Martin A. Fisher School of Physics

April 9, 2024

Eisenbud Seminar: Jonathan Heckman, University of Pennsylvania

Abstract: Quantum field theory (QFT) is the universal language used by physicists to describe a wide variety of phenomena in Nature. Quite remarkably, this framework has also found many applications within pure mathematics. But what is quantum field theory and how is it characterized? In this talk, I highlight recent progress made in understanding QFT using the geometry of extra dimensions predicted by string theory. This includes the discovery of entirely new kinds of QFTs in a wide range of spacetime dimensions, leading to a remarkable interplay between physics and geometry. 

Lunch reception at 12:30 in Abelson 333

March 26, 2024

Quentin Changeat, STScl

Abstract: The James Webb Space Telescope (JWST), launched in 2022, has already revolutionized the field of exoplanetary atmospheres by providing a much higher sensitivity and access to new wavelength ranges compared to previous observatories. For instance, the first studies of exo-atmospheres using JWST data have unveiled previously unseen molecular species in exoplanet atmosphere, provided precise measurements of atmospheric thermal structures, and shed light on cloud and haze properties for the first time. Simultaneously, the European Space Agency (ESA) is preparing Ariel, a dedicated facility that will study the atmospheres of approximately 1000 exoplanets. This mission will enable the first detailed population studies of exo-atmospheres to understand the nature and formation of these worlds.

Such a revolution in our observing capabilities creates both opportunities and challenges for the field of exoplanet atmospheres. In this seminar, I will present recent observational campaigns and simulation efforts highlighting the pivotal role of JWST and Ariel for our field, and comparing with past generation observatories such as the Hubble Space Telescope. The presentation will focus on the description of modern interpretation techniques and outline the role of exoplanet atmospheres in addressing fundamental questions of planetary science.

March 12, 2024

Arup Chakraborty, MIT

Abstract: Infectious disease-causing pathogens have plagued humanity since antiquity, and the COVID-19 pandemic has been a vivid reminder of this perpetual existential threat. Vaccination has saved millions of lives, and effective vaccines have helped control the COVID-19 pandemic. However, we do not have effective vaccines against rapidly mutating viruses, such as HIV; nor do we have a universal vaccine against seasonal variants of influenza or new variants of SARS-CoV-2. I will describe how by bringing together approaches from statistical physics, virology and immunology, progress is being made to address this challenge. I will focus on the antibody arm of this challenge. Antibodies are produced by a far from equilibrium stochastic dynamic evolutionary process. I will describe statistical physics-based models of antibody evolution and complementary data from animals and humans that shed light on how this process might be modulated to produce desired antibody responses.

February 27, 2024

Sumantra Sarkar, IISc Bangalore

Abstract: The plasma membrane of a cell gives the cell its shape, protects it from intruders, and acts as a communication hub. The diversity of the membrane's functions reflects the diversity of patterns and structures found on the membrane. Therefore, understanding the origin and the dynamics of membrane patterns has been of recent interest. Specifically, we have come to appreciate biological activity's key role in creating and maintaining these patterns. In this talk, I shall provide an overview of the field and describe some of the ongoing projects in my group on active pattern formation. Specifically, I'll show (a) how arrested coarsening of topological defects on active surfaces can help us understand the formation of signaling platforms on the cell membrane and (b) how the same defects can make molecular transport robust against thermal fluctuations.

January 30, 2024

Bernd Surrow, Temple University

Abstract: Understanding the properties of nuclear matter and its emergence through the underlying partonic structure and dynamics of quarks and gluons requires a new experimental facility in hadronic physics known as the Electron-Ion Collider (EIC). A US-based facility capable of colliding high-energy polarized electron and ion beams at high luminosity has been envisaged for a long time and articulated as the highest priority for new construction. The EIC will address some of the most profound questions concerning the emergence of nuclear properties by precisely imaging gluons and quarks inside protons and nuclei, such as the distribution of gluons and quarks in space and momentum, their role in building the nucleon spin and the properties of gluons in nuclei at high energies. The EIC facility will be realized at Brookhaven National Laboratory, profiting from the existing Relativistic Heavy-Ion Collider (RHIC) facility, allowing to collide both polarized proton beams and heavy ion beams for more than two decades. High energy polarized p+p collisions at √ s = 200−500 GeV at RHIC provide a unique way to probe the proton spin structure and dynamics using well-established scattering processes. The production of jets and hadrons is the prime focus of gluon polarization studies. The production of W−(+) bosons at √ s = 500 GeV provides an ideal tool to study the spin-flavor structure of
the proton.

After a summary of final results concerning the spin structure and dynamics of quarks and gluons obtained by the STAR experiment at RHIC, the status and perspectives of a US-based ElC facility will be presented in this colloquium, including highlights of the planned physics program, the current detector design of a new EIC experiment, and anticipated next steps.

January 16, 2024

Aparna Baskaran, Brandeis

Abstract:  In this talk I will do three things : i) give a philosophical overview of active matter research, ii) present a pedagogical discussion active nematohydrodynamics and iii) briefly show some ongoing research efforts to use data driven approaches to leverage theory for prediction and design of active flows. 

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.

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.

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.

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.

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.

September 17, 2023

Gabriella Sciolla, Brandeis University

Abstract: In 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.

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.