7 research outputs found
Evidence against or for topological defects in the BOOMERanG data ?
The recently released BOOMERanG data was taken as ``contradicting topological
defect predictions''. We show that such a statement is partly misleading.
Indeed, the presence of a series of acoustic peaks is perfectly compatible with
a non-negligible topological defects contribution. In such a mixed perturbation
model (inflation and topological defects) for the source of primordial
fluctuations, the natural prediction is a slightly lower amplitude for the
Doppler peaks, a feature shared by many other purely inflationary models. Thus,
for the moment, it seems difficult to rule out these models with the current
data.Comment: 4 pages, 1 figure. Some changes following extraordinarily slow
referee Reports and new data. Main results unchanged (sorry
Non-Vacuum Initial States for Cosmological Perturbations of Quantum-Mechanical Origin
In the context of inflation, non-vacuum initial states for cosmological
perturbations that possess a built in scale are studied. It is demonstrated
that this assumption leads to a falsifiable class of models. The question of
whether they lead to conflicts with the available observations is addressed.
For this purpose, the power spectrum of the Bardeen potential operator is
calculated and compared with the CMBR anisotropies measurements and the
redshift surveys of galaxies and clusters of galaxies. Generic predictions of
the model are: a high first acoustic peak, the presence of a bump in the matter
power spectrum and non-Gaussian statistics. The details are controlled by the
number of quanta in the non-vacuum initial state. Comparisons with observations
show that there exists a window for the free parameters such that good
agreement between the data and the theoretical predictions is possible.
However, in the case where the initial state is a state with a fixed number of
quanta, it is shown that this number cannot be greater than a few. On the other
hand, if the initial state is a quantum superposition, then a larger class of
initial states could account for the observations, even though the state cannot
be too different from the vacuum. Planned missions such as the MAP and Planck
satellites and the Sloan Survey, will demonstrate whether the new class of
models proposed here represents a viable alternative to the standard theory.Comment: revtex, 15 pages, 10 figures. Submitted to Phys.Rev.
Black Hole Lasers Revisited
The production of Hawking radiation by a single horizon is not dependent on
the high-frequency dispersion relation of the radiated field. When there are
two horizons, however, Corley and Jacobson have shown that superluminal
dispersion leads to an amplification of the particle production in the case of
bosons. The analytic theory of this "black hole laser" process is quite
complicated, so we provide some numerical results in the hope of aiding
understanding of this interesting phenomenon. Specifically, we consider sonic
horizons in a moving fluid. The theory of elementary excitations in a
Bose-Einstein condensate provides an example of "superluminal" (Bogoliubov)
dispersion, so we add Bogoliubov dispersion to Unruh's equation for sound in
the fluid. A white-hole/black-hole horizon pair will then display black hole
lasing. Numerical analysis of the evolution of a wave packet gives a clear
picture of the amplification process. By utilizing the similarity of a
radiating horizon to a parametric amplifier in quantum optics we also analyze
the black hole laser as a quantum-optical network.Comment: 16 page
How generic is cosmic string formation in SUSY GUTs
We study cosmic string formation within supersymmetric grand unified
theories. We consider gauge groups having a rank between 4 and 8. We examine
all possible spontaneous symmetry breaking patterns from the GUT down to the
standard model gauge group. Assuming standard hybrid inflation, we select all
the models which can solve the GUT monopole problem, lead to baryogenesis after
inflation and are consistent with proton lifetime measurements. We conclude
that in all acceptable spontaneous symmetry breaking schemes, cosmic string
formation is unavoidable. The strings which form at the end of inflation have a
mass which is proportional to the inflationary scale. Sometimes, a second
network of strings form at a lower scale. Models based on gauge groups which
have rank greater than 6 can lead to more than one inflationary era; they all
end by cosmic string formation.Comment: 31 pages, Latex, submitted to PR
Enhanced Non-Gaussianity from Excited Initial States
We use the techniques of effective field theory in an expanding universe to
examine the effect of choosing an excited inflationary initial state built over
the Bunch-Davies state on the CMB bi-spectrum. We find that even for Hadamard
states, there are unexpected enhancements in the bi-spectrum for certain
configurations in momentum space due to interactions of modes in the early
stages of inflation. These enhancements can be parametrically larger than the
standard ones and are potentially observable in current and future data. These
initial state effects have a characteristic signature in -space which
distinguishes them from the usual contributions, with the enhancement being
most pronounced for configurations corresponding to flattened triangles for
which two momenta are collinear.Comment: 33 pages, 1 figure. Refs added and minor addition