Talks & Events
KICP Friday Noon Seminars
Current & Future KICP Seminars
Past KICP Seminars
Searching for the aftermath of binary neutron star mergers
Binary neutron star mergers provide one of the richest laboratories for studying physics with ground-based interferometric gravitational-wave detectors such as advanced LIGO and Virgo. After such a merger, a compact remnant is left over whose nature depends primarily on the masses of the inspiralling objects and on the equation of state of nuclear matter. We will discuss the search for short and intermediate-duration post-merger signals from GW170817, as well as all-sky, all-time searches for the same. In addition, we will describe ongoing searches for the detection of transients like GW170817 in electromagnetic wavelengths. With the Zwicky Transient Facility recently achieving first light, it is now fruitful to use its unprecedented combination of depth, field of view, and survey cadence to perform Target of Opportunity observations. Using the 50 square degree field of view of the instrument, it is possible to follow-up events from systems like the Fermi Gamma-Ray Burst Monitor, where it can be necessary to cover thousands of square degrees. We will demonstrate on short gamma-ray bursts how it is possible to use this system to do follow-up on this scale.
Inflation with Spooky Correlations
Famous "information paradoxes" in black hole theory can be solved if quantum information on horizons is delocalized or "spooky", like states of entangled particles. Similar spooky correlations on the inflationary horizon are estimated to produce curvature perturbations with a dimensionless power spectral density given by the inflationary expansion rate H in Planck units, larger than standard inflaton fluctuations. Current measurements of the spectrum are used to derive constraints on parameters of the effective potential in a slow-roll background. A distinctive and robust new prediction, in the sense of being insensitive to the details of specific spooky models, is an exact directional antisymmetry, traceable directly to the nonlocality and directional correlation of initial conditions on the horizon, which is forbidden in standard models. Signatures of this primordial antisymmetry might already be measured in CMB anisotropy, and if they are indeed due to nearly-scale-invariant primordial spookiness, should also be observable in large scale 3D galaxy surveys, possibly even in existing data. DES may be the first dataset capable of detecting this direct signature of Planck scale quantum physics.
New Directions for Direct Detection of MeV-Scale Dark Matter
While the case for dark matter continues to strengthen from the astrophysical side, particle dark matter has so far eluded the current generation of experiments, designed to probe the SUSY-motivated mass range of GeV-TeV scale dark matter. Meanwhile, the LHC has ruled out the simpler SUSY models, and the simple picture of a weak-scale, 30 GeV supersymmetric dark matter particle has begun to fade. In this talk, I will discuss recent advances in the search for Sub-GeV dark matter down to MeV-scale masses, and the path forward to new technologies capable of probing down to keV-scale mass fermionic dark matter scattering and meV-scale mass bosonic dark matter absorption. These include, but are not limited to, the use of superconductors as well as novel semiconductors as the target medium and readout stages. The energy resolution required to search for low-mass dark matter makes these technologies interesting as general imaging techniques for infrared and UV astronomy, as well as for coherent neutrino scattering and other low-energy rare event search experiments, and I will briefly touch on applications of these new technologies to those fields.
Scalar fields and strong-field gravity: spontaneous scalarization of compact objects
General Relativity remains to this day our best description of gravitational phenomena. The theory has shown remarkable agreement with observations in situations ranging from the slow-velocities, weak-gravitational fields regime from the confines of our Solar System, to the highly nonlinear, dynamical regime of binary black holes mergers. Despite its tremendous successes, issues such as its quantization and the cosmological constant problem suggest that Einstein's theory might not be final theory of the gravitational interaction. Motivated by these questions, theorists have proposed a myriad of extensions to General Relativity over the decades. In this talk I will focus on theories with additional scalar fields. In particular, I will describe how some of these theories can evade Solar System constraints and yet yield interesting new phenomenology in the strong-gravity situations involving compact objects, i.e. neutron stars and black holes.
Constraining Self-Interacting Dark Matter with Galaxy Warps
Self-interacting dark matter remains a viable and interesting model for dark matter. For some types of self-interactions, the passage of a galaxy through some background dark matter overdensity will cause a separation between the centroids of the collisionless stars and the dark matter halo of the galaxy, which experiences a drag force from the self-interactions. For stars arranged in a disk, this would cause a U-shaped warp. In this talk, I will discuss our efforts to place constraints on self-interacting dark matter by looking for these U-shaped warps in SDSS galaxies. Our preliminary results show that this method can place competitive constraints on the self-interaction cross section.
Early Dark Energy and the Hubble Tension
Although the standard Lambda-CDM model of cosmology is in excellent agreement with the observed cosmic microwave background (CMB) power spectrum, its prediction for the current rate of expansion H0 of the Universe is in tension with observations of the local universe at > 3 sigma, with local measurements preferring a higher value. Systematic causes have been investigated and not found to be the culprit. Could this then indicate new physics?
My talk will present a new-physics solution to the Hubble tension that modifies the early expansion history of the Universe through the addition of an early dark energy (EDE) component. This behaves like a cosmological constant at early times and then dilutes quickly with redshift after some critical time. It therefore only influences the Universe over a small range in redshift.
This solution is successful because the Hubble tension can be translated into an equivalent tension in the size of the sound horizon.
If such an EDE becomes dynamical before recombination, it increases the pre-recombination expansion rate and decreases the sound horizon, shifting the expected peaks in the CMB power spectrum to smaller angular scales. These can be brought back in agreement with observations by an increase in the predicted value of H0, reducing the Hubble tension.
I will present two physical scalar-field models for such an EDE, and their success with resolving the Hubble tension while still finding a good fit to most cosmological datasets.
kSZ Cosmology without the optical depth degeneracy
We show how kSZ tomography measures a bispectrum containing a cosmological power spectrum of the velocity field and an astrophysical power spectrum of the electron density. While these are degenerate up to an overall amplitude, scale-dependent effects on large scales are much better constrained by the inclusion of kSZon top of galaxy clustering while assuming nothing about the optical depth of galaxy clusters. This allows for factors of >2x improvement on the amplitude of local primordial non-gaussianity fNL with the absolute constraint from Simons Observatory + LSST crossing the theoretically interesting threshold of sigma(fNL)<1. We also discuss ways of measuring the (scale-independent) growth rate by breaking the optical depth degeneracy using either (1) redshift-space distortions or more ambitiously (2) the dispersion measures of fast radio bursts (FRBs).
The Population of Binary Black Holes from Gravitational-wave Observations
I will present the current inventory of binary black holes (BBH) collected during the first and second observing runs of the LIGO/Virgo gravitational-wave interferometer network. The ten BBH observed to date provide the means to resolve questions about their formation and population properties. As such, I will also present new estimates of the mass, spin, and merger rate distributions of stellar mass BBH. All analyses consistently find merger rate distributions over the primary mass which predict almost no black holes above 45 solar masses. We also find that probes of the rate evolution with redshift prefer inclining or flat models. The inferred spin magnitude distribution strongly disfavors high spin magnitudes when the component spins are aligned to the orbital angular momentum. Finally, I will describe prospects for what the future might hold for BBH in future observing runs.
Fundamental physics with gravitational waves