Research Projects

Although extremely successful, today, the standard model (SM) of particle physics faces several challenges from new data. Tiny non-zero neutrino masses and the existence of matter-antimatter asymmetry in the universe are two such crucial observations. Several theories beyond the SM (BSM) address these issues, but their collider tests are limited by energy and luminosity constraints. The discovery of gravitational waves (GWs) in 2015 by LIGO has opened a new possibility of using GWs to probe BSM theories. Upcoming GW detectors will be sensitive to the GW imprints of cosmological phase transitions (PTs), produced during strong first-order phase transitions (FOPT), and by topological defects such as domain walls and cosmic strings. The features of the GW spectrum contain information about the underlying BSM model, allowing the upcoming detectors to probe particle physics scales ranging from 10² MeV to as high as 10⁷ GeV. This project is aimed at exploring well-motivated neutrino mass and baryogenesis models with the intent to probe them indirectly at GW experiments. Many of these models feature spontaneous symmetry breaking via a scalar field and would exhibit a PT in the early universe. Such models are already constrained by the bounds on neutrino masses and mixing parameters, the observed baryon-to-photon ratio, etc. The objective is to supplement current bounds with those obtained from GW signals associated with PTs. We also aim to refine the theoretical and numerical techniques used in the analysis. The results will be published in a series of papers. The first step is to survey popular neutrino mass and baryogenesis scenarios and study the existing constraints on their parameter space. For each model, we construct the finite-temperature effective potential and analyze the nature of PT numerically/analytically. We constrain the parameter space using the existing bounds from LIGO-VIRGO-KAGRA and pulsar timing arrays, while for upcoming GW detectors, we calculate the signal-to-noise ratio (SNR) using their sensitivity curves. Models featuring supercooled PTs may have other interesting consequences, such as the formation of primordial black holes (PBH) and primordial magnetic fields (PMF), which can lead to further constraints. We also plan to pursue novel model-building avenues and explore their detection prospects at GW experiments. Using GWs to probe particle physics is a nascent field with a lot of scope for development. As several GW detectors are expected to be operational in the coming years, this project will help us gain useful insights into baryogenesis and neutrino mass models, based on their detectability. This would allow us to constrain the models far beyond the reach of colliders, which is typically the case in the scenarios of interest. Moreover, calculating the GW spectrum for these models can help us identify useful patterns, with the possibility of distinguishing them.