Date of Award
Doctor of Philosophy (PhD)
Ultra-high energy (UHE) astrophysical neutrinos are unique in the sense that they are the
only known particles that could travel through incredibly long distance unattenuated, with
TeV to EeV energy, much higher than the most powerful man-made collider could provide.
The detection of these UHE neutrinos has ushered a new era in neutrino astrophysics, as they
carry important information directly from the inside of energetic astrophysical objects. On the
other hand, from the particle physics point of view, the UHE neutrinos also offer a new window
of opportunity for studying beyond the Standard Model (BSM) phenomena. This is the main
theme of this dissertation. We show by explicit examples that by studying the generation
and detection mechanism of the UHE neutrinos and their energy spectra at ground-based or
airborne neutrino detectors, we can effectively probe some BSM physics with unprecedented
sensitivity. Specifically, we discuss how models of heavy dark matter (DM) decay, Zee model
with light charged scalars, and R-parity violating supersymmetry (RPV-SUSY) can be probed
using the UHE neutrino data from IceCube and ANITA experiments.
In the dissertation, we first give a brief review of the SM with special focus on electroweak
interactions and then discuss in general the mechanism of astrophysical neutrino generation
and interaction with matter under the SM framework. Then, we discuss in detail four projects
related to different aspects of BSM extensions of the UHE neutrino physics.
In the first project, we mainly focus on the astrophysical aspect of the UHE neutrinos such
as the neutrino flux model, flavor composition due to standard or muon-damped pion source
and the correlation between the neutrino flux and the gamma-ray flux. A two-component
neutrino flux model, with either astrophysical or dark matter origin, and with different flavor
compositions is studied. Our combined likelihood analysis, comparing the simulated data
from various scenarios of this new flux model and the IceCube high-energy neutrino data,
finds that the scenario with a heavy dark matter decay component is mildly preferred over
the purely astrophysical flux model. We derive the corresponding best-fit contours in the
dark matter mass and lifetime plane.
In the second project we turn our eyes back on Earth and focus on a BSM extension of
neutrino-matter interaction – the so-called non-standard neutrino interactions (NSI). We
propose that a leptophilic light charged scalar could induce a Glashow-like resonance which
gives distinguishing signal pattern in the UHE neutrino event spectrum. We study the Zee
model of radiative neutrino mass generation as a prototype and show that with a 100 GeV light
charged scalar, which is still allowed by current constraints, a peak around 10 PeV in the UHE
neutrino energy should be seen with the sensitivity of the upgraded IceCube-Gen2 detector.
This provides a new probe of NSI complementary to neutrino oscillation experiments.
In the third project we move further into the high energy regime and make an attempt
at explaining the up-going anomalous EeV energy neutrino events seen by ANITA balloon
experiment by some BSM physics. We propose that under the framework of RPV-SUSY, a
GeV-scale, long-lived neutral bino could be a suitable candidate to resolve the discrepancy
between the observed up-going EeV events and the short interaction length of UHE neutrinos
in Earth material under SM. In this interpretation, the binos are generated by the modified
neutrino-nucleus interaction and propagate through around 6000 km of Earth material before
decaying back to neutrinos near Earth’s surface and producing extensive up-going air showers
that are detected by ANITA as the anomalous events. We derive the best-fit region of
parameter space in the RPV-SUSY framework to explain the ANITA events and find that
it is still consistent with current constraints, but should be completely testable in the near
Finally in the fourth project, we extend the RPV-SUSY framework to the so-called RPV3,
where the third-generation superpartners are presumed to be the lightest. In this scenario,
we simultaneous explain the following seemingly unrelated anomalies: (i) the lepton flavor
universality violation manifested as RD() and RK() flavor anomalies; (ii) the long-standing
discrepancy in muon anomalous magnetic moment; and (iii) the ANITA EeV anomalous
up-going events. Three different benchmarks are discussed in detail and all the thirdgeneration
superpartners needed are confined in 1-10 TeV mass range, accessible at the LHC
or next-generation hadron collider.
Chair and Committee
James H. Buckley, Ramanath Cowsik, Renato Feres, Francesc Ferrer,
Sui, Yicong, "New Physics with Ultra-High Energy Neutrinos" (2020). Arts & Sciences Electronic Theses and Dissertations. 2350.