* Astronomy

Blobrana · L

Higgs inflation

Blobrana · L

RE: Inflation

Blobrana · L

Title: Primordial Fluctuations from Inflation with a Triad of Background Gauge Fields
Authors: Kei Yamamoto

We study the linear perturbation of the recently proposed model of inflation where a uniform gauge-kinetic coupling of the inflaton to multiple vector fields breaks the cosmic no-hair conjecture while maintaining the isotropy. We derive the general quadratic action for the perturbation and calculate the power spectra of scalar and tensor modes at the end of inflation by in-in formalism. It is shown that the model predicts slightly red spectra and the tensor-to-scalar ratio tends to be suppressed. The comparison with the data from WMAP 7-year does not impose strong constraints on the parameters and both weak- and strong- gauge-field regimes are consistent with the current observations.

Read more (17kb, PDF)

Blobrana · L

Title: Cosmological bootstrap
Authors: V. V. Kiselev, S. A. Timofeev

A huge value of cosmological constant characteristic for the particle physics and the inflation of early Universe are inherently related to each other: one can construct a fine-tuned superpotential, which produces a flat potential of inflaton with a constant density of energy V=\Lambda^4 after taking into account for leading effects due to the supergravity, so that an introduction of small quantum loop-corrections to parameters of this superpotential naturally results in the dynamical instability relaxing the primary cosmological constant by means of inflationary regime. The model phenomenologically agrees with observational data on the large scale structure of Universe at \Lambda~10^{16} GeV.

Read more (611kb, PDF)

Blobrana · L

Title: On the origin of inflation
Authors: Torsten Asselmeyer-Maluga, Jerzy Król

In this paper we discuss a space-time having the topology of S^{3}xR but with different smoothness structure. This space-time is not a global hyperbolic space-time. Especially we obtain a time line with a topology change of the space from the 3-sphere to a homology 3-sphere and back but without a topology-change of the space-time. Among the infinite possible smoothness structures of this space-time, we choose a homology 3-sphere with hyperbolic geometry admitting a homogenous metric. Then the topology change can be described by a time-dependent curvature parameter k changing from k=+1 to k=-1 and back. The solution of the Friedman equation for dust matter (p=0) after inserting this function shows an exponential growing which is typical for inflation. In contrast to other inflation models, this process stops after a finite time.

Read more (23kb, PDF)

Blobrana · L

Title: Distinguishing between R²-inflation and Higgs-inflation
Authors: Fedor Bezrukov, Dmitry Gorbunov

We present three features which can be used to distinguish the Higgs-inflation from R²-inflation with ongoing, upcoming and planned experiments. (i) Slightly different tilt of the scalar perturbation spectrum n_s and ratio r of scalar-to-tensor perturbation amplitudes. (ii) Gravity waves produced within R²-model by collapsing, merging and evaporating scalaron clumps formed in the post-inflationary Universe. (iii) Different ranges of the possible Standard Model Higgs boson masses, where the electroweak vacuum remains stable while the Universe evolves after inflation. Specifically, in the R²-model Higgs boson can be as light as 116 GeV. These effects mainly rely on the lower reheating temperature in the R²-inflation.

Read more (10kb, PDF)

Blobrana · L

Title: Eternal Inflation, Global Time Cutoff Measures, and a Probability Paradox
Authors: Alan H. Guth, Vitaly Vanchurin

The definition of probabilities in eternally inflating universes requires a measure to regulate the infinite spacetime volume, and much of the current literature uses a global time cutoff for this purpose. Such measures have been found to lead to paradoxical behaviour, and recently Bousso, Freivogel, Leichenauer, and Rosenhaus have argued that, under reasonable assumptions, the only consistent interpretation for such measures is that time must end at the cutoff. Here we argue that there is an alternative, consistent formulation of such measures, in which time extends to infinity. Our formulation begins with a mathematical model of the infinite multiverse, which can be constructed without the use of a measure. Probabilities, which obey all the standard requirements for a probability measure, can then be defined by mathematical limits. They have a peculiar feature, however, which we call time-delay bias: if the outcome of an experiment is reported with a time delay that depends on the outcome, then the observation of the reports will be biased in favour of the shorter time delay. We show how the paradoxes can be resolved in this interpretation of the measure.

Read more (303kb, PDF)

Blobrana · L

Title: Bubbles from Nothing
Authors: Jose J. Blanco-Pillado, Handhika S. Ramadhan, Benjamin Shlaer

Within the framework of flux compactifications, we construct an instanton describing the quantum creation of an open universe from nothing. The solution has many features in common with the smooth 6d bubble of nothing solutions discussed recently, where the spacetime is described by a 4d compactification of a 6d Einstein-Maxwell theory on S² stabilised by flux. The four-dimensional description of this instanton reduces to that of Hawking and Turok. The choice of parameters uniquely determines all future evolution, which we additionally find to be stable against bubble of nothing instabilities.

Read more (800kb, PDF)

Blobrana · L

Title: Is the Spectrum of Gravitational Waves the "Holy Grail" of Inflation?
Authors: Robert H. Brandenberger (McGill University)

It is often said that detecting a spectrum of primordial gravitational waves via observing B-mode polarisation of the Cosmic Microwave Background is the "Holy Grail" of inflation. The purpose of this short note is to point out that it is indeed of immense scientific interest to search for a signal of gravitational waves in B-mode polarisation. However, rather than proving that inflation is the right paradigm of early universe cosmology, a positive signal of direct primordial B-mode polarisation might well be due to other sources than inflation. In fact, a careful characterisation of the spectrum of B-mode polarisation might even falsify the inflationary paradigm.

Read more (85kb, PDF)

Blobrana · L

Inflation at South Pole
New telescopes search universe for signs of rapid expansion after the Big Bang

The theory of inflation holds that just a fraction of a second after the universe exploded into existence, it expanded exponentially. The search for the evidence that will finally prove or disprove one of the key concepts of the Big Bang model of cosmology has similarly expanded in the last decade or so. The South Pole Station has become one of the preeminent locations for that quest.
Read more