### Links to Colloquia

List of past colloquia videos (*Restricted: Only members of the Brandeis community can view this list and access the videos*)

Eisenbud Lecture Series in Mathematics and Physics

All colloquium videos are under copyright and may not be reproduced, in part or in total, without written permission of the speaker and of the Physics Department.

## Department Colloquia

**Martin Weiner Lecture Series
Department of Physics Colloquium
4 pm, Abelson 131
Refreshments at 3:30 pm outside Abelson 131**

**Fall 2018 Colloquia**

**Tuesday, September 4, 2018**

Marcelle Soares-Santos, Brandeis

**"Cosmology in the era of multi-messenger astronomy with gravitational waves"**

Abstract: Motivated by the exciting prospect of a new wealth of information arising from the first observations of gravitational and electromagnetic radiation from the same astrophysical phenomena, the Dark Energy Survey (DES) has established a search and discovery program for the optical transients associated with LIGO/Virgo events using the Dark Energy Camera (DECam). This talk presents the discovery of the optical transient associated with the neutron star merger GW170817 using DECam and discusses its implications for the emerging field of multi-messenger cosmology with gravitational waves and optical data.

**Tuesday, September 11, 2018
** No colloquium (Rosh Hashanah)

**Tuesday, September 18, 2018
** David Roberts, Brandeis

**"X-Shaped Radio Galaxies and the Low Frequency Gravitational Wave Background"**

Abstract: The collision and coalescence of supermassive black holes (SMBHs), such as those that lie at the heart of every galaxy, are expected to produce an enormous flux of gravitational waves (GWs) at very low frequencies (on the order of nanohertz, wavelengths of parsecs). The required pairs of SMBHs are presumably formed after the merger of two large galaxies to create a single larger galaxy initially containing two SMBHs. These each are expected to travel to the dynamical center of the resulting galaxy and eventually merge. The ensemble of such collisions should produce a GW background that is detectable using pulsar timing arrays (PTAs). However, current observational limits from the Australian PTA on the low frequency GW background lie below the levels expected based on theoretical considerations of the rate of such SMBH collisions. We have undertaken a project to study the fraction of large galaxies that harbor a pair of SMBHs using the structure of radio galaxies (RGs) as signposts. Out of a sample of over 1600 bright RGs Cheung selected 100 candidates that showed structures that suggested possible disruption of the central BHs. We have used the Jansky Very Large Array to make multi-frequency multi-array images of these "X-shaped radio galaxies" (XRGs) and created a well-studied sample of 87. Analysis of their structures suggests that most are created by backflow from the extended lobes. However, a small fraction (>=4%) show clear evidence for precession of the BH axis, presumably driven by interactions with a nearby second SMBH. We conclude that study of the structure of XRGs is useful in the search for binary SMBHs, and that such searches can help set limits on the expected low-frequency GW background.

**Tuesday, September 25, 2018
** No colloquium (Brandeis Monday)

**Tuesday, October 2, 2018**

Stefan Söldner-Rembold, University of Manchester

**"DUNE – an International Neutrino Observatory"
** Abstract: The Deep Underground Neutrino Experiment (DUNE) will be an international observatory for neutrino science, designed, constructed and operated by a global collaboration of scientists. Primary science drivers are the discovery of CP violation in the neutrino sector, the detection of neutrinos from supernovae, and the search for baryon number violation. DUNE will consist of two neutrino detectors placed in the world’s most intense neutrino beam. A near detector will record particle interactions near the source of the beam at Fermilab close to Chicago. A second, much larger, far detector operating with more than 40 kt of liquid-argon will be installed a mile underground in South Dakota. Several mid-size liquid-argon detectors at Fermilab and CERN are being constructed to demonstrate the potential of the cutting-edge liquid-argon technology employed for DUNE. I will introduce the technology and give an overview of the current status and future discovery potential of the DUNE programme.

**Tuesday, October 9, 2018**

Kerstin Perez, Massachusetts Institute of Technology

**"In Search of Cosmic-Ray Antinuclei from Dark Matter"
** Abstract: Cosmic-ray antiprotons have been a valuable tool for dark matter searches since the 1970s. Recent years have seen increased theoretical and experimental effort towards the first-ever detection of cosmic-ray antideuterons, in particular as an indirect signature of dark matter annihilation or decay in the Galactic halo. In contrast to other indirect detection signatures, which have been hampered by the large and uncertain background rates from conventional astrophysical processes, low-energy antideuterons provide an essentially background-free signature of dark matter, and low-energy antiprotons are a vital partner for this analysis. I will discuss the upcoming balloon-borne GAPS experiment, which exploits a novel detection technique utilizing exotic atom capture and decay to provide sensitivity to antiproton, antideuteron, and antihelium cosmic-ray signatures. In particular, I will detail the fabrication of the lithium-drifted Silicon detectors that are essential to its success.

**Tuesday, October 16, 2018**

(No colloquium this week)

**Tuesday, October 23, 2018**

Greg Landsberg, Brown University

**"New ideas in searches for new physics at the LHC"
** Abstract: With any evidence for new physics yet to be found at the LHC, there has been a significant shift in both the direction of searches for new physics and the methods used to purse them. With no clear peaking excesses and only mild hints for any deviations from the standard model in the LHC data, we are pursuing new avenues of searches by looking at the places missed both by the early LHC running and by previous machines. Many of these new searches required a significant development of new experimental and theoretical tools. Using mainly CMS as an example, I'll discuss these new directions in our quest for new physics and show a few recent results illustrating their power and novelty.

**Tuesday, October 30, 2018**

Ian Crossfield, Massachusetts Institute of Technology

**"Infrared Spectroscopy of Stars and Planets"
** Abstract: Extrasolar planets and cool stars emit most of their light beyond the range of standard optical observations. These objects are often best studied using infrared spectroscopy. I will present recent results from my group on two topics: space-based IR spectroscopy of exoplanet atmospheres, and ground-based, high-resolution spectroscopy of both planets and stars. I will also conclude with a brief discussing of how future IR-optimized observatories will also enable exciting new science in these areas.

**Tuesday, November 6, 2018
CANCELLED**

Prineha Narang, Harvard University

**"Excited-State Dynamics and Quantum Interactions from First Principles"**

Abstract: Exciting discoveries during the past few decades in quantum science and technology have brought us to this next step in the quantum revolution: the ability to fabricate, image and measure materials and their properties at the level of single atoms is almost within our grasp. Yet, at the most fundamental level a tractable quantum mechanical description and understanding of these materials does not exist. The physics of quantum materials is rich with spectacular excited-state and non-equilibrium effects, but many of these phenomena remain poorly understood and consequently technologically unexplored. Therefore, my research focuses on understanding how quantum-engineered materials behave, particularly away from equilibrium, and how we can harness these effects for technologies of the future. I will present my approach, from a theoretical and computational standpoint, in this seminar. Electron-photon, electron-electron as well as electron-phonon dynamics and far-from-equilibrium transport are critical to describe ultrafast and excited-state interactions in materials. Ab initio descriptions of phonons are essential to capture both excitation and loss (decoherence) mechanisms, and are challenging to incorporate directly in calculations due to a large mismatch in energy scales between electrons and phonons. I will show results using a new theoretical method we have developed to calculate arbitrary electron-phonon and electron-optical interactions in a Feynman diagram many-body framework integrated with a nonequilibrium carrier transport method. Further, I will discuss a new formalism at the intersection of cavity quantum-electrodynamics and electronic structure methods, quantum-electrodynamical density functional theory (QEDFT), to treat electrons and photons on the same quantized footing. I will demonstrate how these ab initio techniques can guide the search for relevant quantum properties in 2D and 3D materials, including new quantum emitters. In the second part of the seminar, I will show recent results using newly developed theoretical methods to evaluate the linear optical properties of low dimensional and heterostructured quantum materials. Further I will discuss how we extend these methods as a computational probe of hydrodynamic materials, for which electronic transport behaves according to the laws of hydrodynamics over conventional scattering descriptions. Finally, I will discuss the linear and nonlinear optical properties of these hydrodynamic and other similar Dirac and Weyl compounds to better understand the effect of linear dispersion on overall transport and optical properties.

**Tuesday, November 13, 2018 to Thursday, November 15, 2018
**

**Eisenbud Lecture Series in Mathematics and Physics**

Spencer Bloch, Yau Mathematical Sciences Center, Tsinghua University

Tuesday, November 13 (Lecture I), 4:00pm, Abelson 131

**"Multiple Zeta Values and Mixed Tate Motives over ℤ"**

Abstract: Basic ideas and results in the subject. Nilpotent completion of π1(ℙ1- {0, 1, ∞}, ⃗0 multiple zeta values, F. Brown's theorem on mixed Tate motives over ℤ.

Wednesday, November 14 (Lecture II), 4:00pm, Brown 316

**"Motivic Г-functions"**

Abstract: (Joint work with F. Brown and M. Vlasenko) Motivic Г functions are Mellin transforms of period functions. They interpolate Picard Fuchs recurrences, and, in interesting cases, their Taylor series expansions are generating series for monodromy variations.

Thursday, November 15 (Lecture III), 4:00pm, Goldsmith 317

**"Relative completions"**

Abstract: (Joint with Brown and Vlasenko) The theory of relative completions (Hain) generalizes nilpotent completion. It is the right setting to study the iterated integrals arising in Lecture II.

**Tuesday, November 20, 2018**

No colloquium (Thanksgiving week)

**Tuesday, November 27, 2018
** John Wilmes, Brandeis University

**"Neural Networks and Statistical Query Algorithms"**

Abstract: In joint work with Santosh Vempala, we study the complexity of training neural network models with one hidden nonlinear activation layer and an output weighted sum layer. We obtain essentially matching upper and lower bounds. We begin with the observation that the concepts computed by simple neural networks are well-approximated by low-degree polynomials when inputs are drawn uniformly from the sphere, so regression problems for data labelled by an unknown neural network can be captured by agnostic polynomial learning. We give an agnostic learning guarantee for training neural networks via gradient descent, establishing convergence within error ϵ of the optimum when the number of gates, samples, and iterations are all bounded by n

^{O(k)}log(1/ε) for concepts approximated by degree-k polynomials. On the other hand, any statistical query algorithm (including gradient descent in its many variations) requires n

^{Ω(k)} queries for the same problem.

**Tuesday, December 4, 2018
CANCELLED
** Mark Van Raamsdonk, University of British Columbia

**"Gravity and Entanglement"**

Abstract: The AdS/CFT correspondence provides a quantum theory of gravity in which spacetime and gravitational physics emerge from an ordinary non-gravitational quantum system with many degrees of freedom. In this talk, I will explain how quantum entanglement between these degrees of freedom is crucial for the emergence of a classical spacetime, and describe progress in understanding how spacetime dynamics (gravitation) arises from the physics of quantum entanglement.

**Tuesday, December 11, 2018**

Gabriel Redner

**"Building Blocks of the Internet"
**Biography: Since completing his PhD in Physics at Brandeis in 2015, Gabriel has worked as a Software Engineer at Google, focusing on networking infrastructure and security.

Abstract: The internet is many contradictory things: complex yet fundamentally simple, indispensable yet dangerous, easy to use but hard to understand. Or is it? In this talk, I'll work to demystify what happens under the hood of the global internet, and show how just as in physics, complex behaviors rest on simple foundations. I'll also discuss how my career has taken me from physics to software engineering and back again, and then back again.

**Spring 2019 Colloquia**

**Tuesday, January 15, 2019
** TBA

**Tuesday, January 22, 2019**

No colloquium (Brandeis Monday)

**Tuesday, January 29, 2019
** Robin Wordsworth, Harvard University

Title and abstract: TBA

**Tuesday, February 5, 2019**

TBA

**Tuesday, February 12, 2019**

Gabriela González, Louisiana State University

Title and abstract: TBA

**Tuesday, February 19, 2019
** No colloquium (Midterm Recess)

**Tuesday, February 26, 2019**

TBA

**Tuesday, April 23, 2019**

No colloquium (Passover and Spring Recess)