam mediated processes. However, they are also a fundamental physical model system to decipher subtle interfacial physics. An understanding of the fundamental physics governing bubbles starts by understanding their lifetime and stability in a base-state prior to studying the effect of contamination and additives. We show how for clean air bubbles at the interface a large class of Marangoni flow-inducing effects fundamentally change the thinning of bubble films and, in doing so, can dramatically enhance bubble lifetime, on average. The clean base-state is compared to the bubble physics in various states of contamination to elucidate how, for example additives or organisms  affect the underlying interfacial dynamics, and in turn, if and how such effects can shape the age of bubbles and their stability in addition to the dispersal of contaminants and/or organisms and compounds.

Gravitational wave results from NANOGrav

October 31, 2023

Ken Olum, Tufts University

Abstract: On June 29, 2023, the North American Nanohertz Observatory for
Gravitational waves (NANOGrav) announced strong evidence for a
gravitational wave background at very low frequencies.  This background
may come from supermassive black holes orbiting each other at the
centers of galaxies, or from a more exotic source, such as cosmic
strings.  I will present our results, how we achieved them, and what
they mean for the present and future of gravitational wave astronomy.

Physics and the Origins of Life

November 17, 2023

Robijn Bruinsma, UCLA

Abstract: The self-assembly of closed membranes and the self-replication of nucleic acids play a central role in current attempts to recreate the earliest living systems. The colloquium will discuss experiments that highlight aspects of the assembly, growth and division of proto-cells under laboratory conditions and the physical mechanisms that are involved. A focus of the colloquium will be on the question how proto-cells could capture free energy from the environment to power these processes.

The Black Hole Information Paradox: A Resolution on the Horizon?

October 3, 2023

Netta Engelhardt, MIT

Abstract: The black hole information paradox — whether information escapes an evaporating black hole or not —  remains one of the most longstanding mysteries of theoretical physics. The apparent conflict between validity of semiclassical gravity at low energies and unitarity of quantum mechanics has long been expected to find its resolution in a complete quantum theory of gravity. Recent developments in the holographic dictionary, and in particular its application to entanglement and complexity, however, have shown that a semiclassical analysis of gravitational physics can reproduce a hallmark feature of unitary evolution. I will describe this recent progress and discuss some promising indications of a full resolution of the information paradox.

Enabling New Discoveries: Designing and building new detectors for the High-Luminosity LHC

September 17, 2023

Gabriella Sciolla, Brandeis University

AbstractIn ten years of operation, the Large Hadron Collider (LHC) has made major strides in our understanding of Particle Physics: the Higgs boson was discovered and its properties have been measured. So far, all measurements point toward yet another confirmation of the Standard Model of Particle Physics. However, we know that New Physics beyond the Standard Model must exist. The High-Energy Physics community is gearing up to upgrade both the LHC accelerator and detectors to boost our sensitivity to New Physics in what is known as the High-Luminosity LHC (HL-LHC) program.

In this talk I will summarize what motivates this upgrade, how we are designing new detectors to meet the challenges presented by a high-luminosity collider, and what physics the HL-LHC will unlock.

Berko Symposium

September 5, 2023

Sagar Addepalli:  Searching for New Physics in the Higgs sector 

Abstract: Between 2015 and 2018, the ATLAS experiment at the LHC recorded proton-proton collision data at an unprecedented center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 139 fb-1. This large dataset allows us to study the Higgs boson’s properties with much higher precision than ever before, opening up the hunt for inconsistencies between the Standard Model predictions and measurements. In this talk, I will present our latest measurement of the cross section of Higgs bosons produced via vector boson fusion and reconstructed in final states containing two W bosons. Despite the distinct signature typical of this final state and the relatively high production rate, many other processes lead to the same final state, making it challenging to isolate the signal. We use cutting-edge machine learning-based methods to enhance the precision on our measurements while ensuring low model dependencies, which is imperative for robust interpretation of these results. The interpretation of this measurement in the framework of Effective Field Theories allows us to set constraints on anomalous couplings of the Higgs boson.

Saptorshi Ghosh: Optimal control of bulk active fluids

Abstract: Being intrinsically non-equilibrium, active materials have the ability to perform functions that would be thermodynamically forbidden in passive materials. However, active systems exhibit diverse local attractors that correspond to distinct dynamical states, many of which exhibit chaotic turbulent-like dynamics. Designing such a system to choose a specific dynamical state to perform a desired function is a formidable challenge. Motivated by recent advances enabling optogenetic control of experimental active materials, we use optimal control theory to identify spatiotemporal sequences of light-generated activity that direct the dynamics of active matter towards a predetermined steady-state. We put this framework to the test in two scenarios: a dry polar fluid that forms asters and propagating stripes, and a wet nematic fluid whose natural dynamics are chaotic and mediated by defect motion. The findings in these studies offer a roadmap, showcasing how optimal control methods can be harnessed to craft structure, dynamics, and function across a wide spectrum of active materials.