Hello! I'm Jamie, a third-year Ph.D. student at the Unversity of Minnesota's Minnesota Institute for Astrophysics. I'm originally from Nashville, Tennessee, and graduated with a Bachelor of Science degree in Physics and Astronomy (plus a minor in Computer Science) from the University of Illinois at Urbana-Champaign in 2017.

### Research

I study the cosmic microwave background (CMB): the 13.8 billion year-old afterglow of the Big Bang, from when the primordial hot, dense plasma cooled off enough for light to stream through the Universe. Though at first glance it appears remarkably uniform, if we look a bit more closely to examine the tiny fluctuations in its temperature across the sky, we can obtain a wealth of information about the primordial Universe. The name of the game now, however, is measuring the fluctuations not just in the CMB's temperature, but in the polarization of its light. A particular curl-only "B-mode" pattern in its polarization would signal the presence of primordial gravitational waves in the very early unverse, arising from a process called cosmic inflation. Positing that the Universe underwent a period of extremely rapid expansion in its earliest moments, the inflationary paradigm neatly solves a number of critical issues with the current $$\Lambda$$CDM "standard model" of cosmology. Balooning microscopic quantum fluctuations to cosmic size, inflation would have seeded the large scale structure of our Universe. A detection of B-modes in the CMB would not only provide the smoking gun to confirm inflation, but allow us to place crucial constraints on the variety of theoretical models describing it.

If they're there to be found, primordial B-modes have proven to at least be extremely faint, requiring targeted experiments with extensive control of systematic errors to push the limits further. What's more, dust grains in our own Milky Way aligned along turbulent galactic magnetic fields may generate B-mode polarization at the relevant frequencies and angular scales, as may synchrotron radiation from fast-moving electrons within our galaxy. The presence of polarized foreground emission necessitates observations at multiple frequencies in order to separate their contributions from that of the component of interest (the CMB). Not only that, but part of the dominant curl-free E-mode polarization in the CMB will be distorted into B-mode polarization due to gravitational lensing by intervening large-scale structure between the observer (us) and the last-scattering surface of the CMB. This contribution must be carefully accounted for, a process known as "delensing".

I currently work with Professor Clem Pryke on instrumentation and analysis for the BICEP/Keck Array collaboration, to search for these B-modes in the CMB and constrain theories of cosmic inflation. BICEP3 and the Keck Array are cutting-edge CMB polarimeters located at the geographic South Pole. They utilize small-aperture, all-cold refractive optics coupled to superconducting Transition Edge Sensor (TES) bolometers through polarized slot dipole antenna arrays to achieve extreme systematic error control and sensitivity, while retaining modularity and upgradability. The BICEP/Keck program has set the strongest constraints to date on the amplitude of primordial gravitational waves, $$\mathcal{r}_{0.05} < 0.06$$ at 95% confidence, in conjuction with Planck and WMAP data (The Keck Array and BICEP2 Collaborations, Phys. Rev. Lett. 121, 221301, 2018). I'm also working on BICEP Array, a brand-new instrument which will replace the Keck Array in the 2019-2020 austral summer. BICEP Array will ultimately represent an order of magnitude increase in detector count relative to its predecessor, the Keck Array, and will continue to expand the BICEP program's frequency coverage to higher and lower frequencies to characterize polarized dust and synchrotron foregrounds, respectively. In addition, we are cross-collaborating with the South Pole Telescope (SPT) collaboration to delens using the high-resolution polarized maps from SPTpol and from its new camera, SPT-3G, and with the S-band Polarized All-Sky Survey (S-PASS) collaboration to better study the characteristics of galactic synchrotron foregrounds.

I have previously worked on the South Pole Telescope's SPT-3G instrument, focusing on sub-millimeter multichroic anti-reflection coatings and readout electronics.

### Teaching

I am not currently teaching any courses. Information for Astronomy 1001: Exploring the Universe may be found on Canvas.

### Contact Me

Email: cheshire@umn.edu
Office: 320 Physics and Nanotechnology Building, 115 Union St SE, Minneapolis, MN 55455
Lab: 382C PAN
Phone (Lab): 612-625-1802