69,937 research outputs found
The inflationary origin of the Cold Spot anomaly
Single-field inflation, arguably the simplest and most compelling paradigm
for the origin of our Universe, is strongly supported by the recent results of
the Planck satellite and the BICEP2 experiment. The results from Planck,
however, also confirm the presence of a number of anomalies in the Cosmic
Microwave Background (CMB), whose origin becomes problematic in single-field
inflation. Among the most prominent and well-tested of these anomalies is the
Cold Spot, which constitutes the only significant deviation from gaussianity in
the CMB. Planck's non-detection of primordial non-gaussianity on smaller scales
thus suggests the existence of a physical mechanism whereby significant
non-gaussianity is generated on large angular scales only. In this letter, we
address this question by developing a localized version of the inhomogeneous
reheating scenario, which postulates the existence of a scalar field able to
modify the decay of the inflaton on localized spatial regions only. We
demonstrate that if the Cold Spot is due to an overdensity in the last
scattering surface, the localization mechanism offers a feasible explanation
for it, thus providing a physical mechanism for the generation of localized
non-gaussianity in the CMB. If, on the contrary, the Cold Spot is caused by a
newly discovered supervoid (as recently claimed), we argue that the
localization mechanism, while managing to enhance underdensities, may well shed
light on the rarity of the discovered supervoid.Comment: 12 pages, 4 figures. v3 Comments and references added. It matches
published versio
The vector BPS baby Skyrme model
We investigate the relation between the BPS baby Skyrme model and its vector
meson formulation, where the baby Skyrme term is replaced by a coupling between
the topological current and the vector meson field . The
vector model still possesses infinitely many symmetries leading to infinitely
many conserved currents which stand behind its solvability. It turns out that
the similarities and differences of the two models depend strongly on the
specific form of the potential. We find, for instance, that compactons (which
exist in the BPS baby Skyrme model) disappear from the spectrum of solutions of
the vector counterpart. Specifically, for the vector model with the old baby
Skyrme potential we find that it has compacton solutions only provided that a
delta function source term effectively screening the topological charge is
inserted at the compacton boundary. For the old baby Skyrme potential squared
we find that the vector model supports exponentially localized solitons, like
the BPS baby Skyrme model. These solitons, however, saturate a BPS bound which
is a nonlinear function of the topological charge and, as a consequence, higher
solitons are unstable w.r.t. decay into smaller ones, which is at variance with
the more conventional situation (a linear BPS bound and stable solitons) in the
BPS baby Skyrme model.Comment: 20 pages, 4 figure
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