174 research outputs found
Summer coastal rookeries and perspectives of the Baikal seal (Pusa sibirica) population in the conditions of the global warming
Based on the secondary literature, a retrospective characterization of the climate in the Baikal region, starting from the end of the Pleistocene, is given. According to satellite monitoring data, the characteristics of the ice regime of the Lake Baikal in the conditions of climate warming are presented. Moreover, we briefly discuss the impact of climate change on the ecology and biology of the Baikal seal (Pusa sibirica Gm.). Using video materials obtained online at one of the main island coastal rookeries of seals (on the island of Tonkyi, the archipelago of the Ushkany Islands, Lake Baikal) in 2011–2017, the dependence of the number of seals hauled out on the lake level and the peculiarities of the fishing regime was determined (the survey was conducted from May–June to October). A direct relationship was determined between the relative number of animals that had a moulting delay and the ice regime of a given year: the longer the floating ice in the northern part of Lake Baikal remained, the more numerous were the first approaches of seals to the studied rookery and the greater was the proportion of moulting individuals. It is reasonable to assume that the main reason for the Baikal seal to come ashore is not prolongued moulting time, but a physiological need for sunlight, which has a healing effect on the body of animals that lack solar radiation in winter. In general, climate warming has a negative impact on the state of the Baikal seal population. The available paleoclimatic reconstructions of the Holocene indicate that the population of the Baikal seal has experienced a lot of climate changes in its history. Nevertheless, if the current trends of climatic changes persist until the end of the 21st century, the ecology and biology of the seal will drastically change (up to the beginning of terrestrial reproduction), and the population will significantly decrease. However, the Baikal seal as a species would remain
A search for concentric rings with unusual variance in the 7-year WMAP temperature maps using a fast convolution approach
We present a method for the computation of the variance of cosmic microwave
background (CMB) temperature maps on azimuthally symmetric patches using a fast
convolution approach. As an example of the application of the method, we show
results for the search for concentric rings with unusual variance in the 7-year
WMAP data. We re-analyse claims concerning the unusual variance profile of
rings centred at two locations on the sky that have recently drawn special
attention in the context of the conformal cyclic cosmology scenario proposed by
Penrose (2009). We extend this analysis to rings with larger radii and centred
on other points of the sky. Using the fast convolution technique enables us to
perform this search with higher resolution and a wider range of radii than in
previous studies. We show that for one of the two special points rings with
radii larger than 10 degrees have systematically lower variance in comparison
to the concordance LambdaCDM model predictions. However, we show that this
deviation is caused by the multipoles up to order l=7. Therefore, the deficit
of power for concentric rings with larger radii is yet another manifestation of
the well-known anomalous CMB distribution on large angular scales. Furthermore,
low variance rings can be easily found centred on other points in the sky. In
addition, we show also the results of a search for extremely high variance
rings. As for the low variance rings, some anomalies seem to be related to the
anomalous distribution of the low-order multipoles of the WMAP CMB maps. As
such our results are not consistent with the conformal cyclic cosmology
scenario.Comment: 12 pages, 11 figures, 1 table. Published in MNRAS. This research was
supported by the Agence Nationale de la Recherche (ANR-08-CEXC-0002-01
CMB Imprints of a Pre-Inflationary Climbing Phase
We discuss the implications for cosmic microwave background (CMB)
observables, of a class of pre-inflationary dynamics suggested by string models
where SUSY is broken due to the presence of D-branes and orientifolds
preserving incompatible portions of it. In these models the would-be inflaton
is forced to emerge from the initial singularity climbing up a mild exponential
potential, until it bounces against a steep exponential potential of "brane
SUSY breaking" scenarios, and as a result the ensuing descent gives rise to an
inflationary epoch that begins when the system is still well off its eventual
attractor. If a pre-inflationary climbing phase of this type had occurred
within 6-7 e-folds of the horizon exit for the largest observable wavelengths,
displacement off the attractor and initial-state effects would conspire to
suppress power in the primordial scalar spectrum, enhancing it in the tensor
spectrum and typically superposing oscillations on both. We investigate these
imprints on CMB observables over a range of parameters, examine their
statistical significance, and provide a semi-analytic rationale for our
results. It is tempting to ascribe at least part of the large-angle anomalies
in the CMB to pre-inflationary dynamics of this type.Comment: 38 pages, LaTeX, 11 eps figures, references added, matches version to
appear in JCA
Decoupling Inflation From the String Scale
When Inflation is embedded in a fundamental theory, such as string theory, it
typically begins when the Universe is already substantially larger than the
fundamental scale [such as the one defined by the string length scale]. This is
naturally explained by postulating a pre-inflationary era, during which the
size of the Universe grew from the fundamental scale to the initial
inflationary scale. The problem then arises of maintaining the [presumed]
initial spatial homogeneity throughout this era, so that, when it terminates,
Inflation is able to begin in its potential-dominated state. Linde has proposed
that a spacetime with compact negatively curved spatial sections can achieve
this, by means of chaotic mixing. Such a compactification will however lead to
a Casimir energy, which can lead to effects that defeat the purpose unless the
coupling to gravity is suppressed. We estimate the value of this coupling
required by the proposal, and use it to show that the pre-inflationary
spacetime is stable, despite the violation of the Null Energy Condition
entailed by the Casimir energy.Comment: 24 pages, 5 eps figures, references added, stylistic changes, version
to appear in Classical and Quantum Gravit
Recommended from our members
The Cosmic Dawn and Epoch of Reionisation with SKA
Concerted effort is currently ongoing to open up the Epoch of Reionization (z ∼15-6) for studies with IR and radio telescopes. Whereas IR detections have been made of sources (Lyman-α emitters, quasars and drop-outs) in this redshift regime in relatively small fields of view, no direct detection of neutral hydrogen, via the redshifted 21-cm line, has yet been established. Such a direct detection is expected in the coming years, with ongoing surveys, and could open up the entire universe from z ∼6-200 for astrophysical and cosmological studies, opening not only the Epoch of Reionization, but also its preceding Cosmic Dawn (z ∼30-15) and possibly even the later phases of the Dark Ages (z ∼200-30). All currently ongoing experiments attempt statistical detections of the 21-cm signal during the Epoch of Reionization, with limited signal-to-noise. Direct imaging, except maybe on the largest (degree) scales at lower redshifts, as well as higher redshifts will remain out of reach. The Square Kilometre Array (SKA) will revolutionize the field, allowing direct imaging of neutral hydrogen from scales of arc-minutes to degrees over most of the redshift range z ∼6-28 with SKA1-LOW, and possibly even higher redshifts with the SKA2-LOW. In this SKA will be unique, and in parallel provide enormous potential of synergy with other upcoming facilities (e.g. JWST). In this chapter we summarize the physics of 21-cm emission, the different phases the universe is thought to go through, and the observables that the SKA can probe, referring where needed to detailed chapters in this volume. This is done within the framework of the current SKA1 baseline design and a nominal CD/EoR straw-man survey, consisting of a shallow, medium-deep and deep survey, the latter probing down to ∼1 mK brightness temperature on arc-minute scales at the end of reionization. Possible minor modifications to the design of SKA1 and the upgrade to SKA2 are discussed, in addition to science that could be done already during roll-out when SKA1 still has limited capabilities and/or core collecting area
A Terminal Velocity on the Landscape: Particle Production near Extra Species Loci in Higher Dimensions
We investigate particle production near extra species loci (ESL) in a higher
dimensional field space and derive a speed limit in moduli space at weak
coupling. This terminal velocity is set by the characteristic ESL-separation
and the coupling of the extra degrees of freedom to the moduli, but it is
independent of the moduli's potential if the dimensionality of the field space
is considerably larger than the dimensionality of the loci, D >> d. Once the
terminal velocity is approached, particles are produced at a plethora of nearby
ESLs, preventing a further increase in speed via their backreaction. It is
possible to drive inflation at the terminal velocity, providing a
generalization of trapped inflation with attractive features: we find that more
than sixty e-folds of inflation for sub-Planckian excursions in field space are
possible if ESLs are ubiquitous, without fine tuning of initial conditions and
less tuned potentials. We construct a simple, observationally viable model with
a slightly red scalar power-spectrum and suppressed gravitational waves; we
comment on the presence of additional observational signatures originating from
IR-cascading and individual massive particles. We also show that
moduli-trapping at an ESL is suppressed for D >> d, hindering dynamical
selection of high-symmetry vacua on the landscape based on this mechanism.Comment: 46 pages, 6 figures. V3: typos corrected compared to JHEP version,
conclusions unchange
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