10,090 research outputs found
Quasiconformality and mass
We identify universal quasiconformal (walking) behaviour in non-Abelian gauge
field theories based on the mass-dependent all-order beta-function introduced
in arXiv:0908.1364. We find different types of walking behaviour in the
presence of (partially) massive species. We employ our findings to the
construction of candidate theories for dynamical electroweak symmetry breaking
by walking technicolour.Comment: 16 pages, 8 figures
The nature of the red disk-like galaxies at high redshift: dust attenuation and intrinsically red stellar populations
We investigate which conditions of dust attenuation and stellar populations
allow models of dusty, continuously star-forming, bulge-less disk galaxies at
0.8<z<3.2 to meet the different colour selection criteria of high-z ``red''
galaxies (e.g. Rc-K>5.3, Ic-K>4, J-K>2.3). As a main novelty, we use stellar
population models that include the thermally pulsating Asymptotic Giant Branch
(TP-AGB) phase of stellar evolution. The star formation rate of the models
declines exponentially as a function of time, the e-folding time being longer
than 3 Gyr. In addition, we use calculations of radiative transfer of the
stellar and scattered radiation through different dusty interstellar media in
order to explore the wide parameter space of dust attenuation. We find that
synthetic disks can exhibit red optical/near-infrared colours because of
reddening by dust, but only if they have been forming stars for at least about
1 Gyr. Extremely few models barely exhibit Rc-K>5.3, if the inclination i=90
deg and if the opacity 2*tauV>6. Hence, Rc-K-selected galaxies at 1<z<2 most
probably are either systems with an old, passively evolving bulge or
starbursts. Synthetic disks at 1<z<2 exhibit 4<Ic-K<4.8, if they are seen edge
on (i.e. at i about 90 deg) and if 2*tauV>0.5. This explains the large fraction
of observed, edge-on disk-like galaxies with Ks4. Finally,
models with 2<z<3.2 exhibit 2.3<J-K<3, with no bias towards i about 90 deg and
for a large range in opacity (e.g. 2*tauV>1 for i about 70 deg). In conclusion,
red disk-like galaxies at 0.8<z<3.2 may not necessarily be dustier than nearby
disk galaxies (with 0.5<2*tauV<2) and/or much older than about 1 Gyr. This
result is due both to a realistic description of dust attenuation and to the
emission contribution by TP-AGB stars... (Abridged)Comment: 16 pages, 8 ps figures, accepted for publication in MNRA
Discovery of Blue Luminescence in the Red Rectangle: Possible Fluorescence from Neutral Polycyclic Aromatic Hydrocarbon Molecules?
Here we report our discovery of a band of blue luminescence (BL) in the Red
Rectangle (RR) nebula. This enigmatic proto-planetary nebula is also one of the
brightest known sources of extended red emission as well as of unidentified
infra-red (UIR) band emissions. The spectrum of this newly discovered BL is
most likely fluorescence from small neutral polycyclic aromatic hydrocarbon
(PAH) molecules. PAH molecules are thought to be widely present in many
interstellar and circumstellar environments in our galaxy as well as in other
galaxies, and are considered likely carriers of the UIR-band emission. However,
no specific PAH molecule has yet been identified in a source outside the solar
system, as the set of mid-infra-red emission features attributed to these
molecules between the wavelengths of 3.3 micron and 16.4 micron is largely
insensitive to molecular sizes. In contrast, near-UV/blue fluorescence of PAHs
is more specific as to size, structure, and charge state of a PAH molecule. If
the carriers of this near-UV/blue fluorescence are PAHs, they are most likely
neutral PAH molecules consisting of 3-4 aromatic rings such as anthracene
(C14H10) and pyrene (C16H10). These small PAHs would then be the largest
molecules specifically identified in the interstellar medium.Comment: 4 pages, 4 figures, Accepted for publication in ApJL (LaTeX, uses
emulateapj.sty
Magnification relations in gravitational lensing via multidimensional residue integrals
We investigate the so-called magnification relations of gravitational lensing
models. We show that multidimensional residue integrals provide a simple
explanation for the existence of these relations, and an effective method of
computation. We illustrate the method with several examples, thereby deriving
new magnification relations for galaxy lens models and microlensing (point mass
lensing).Comment: 16 pages, uses revtex4, submitted to Journal of Mathematical Physic
A formal approach toward authenticated authorization without identification
Anonymity is a valued commodity on the Internet many uses take advantage of. Unfortunately, anonymity and credibility are essentially mutually exclusive. A practical method to determine request creditability without also inheriting the capability to identify the exclusive source of a request is not in practice. Previous research efforts have proposed methods to ensure anonymous communication, but most sacrifice either authorization or privacy. We propose a scheme that allows a message sender to prove his or her creditability without also providing any participant capability to identify the source. In addition, the scheme is resists sybil attacks and disjoints correlation of independent message to a similar source
Segregation during directional melting and its implications on seeded crystal growth: A theoretical analysis
Directional melting of binary systems, as encountered during seeding in melt growth, is analyzed for concurrent compositional changes at the crystal-melt interface. It is shown that steady state conditions cannot normally be reached during seeding and that the growth interface temperature at the initial stages of seeded growth is a function of backmelt conditions. The theoretical treatment is numerically applied to Hg1-xCdXTe and Ga-doped Ge
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