Inflation, Symmetry, and B-Modes

We examine the role of using symmetry and effective field theory in inflationary model building. We describe the standard formulation of starting with an approximate shift symmetry for a scalar field, and then introducing corrections systematically in order to maintain control over the inflationary potential. We find that this leads to models in good agreement with recent data. 

On the other hand, there are attempts in the literature to deviate from this paradigm by envoking other symmetries and corrections. In particular: in a suite of recent papers, several authors have made the claim that standard Einstein gravity with a cosmological constant and a massless scalar carries conformal symmetry. They further claim that such a theory carries another hidden symmetry; a global SO(1,1) symmetry. By deforming around the global SO(1,1) symmetry, they are able to produce a range of inflationary models with asymptotically flat potentials, whose flatness is claimed to be protected by these symmetries. 

Image : alice.loria.fr

These models tend to give rise to B-modes with small amplitude. Here we explain that these authors are merely introducing a redundancy into the description, not an actual conformal symmetry. Furthermore, we explain that the only real (global) symmetry in these models is not at all hidden, but is completely manifest when expressed in the Einstein frame; it is in fact the shift symmetry of a scalar field. When analyzed systematically as an effective field theory, deformations do not generally produce asymptotically flat potentials and small B-modes, but other types of potentials with B-modes of large amplitude; nicely compatible with recent BICEP2 data. Such simple models typically also produce the observed red spectral index, Gaussian fluctuations, etc. In short: simple models of inflation, organized by expanding around a shift symmetry, are in excellent agreement with recent data.

Link : http://arxiv.org/pdf/1403.5253

Claim New Study, Every Blackhole is a Portal to Another Universe

A black hole is a region of spacetime from which gravity prevents anything, including light, from escaping. The theory of general relativity predicts that a sufficiently compact mass will usually deform spacetime to form a black hole. Around a black hole, there is a mathematically defined surface called an event horizon that marks the point of no return.  [wikipedia]

The new theory was developed by Jorge Pullin of the State University of Louisiana and Rodolfo Gambino of the University of the Republic of Uruguay. The two scientists decided to study the predictions of the theory of quantum gravity in black holes. More specifically, they applied the equations of quantum gravity in a non-rotating black hole with spherical symmetry.

As described in other theories, as the matter approaches the core of the black hole, the gravitational field becomes more and more powerful, but it does not disappear into a spacetime singularity as the prevailing theory states. According to the study results of the two researchers, the matter does not disappear in the middle of the hole but continues its way up the other end and into another universe. “Like part of a cosmic Russian doll, our universe may be nested inside a black hole that is itself part of a larger universe.

image: http://www.shutterstock.com/pic.mhtml?id=25016035

In turn, all the black holes found so far in our universe—from the microscopic to the supermassive—may be doorways into alternate realities.” According to the new equations, the matter black holes absorb and seemingly destroy is actually expelled and becomes the building blocks for galaxies, stars, and planets in another reality. Essentially, every black hole contains a smaller alternate universe. And our universe might just exist inside a black hole of a galaxy in a much larger universe. So within the 100 billion galaxies in our known universe lies 100 billion universes in the galactic black holes of our universe, with 100 billion more galaxies each containing another universe with more galaxies, and so on infinitely.

The new model isn't the first to propose that other universes exist inside black holes. Damien Easson, a theoretical physicist at Arizona State University, has made the speculation in previous studies. “What is new here is an actual wormhole solution in general relativity that acts as the passage from the exterior black hole to the new interior universe,” said Easson, who was not involved in the new study. So the idea that black holes are portals to other worlds rather than a place of absolute destruction is not new. But they all stumbled on the spacetime singularity.

This is the first time when this barrier is bypassed with the help of scientific tools. The results of the study were published in the journal Physical Review Letters. Furthermore, a recent study published in the scientific journal Nature shows that our entire universe may have been born out of a black hole from another universe. In other words, the Big Bang was really just an extension of a black hole in a different universe.

Source : http://www.whydontyoutrythis.com/2014/03/every-black-hole-contains-another-universe-claims-new-study.html

Discovery of Large Scale Tensor Mode and Chaotic Inflation in Supergravity

SUGRA, or SUper GRAvity, was discovered in 1976 by Dan Freedman, Sergio Ferrara and Peter Van Nieuwenhuizen. In theoretical physics, supergravity (supergravity theory) is a field theory that combines the principles of supersymmetry and general relativity. Together, these imply that, in supergravity, the supersymmetry is a local symmetry (in contrast to non-gravitational supersymmetric theories, such as the Minimal Supersymmetric Standard Model). Since the generators of supersymmetry (SUSY) are convoluted with the Poincaré group to form a super-Poincaré algebra, it can be seen that supergravity follows naturally from supersymmetry.

Like any field theory of gravity, a supergravity theory contains a spin-2 field whose quantum is the graviton. Supersymmetry requires the graviton field to have a superpartner. This field has spin 3/2 and its quantum is the gravitino. The number of gravitino fields is equal to the number of supersymmetries.

The BICEP2 collaboration has recently reported a large tensor fluctuation in the cosmic microwave background, which suggests chaotic inflation models. In this letter, we reconsider the chaotic inflation model in the supergravity. We introduce a non-holomorphic shift-symmetry breaking parameter, which we expect to exist in general, and discuss its effect on the inflaton dynamics. We show that the model predicts a sizable deviation from the original chaotic inflation model and the predicted tensor fluctuation can lie between the BICEP2 result and the upper bound given by the Planck experiment with a small shift-symmetry breaking parameter. The model is characterized by only two parameters, which yields predictability and testability in future experiments.

Cosmic inflation is a natural scenario which not only solves the flatness and the horizon problem, but also explains the large scale structure of the universe and the fluctuation of the cosmic microwave background (CMB) radiation. Precise observations of the CMB begins to reveal nature of inflation. Chaotic inflation models have been studied in the literature, especially in the context of the supergravity theory (SUGRA). In this letter, we reconsider chaotic in ation models in the SUGRA...

Read more : http://en.wikipedia.org/wiki/Supergravity || http://arxiv.org/pdf/1403.4729