Ramanujan Auditorium

How many parameters for our Universe?

Supratik Pal

ISI, Kolkata

Several cosmological observations together confirm that our Universe
is expanding at an accelerated rate in recent times. The cosmic
constituent responsible for this acceleration, generically called dark
energy, contributes to around 70% of the cosmic budget today.
Although there are several theoretically motivated candidates for dark
energy, its exact nature is still a mystery to us. With recent data we
can more or less be happy with a 6-parameter description of our
Universe – the so-called Lambda-CDM model, where the term CDM
stands for Cold Dark Matter and Lambda is the Cosmological
Constant, however, there are several alternatives to this baseline
model. In this colloquium, I will try to give a broad overview of the
theoretical and observations aspects of dark energy followed by our
current understanding of the Universe. I will further discuss certain
disturbing issues involving the minimal Lambda-CDM model based
on present observations, which generically go by the name of
cosmological tensions, and will investigate if going beyond the 6-
parameter description of the Universe can help us in this regard. I will
end up with some future directions in this field of research.