Speaker
Description
Recent cosmological observations, including those from the Dark Energy Spectroscopic Instrument (DESI), hint at a dynamical nature of dark energy. Motivated by phenomenological parametrizations of the equation-of-state parameter $w(a)$ with sharp transitional features, we study their realization in quintessence models. In our scenario, the quintessence field begins to oscillate abruptly in the late Universe, leading to a rapid change in $w$. This dynamics naturally involves tachyonic instability and particle production, which in turn affects the evolution of $w$. We perform numerical lattice simulations to study the resulting dynamics. The associated particle production also generates significant density perturbations and a stochastic gravitational-wave background, with characteristic scales set by the quintessence mass around the potential minimum. We discuss the observational prospects of these late-time signals, including those in the cosmic microwave background, quasar astrometry, pulsar timing arrays, and other probes.