BSM PANDEMIC Delta Series: Hongwan Liu (Princeton/NYU) and Nashwan Sabti (King's College)


Hongwan Liu (Princeton/NYU):

Title: Low-Energy Signals from the Formation of Dark Matter-Nuclear Bound States
Abstract: Dark matter particles may bind with nuclei if there exists an attractive force of sufficient strength. We show that a dark photon mediator of mass (10 -- 100) MeV with a small kinetic mixing with Standard Model electromagnetism generates keV-scale binding energies between dark matter and heavy elements, while forbidding the ability to bind with light elements. In underground direct detection experiments, the formation of such bound states liberates keV-scale energy in the form of electrons and photons, giving rise to mono-energetic electronic signals with a time-structure that may contain daily and seasonal modulations. We show that data from liquid-xenon detectors provides exquisite sensitivity to this scenario, constraining the galactic abundance of such dark particles to be a small subcomponent of the galactic dark matter density, with a mass of between 1 GeV and 100 TeV. However, an exponentially small fractional abundance of these dark particles is enough to explain the observed electron recoil excess at XENON1T.


Nashwan Sabti (King's College):

Title: New Roads to the Small-Scale Universe: Measurements of the Clustering of Matter with the High-Redshift UV Galaxy Luminosity Function

Abstract: The epochs of cosmic dawn and reionisation present promising avenues for understanding the role of dark matter (DM) in our cosmos. The first galaxies that populated our Universe during these eras resided in DM halos that were much less massive than their counterparts today. Consequently, observations of such galaxies can provide us with a handle on the clustering properties of DM in an otherwise inaccessible regime. In this talk, I will show how high-redshift UV galaxy luminosity-function (UV LF) data from the Hubble Space Telescope can be used to study the clustering of DM at small scales. In particular, I will show how it provides a measurement of the matter power spectrum at wavenumbers 0.5 Mpc^-1 < k < 10 Mpc^-1, after marginalising over astrophysical parameters. This measurement covers the uncharted redshift range 4 <= z <= 10 and reaches scales beyond those covered by Cosmic Microwave Background and Large-Scale Structure observations.