Hamsa Padmanabhan

CosMIn: THE SOLUTION TO THE COSMOLOGICAL CONSTANT PROBLEM

The current acceleration of the universe can be modeled in terms of a cosmological constant Λ. We show that the extremely small value of , the holy grail of theoretical physics, can be understood in terms of a new, dimensionless, conserved number Cosmic Mode Index (CosMIn), which counts the number of modes crossing the Hubble radius during the three phases of evolution of the universe. Theoretical considerations suggest that N ≈ 4π. This single postulate leads us to the correct, observed numerical value of the cosmological constant! This approach also provides a unified picture of cosmic evolution relating the early inflationary phase to the late accelerating phase.

Cosmological constant from the emergent gravity perspective

Observations indicate that our universe is characterized by a late-time accelerating phase, possibly driven by a cosmological constant

Constraining a halo model for cosmological neutral hydrogen

\Lambda

A halo model for cosmological neutral hydrogen : abundances and clustering

, with the dimensionless parameter

Constraints on the evolution of the relationship between H i mass and halo mass in the last 12 Gyr

\Lambda L_P^2 \simeq 10^{-122}

Cosmic information, the cosmological constant and the amplitude of primordial perturbations

, where

Photon number conserving models of H ii bubbles during reionization

L_P = (G \hbar /c^3)^{1/2}

Constraining the CO intensity mapping power spectrum at intermediate redshifts

is the Planck length. In this review, we describe how the emergent gravity paradigm provides a new insight and a possible solution to the cosmological constant problem. After reviewing the necessary background material, we identify the necessary and sufficient conditions for solving the cosmological constant problem. We show that these conditions are naturally satisfied in the emergent gravity paradigm in which (i) the field equations of gravity are invariant under the addition of a constant to the matter Lagrangian and (ii) the cosmological constant appears as an integration constant in the solution. The numerical value of this integration constant can be related to another dimensionless number (called CosMIn) that counts the number of modes inside a Hubble volume that cross the Hubble radius during the radiation and the matter dominated epochs of the universe. The emergent gravity paradigm suggests that CosMIn has the numerical value

Quantum gravity at Hubble scales determines the cosmological constant and the amplitude of primordial perturbations

4 \pi

Neutral hydrogen in the post-reionization universe

, which, in turn, leads to the correct, observed value of the cosmological constant. Further, the emergent gravity paradigm provides an alternative perspective on cosmology and interprets the expansion of the universe itself as a quest towards holographic equipartition. We discuss the implications of this novel and alternate description of cosmology.