Discussion Meeting on Cosmology
February 14, 2012
Chandrasekhar Hall, IMSc, Chennai

This Discussion Meeting on Cosmology is organized with emphasis on observational aspects in the inflationary scenario and ideas on tests of loop quantum gravity. There will be four talks and time for discussions.
List of Participants





10:00 - 11:15

L Sriramkumar

Essentials of inflation and cosmological perturbation theory

11:15 - 11:45


11:45 - 13:00

Martin Bojowald

Observational tests of loop quantum gravity (inverse-triad corrections)

13:00 - 14:00


14:00 - 15:15

Martin Bojowald

Signature change and the emergence of the universe in loop quantum gravity (holonomy corrections)

15:15 - 15:45


15:45 - 17:00

L Sriramkumar

Primordial features and non-Gaussianities


Essentials of inflation and cosmological perturbation theory:

In this talk, I shall provide a pedagogical but rapid introduction to the essential aspects of inflation and cosmological perturbation theory. I will touch upon the basics of inflation, linear perturbation theory, the power spectra that arise in slow roll inflation, and discuss how simple inflationary models compare with the CMB data.

Observational tests of loop quantum gravity (inverse-triad corrections):

The new form of quantum geometry encountered in loop quantum gravity gives rise to characteristic modifications of the classical equations and symmetries. The more significant ones for cosmological observations, inverse-triad corrections, are introduced and evaluated from a cosmological perspective in this talk. (arXiv:1101.5391, arXiv:1107.1540)

Signature change and the emergence of the universe in loop quantum gravity (holonomy corrections):

Holonomy corrections, the second type of quantum-geometry effects in loop quantum cosmology, are relevant at high, nearly Planckian curvature. They therefore compete with higher-curvature terms in effective actions, but also have their own recognizable implications. In particular, when dominant they change the space-time signature from Lorentzian to Euclidean and provide a natural non-singular point to pose cosmological initial values. (arXiv:1111.3535, arXiv:1112.1899)

Primordial features and non-Gaussianities:

While a featureless, nearly scale invariant, primordial scalar power spectrum fits the most recent CMB data rather well, certain features in the spectrum are known to result in a better fit to the data. Interestingly, the presence of features in the scalar power spectrum can also lead to as large an amount of non-Gaussianity as the mean value of the non-Gaussianity parameter f_nl that has been arrived at from the WMAP seven year data.

In this talk, divided into parts, I shall first discuss the Starobinsky model, which, remarkably, allows for the analytic computation of the non-Gaussianity parameter f_nl in the equilateral limit (viz. f_nl^eq), despite the deviation from slow roll that occurs in the model. The analytic results obtained in the case of the Starobinsky model can be utilized to calibrate numerical codes, thereby permitting the computation of the bi-spectrum in a wide variety of inflationary models that contain departures from slow roll.

In the second part of the talk, I shall consider different sets of models that lead to similar features in the power spectrum (and, hence, to the same extent of improvement in the fit to the data), and discuss if f_nl^eq can possibly help us discriminate between the models. I shall point out that certain differences in the background dynamics -- reflected in the behavior of the slow roll parameters -- can lead to a reasonably large difference in the f_nl^eq generated by the competing models.

List of Participants:

Ghanashyam Date, IMSc
Martin Bojowald, IGC, Penn State Univ
L Sriramkumar, IIT-M
Bala Sathiapalan, IMSc
T R Govindarajan, IMSc
Romesh Kaul, IMSc
H S Mani, CMI
Upayan Baul, IMSc
Seema Satin, IMSc
Ramesh Anishetty, IMSc
Jahanur, IMSc
Trisha Nath, IMSc
Swastik Bhattacharya, IMSc
Gaurav Narain, IMSc
Ayan Chatterjee, IMSc
Sudipto Paul Chowdhary, IMSc
Nirmalya Kajuri, IMSc
Pinaki Banerjee, IMSc
Aditya Bawane, IMSc
Pramod Padmanabhan, IMSc
V. Sreenath, IIT-M
D. Jaffino Stargen, IIT-M
Taniya Mandal, IIT-M
Tirthankar Banerjee, IIT-M
Chandan Gupta, IIT-M
Deb Sankar Banerjee, IIT-M
Arpita Mitra, IIT-M
Prashant Kocherlakota, IIT-M
P. K. Adithya, IIT-M,
Ashish George, IIT-M,
Ramit Dey, IIT-M,