Theses, Captstones, and Dissertations
Squirks are theoretical particles predicted in many realizations of neutral naturalness, a framework which extends the Standard Model to address the electroweak hierarchy problem. For a two-squirk bound state with net electric charge, the annihilation branching ratios depend on the mass difference $\Delta$ between the squirks. In this work, I show that as $\Delta$ increases, the $\Delta$-dependent branching ratios weaken experimental bounds on squirk masses. In particular, I find that some squirk masses less than 1 TeV have not yet been excluded by searches at the Large Hadron Collider (LHC). These masses are accessible at the LHC's current energy levels, so with a new strategy, we can search for squirks more effectively, increasing the discovery power of the LHC while maintaining its current collision energy. In this paper, I present one such new strategy, which is to search for events where the collision produces a pair of squirks with a glueball. The squirks annihilate into a pair of bosons, and the glueball creates a displaced vertex when it decays in the detector. I also present our simulations of searching for this combination of a bosonic resonance and a displaced vertex. I find that this strategy complements and extends current methods, probing a larger region of squirk mass parameter space than the region excluded by current search strategies, especially for large $\Delta$.
We derive the Unruh effect using the method of Bogoliubov transformations. We begin by constructing the Bogoliubov transformations which relate different sets of QFT operators to each other. We then consider the specific case of comparing an inertial reference frame to an accelerating reference frame. We calculate the Bogoliubov coefficients for this situation and use these to show that the state which is a vacuum from the perspective of the inertial observer contains particles from the perspective of the accelerating observer. The particle density has the form of a thermal bath with a temperature proportional to the acceleration. We discuss the interpretation of this result and possible other applications of the techniques used in this derivation.
Early universe measurements of the Hubble constant usually find the best-fit value for H0 given a specific data set and a particular cosmological model. Planck’s all-sky survey of the Cosmic Microwave Background is a common choice for this data, and is often supplemented with additional constraints from other measurements of cosmological phenomena. For example, the SH0ES collaboration’s measurement of H0 from local type Ia supernovae is a common constraint to include, in the hope of reconciling the tension between late and early universe measurements. We attempt to quantify the effect of this constraint on early universe measurements of H0. We obtain values for H0 from several cosmological models—ΛCDM, CPL dark energy, and exponential acoustic dark energy—under two sets of constraints: only CMB data, and CMB data as well as the SH0ES measurement. We compare these results to each other and find that, for these models, constraining the H0 measurement with SH0ES’ measurement generally reduces the Hubble tension by ~0.5σ. Given the limited scope of this study, our results are probably not generalizable to models other than the ones we examined.
An approximation for the fractional neutron abundance in the 1 MeV to .1 MeV range in the early universe is derived. This is then computed and plotted using the Mathematica software. It is compared with and found in agreement with similar plots and acts as an upper limit on $^4$He during Big bang nucleosynthesis. The approximation falls short at around 0.1 MeV due the onset of neutron decay and D production, changing effective degrees of relativistic freedom, and the increasing consequence of the mass of the electron as the universe cooled.
An extension of the Standard Model of particle physics is proposed that is motivated primarily by the hierarchy problem. The model expands the gauge group of quantum chromodynamics in an attempt to provide a viable model of dark matter and a reason for the unexpected nature of the Higgs vacuum expectation value. These changes introduce new fermion and boson fields to the Standard Model, as well as interesting new collider phenomenology.
Large collider facilities such as the Large Hadron Collider (LHC) employ a variety of search methods in hopes of finding new particles. It may be that new physics beyond the SM is waiting to be discovered at energies accessible to the LHC. Quirks are particles charged under a new confining gauge group with masses much larger than their confinement scale. This project details the dynamics of quirks, as well as the production and decay of electrically charged bound states of scalar quirks. The cross section for these states is compared to existing Wγ resonance searches at the LHC. Such a state is above the most sensitive LHC search up to an invariant mass of about M ≲ 640 GeV.