9,111 research outputs found
Wormhole geometries in fourth-order conformal Weyl gravity
We present an analysis of the classic wormhole geometries based on conformal
Weyl gravity, rather than standard general relativity. The main characteristics
of the resulting traversable wormholes remain the same as in the seminal study
by Morris and Thorne, namely, that effective super-luminal motion is a viable
consequence of the metric. Improving on previous work on the subject, we show
that for particular choices of the shape and redshift functions the wormhole
metric in the context of conformal gravity does not violate the main energy
conditions at or near the wormhole throat. Some exotic matter might still be
needed at the junction between our solutions and flat spacetime, but we
demonstrate that the averaged null energy condition (as evaluated along radial
null geodesics) is satisfied for a particular set of wormhole geometries.
Therefore, if fourth-order conformal Weyl gravity is a correct extension of
general relativity, traversable wormholes might become a realistic solution for
interstellar travel.Comment: Minor changes and one equation added, 22 pages, including 4 figures,
published in Int. J. Mod. Phys. D, Online Ready: 12 April 201
The Non-Abelian Self Dual String on the Light Cone
We construct the scalar profile for the non-abelian self dual string
connecting two M5-branes compactified on a light-like circle. The construction
is based on a conjectured modified version of Nahm's equations describing a
D2-brane, with a magnetic field on it, suspended between two D4-branes. Turning
on a constant magnetic field on the D2-brane corresponds to a boost in the
eleventh direction. In the limit of infinite boost the D4-branes correspond to
light-like compactified M5-branes. The solution for the scalar profile of the
brane remains finite in this limit and displays all the correct expected
features such as smooth interpolation between the unbroken and broken phase
with the correct value for the Higgs field at infinity.Comment: 13 pages, LaTeX 2e, 2 figure
Seasonality of birth in nineteenth and twentieth century Austria: steps toward a unified theory of human reproductive seasonality
We present an analysis of birth seasonality in nine geographical regions within Austria for two time periods, 1881-1912 and 1947-1959. In the early period, geography, climate, and agricultural patterns were related to birth seasonality. By the later time period, these factors were no longer related to birth seasonality. We propose a âresilience hypothesis,â which suggests two levels of causal influences on birth seasonality. First, underlying the three significant features of birth seasonality patterns around the world are only a small number of major causes. But, second, there are a multiplicity of minor causes that result in small perturbations in the patterns.(AUTHORS)
Anomalous spin-resolved point-contact transmission of holes due to cubic Rashba spin-orbit coupling
Evidence is presented for the finite wave vector crossing of the two lowest
one-dimensional spin-split subbands in quantum point contacts fabricated from
two-dimensional hole gases with strong spin-orbit interaction. This phenomenon
offers an elegant explanation for the anomalous sign of the spin polarization
filtered by a point contact, as observed in magnetic focusing experiments.
Anticrossing is introduced by a magnetic field parallel to the channel or an
asymmetric potential transverse to it. Controlling the magnitude of the
spin-splitting affords a novel mechanism for inverting the sign of the spin
polarization.Comment: 4 pages, 3 figure
Entanglement detection in hybrid optomechanical systems
We study a device formed by a Bose Einstein condensate (BEC) coupled to the
field of a cavity with a moving end-mirror and find a working point such that
the mirror-light entanglement is reproduced by the BEC-light quantum
correlations. This provides an experimentally viable tool for inferring
mirror-light entanglement with only a limited set of assumptions. We prove the
existence of tripartite entanglement in the hybrid device, persisting up to
temperatures of a few milli-Kelvin, and discuss a scheme to detect it.Comment: 6 pages, 7 figures, published versio
Spine-sheath layer radiative interplay in subparsec-scale jets and the TeV emission from M87
Simple one-zone homogeneous synchrotron self-Compton models have severe
difficulties in explaining the TeV emission observed in the radiogalaxy M87.
Also the site of the TeV emission region is uncertain: it could be the
unresolved jet close to the nucleus, analogously to what proposed for blazars,
or an active knot, called HST-1, tens of parsec away. We explore the
possibility that the TeV emission of M87 is produced in the misaligned subpc
scale jet. We base our modelling on a structured jet, with a fast spine
surrounded by a slower layer. In this context the main site responsible for the
emission of the TeV radiation is the layer, while the (debeamed) spine accounts
for the emission from the radio to the GeV band: therefore we expect a more
complex correlation with the TeV component than that expected in one-zone
scenarios, in which both components are produced by the same region. Observed
from small angles, the spine would dominate the emission, with an overall
Spectral Energy Distribution close to those of BL Lac objects with a
synchrotron peak located at low energy (LBLs).Comment: 5 pages, 2 figures. Accepted for publication in MNRAS Letter
Separaxion anxiety in pediatric migraine without aura: A pilot study
Background: Separation anxiety (SA) can be defined as the fear reaction and protest manifested by children when the main caregivers move away from him/her or in front of unfamiliar person. SA near eight months may be considered as an important and normal phase of the correct and typical social neurodevelopment. Aims of the present pilot study is assessing the prevalence of separation anxiety in a population of patients with migraine without aura (MwA). Materials and methods: 119 children (69 males) suffering from MwA (mean age 1.78 ± 7:59) were consecutively recruited. The control population consisted of 231 (114 males) healthy subjects similar for age (7.64 ± 1:34; p = 0.768) and gender (p=0.987) The Screen for child anxiety related emotional disorders (SCARED) test was used to assess the prevalence of separation anxiety among MwA children. Results: Healthy individuals are on average less affected (mean 4.72 ± 0:32) of the Separation Anxiety Disorder respect of MwA children (mean 6.83 ± 0.97; p < 0.001) (Figure 1). Conclusion. MwA presents many psychiatric comorbidities and among ones separation anxiety may be considered in the clinical and therapeutic management of pediatric primary headache
Thermal and quantum fluctuations in chains of ultracold polar molecules
Ultracold polar molecules, in highly anisotropic traps and interacting via a
repulsive dipolar potential, may form one-dimensional chains at high densities.
According to classical theory, at low temperatures there exists a critical
value of the density at which a second order phase transition from a linear to
a zigzag chain occurs. We study the effect of thermal and quantum fluctuations
on these self-organized structures using classical and quantum Monte Carlo
methods, by means of which we evaluate the pair correlation function and the
static structure factor. Depending on the parameters, these functions exhibit
properties typical of a crystalline or of a liquid system. We compare the
thermal and the quantum results, identifying analogies and differences.
Finally, we discuss experimental parameter regimes where the effects of quantum
fluctuations on the linear - zigzag transition can be observed.Comment: Submitted to the Special issue on modern applications of trapped
ions, J. Phys. B: At. Mol. Opt. Phy
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