134 research outputs found
The Entropy Principle and the Influence of Sociological Pressures on SETI
We begin with the premise that the law of entropy could prove to be
fundamental for the evolution of intelligent life and the advent of
technological civilization. Building on recent theoretical results, we combine
a modern approach to evolutionary theory with Monte Carlo Realization
Techniques. A numerical test for a proposed significance of the law of entropy
within the evolution of intelligent species is performed and results are
compared with a neutral test hypothesis. Some clarifying aspects on the
emergence of intelligent species arise and are discussed in the framework of
contemporary astrobiology.Comment: 11 pages, 5 figures, accepted for publication in the International
Journal of Astrobiolog
Open Cosmic Strings in Black Hole Space-Times
We construct open cosmic string solutions in Schwarzschild black hole and
non-dilatonic black p-brane backgrounds. These strings can be thought to
stretch between two D-branes or between a D-brane and the horizon in curved
space-time. We study small fluctuations around these solutions and discuss
their basic properties.Comment: 11 pages, REVTex, 5 figures, a reference adde
Mirage Cosmology of U(1) Gauge Field on Unstable D3 Brane Universe
An unstable -brane universe governed by the DBI action of the tachyon
field minimally coupled to a U(1) gauge boson is examined. The cosmological
evolution of this coupled system, is further analyzed, in terms of the
expansion rate of the inflating brane, which is highly affected by the presence
of the tachyonic and gauge field charges. We show, that the minimal coupling
makes the effective brane density less divergent. However, for some sectors of
the theory the tachyon is not able to regulate it in an efficient fashion.
Also, a detailed analysis of the dependance of the effective brane density on
the scale factor of the universe is performed, which leads to various
cosmological models.Comment: ReVTeX format 20 pages; v2 1 figure added, one additional paragraph
with extra comments added, enlarged list of references, version to appear in
JHE
Integrable Rosochatius deformations of higher-order constrained flows and the soliton hierarchy with self-consistent sources
We propose a systematic method to generalize the integrable Rosochatius
deformations for finite dimensional integrable Hamiltonian systems to
integrable Rosochatius deformations for infinite dimensional integrable
equations. Infinite number of the integrable Rosochatius deformed higher-order
constrained flows of some soliton hierarchies, which includes the generalized
integrable Hnon-Heiles system, and the integrable Rosochatius
deformations of the KdV hierarchy with self-consistent sources, of the AKNS
hierarchy with self-consistent sources and of the mKdV hierarchy with
self-consistent sources as well as their Lax representations are presented.Comment: 18 pages. to appear in J. Phys. A: Math. Ge
Tensionless supersymmetric M2 branes in and Giant Diabolo
We find various supersymmetric configurations of toroidal M2 brane solutions
in \AdS_4 \times S^7 or, more generally, in \AdS_4 \times S^7/Z_k. In this
class we identify solutions preserving 1/4 and 1/8 supersymmetries of the
background. The supersymmetric M2 branes have angular momenta and winding on
, and null world-volumes. In certain cases they collapse to string-like
configurations. These configurations can be viewed as a higher-dimensional
(membrane) analog of BMN states. We compute the energy and angular momenta,
showing that all supersymmetric configurations obey the BPS relation ,\
with . Finally, we also study another
class of supersymmetric M2-branes, including uncompact rotating membranes of
"diabolo" shape.Comment: 27 pages, 3 figures. Small correction
Dissecting the long-term emission behaviour of the BL Lac object Mrk 421
We report on long-term multiwavelengthmonitoring of blazar Mrk 421 by the GLAST-AGILE
Support Program of the Whole Earth Blazar Telescope (GASP-WEBT) collaboration and
Steward Observatory, and by the Swift and Fermi satellites. We study the source behaviour in
the period 2007–2015, characterized by several extreme flares. The ratio between the optical,
X-ray and γ -ray fluxes is very variable. The γ -ray flux variations show a fair correlation with
the optical ones starting from 2012.We analyse spectropolarimetric data and find wavelengthdependence
of the polarization degree (P), which is compatible with the presence of the
host galaxy, and no wavelength dependence of the electric vector polarization angle (EVPA).
Optical polarimetry shows a lack of simple correlation between P and flux and wide rotations of
the EVPA.We build broad-band spectral energy distributions with simultaneous near-infrared
and optical data from the GASP-WEBT and ultraviolet and X-ray data from the Swift satellite.
They show strong variability in both flux and X-ray spectral shape and suggest a shift of
the synchrotron peak up to a factor of ∼50 in frequency. The interpretation of the flux and
spectral variability is compatible with jet models including at least two emitting regions that
can change their orientation with respect to the line of sight.http://10.0.4.69/mnras/stx2185Accepted manuscrip
High-Energy Polarimetry - a new window to probe extreme physics in AGN jets
The constantly improving sensitivity of ground-based and space-borne
observatories has made possible the detection of high-energy emission (X-rays
and gamma-rays) from several thousands of extragalactic sources. Enormous
progress has been made in measuring the continuum flux enabling us to perform
imaging, spectral and timing studies. An important remaining challenge for
high-energy astronomy is measuring polarization. The capability to measure
polarization is being realized currently at X-ray energies (e.g. with IXPE),
and sensitive gamma-ray telescopes capable of measuring polarization, such as
AMEGO, AdEPT, e-ASTROGAM, etc., are being developed. These future gamma-ray
telescopes will probe the radiation mechanisms and magnetic fields of
relativistic jets from active galactic nuclei at spatial scales much smaller
than the angular resolution achieved with continuum observations of the
instrument. In this white paper, we discuss the scientific potentials of
high-energy polarimetry, especially gamma-ray polarimetry, including the
theoretical implications, and observational technology advances being made. In
particular, we will explore the primary scientific opportunities and wealth of
information expected from synergy of multi-wavelength polarimetry that will be
brought to multi-messenger astronomy.Comment: submitted to Astro2020 (Astronomy and Astrophysics Decadal Survey
The WEBT campaign on the BL Lac object PG 1553+113 in 2013. An analysis of the enigmatic synchrotron emission
A multifrequency campaign on the BL Lac object PG 1553+113 was organized by the Whole Earth Blazar Telescope (WEBT) in 2013 April-August, involving 19 optical, two near-IR, and three radio telescopes. The aim was to study the source behaviour at low energies during and around the high-energy observations by the Major Atmospheric Gamma-ray Imaging Cherenkov telescopes in April-July. We also analyse the UV and X-ray data acquired by the Swift and XMM-Newton satellites in the same period. The WEBT and satellite observations allow us to detail the synchrotron emission bump in the source spectral energy distribution (SED). In the optical, we found a general bluer-when-brighter trend. The X-ray spectrum remained stable during 2013, but a comparison with previous observations suggests that it becomes harder when the X-ray flux increases. The long XMM-Newton exposure reveals a curved X-ray spectrum. In the SED, the XMM-Newton data show a hard near-UV spectrum, while Swift data display a softer shape that is confirmed by previous Hubble Space Telescope/Cosmic Origins Spectrograph and International Ultraviolet Explorer observations. Polynomial fits to the optical-X-ray SED show that the synchrotron peak likely lies in the 4-30eV energy range, with a general shift towards higher frequencies for increasing X-ray brightness. However, the UV and X-ray spectra do not connect smoothly. Possible interpretations include: (i) orientation effects, (ii) additional absorption, (iii) multiple emission components, and (iv) a peculiar energy distribution of relativistic electrons. We discuss the first possibility in terms of an inhomogeneous helical jet mode
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