Simran Kaur Nerval
(she/her), MSc

Constraining the primordial and matter power spectrum

Measurements of the microwave sky provide a window into the earliest moments of the cosmos. Using data from ACT, which operated from 2007 to 2022, we offered the tightest constraints on the CMB to date. I determined constraints on the primordial power spectrum using new data from the ACT Data Release 6 (DR6), as well as Planck legacy data, baryon acoustic oscillation data from DESI Year-1, and CMB lensing data from both ACT and Planck. While the concordance cosmology Lambda Cold Dark Matter (\( \Lambda \mathrm{CDM} \)) model is a good fit to our data, the ACT data allow us to study models beyond this standard picture. In order to explore a broader range of deviations from the simple power-law primordial adiabatic power spectrum than those captured solely by constraining the running of the scalar spectral index, we consider a more model-independent approach. We reconstruct the primordial power spectrum of curvature scalar perturbations for 30 \(k\) bins from \(k = 10^{-4} - 0.43 ~\mathrm{Mpc^{-1}}\), and constrain the amplitude per bin. Given the degeneracy between the primordial power and the optical depth (often described in terms of the \({A_s-\tau}\) degeneracy), we sample the value of \(e^{-2\tau}P_{\mathcal{R}}(k_{i})\) for each \(i^{\rm th}\) bin. We find that the constraints from our combined analysis with all listed data sets are improved over the Planck-alone measurements wherever ACT data are included (for \(\ell \gtrsim 850\)). I mapped this measurement onto the linear matter power spectrum and compared with other measurements from the Dark Energy Survey (DES), the Sloan Digital Sky Survey (SDSS), the extended Baryon Oscillation Spectroscopic Survey (eBOSS), and the Hubble Space Telescope (HST) measurements of the UV galaxy luminosity function (UV LF). These results can be seen in the ACT DR6 extended models paper here!

SGWB from low-scale inflation

My MSc research focused on determining the SGWBs from both inhomogeneities in the inflaton field which drove inflation and from self-interaction of the inflaton after inflation. I focused on E- and T-model inflation because they are used as generic inflation models. For different parameter values, E- and T-model inflation are identical to a range of inflationary models which match present CMB observations, including Starobinsky and Higgs inflation. The dynamics of these low-scale inflaton fluctuations are complicated, and need to be studied computationally. I used the lattice simulation code HLattice to determine the SGWBs from these E- and T-models. Notably, all these SGWB spectra peak in the MHz - GHz range. Current and upcoming experiments such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Laser Interferometer Space Antenna (LISA) will not be sensitive here, motivating the development of sensitivity in this regime. Two examples of prospective gravitational wave probes in this regime include, laboratory gravitational wave detectors at GHz frequencies or using the cosmological impact of MHz-GHz gravitational waves, which can contribute to the number of relativistic degrees of freedom in the early universe. This work can be seen both in this paper and my MSc thesis!

Coding the Cosmos

Logo Credit: Eesha Das Gupta/@stelllararts

Image Credit: Margaret Ikape and Mark Dodici

I founded and served as the principal investigator (PI) for Coding the Cosmos, receiving a $36,000 grant from the Dunlap Institute to run coding and astronomy camps for marginalized and low socio-economic high school students. Unlike most STEM camps which can cost a significant amount of money to attend, we used our funding to cover all costs for students attending including their transit to and from the workshop, lunches, snacks, and provided computers for the students to use during the camp. Our camps had the goals to provide an educational experience to the students through hands-on but no-experience-required approach to cutting-edge astrophysics to both enhance their interest in astrophysics and increase their confidence. Generally, STEM is thought to be, and discussed as being, very difficult which can discourage students from pursuing it. By completing these camps and the mini research projects we aim to help the students realize that they can complete tasks they originally thought may be too difficult even if they decide to go into a non-STEM career. You can access the materials from our 2023 camp here and 2024 camps here.

AstroTours

Image Credit: Dang Pham

Image Credit: Nolan Koblischke

I was the co-director for AstroTours from 2021 to 2023 which is a monthly outreach event run by the graduate students in the Astronomy & Astrophysics department at the University of Toronto. Our events are free and open to the public which cultivates a consistent (typically 100+ attendees per talk) but varied audience of students, professionals, enthusiasts, families, and even occasionally school groups. We design our activities and talks to be appealing and approachable for a variety of demographics. Not only do we aim to run accessible outreach events for the public, but also to increase the science communication skills of undergraduate and graduate students. We train the volunteers on how to use the telescopes, how to run the science demos, and have the monthly speaker give a practice talk to get feedback from our executives. Additionally, during my time as co-director, we introduced lab tours of the different astronomy instrumentation labs. Attendee feedback indicates that they really enjoy having the opportunity to see how research is conducted. I also gave two of the AstroTours talks, in both November 2022 and February 2025.

Let's Talk Science

Let's Talk Science is a national Canada-wide outreach organization which runs both large events and classroom visits to schools across the country with the goal to improve science literacy and building youth interest in STEM. I was a part of Let's Talk Science from 2019 to 2021 as first a volunteer then coordinator for the Queen's University branch. As a volunteer I ran classroom visits at elementary schools involving leading demonstrations, giving quick lectures on the science behind the activities, and supporting students in conducting their own experiments. For example, I ran sessions on circuits, bottle rockets, egg drop, etc. As a coordinator I managed volunteers and connected them with outreach opportunities, organized virtual outreach for K-12 classes and developed new kits for topics such as physics, astronomy, and computer science.

IDEAS Initiative

Logo Credit: Jasmine Corning

The Innovation, Diversity, Exploration, & Advancement in STEM (IDEAS) Initiative is an organization that promotes diversity in physics by supporting under-represented youth, in particular gender minorities, across Canada. During Covid-19, we pivoted our programming to be fully online. Some notable events included an online Canada-wide science fair for middle school students and a weekly YouTube live Q&A series that I organized and ran highlighting top female scientists in a broad variety of STEM disciplines called STEM Stories.

In both my Let's Talk Science and IDEAS Initiative roles, I organized a virtual Canada-wide national symposium called Let's Talk Astrophysics where we taught high school and CÉGEP students the basics of python using a Jupyter Notebook and go through making a galactic rotation curve. You can access these materials here.

Mentorship

In my role as mentorship coordinator for Gender Minorities in Physics (GEMINI-P) at Queen's University I ran a pilot mentorship program for upper year undergraduates at Queen's University that matched students and mentors based on their research interests and intersecting identities. I sourced mentors from around the world, in order to have mentors in the specific fields and identities with the mentee pool. I've also personally mentored multiple students and co-supervised three undergrad research projects.

National Advocacy

I have served on three committees within the Canadian Astronomical Society (CASCA), contributing to outreach, graduate student support, and equity. I co-designed an ethics-approved national demographics and harassment survey to assess and improve the culture of Canadian astronomy.