Abstract

Ultra-high energy (UHE) astrophysical neutrinos are unique in the sense that they are theonly known particles that could travel through incredibly long distance unattenuated, withTeV 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 theycarry important information directly from the inside of energetic astrophysical objects. On theother hand, from the particle physics point of view, the UHE neutrinos also offer a new windowof opportunity for studying beyond the Standard Model (BSM) phenomena. This is the maintheme of this dissertation. We show by explicit examples that by studying the generationand detection mechanism of the UHE neutrinos and their energy spectra at ground-based orairborne neutrino detectors, we can effectively probe some BSM physics with unprecedentedsensitivity. Specifically, we discuss how models of heavy dark matter (DM) decay, Zee modelwith light charged scalars, and R-parity violating supersymmetry (RPV-SUSY) can be probedusing 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 electroweakinteractions and then discuss in general the mechanism of astrophysical neutrino generationand interaction with matter under the SM framework. Then, we discuss in detail four projectsrelated to different aspects of BSM extensions of the UHE neutrino physics.xviIn the first project, we mainly focus on the astrophysical aspect of the UHE neutrinos suchas the neutrino flux model, flavor composition due to standard or muon-damped pion sourceand the correlation between the neutrino flux and the gamma-ray flux. A two-componentneutrino flux model, with either astrophysical or dark matter origin, and with different flavorcompositions is studied. Our combined likelihood analysis, comparing the simulated datafrom 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 overthe purely astrophysical flux model. We derive the corresponding best-fit contours in thedark matter mass and lifetime plane.In the second project we turn our eyes back on Earth and focus on a BSM extension ofneutrino-matter interaction – the so-called non-standard neutrino interactions (NSI). Wepropose that a leptophilic light charged scalar could induce a Glashow-like resonance whichgives distinguishing signal pattern in the UHE neutrino event spectrum. We study the Zeemodel of radiative neutrino mass generation as a prototype and show that with a 100 GeV lightcharged scalar, which is still allowed by current constraints, a peak around 10 PeV in the UHEneutrino 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 attemptat explaining the up-going anomalous EeV energy neutrino events seen by ANITA balloonexperiment by some BSM physics. We propose that under the framework of RPV-SUSY, aGeV-scale, long-lived neutral bino could be a suitable candidate to resolve the discrepancybetween the observed up-going EeV events and the short interaction length of UHE neutrinosin Earth material under SM. In this interpretation, the binos are generated by the modifiedneutrino-nucleus interaction and propagate through around 6000 km of Earth material beforedecaying back to neutrinos near Earth’s surface and producing extensive up-going air showersxviithat are detected by ANITA as the anomalous events. We derive the best-fit region ofparameter space in the RPV-SUSY framework to explain the ANITA events and find thatit is still consistent with current constraints, but should be completely testable in the nearfuture.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 flavoruniversality violation manifested as RD() and RK() flavor anomalies; (ii) the long-standingdiscrepancy in muon anomalous magnetic moment; and (iii) the ANITA EeV anomalousup-going events. Three different benchmarks are discussed in detail and all the thirdgenerationsuperpartners needed are confined in 1-10 TeV mass range, accessible at the LHCor next-generation hadron collider.

Committee Chair

Bhupal Dev

Committee Members

James H. Buckley, Ramanath Cowsik, Renato Feres, Francesc Ferrer,

Degree

Doctor of Philosophy (PhD)

Author's Department

Physics

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

Summer 8-15-2020

Language

English (en)

Author's ORCID

http://orcid.org/0000-0002-2573-0216

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