Speaker
Description
We investigate the dynamical impact of a time-dependent curvature–scalar coupling function $S(t)$ within a modified scalar–tensor framework. By analysing the generalized acceleration equation, we show that, in contrast to standard $\Lambda$CDM, where pressureless matter contributes exclusively to deceleration, modifications induced by $S(t)$ alter the gravitational response, leading to a nontrivial modulation of matter contributions. In particular, the effective coupling of pressureless matter is rescaled by a factor proportional to $(1-2S)$, which induces a critical transition at $2S=1$. At this point, dust becomes gravitationally neutral with respect to cosmic acceleration, while for $2S>1$ it contributes with the opposite sign, effectively driving accelerated expansion despite remaining pressureless. This behaviour arises dynamically through the dependence of $S(t)$ on the Ricci scalar and scalar field evolution, enabling curvature-triggered transitions in the gravitational role of ordinary matter. We further identify the domain $\vert S\vert<1$ as the branch continuously connected to general relativity, with $\vert S\vert=1$ marking a structural singularity in the field equations. These results suggest that coupling-induced modifications to matter dynamics can qualitatively alter the role of standard matter, providing an alternative mechanism for late-time acceleration within scalar-tensor theories.
| Apply for student award at which level: | PhD |
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| Consent on use of personal information: Abstract Submission | Yes, I ACCEPT |