63,598 research outputs found
The Effective Potential And Additional Large Radius Compactified Space-Time Dimensions
The consequences of large radius extra space-time compactified dimensions on
the four dimensional one loop effective potential are investigated for a model
which includes scalar self interactions and Yukawa coupling to fermions. The
Kaluza-Klein tower of states associated with the extra compact dimensions
shifts the location of the effective potential minimum and modifies its
curvature. The dependence of these effects on the radius of the extra dimension
is illustrated for various choices of coupling constants and masses. For large
radii, the consequence of twisting the fermion boundary condition on the
compactified dimensions is numerically found to produce but a negligible effect
on the effective potential.Comment: 14 pages, LaTeX, 6 Postscript figure
The Akulov-Volkov Lagrangian, Symmetry Currents and Spontaneously Broken Extended Supersymmetry
A generalization of the Akulov-Volkov effective Lagrangian governing the self
interactions of the Nambu-Goldstone fermions associated with spontaneously
broken extended supersymmetry as well as their coupling to matter is presented
and scrutinized. The resulting currents associated with R-symmetry,
supersymmetry and space-time translations are constructed and seen to form a
supermultiplet structure.Comment: 17 pages, LaTeX; Title, abstract and introduction changes, references
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On the influence of social bots in online protests. Preliminary findings of a Mexican case study
Social bots can affect online communication among humans. We study this
phenomenon by focusing on #YaMeCanse, the most active protest hashtag in the
history of Twitter in Mexico. Accounts using the hashtag are classified using
the BotOrNot bot detection tool. Our preliminary analysis suggests that bots
played a critical role in disrupting online communication about the protest
movement.Comment: 10 page
Ionisation-induced star formation II: External irradiation of a turbulent molecular cloud
In this paper, we examine numerically the difference between triggered and
revealed star formation. We present Smoothed Particle Hydrodynamics (SPH)
simulations of the impact on a turbulent 10^4 solar-mass molecular cloud of
irradiation by an external source of ionising photons. In particular, using a
control model, we investigate the triggering of star formation within the
cloud. We find that, although feedback has a dramatic effect on the morphology
of our model cloud, its impact on star formation is relatively minor. We show
that external irradiation has both positive and negative effects, accelerating
the formation of some objects, delaying the formation of others, and inducing
the formation of some that would not otherwise have formed. Overall, the
calculation in which feedback is included forms nearly twice as many objects
over a period of \sim0.5 freefall times (\sim2.4 Myr), resulting in a
star--formation efficiency approximately one third higher (\sim4% as opposed to
\sim3% at this epoch) as in the control run in which feedback is absent.
Unfortunately, there appear to be no observable characteristics which could be
used to differentiate objects whose formation was triggered from those which
were forming anyway and which were simply revealed by the effects of radiation,
although this could be an effect of poor statistics.Comment: 12 pages, 9 figures, accepted by MNRA
CLAVATA1, a regulator of meristem and flower development in Arabidopsis
We have investigated the effects on plant development of mutations in the Arabidopsis thaliana CLAVATA1 gene. In clavata1 plants, vegetative, inflorescence and floral meristems are all enlarged relative to wild type. The apical meristem can fasciate in the more severe mutant alleles, and this fasciation can occur prior to the transition to flowering. Flowers of clavata1 plants can have increased numbers of organs in all four whorls, and can also have additional whorls not present in wild-type flowers. Double mutant combinations of clavata1 with agamous, apetala2, apetala3 and pistillata indicate that CLAVATA1 controls the underlying floral meristem structure upon which these homeotic genes act. Double mutant combinations of clavata1 with apetala1 and leafy indicate CLAVATA1 plays a role in establishing and maintaining floral meristem identity, in addition to its role in controlling meristem size. In support of this, RNA expression patterns of AGAMOUS and APETALA1 are altered in clavata1 flowers
Evidence that widespread star formation may be underway in G0.253+016, "The Brick"
Image cubes of differential column density as a function of dust temperature
are constructed for Galactic Centre molecular cloud G0.253+0.016 ("The Brick")
using the recently described PPMAP procedure. The input data consist of
continuum images from the Herschel Space Telescope in the wavelength range
70-500 m, supplemented by previously published interferometric data at 1.3
mm wavelength. While the bulk of the dust in the molecular cloud is consistent
with being heated externally by the local interstellar radiation field, our
image cube shows the presence, near one edge of the cloud, of a filamentary
structure whose temperature profile suggests internal heating. The structure
appears as a cool ( K) tadpole-like feature, pc in length, in
which is embedded a thin spine of much hotter ( 40-50 K) material. We
interpret these findings in terms of a cool filament whose hot central region
is undergoing gravitational collapse and fragmentation to form a line of
protostars. If confirmed, this would represent the first evidence of widespread
star formation having started within this cloud.Comment: 5 pages, 4 figures; accepted for publication in MNRAS Letter
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