# Cosmological Constant

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## Recording Details

Scientific Areas:
Subjects:
PIRSA Number:
12100126

## Abstract

Dark Matter and Dark Energy as a Possible Manifestation of a Fundamental Scale
If we take the idea of the Planck length as a fundamental (minimum) scale and if additionally we impose the Cosmological Constant ($Lambda$) as and infrared (IR) cut-off parameter. Then it is possible to demonstrate that Dark Matter effects can emerge as a consequence of an IR-UV mix effect. This opens the possibility of unifying the Dark Energy and Dark matter effects in a single approach.

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Geometric Operators in Loop Quantum Gravity with a Cosmological Constant
Loop quantum gravity is a candidate to describe the quantum
gravity regime with zero cosmological constant. One of its key results
is that geometric operators such as area angle volume are quantized. Not
much is known when the cosmological constant is not zero. It is usually
believed that to introduce this parameter in the game we need to use
quantum groups. However due to the complicated algebraic structure
inherent to quantum groups the geometric operators are not yet properly
defined (except the area operator). I will discuss how the use of tensor
operators can circumvent the difficulties and allow to construct a
natural set of observables. In particular I will construct the natural
geometric observables such as angle or volume and discuss some of their
implications.

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Interplay Between Cosmological Constant and DSR Scale
I offer brief remarks on several ways in which the cosmological
constant could provide a clue toward quantum gravity.  I then focus on
how DSR-relativistic theories can be made compatible with spacetime
expansion (possibly cosmological-constant-governed spacetime expansion),
and how this interplay could manifest itself in data.

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Quantum Gravity RG Flow: A Cosmological Limit Cycle
I will discuss evidence for the existence of a limit cycle in the
renormalization group for quantum gravity which is visible in a
minisuperspace approximation. The emergence of the limit cycle can be
studied through a tuning parameter representing the number of dimensions
in which fluctuations of the conformal factor are suppressed. At the
critical value of the tuning parameter all RG trajectories reaching the
UV fixed point have an extended semiclassical regime with a small
positive cosmological constant providing a possible model for a viable
cosmology without fine-tuning.