About

Nancy Aggarwal is an Assistant Professor in the Department of Physics at the University of California, Davis. Her research interests focus on precision measurements for fundamental physics, utilizing techniques from Quantum Optics, atomic physics, and condensed matter physics. She investigates the search for new physics phenomena, including dark matter candidates and gravitational waves originating from astrophysical, cosmological, and exotic sources. Professor Aggarwal is a member of several collaborative efforts, including the Laser Interferometer Gravitational Wave Observatory (LIGO), the Levitated Sensor Detector (LSD), and the Axion Resonant Interaction Detection Experiment (ARIADNE). She is also involved in a global initiative to develop detectors for Ultra High Frequency gravitational waves, contributing to advancements in the detection and understanding of gravitational phenomena.

Research topics

• Astronomy
• Physics
• Computer Science
• Astrophysics
• Telecommunications
• Operating system

Selected publications

• Challenges and opportunities of gravitational-wave searches above 10 kHz

  Living Reviews in Relativity · 2025-11-03 · 16 citations

  preprintOpen access1st authorCorresponding

  Abstract The first direct measurement of gravitational waves by the LIGO and Virgo collaborations has opened up new avenues to explore our Universe. This White Paper outlines the challenges and gains expected in gravitational-wave searches at frequencies above the LIGO/Virgo band. The scarcity of possible astrophysical sources in most of this frequency range provides a unique opportunity to discover physics beyond the Standard Model operating both in the early and late Universe, and we highlight some of the most promising of these sources. We review several detector concepts that have been proposed to take up this challenge, and compare their expected sensitivity with the signal strength predicted in various models. This report is the summary of a series of workshops on the topic of high-frequency gravitational wave detection, held in 2019 (ICTP, Trieste, Italy), 2021 (online) and 2023 (CERN, Geneva, Switzerland).

  PublisherDOI

• Simulating the Galactic population of axion clouds around stellar-origin black holes: Gravitational wave signals in the 10–100 kHz band

  Physical review. D/Physical review. D. · 2024-12-18 · 3 citations

  article

  Ultralight scalar fields can experience runaway ``superradiant'' amplification near spinning black holes, resulting in a macroscopic ``axion cloud,'' which slowly dissipates via continuous monochromatic gravitational waves. For a particular range of boson masses, $\mathcal{O}({10}^{\ensuremath{-}11}--{10}^{\ensuremath{-}10})\text{ }\text{ }\mathrm{eV}$, an axion cloud will radiate in the 10--100 kHz band of the levitated sensor detector (LSD). Using fiducial models of the mass, spin, and age distributions of stellar-origin black holes, we simulate the present-day Milky Way population of these hypothetical objects. As a first step toward assessing the LSD's sensitivity to the resultant ensemble of gravitational wave signals, we compute the corresponding signal-to-noise ratios which build up over a nominal integration time of ${10}^{7}\text{ }\text{ }\mathrm{s}$, assuming the projected sensitivity of the 1 m LSD prototype currently under construction, as well as for future 10 m and 100 m concepts. For a 100 m cryogenic instrument, hundreds of resolvable signals could be expected if the boson mass $\ensuremath{\mu}$ is around $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\text{ }\text{ }\mathrm{eV}$, and this number diminishes with increasing $\ensuremath{\mu}$ up to $\ensuremath{\approx}5.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\text{ }\text{ }\mathrm{eV}$. The much larger population of unresolved sources will produce a confusion foreground which could be detectable by a 10-m instrument if $\ensuremath{\mu}\ensuremath{\in}(3--4.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\text{ }\text{ }\mathrm{eV}$ or by a 100-m instrument if $\ensuremath{\mu}\ensuremath{\in}(3--6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\text{ }\text{ }\mathrm{eV}$.

  PublisherDOI

• GWTC-2.1: Deep extended catalog of compact binary coalescences observed by LIGO and Virgo during the first half of the third observing run

  Physical review. D/Physical review. D. · 2024-01-05 · 440 citations

  articleOpen access

  GWTC-2.1 is a catalog of gravitational wave events from compact binary coalescences from the first half of the third observing run of Advanced LIGO and Advanced Virgo. It improves on GWTC-2, which covered the same period but with less refined analysis methods. GWTC-2.1 identifies 8 new events, all identified as sourced by binary black holes with one exception identified as a neutron star-black hole coalescence. These events expand significantly on the parameters characterizing the sources of observed gravitational-wave transients.

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• Method to search for inspiraling planetary-mass ultracompact binaries using the generalized frequency-Hough transform in LIGO O3a data

  Physical review. D/Physical review. D. · 2024-10-10 · 3 citations

  articleOpen access

  Gravitational waves from subsolar mass primordial black holes could be detected in LIGO, Virgo, and KAGRA data. Here, we apply a method originally designed to look for rapidly spinning-down neutron stars, the generalized frequency-Hough transform, to search for planetary-mass primordial black holes using data from the first half of the third observing run of advanced LIGO. In this companion paper to Miller et al. [Phys. Rev. Lett. 133, 111401 (2024)], in which the main results of our search are presented, we delve into the details of the search methodology, the choices we have made regarding the parameter space to explore, the follow-up procedure we use to confirm or reject possible candidates returned in our search, and a comparison of our analytic procedure of generating upper limits to those obtained through injections.

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• Gravitational Wave Constraints on Planetary-Mass Primordial Black Holes Using LIGO O3a Data

  Physical Review Letters · 2024-09-10 · 19 citations

  articleOpen access

  Gravitational waves from subsolar mass inspiraling compact objects would provide almost smoking-gun evidence for primordial black holes (PBHs). We perform the first search for inspiraling planetary-mass compact objects in equal-mass and highly asymmetric mass-ratio binaries using data from the first half of the LIGO-Virgo-KAGRA third observing run. Though we do not find any significant candidates, we determine the maximum luminosity distance reachable with our search to be of $\mathcal{O}(0.1--100)\text{ }\text{ }\mathrm{kpc}$, and corresponding model-independent upper limits on the merger rate densities to be $\mathcal{O}({10}^{3}--{10}^{\ensuremath{-}7})\text{ }\text{ }{\mathrm{kpc}}^{\ensuremath{-}3}\text{ }{\mathrm{yr}}^{\ensuremath{-}1}$ for systems with chirp masses of $\mathcal{O}({10}^{\ensuremath{-}4}--{10}^{\ensuremath{-}2}){M}_{\ensuremath{\bigodot}}$, respectively. Furthermore, we interpret these rate densities as arising from PBH binaries and constrain the fraction of dark matter that such objects could comprise. For equal-mass PBH binaries, we find that these objects would compose less than 4%--100% of DM for PBH masses of ${10}^{\ensuremath{-}2}{M}_{\ensuremath{\bigodot}}$ to $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}{M}_{\ensuremath{\bigodot}}$, respectively. For asymmetric binaries, assuming one black hole mass corresponds to a peak in the mass function at $2.5{M}_{\ensuremath{\bigodot}}$, a PBH dark-matter fraction of 10% and a second, much lighter PBH, we constrain the mass function of the second PBH to be less than 1 for masses between $1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}{M}_{\ensuremath{\bigodot}}$ and $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}{M}_{\ensuremath{\bigodot}}$. Our constraints, recently released, are robust enough to be applied to any PBH or exotic compact object binary formation models, and complement existence microlensing results.

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• Simulating the Galactic population of axion clouds around stellar-origin black holes: Gravitational wave signals in the 10-100 kHz band

  arXiv (Cornell University) · 2024-09-05

  preprintOpen access

  Ultralight scalar fields can experience runaway `superradiant' amplification near spinning black holes, resulting in a macroscopic `axion cloud' which slowly dissipates via continuous monochromatic gravitational waves. For a particular range of boson masses, $\mathcal{O}(10^{-11}$ -- $10^{-10})$ eV, an axion cloud will radiate in the $10$ -- $100$ kHz band of the Levitated Sensor Detector (LSD). Using fiducial models of the mass, spin, and age distributions of stellar-origin black holes, we simulate the present-day Milky Way population of these hypothetical objects. As a first step towards assessing the LSD's sensitivity to the resultant ensemble of GW signals, we compute the corresponding signal-to-noise ratios which build up over a nominal integration time of $10^{7}$ s, assuming the projected sensitivity of the $1$-m LSD prototype currently under construction, as well as for future $10$-m and $100$-m concepts. For a $100$-m cryogenic instrument, hundreds of resolvable signals could be expected if the boson mass $μ$ is around $3\times10^{-11}$ eV, and this number diminishes with increasing $μ$ up to $\approx 5.5\times10^{-11}$ eV. The much larger population of unresolved sources will produce a confusion foreground which could be detectable by a $10$-m instrument if $μ\in (3-4.5)\times10^{-11}$ eV, or by a $100$-m instrument if $μ\in (3-6)\times10^{-11}$ eV.

  PublisherOA PDFDOI

• Gravitational wave constraints on planetary-mass primordial black holes using LIGO O3a data

  arXiv (Cornell University) · 2024-02-29

  preprintOpen access

  Gravitational waves from sub-solar mass inspiraling compact objects would provide almost smoking-gun evidence for primordial black holes (PBHs). We perform the first search for inspiraling planetary-mass compact objects in equal-mass and highly asymmetric mass-ratio binaries using data from the first half of the LIGO-Virgo-KAGRA third observing run. Though we do not find any significant candidates, we determine the maximum luminosity distance reachable with our search to be of $O(0.1-100)$ kpc, and corresponding model-independent upper limits on the merger rate densities to be $O(10^{3}-10^{-7})$ kpc$^{-3}$yr$^{-1}$ for systems with chirp masses of $O(10^{-4}-10^{-2})M_\odot$, respectively. Furthermore, we interpret these rate densities as arising from PBH binaries and constrain the fraction of dark matter that such objects could comprise. For equal-mass PBH binaries, we find that these objects would compose less than 4-100% of DM for PBH masses of $10^{-2}M_\odot$ to $2\times 10^{-3}M_\odot$, respectively. For asymmetric binaries, assuming one black hole mass corresponds to a peak in the mass function at 2.5$M_\odot$, a PBH dark-matter fraction of 10% and a second, much lighter PBH, we constrain the mass function of the second PBH to be less than 1 for masses between $1.5\times 10^{-5}M_\odot$ and $2\times 10^{-4}M_\odot$. Our constraints, released on Zenodo, are robust enough to be applied to any PBH or exotic compact object binary formation models, and complement existence microlensing results. More details about our search can be found in our companion paper.

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• Population of Merging Compact Binaries Inferred Using Gravitational Waves through GWTC-3

  Physical Review X · 2023-03-29 · 866 citations

  articleOpen access

  We report on the population properties of compact binary mergers inferred from gravitational-wave observations of these systems during the first three LIGO-Virgo observing runs. The Gravitational-Wave Transient Catalog 3 (GWTC-3) contains signals consistent with three classes of binary mergers: binary black hole, binary neutron star, and neutron star–black hole mergers. We infer the binary neutron star merger rate to be between 10 and <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mn>1700</a:mn><a:mtext> </a:mtext><a:mtext> </a:mtext><a:msup><a:mrow><a:mi>Gpc</a:mi></a:mrow><a:mrow><a:mo>−</a:mo><a:mn>3</a:mn></a:mrow></a:msup><a:mtext> </a:mtext><a:msup><a:mrow><a:mi>yr</a:mi></a:mrow><a:mrow><a:mo>−</a:mo><a:mn>1</a:mn></a:mrow></a:msup></a:mrow></a:math> and the neutron star–black hole merger rate to be between 7.8 and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:mn>140</c:mn><c:mtext> </c:mtext><c:mtext> </c:mtext><c:msup><c:mrow><c:mi>Gpc</c:mi></c:mrow><c:mrow><c:mo>−</c:mo><c:mn>3</c:mn></c:mrow></c:msup><c:mtext> </c:mtext><c:msup><c:mrow><c:mi>yr</c:mi></c:mrow><c:mrow><c:mo>−</c:mo><c:mn>1</c:mn></c:mrow></c:msup></c:mrow></c:math>, assuming a constant rate density in the comoving frame and taking the union of 90% credible intervals for methods used in this work. We infer the binary black hole merger rate, allowing for evolution with redshift, to be between 17.9 and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:mn>44</e:mn><e:mtext> </e:mtext><e:mtext> </e:mtext><e:msup><e:mrow><e:mi>Gpc</e:mi></e:mrow><e:mrow><e:mo>−</e:mo><e:mn>3</e:mn></e:mrow></e:msup><e:mtext> </e:mtext><e:msup><e:mrow><e:mi>yr</e:mi></e:mrow><e:mrow><e:mo>−</e:mo><e:mn>1</e:mn></e:mrow></e:msup></e:mrow></e:math> at a fiducial redshift (<g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>z</g:mi><g:mo>=</g:mo><g:mn>0.2</g:mn></g:math>). The rate of binary black hole mergers is observed to increase with redshift at a rate proportional to <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mo stretchy="false">(</i:mo><i:mn>1</i:mn><i:mo>+</i:mo><i:mi>z</i:mi><i:msup><i:mo stretchy="false">)</i:mo><i:mi>κ</i:mi></i:msup></i:math> with <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mi>κ</m:mi><m:mo>=</m:mo><m:mn>2.</m:mn><m:msubsup><m:mn>9</m:mn><m:mrow><m:mo>−</m:mo><m:mn>1.8</m:mn></m:mrow><m:mrow><m:mo>+</m:mo><m:mn>1.7</m:mn></m:mrow></m:msubsup></m:math> for <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mi>z</o:mi><o:mo>≲</o:mo><o:mn>1</o:mn></o:math>. Using both binary neutron star and neutron star–black hole binaries, we obtain a broad, relatively flat neutron star mass distribution extending from <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:msubsup><q:mn>1.2</q:mn><q:mrow><q:mo>−</q:mo><q:mn>0.2</q:mn></q:mrow><q:mrow><q:mo>+</q:mo><q:mn>0.1</q:mn></q:mrow></q:msubsup></q:math> to <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"><s:msubsup><s:mn>2.0</s:mn><s:mrow><s:mo>−</s:mo><s:mn>0.3</s:mn></s:mrow><s:mrow><s:mo>+</s:mo><s:mn>0.3</s:mn></s:mrow></s:msubsup><s:msub><s:mi>M</s:mi><s:mo stretchy="false">⊙</s:mo></s:msub></s:math>. We confidently determine that the merger rate as a function of mass sharply declines after the expected maximum neutron star mass, but cannot yet confirm or rule out the existence of a lower mass gap between neutron stars and black holes. We also find the binary black hole mass distribution has localized over- and underdensities relative to a power-law distribution, with peaks emerging at chirp masses of <v:math xmlns:v="http://www.w3.org/1998/Math/MathML" display="inline"><v:msubsup><v:mn>8.3</v:mn><v:mrow><v:mo>−</v:mo><v:mn>0.5</v:mn></v:mrow><v:mrow><v:mo>+</v:mo><v:mn>0.3</v:mn></v:mrow></v:msubsup></v:math> and <x:math xmlns:x="http://www.w3.org/1998/Math/MathML" display="inline"><x:msubsup><x:mn>27.9</x:mn><x:mrow><x:mo>−</x:mo><x:mn>1.8</x:mn></x:mrow><x:mrow><x:mo>+</x:mo><x:mn>1.9</x:mn></x:mrow></x:msubsup><x:msub><x:mi>M</x:mi><x:mo stretchy="false">⊙</x:mo></x:msub></x:math>. While we continue to find that the mass distribution of a binary’s more massive component strongly decreases as a function of primary mass, we observe no evidence of a strongly suppressed merger rate above approximately <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"><ab:mn>60</ab:mn><ab:msub><ab:mi>M</ab:mi><ab:mo stretchy="false">⊙</ab:mo></ab:msub></ab:math>, which would indicate the presence of a upper mass gap. Observed black hole spins are small, with half of spin magnitudes below <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline"><db:msub><db:mi>χ</db:mi><db:mi>i</db:mi></db:msub><db:mo>≈</db:mo><db:mn>0.25</db:mn></db:math>. While the majority of spins are preferentially aligned with the orbital angular momentum, we infer evidence of antialigned spins among the binary population. We observe an increase in spin magnitude for systems with more unequal-mass ratio. We also observe evidence of misalignment of spins relative to the orbital angular momentum. Published by the American Physical Society 2023

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• Limits on Neutrino Emission from GRB 221009A from MeV to PeV Using the IceCube Neutrino Observatory

  The Astrophysical Journal Letters · 2023-03-01 · 56 citations

  articleOpen access

  Abstract Gamma-ray bursts (GRBs) have long been considered a possible source of high-energy neutrinos. While no correlations have yet been detected between high-energy neutrinos and GRBs, the recent observation of GRB 221009A—the brightest GRB observed by Fermi-GBM to date and the first one to be observed above an energy of 10 TeV—provides a unique opportunity to test for hadronic emission. In this paper, we leverage the wide energy range of the IceCube Neutrino Observatory to search for neutrinos from GRB 221009A. We find no significant deviation from background expectation across event samples ranging from MeV to PeV energies, placing stringent upper limits on the neutrino emission from this source.

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• D-Egg: a dual PMT optical module for IceCube

  Journal of Instrumentation · 2023-04-01 · 12 citations

  articleOpen access

  Abstract The D-Egg, an acronym for “Dual optical sensors in an Ellipsoid Glass for Gen2,” is one of the optical modules designed for future extensions of the IceCube experiment at the South Pole. The D-Egg has an elongated-sphere shape to maximize the photon-sensitive effective area while maintaining a narrow diameter to reduce the cost and the time needed for drilling of the deployment holes in the glacial ice for the optical modules at depths up to 2700 m. The D-Egg design is utilized for the IceCube Upgrade, the next stage of the IceCube project also known as IceCube-Gen2 Phase 1, where nearly half of the optical sensors to be deployed are D-Eggs. With two 8-inch high-quantum efficiency photomultiplier tubes (PMTs) per module, D-Eggs offer an increased effective area while retaining the successful design of the IceCube digital optical module (DOM). The convolution of the wavelength-dependent effective area and the Cherenkov emission spectrum provides an effective photodetection sensitivity that is 2.8 times larger than that of IceCube DOMs. The signal of each of the two PMTs is digitized using ultra-low-power 14-bit analog-to-digital converters with a sampling frequency of 240 MSPS, enabling a flexible event triggering, as well as seamless and lossless event recording of single-photon signals to multi-photons exceeding 200 photoelectrons within 10 ns. Mass production of D-Eggs has been completed, with 277 out of the 310 D-Eggs produced to be used in the IceCube Upgrade. In this paper, we report the design of the D-Eggs, as well as the sensitivity and the single to multi-photon detection performance of mass-produced D-Eggs measured in a laboratory using the built-in data acquisition system in each D-Egg optical sensor module.

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Frequent coauthors

• J. van den Brand

  239 shared

• A. Heidmann

  127 shared

• L. Sun

  Bundesministerium für Klimaschutz, Umwelt, Energie, Mobilität, Innovation und Technologie

  117 shared

• E. Chassande–Mottin

  Laboratoire AstroParticule et Cosmologie

  107 shared

• I. W. Harry

  University of Portsmouth

  107 shared

• R. Flaminio

  Laboratoire d’Annecy de Physique des Particules

  107 shared

• T. Briant

  Collège de France

  106 shared

• N. Christensen

  Observatoire de la Côte d’Azur

  104 shared