226 research outputs found
Generation of Coherent Structures After Cosmic Inflation
We investigate the nonlinear dynamics of hybrid inflation models, which are
characterized by two real scalar fields interacting quadratically. We start by
solving numerically the coupled Klein-Gordon equations in static Minkowski
spacetime, searching for possible coherent structures. We find long-lived,
localized configurations, which we identify as a new kind of oscillon. We
demonstrate that these two-field oscillons allow for "excited" states with much
longer lifetimes than those found in previous studies of single-field
oscillons. We then solve the coupled field equations in an expanding
Friedmann-Robertson-Walker spacetime, finding that as the field responsible for
inflating the Universe rolls down to oscillate about its minimum, it triggers
the formation of long-lived two-field oscillons, which can contribute up to 20%
of the total energy density of the Universe. We show that these oscillons
emerge for a wide range of parameters consistent with WMAP 7-year data. These
objects contain total energy of about 25*10^20 GeV, localized in a region of
approximate radius 6*10^-26 cm. We argue that these structures could have
played a key role during the reheating of the Universe.Comment: 12 pages, 10 .pdf figures, uses RevTex4; v2: expanded discussion in
section IV, accepted for publication in Phys.Rev. D. Results remain the sam
Drake Equation for the Multiverse: From the String Landscape to Complex Life
It is argued that selection criteria usually referred to as "anthropic
conditions" for the existence of intelligent (typical) observers widely adopted
in cosmology amount only to preconditions for primitive life. The existence of
life does not imply in the existence of intelligent life. On the contrary, the
transition from single-celled to complex, multi-cellular organisms is far from
trivial, requiring stringent additional conditions on planetary platforms. An
attempt is made to disentangle the necessary steps leading from a selection of
universes out of a hypothetical multiverse to the existence of life and of
complex life. It is suggested that what is currently called the "anthropic
principle" should instead be named the "prebiotic principle."Comment: 6 pages, RevTeX, in press, Int. J. Mod. Phys.
Gravitational instability of Einstein-Gauss-Bonnet black holes under tensor mode perturbations
We analyze the tensor mode perturbations of static, spherically symmetric
solutions of the Einstein equations with a quadratic Gauss-Bonnet term in
dimension . We show that the evolution equations for this type of
perturbations can be cast in a Regge-Wheeler-Zerilli form, and obtain the exact
potential for the corresponding Schr\"odinger-like stability equation. As an
immediate application we prove that for and , the sign
choice for the Gauss-Bonnet coefficient suggested by string theory, all
positive mass black holes of this type are stable. In the exceptional case , we find a range of parameters where positive mass asymptotically flat
black holes, with regular horizon, are unstable. This feature is found also in
general for .Comment: 7 pages, 1 figure, minor corrections, references adde
Mass loss and longevity of gravitationally bound oscillating scalar lumps (oscillatons) in D-dimensions
Spherically symmetric oscillatons (also referred to as oscillating soliton
stars) i.e. gravitationally bound oscillating scalar lumps are considered in
theories containing a massive self-interacting real scalar field coupled to
Einstein's gravity in 1+D dimensional spacetimes. Oscillations are known to
decay by emitting scalar radiation with a characteristic time scale which is,
however, extremely long, it can be comparable even to the lifetime of our
universe. In the limit when the central density (or amplitude) of the
oscillaton tends to zero (small-amplitude limit) a method is introduced to
compute the transcendentally small amplitude of the outgoing waves. The results
are illustrated in detail on the simplest case, a single massive free scalar
field coupled to gravity.Comment: 23 pages, 2 figures, references on oscillons added, version to appear
in Phys. Rev.
Long-Lived Time-Dependent Remnants During Cosmological Symmetry Breaking: From Inflation to the Electroweak Scale
Through a detailed numerical investigation in three spatial dimensions, we
demonstrate that long-lived time-dependent field configurations emerge
dynamically during symmetry breaking in an expanding de Sitter spacetime. We
investigate two situations: a single scalar field with a double-well potential
and the bosonic sector of an SU(2) non-Abelian Higgs model. For the single
scalar, we show that large-amplitude oscillon configurations emerge
spontaneously and persist to contribute about 1.2% of the energy density of the
universe. We also show that for a range of parameters, oscillon lifetimes are
enhanced by the expansion and that this effect is a result of parametric
resonance. For the SU(2) case, we see about 4% of the final energy density in
oscillons.Comment: 10 pages, RevTex4, 6 figures; v2: expanded SU(2) model section, added
2 figures, added one section, improved overall presentation and updated
references, accepted for publication in Phys. Rev. D. Results remain the sam
Oscillons in Scalar Field Theories: Applications in Higher Dimensions and Inflation
The basic properties of oscillons -- localized, long-lived, time-dependent
scalar field configurations -- are briefly reviewed, including recent results
demonstrating how their existence depends on the dimensionality of spacetime.
Their role on the dynamics of phase transitions is discussed, and it is shown
that oscillons may greatly accelerate the decay of metastable vacuum states.
This mechanism for vacuum decay -- resonant nucleation -- is then applied to
cosmological inflation. A new inflationary model is proposed which terminates
with fast bubble nucleation.Comment: 11 pages, 4 figures, to appear in Int. J. Mod. Phys.
Frontoparietal Connectivity and Hierarchical Structure of the Brain’s Functional Network during Sleep
Frontal and parietal regions are associated with some of the most complex cognitive functions, and several frontoparietal resting-state networks can be observed in wakefulness. We used functional magnetic resonance imaging data acquired in polysomnographically validated wakefulness, light sleep, and slow-wave sleep to examine the hierarchical structure of a low-frequency functional brain network, and to examine whether frontoparietal connectivity would disintegrate in sleep. Whole-brain analyses with hierarchical cluster analysis on predefined atlases were performed, as well as regression of inferior parietal lobules (IPL) seeds against all voxels in the brain, and an evaluation of the integrity of voxel time-courses in subcortical regions-of-interest. We observed that frontoparietal functional connectivity disintegrated in sleep stage 1 and was absent in deeper sleep stages. Slow-wave sleep was characterized by strong hierarchical clustering of local submodules. Frontoparietal connectivity between IPL and superior medial and right frontal gyrus was lower in sleep stages than in wakefulness. Moreover, thalamus voxels showed maintained integrity in sleep stage 1, making intrathalamic desynchronization an unlikely source of reduced thalamocortical connectivity in this sleep stage. Our data suggest a transition from a globally integrated functional brain network in wakefulness to a disintegrated network consisting of local submodules in slow-wave sleep, in which frontoparietal inter-modular nodes may play a role, possibly in combination with the thalamus
Long-Lived Localized Field Configurations in Small Lattices: Application to Oscillons
Long-lived localized field configurations such as breathers, oscillons, or
more complex objects naturally arise in the context of a wide range of
nonlinear models in different numbers of spatial dimensions. We present a
numerical method, which we call the {\it adiabatic damping method}, designed to
study such configurations in small lattices. Using 3-dimensional oscillons in
models as an example, we show that the method accurately (to a part in
10^5 or better) reproduces results obtained with static or dynamically
expanding lattices, dramatically cutting down in integration time. We further
present new results for 2-dimensional oscillons, whose lifetimes would be
prohibitively long to study with conventional methods.Comment: LaTeX, 8 pages using RevTeX. 6 PostScript figures include
Oscillons: Resonant Configurations During Bubble Collapse
Oscillons are localized, non-singular, time-dependent, spherically-symmetric
solutions of nonlinear scalar field theories which, although unstable, are
extremely long-lived. We show that they naturally appear during the collapse of
subcritical bubbles in models with symmetric and asymmetric double-well
potentials. By a combination of analytical and numerical work we explain
several of their properties, including the conditions for their existence,
their longevity, and their final demise. We discuss several contexts in which
we expect oscillons to be relevant. In particular, their nucleation during
cosmological phase transitions may have wide-ranging consequences.Comment: 31 pages Revtex, 20 uufiles-encoded figures. Section "Possible
Applications of Oscillons" slightly expande
A Class of Nonperturbative Configurations in Abelian-Higgs Models: Complexity from Dynamical Symmetry Breaking
We present a numerical investigation of the dynamics of symmetry breaking in
both Abelian and non-Abelian Higgs models in three spatial
dimensions. We find a class of time-dependent, long-lived nonperturbative field
configurations within the range of parameters corresponding to type-1
superconductors, that is, with vector masses () larger than scalar masses
(). We argue that these emergent nontopological configurations are related
to oscillons found previously in other contexts. For the Abelian-Higgs model,
our lattice implementation allows us to map the range of parameter space -- the
values of -- where such configurations exist and to
follow them for times t \sim \O(10^5) m^{-1}. An investigation of their
properties for -symmetric models reveals an enormously rich structure
of resonances and mode-mode oscillations reminiscent of excited atomic states.
For the SU(2) case, we present preliminary results indicating the presence of
similar oscillonic configurations.Comment: 21 pages, 19 figures, prd, revte
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