UC Riverside

In the conventional misalignment mechanism, the axion field is assumed to start with zero initial velocity. However, we introduce an alternative scenario in which the axion field possesses a nonzero initial velocity, potentially due to the breaking of the Peccei–Quinn (PQ) symmetry during the early Universe. Depending on the initial velocity and the sequence of events between PQ symmetry breaking and inflation, this novel scenario can amplify or diminish the expected axion relic abundance compared to the conventional prediction. Consequently, this opens up new parameter regions for axion dark matter models.

Global cosmic strings, anticipated in various non-standard models, generate primordial gravitational waves detectable by instruments. We refine the analytical Velocity-dependent One-Scale (VOS) model through recent simulation outcomes, revealing the gravitational wave spectrum produced by global string networks, including Goldstone emission. Our findings present a technique to detect signals from the early universe before Big Bang nucleosynthesis, impacted by the non-standard pre-BBN equation of state and new relativistic particles.

Early dark energy, relieving the Hubble tension, imprints discernible characteristics on the primordial stochastic gravitational wave background originating from cosmic string networks. This signal stands out in planned gravitational wave experiments, distinctly separate from other cosmological and astrophysical signals in the gravitational wave frequency spectrum.

In the context of axion-like particle (ALP) dark matter theories, we explore enhanced early galaxy formation through the kinetic misalignment mechanism. This has potential relevance to the excess observed by the James Webb Space Telescope (JWST) while adhering to constraints. Viable parameter space is identified for ALP mass within the range of $10^{-22}{\rm eV}

Through advanced simulations and analytical modeling, we conduct an updated analysis of long-lived axion domain wall (DW) networks. By scrutinizing energy loss mechanisms and calculating axion emissions from the DW network, we determine their contribution to axion dark matter density. While our results are consistent with prior research, disparities arise, particularly in predicting DM abundance. These disparities could profoundly impact axion phenomenology on a larger scale.