Ultrahigh energy cosmic rays ($E > 10^{18}$ eV $=1$ EeV) have been observed since the 1960s,
yet their origin, or how they are accelerated to such extreme energies, still remains a mystery.
Ultrahigh energy cosmic rays represent an enormous opportunity for astroparticle physicists:
they probe the most extreme astrophysical environments in the universe, while also giving
access to particle physics beyond LHC-energies.
As ultrahigh energy cosmic rays propagate from their accelerator, through the surrounding host
environment, and through extragalactic space towards Earth. Along the way cosmic rays will interact
with ambient photons and gas in the source environment, as well as, with the cosmic microwave background
(CMB) and extragalactic background lights (EBL). These interactions have two important effects: first,
they break up heavier nuclei into lighter nuclei (i.e. photodisintegrate and spallate nuclei); and second,
they produce secondary particles, primarily photons, electrons/positrons, and pions. These photons and
electrons/positrons will initiate electromagnetic cascades which can be observed on Earth via the gamma-rays
which they produce. Pions, on the other hand, will decay into two photons or into a anti-muon neutrino and a muon
(which subsequently decays into an electron, muon neutrino, and anti-electron neutrino). These will again produce
observable gamma-rays, via EM cascades, and neutrinos, which propagate uninhibited to Earth.
The fact that ultrahigh energy cosmic rays will necessarily produce gamma-rays and neutrinos means that they are
inherently multimessenger in nature. Therefore, by approaching them through a multimessenger lens we can fully
leverage this characteristic and gain insight into their source properties directly. To do this, my research
takes a flexible, phenomenological approach to studying ultrahigh energy cosmic rays which is agnostic to
any particular source (e.g. active galactic nuclei, gamma-ray bursts, tidal disruption events, etc.). In this way
I seek to reveal cosmic ray source properties, make new connections between cosmic messengers, discover new
observational opportunities and targets, and find new probes of beyond the Standard Model physics.
Below are some selected results from my work:
