# Institute for Fundamental Science Seminars

Seminars, Colloquia and Workshops

Organizer: Tim Cohen

Unless otherwise noted, seminars are at 4pm in 472 Willamette.

Refreshments at 3:45.

# Winter Term 2020

## Monday, January 13    IFS seminar

Title: Searching for Dark Matter Interactions in Cosmology

Speaker: Kimberly Boddy (Johns Hopkins University/UT-Austin)

Abstract: There is a substantial effort in the physics community to search for dark matter interactions with the Standard Model of particle physics. Collisions between dark matter particles and baryons exchange heat and momentum in the early Universe, enabling a search for dark matter interactions using cosmological observations in a parameter space that is complementary to that of direct detection. In this talk, I will describe the effects of scattering in cosmology and show constraints using Planck 2015 data and SDSS-identified satellite galaxies of the Milky Way. I will also discuss the implications of late-time scattering during the era of Cosmic Dawn.

Host: Tien-Tien Yu

## Monday, January 20 IFS seminar

Title: No Seminar (MLK holiday)

## Monday, January 27 IFS seminar

Title: New ideas in light dark matter direct detection

Speaker: Zhengkang Zhang (UC Berkeley & Caltech)

Abstract: Direct detection experiments have traditionally focused on dark matter mass near the weak scale. Below a GeV, conventional detection techniques based on nuclear recoils lose sensitivity as the energy deposition falls below detector thresholds. I will discuss the motivation for several recently proposed novel detection channels and the theoretical tools for detection rate calculations from first principles. I will highlight the role of collective excitations in condensed matter systems, such as phonons and magnons, in probing unexplored parameter space of well-motivated theories.

Host: Spencer Chang

## Wednesday, February 5 IFS seminar

Title: Deep CMB: Disentangling signals in the Cosmic Microwave Background using Artificial Intelligence

Speaker: Brian Nord (Fermilab/UChicago)

Abstract: The Cosmic Microwave Background (CMB), the earliest light of the universe that we can see, is a critical probe of cosmic physics — e.g., the shape of the universe, its particle content, and even the evolution of large-scale structure. A period of rapid cosmic growth, Inflation, is theorized to have preceded the origin point of the CMB. A key signature of inflation is a pattern imprinted on the CMB by primordial gravitational waves. This pattern very closely resembles others in the CMB, such as that left by weak gravitational lensing. Disentangling these patterns is a critical-path challenge for current and next-generation physics experiments, like the South Pole Telescope and Stage-IV CMB surveys. Current conventional modeling techniques require physics-based parameterizations of noise and signal; as such, they face challenges in distinguishing between signatures at low signal-to-noise. Deep learning comprises a subset of artificial intelligence (AI) algorithms — modeling techniques that learn important distinguishing features from the data itself and are not limited to pre-defined physical parameters. Our recent work has shown that deep learning can provide additional insight for disentangling patterns in the CMB. This talk will describe our latest progress in the development of these models, the outlook for future developments, and considerations for applications of deep learning for other physics problems.

Host: Tien-Tien Yu

## Monday, February 10 IFS seminar

Title: A CMB Millikan experiment with axion strings

Speaker: Prateek Agrawal (Harvard)

Abstract: Very light axions are a generic prediction of string compactifications. If cosmic strings associated with these axions were produced in the early universe, they quickly approach a so-called scaling solution, such that strings persist in the sky today.  I will present some remarkable signals of such strings coupled to photons. In this string background, there is a model-independent polarization rotation of CMB photons equal to $\alpha_{em}$ up to a rational number. This manifests itself as a rotation of E-modes in the CMB polarization to B-modes. The current CMB experimental sensitivity to this rotation is about 1%, with many orders of magnitude improvement expected for future experiments. I will show how measuring the undetermined rational number may shed light on the quantization of electric charge in the standard model. These strings may also be visible in strongly lensed quasar systems.

Host: Tien-Tien Yu

## Monday, February 17 IFS seminar

Title: Observation and measurement of the electroweak W±W± j j process in pp collisions with the ATLAS detector at LHC

Speaker: Giulia Gonella (UO)

Abstract: Measurements of the electroweak sector of the Standard Model are a way to probe the mechanism of electroweak symmetry breaking at the Large Hadron Collider, and to detect small deviations from the Standard Model predictions, through which the effect of new physics could manifest itself. In this context the scattering of vector bosons is a key process. In particular the production of W boson pairs is a vital test of the mechanism, since its scattering amplitude would increase at high energies violating unitarity, without cancellations of divergences due to exchanges involving Z or Higgs bosons. The electroweak production of two W bosons with the same electric charge in the signature of two leptons, missing transverse energy and two jets was observed for the first time with the ATLAS experiment using data recorded in proton-proton collisions at √ s = 13 TeV with an integrated luminosity of 36.1 fb−1 . Among the challenges, the background due to the contributions from opposite-charge di-lepton production processes where the charge of one electron is wrongly reconstructed plays a major role. This talk will present the analysis flow with a focus on the estimation of the electron charge misidentification background, to offer an overview of the techniques that led to the first ATLAS observation of the process and the measurement of its cross-section in a fiducial region.

Host: David Strom

## Monday, February 24 IFS seminar

Title: Probing Axions with Event Horizon Telescope Polarimetric Measurements

Speaker: Yue Zhao (Utah)

Abstract: With high spatial resolution, polarimetric imaging of a supermassive black hole, like M87* or Sgr A*, by the Event Horizon Telescope can be used to probe the existence of ultralight bosonic particles, such as axions. Such particles can accumulate around a rotating black hole through superradiance mechanism, forming an axion cloud. When linearly polarized photons are emitted from accretion disk near the horizon, their position angles oscillate due to the birefringent effect when traveling through the axion background. This is a new way to probe the existence of axion and complimentary to black hole spin measurements.

Host: Tien-Tien Yu

## Tuesday, February 25 IFS seminar

Title: Searching for Dark Photon Dark Matter with Gravitational Wave Detectors

Speaker: Yue Zhao (Utah)

Abstract: If dark matter stems from the background of a very light gauge boson, this gauge boson could exert forces on test masses in gravitational wave detectors, resulting in displacements with a characteristic frequency set by the gauge boson mass. We outline a novel search strategy for such dark matter, assuming the dark photon is the gauge boson of U(1)_B or U(1)_{B-L}. We show that both ground-based and future space-based gravitational wave detectors have the capability to make a 5-sigma discovery in unexplored parameter regimes. We perform a direct dark matter search using data from LIGO’s first (O1) data run, as opposed to an indirect search for dark matter via its production of gravitational waves. Our result has already beat other constraints and starts to probe unexplored parameter space. Substantially improved search sensitivity is expected during the coming years of continued data taking by LIGO and other gravitational wave detectors in a growing global network.

Host: Tien-Tien Yu

## Monday, March 2 IFS seminar

Title: Blowing in the Dark Matter Wind

Speaker: Markus Luty (UC Davis)

Abstract: This talk will discuss models of dark matter where dark matter cannot penetrate ordinary matter due to a dark matter Meisner effect. In such models, the dark matter wind exerts forces on ordinary matter. These forces are very small, but high precision force experiments may be able to measure them.

Host: Spencer Chang

## Monday, March 9 IFS seminar

Title: TBA

Speaker: Yang Bai (University of Wisconsin)

Abstract: TBA

Host: Graham Kribs

## Thursday, March 19 IFS seminar

Title: TBA

Speaker: Yoni Kahn (University of Illinois Urbana Champaign)

Abstract: TBA

Host: Tim Cohen

# Spring Term 2020

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## Monday, April 6 IFS seminar

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Speaker: Jeff Hazboun (UW-Bothell)

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Host: Ben Farr

## Monday, April 13 IFS seminar

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Speaker: Anna-Maria Taki (UO)

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Host: Tim Cohen

## Monday, April 20 IFS seminar

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Speaker: Patrick Fox (Fermilab)

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Host: Tien-Tien Yu

## Monday, April 27 IFS seminar

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Speaker: Aditya Pathak (University of Vienna)

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Host: Tim Cohen

## Monday, May 4 IFS seminar

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Speaker: Matt Reece (Harvard University)

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Host: Graham Kribs

## Monday, May 11 IFS seminar

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Speaker: Ethan Neil (University of Colorado)

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Host: Graham Kribs

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