*October 20, 2015.*

Present well-accepted standard cosmological model is the CDM which gives inflation, the super-fast early-universe acceleration. Scalar field causing inflation is dubbed inflaton. In the model, present and late universe acceleration is driven by cosmological constant which recently dominates the universe since about 3.500 billion years ago. The CDM is built on the solid ground of General Relativity (GR) and standard model of particle physics or upto supersymmetry theory. The model predicts amazingly best-fit result to astrophysical observations which have a few statistical parameters. Data from different and independent sources of observations are well-matched. These are from Cosmic Microwave Background Anisotropy, Galaxy Clusters Survey and Supernovae luminosity as in **Fig. 1.** The GR breaks down at beyond Planck energy scale ( ). Hence CDM is only a low-energy limit of Quantum Gravities. Understanding of physics beyond Planck scale can lay foundation to inflation or might offer new alternatives that could replace inflation. Apart from problem at high-energy early universe, there is as well another problem of low-energy late-time universe. What cause the late acceleration? This is due to the problem that comes with the cosmological constant. in particle theory plays a role of vacuum energy which is predicted to be whereas the as astrophysical observation-matched cosmological constant should take value of only .This big problem motivates other energy models which envisages time-evolving energy density that drives acceleration. These models are called __dark energy__ models. Apart from this, there are other alternatives such as gravitational theory with extra dimensions or modifying the Lagrangian density of the Einstein-Hilbert action of the standard GR to new other types. These modified gravitational theories are such as gravity, Eddington gravities, non-minimum coupling gravities which are class of Scalar-Tensor Theory of Gravitation. IF Research teams, funded by Thailand Center of Excellence in Physics (ThEP Center), are investigating various dark energy as well as modified gravity models. We check if they could agree with observations and strong existing foundation of physics in order to embed the new idea into our understanding of the universe.

**Fig. 1** plane showing three types of cosmological observation joint constrains *(from [1]).*

**Reference :**

- R. A. Knop et al. [The Supernova Cosmology Project Collaboration], “New Constraints on and
*w*from an Independent Set of Eleven High-Redshift Supernovae Observed with HST,” Astrophys. J. 598, 102 (2003) [arXiv:astro-ph/0309368].

**Reported by :**

Assoc. Prof. Dr. Burin Gumjudpai

The Institute for Fundamental Study “The Tah Poe Academia Institute”

2^{nd} Flr., Mahadhammaraja A Bld., Naresuan University

A. Muang, Phitsanulok 65000, Thailand

Telephone : 091 843 8841 E-mail : buring@nu.ac.th