A generalized Hartle-Hawking wavefunction
Postdoctoral associate Gabriel Herczeg, together with Professor Alexander (BTPC/CFPU affiliated faculty member) and João Maguiejo (Imperial College, London) study the quantum mechanics of anisotropic cosmological models and black holes using a new proposal for a generalization of the Hartle-Hawking “wavefunction of the universe.”
Strongly-Interacting Ultralight Millicharged Particle (STUMP) Neutron Stars as Dark Matter Halos
BTPC/CFPU affiliated faculty member Stephon Alexander along with former BTPC affiliated postdoc Evan McDonough and David Spergel put forth a model of ultra-light fermionic dark matter, “STUMP dark matter.” This model shows consistency with observations of dwarf galaxies and can be distinguished from ultra-light boson dark matter through direct detection and collider signals.
Spectroscopic Tomography: A First Weak-lensing Detection Using Spectroscopic Redshifts Only
The distortion of the shape of galaxies depends on the relative distances of the lens and the galaxy whose light is distorted. If the distances are uncertain, the reconstruction of the lensing mass is complicated. In this pilot study, CFPU faculty Ian Dell’Antonio (working with colleagues at the Smithsonian Astrophysical Observatory, NASA JPL and Stony Brook) showed that the combination of a deep redshift survey and accurate lensing measurements can provide a measure of the cluster mass even using a smaller number of galaxies. In addition, they showed that increasing the number of galaxies with known distances makes it possible to measure the expansion history of the Universe directly from the amplitude of the lensing signal as a function of redshift.
Constraints on Axions from Cosmic Distance Measurements
Postdoc Manuel Buen-Abad, Chen Sun (Tel Aviv) and Prof. Fan use different combinations of the most updated distance measurements to constrain the axion-photon coupling. The derived strong bounds are comparable to or stronger than the existing bounds in the literature. The bounds are determined by the shape of Hubble rate as a function of redshift reconstructable from various distance measurements, and insensitive to today’s Hubble rate, of which there is a tension between early and late cosmological measurements.
Accurate background modeling provides the key to unambiguously detecting dark matter
The LUX-ZEPLIN (LZ) collaboration has developed a customized Monte Carlo simulation framework to model how the LZ detector responds to various types of signals. This framework will allow scientists to unambiguously either constrain or discover dark matter in the upcoming LZ search by allowing comparison between generated mock data from simulation and actual detector data.
A novel machine learning technique to mitigate backgrounds in xenon-based dark matter detectors
The LUX collaboration has developed a boosted decision tree machine learning algorithm to classify events in the LUX detector based on their signal shapes. This novel technique effectively mitigates backgrounds originating from the electrodes, and has improved the sensitivity of low-mass dark matter searches for experiments using liquid xenon as the target.
The LUX-ZEPLIN (LZ) collaboration performed an extensive radioassay campaign over a period of six years to ensure a highly radiopure detector. The assay results not only help establish a Radon background model (one of the dominant backgrounds in the LZ detector), but will also help future scientists select and model clean materials for the next generation of dark matter detection experiments.
The impact of tandem redundant/sky-based calibration in MWA Phase II data analysis
Brown master’s student Zheng Zhang and CFPU affiliated faculty member Prof. Pober led a study of new calibration techniques for precisely characterizing the response of the Murchison Widefield Array (MWA) radio telescope. A calibration technique based on redundancy in the layout of the array’s antennas has attracted a lot of attention in the past few years, with studies conflicted about how useful the approach is. We find that redundant calibration can lead to statistically significant improvements in our analysis when our model for the radio sky is poor, but is limited in its efficacy when accurate sky models are available.
Dark matter substructure under the electron scattering lamppost
Graduate student Jatan Buch, postdocs Manuel Buen-Abad and John (Shing-Chau) Leung, and Prof. Fan study the mutual relationship between dark matter-electron scattering experiments and possible new dark matter substructure nearby hinted by the data from Gaia satellite. In particular, they show how future data could probe and constrain the fraction of dark matter in substructure, even when it constitutes a subdominant component of the local dark matter density.
Galactic origin of relativistic bosons and XENON1T excess
Motivated by a possible excess in the low-energy electronic recoil data reported by XENON1T collaboration, Graduate student Jatan Buch, postdocs Manuel Buen-Abad and John (Shing-Chau) Leung, and Prof. Fan explore the exotic possibility that dark matter decays or annihilations taking place in our galaxy may produce a flux of relativistic very weakly-coupled bosons, axions or dark photons. They show that there exist several generic upper bounds for this flux on Earth assuming generic minimal requirements for DM, which will survive even if XENON1T excess doesn’t stay.
Could the 2.6M⊙ object in GW190814 be a primordial black hole?
In June 2020 the LIGO-Virgo collaboration announced the discovery of a strange gravitational wave merger event. It was a merger between a black hole 23 times the mass of the Sun, and a compact object with mass approximately 2.5 times the mass of the Sun. Graduate students Kyriakos Vattis and Isabelle Goldstein working with BTPC/CFPU affiliated faculty member Prof. Koushiappas investigated the possibility of the light object being a primordial black hole, that is a black hole formed right after the big bang.
Deep learning the astrometric signature of dark matter substructure
In an exploratory study, graduate students Kyriakos Vattis and Michael Toomey, together with Prof. Koushiappas (BTPC/CFPU affiliated faculty member) explored whether convolutional neural networks can be used to extract the astrometric signature of dark matter.
CMB constraints on late-universe decaying dark matter as a solution to the H0 tension
Graduate student Kyriakos Vattis together with BTPC postdoc Steven Clark and Prof. Koushiappas (BTPC/CFPU affiliated faculty member) explored the cosmological effects of dark matter that decays to light particles in recent times in the context of the solving the Hubble tension.
The CFPU congratulates Penrose, Ghez and Genzel for winning the 2020 Nobel Prize in Physics! The common thread between their work is the use of black holes to test the fundamental physics of gravity, both of which are topics explored by CFPU members.
Professor Roger Penrose’s contributions over decades focused on understanding the structure of space-time and singularities. His elegant mathematical work demonstrated that singularities and the event horizons around them (what we call black holes) were inescapable consequences of Einstein’s general theory of relativity.
Professors Ghez and Genzel, spent over 20 years using the world’s largest telescopes in Chile and Hawaii to make the most precise positional measurements of stars near the supermassive black hole at the center of the galaxy. These ultra-precise measurements utilizing advanced imaging techniques such as adaptive optics, have provided direct tests of the predictions of general relativity and allowed us to see first-hand the evolution of stellar orbits in highly curved space.
