Cosmological birefringence induced by neutrino current

We review our recent work, Geng et al. (J. Cosmol. Astropart. Phys. 09, 010 (2007)) on the cosmological birefringence. We propose a new type of effective interactions in terms of the CPT-even dimension-six Chern–Simons-like term to generate the cosmological birefringence. We use the neutrino number asymmetry to induce a nonzero rotation polarization angle in the data of the cosmic microwave background-radiation polarization.PACS Nos.: 98.80.Cq, 98.80.Es, 11.30.Fs

Looking beyond inflationary cosmology

In spite of the phenomenological successes of the inflationary universe scenario, the current realizations of inflation making use of scalar fields lead to serious conceptual problems that are reviewed in this lecture. String theory may provide an avenue towards addressing these problems. One particular approach to combining string theory and cosmology is String Gas Cosmology. The basic principles of this approach are summarized.PACS No.: 98.80.Cq}

Aspects of brane-antibrane inflation

I describe a dynamical mechanism for solving the fine-tuning problem of brane-antibrane inflation. By inflating with stacks of branes and antibranes, the branes can naturally be trapped at a metastable minimum of the potential. As branes tunnel out of this minimum, the shape of the potential changes to make the minimum shallower. Eventually the minimum disappears and the remaining branes roll slowly because the potential is nearly flat. I show that even with a small number of branes, there is a good chance of getting enough inflation. Running of the spectral index is correlated with the tilt in such a way as to provide a test of the model by future cosmic microwave background experiments.PACS Nos.: 11.25.Wx, 98.80.Cq

Cosmological implications of a minimal length hypothesis

One of the firm predictions of inflationary cosmology is the consistency relation between scalar and tensor spectra. It has been argued that such a relation — if experimentally confirmed — would offer strong support for the idea of inflation. We examine the possibility that trans-Planckian physics violates the consistency relation in the framework of inflation with a cutoff proposed in astro-ph/0009209. We find that despite the ambiguity that exists in choosing the action, Planck-scale physics modifies the consistency relation considerably. It also leads to the running of the spectral index. For modes that are larger than our current horizon, the tensor spectral index is positive. For a window of k values with amplitudes of the same order as the modes that are the precursors to structure formation, the behavior of the tensor spectral index is oscillatory about the standard Quantum field theory result, taking both positive and negative values. There is a hope that in the light of future experiments, this scenario of short distance physics, can be verified.PACS Nos.: 98.80.Cq , 98.80.-k, 98.80.Qc