Constraining particle physics models with gravitational waves from the early universe
Dhruv Ringe
TL;DR
The thesis develops a framework to constrain high-scale particle physics using stochastic gravitational waves from early-universe phenomena. It analyzes first-order phase transitions and domain walls in UV-complete Froggatt–Nielsen models and in doublet left-right symmetric models, computing finite-temperature effective potentials and GW spectra with CosmoTransitions. For FN models, GW signals at BBO/DECIGO/CE/ET probe flavon symmetry-breaking scales up to $v_s o 10^7$ GeV, with similar spectra across two UV completions and limited discrimination by GW data alone. In DL(R)SM, GW observables at FP-DECIGO, BBO, and Ultimate-DECIGO arise for $v_R o 20$–50 TeV, with strong correlations between GW strength and LRSM parameters like the vev ratios $r,w$ and the heavy scalar masses; collider probes via Higgs couplings and $H_3$ searches provide complementary constraints. The work also fits NANOGrav domain-wall-induced spectra to extract surface tension and bias parameters, highlighting the potential of PT-derived GWs and domain walls as probes of high-scale, accessible through upcoming GW detectors and future colliders.
Abstract
In this Ph.D. thesis, we study the methods to constrain particle physics models using the stochastic GW imprints from cosmological phase transitions (PTs). Beginning with the theory and background, we describe how the GW background from first-order PTs (FOPTs) and topological defects such as domain walls (DWs) can constrain the model parameter space at upcoming GW observatories. The first BSM scenario involves a flavon FOPT in two ultraviolet-complete models of the Froggatt-Nielsen (FN) mechanism. In both models, for the FN symmetry-breaking scale $v_s = 10^{4-7}\,$GeV, the parameter space is constrained by GWs in upcoming observatories such as BBO, DECIGO, CE, and ET. However, the GW spectrum does not discriminate between the two models. Next, we consider FOPT in the doublet left-right symmetric model (DLRSM) during $SU(2)_R\times U(1)_{B-L}$ breaking. For the breaking scale $v_R=20,\,30,\,50\,$TeV, the parameter space can be constrained by GW observations at BBO, FP-DECIGO, and Ultimate DECIGO. A large number of points with detectable GW signals can be ruled out from the precise measurement of the trilinear Higgs coupling at future colliders. Finally, we discuss the GW spectrum generated by DWs formed after the spontaneous breaking of the discrete $\mathcal{P}$-symmetry imposed on DLRSM. Using Bayesian analysis, we fit the 15-year NANOGrav dataset to the GW spectrum from DWs in DLRSM and determine the best-fit values of the DW surface tension and the bias potential. The techniques of this thesis can be applied to other BSM scenarios in the future.