Supercooled First Order Phase Transitions and Gravitational Waves in a B − L-like Model

Sammanfattning

This thesis studies first-order phase-transition dynamics and the associated stochastic gravitational-wave background in classically conformal B − L-like extensions of the Standard Model. The scalar and gauge sectors are formulated at tree level and at one-loop order using a modified on-shell renormalization prescription designed to keep the vacuum structure fixed while allowing the tree-level flat-direction scalar to acquire a loop-induced mass. The finite-temperature effective potential is then used to analyse supercooled first-order phase transitions and the resulting gravitational-wave spectra. Numerical benchmark studies are performed with the Python package TransitionSolver. For the limited benchmark points considered here, the predicted gravitational-wave signals are below the projected detectability of LISA and current pulsar-timing-array searches. These results should therefore be interpreted as an exploratory benchmark analysis rather than as a general exclusion of the model class.