Title: PHENOMENOLOGY OF NEUTRINO PORTAL DARK MATTER AND
SUPERSYMMETRY

Abstract: High energy physics is in an exciting period. The discovery of the Higgs boson, with
properties in accord with the Standard Model predictions, has sharpened our focus towards
questions that go beyond, such as the origin of neutrino masses, the identity of non-baryonic
dark matter, asymmetry of matter and antimatter, and the hierarchy problem. Following
these questions, in this thesis we investigate the neutrino portal dark matter which tries to
explain non-baryonic dark matter and the neutrino masses at the same time. Bearing in
mind that natural theories like the Minimal Supersymmetric Standard Model also provide
a WIMP type candidate for dark matter, we also calculate the sensitivities of the High
Luminosity (HL) and High Energy (HE) upgrades of the Large Hadron Collider (LHC) to
strong supersymmetry signals. This dissertation explores these topics in the following way.
Firstly, we study the feasibility of the indirect detection of dark matter in a simple model
using the neutrino portal. The model is very economical, with right-handed neutrinos gener
ating neutrino masses through the Type-I seesaw mechanism and simultaneously mediating
interactions with dark matter. Given the small neutrino Yukawa couplings expected in a
Type-I seesaw, direct detection and accelerator probes of dark matter in this scenario are
challenging. However, dark matter can efficiently annihilate to right-handed neutrinos, which
then decay via active-sterile mixing through the weak interactions, leading to a variety of
indirect astronomical signatures. We derive the existing constraints on this scenario from
Planck cosmic microwave background measurements, Fermi dwarf spheroidal galaxies and
Galactic Center gamma-rays observations, and AMS-02 antiprotons observations, and also
discuss the future prospects of Fermi and the Cherenkov Telescope Array. This scenario can
also provide a dark matter interpretation of the Fermi Galactic Center gamma ray excess,
and we confront this interpretation with other indirect constraints.
Secondly, by modifying our simple model, we analyze the scenario in which a thermal
dark matter annihilating to standard model neutrinos via the neutrino portal. A (pseudo
)Dirac sterile neutrino serves as a mediator between the visible and the dark sectors, while
an approximate lepton number symmetry allows for a large neutrino Yukawa coupling and,
in turn, efficient dark matter annihilation. The dark sector consists of two particles, a Dirac
fermion and complex scalar, charged under a symmetry that ensures the stability of the
dark matter. A generic prediction of the model is a sterile neutrino with a large active
sterile mixing angle that decays primarily invisibly. We derive existing constraints and
future projections from direct detection experiments, colliders, rare meson and tau decays,
electroweak precision tests, and small scale structure observations. A simple, conservative
scheme to confront the various tests with the thermal relic target is outlined, and we demon
strate that much of the cosmologically-motivated parameter space is already constrained.
We also identify new probes of this scenario such as multi-body kaon decays and Drell-Yan
production of W bosons at the LHC.
Finally, we evaluate the sensitivities of the High Luminosity (HL) and High Energy
(HE) upgrades of the LHC to gluinos and stops, decaying through the simplified topologies
˜ g → q¯ qχ0, ˜ g → t¯ tχ0 and ˜ t → t˜ χ0. Our HL-LHC analyses improve on existing experimental projections by optimizing the acceptance of kinematic variables. The HE-LHC studies represent the first 27 TeV analyses. We find that the HL-(HE-)LHC with 3 ab−1 (15 ab−1) of
integrated luminosity will be sensitive to the masses of gluinos and stops at 3.2 (5.7) TeV
and 1.5 (2.7) TeV, respectively, decaying to massless neutralinos.