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Simran Nerval

Updated: Jul 9, 2025

University of Toronto

Simran recently completed her MSc at Queen’s University and is now a Ph.D. student at the University of Toronto. She believes it is very important to increase the visibility of minoritized groups, increase diversity, and help make academia a more welcoming and accepting place. Alongside her research, she is also very engaged with public outreach. She is the Director of External Affairs for the IDEAS (Innovation, Diversity, Exploration & Advancement in STEM) Initiative and the Education and Public Outreach graduate student representative for CASCA, where she works to promote enthusiasm for science in youth and advocate for diversity.


By linking cosmological observations to theory, her research seeks signals from the earliest moments in our universe. While Big Bang cosmology successfully explains much of the history of our Universe, there are certain features it does not explain, for example, the spatial flatness and uniformity of our Universe. One widely studied explanation for these features is cosmological inflation. The objective of her MSc thesis was to simulate the gravitational wave spectra generated by inflaton field configurations oscillating after inflation for E-Model, T-Model, and General Renormalizable Inflection Point Inflation (GRIPI) using lattice simulations. Her thesis showed that these gravitational wave spectra provide access to some inflation models beyond the reach of any planned CosmicMicrowave Background (CMB) experiments, such as LiteBIRD, Simons Observatory, and CMB-S4. Specifically, while these experiments will be able to resolve the primordial power spectrum tensor-to-scalar ratio (r) down to10−3, she showed that stochastic gravitational-wave background (SGWB) measurements have the potential to probe certain inflation models for values down to10−14.


Figure 1 shows stochastic gravitational wave spectra from inflation and sensitivity curves for upcoming and current gravitational wave experiments. The E-Model SGWB spectra sourced by oscillating inflatons are givenforr= 10−4,10−6,10−8,10−10as shown. The T-Models are given forr= 10−4,10−6,10−8,10−10,10−12,10−14as indicated. Also, GRIPI is plotted forr= 1.152×10−3. Sensitivity curves are also shown, both for direct gravitational wave observatories such as BBO, LISA, LIGO, and aLIGO, as well as indirect cosmological probes. Dashed-dotted projected sensitivity curves include the contribution of astrophysical foregrounds while dotted curves do not include astrophysical foregrounds. Solid curves represent bounds on SGWB. The sensitivity curves forBBO, LISA, and aLIGO were taken from [1] and take into account the number of detectors, mission observation time, and the overlap reduction function of each detector pair. The BBO and LISA curves additionally take into account astrophysical foregrounds. The LIGO sensitivity curve for the first observing run (O1), the first and second observing run (O1+O2), and the design sensitivity is taken from the data supplement to [2]. A bound on SGWB contributions to relativistic degrees of freedom, derived from a fit to CMB power, baryon acoustic oscillations, lensing, and primordial nuclear abundances and prospects for an improvement of this cosmologicalSGWB bound, using projected constraints from the COrE and EUCLID satellites is taken from [3]. Importantly, all the inflationary gravitational wave spectra lie in the MHz-GHz frequency range, motivating the development of gravitational wave detectors in this range.
Figure 1 shows stochastic gravitational wave spectra from inflation and sensitivity curves for upcoming and current gravitational wave experiments. The E-Model SGWB spectra sourced by oscillating inflatons are givenforr= 10−4,10−6,10−8,10−10as shown. The T-Models are given forr= 10−4,10−6,10−8,10−10,10−12,10−14as indicated. Also, GRIPI is plotted forr= 1.152×10−3. Sensitivity curves are also shown, both for direct gravitational wave observatories such as BBO, LISA, LIGO, and aLIGO, as well as indirect cosmological probes. Dashed-dotted projected sensitivity curves include the contribution of astrophysical foregrounds while dotted curves do not include astrophysical foregrounds. Solid curves represent bounds on SGWB. The sensitivity curves forBBO, LISA, and aLIGO were taken from [1] and take into account the number of detectors, mission observation time, and the overlap reduction function of each detector pair. The BBO and LISA curves additionally take into account astrophysical foregrounds. The LIGO sensitivity curve for the first observing run (O1), the first and second observing run (O1+O2), and the design sensitivity is taken from the data supplement to [2]. A bound on SGWB contributions to relativistic degrees of freedom, derived from a fit to CMB power, baryon acoustic oscillations, lensing, and primordial nuclear abundances and prospects for an improvement of this cosmologicalSGWB bound, using projected constraints from the COrE and EUCLID satellites is taken from [3]. Importantly, all the inflationary gravitational wave spectra lie in the MHz-GHz frequency range, motivating the development of gravitational wave detectors in this range.

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