Speaker
Описание
Abstract
Modern precision cosmology is now accurate enough that even small departures from the standard picture can be tested, especially when we combine electromagnetic observations with gravitational waves. In this overview talk, we present our recent work on K-essence cosmology, where a non-canonical scalar field can simultaneously shape cosmic expansion and endow spacetime with an effective (emergent) geometry controlled by the field’s nonlinear kinetic structure. Framing the theory this way lets us connect the underlying geometry directly to observables. We first revisit the Raychaudhuri equation in the emergent K-essence spacetime and use it to track the behavior of timelike congruences: when geodesics focus, when they defocus, and under what conditions the evolution leads to singular or non-singular cosmological histories. We then extend the analysis to non-affinely parametrized congruences, showing how the extra geometric terms can be interpreted as effective contributions to the expansion dynamics, including a time-dependent dark-energy equation of state at late times. We next turn to gravitational-wave propagation on curved cosmological backgrounds. Within linearized gravity, we show that the emergent geometry can modify the tensor-mode evolution through effective friction/mass-like terms while remaining compatible with the near-luminal speed indicated by multi-messenger constraints. The net effect is a characteristic, model-dependent imprint on gravitational-wave phases and amplitudes, making standard sirens a clean probe of the K-essence sector. Finally, we discuss how to confront these scenarios with data by combining expansion-history probes (such as supernova distances, BAO, and cosmic chronometers) with gravitational-wave standard sirens in Bayesian parameter inference. We conclude by highlighting the key discriminants that can separate emergent-geometry K-essence models from $\Lambda$CDM and other modified-gravity proposals, and we outline the most promising directions for future tests.
Links
1. https://doi.org/10.1002/prop.202200193
2. https://doi.org/10.1002/prop.202400134
3. https://doi.org/10.1016/j.physletb.2025.139622
4. https://arxiv.org/abs/2605.25466