6,580 research outputs found
Non-Gaussianity of scalar perturbations generated by conformal mechanisms
We consider theories which explain the flatness of the power spectrum of
scalar perturbations in the Universe by conformal invariance, such as conformal
rolling model and Galilean Genesis. We show that to the leading {\it
non-linear} order, perturbations in all models from this class behave in one
and the same way, at least if the energy density of the relevant fields is
small compared to the total energy density (spectator approximation). We then
turn to the intrinsic non-Gaussianities in these models (as opposed to
non-Gaussianities that may be generated during subsequent evolution). The
intrinsic bispectrum vanishes, so we perform the complete calculation of the
trispectrum and compare it with the trispecta of local forms in various limits.
The most peculiar feature of our trispectrum is a (fairly mild) singularity in
the limit where two momenta are equal in absolute value and opposite in
direction (folded limit). Generically, the intrinsic non-Gaussianity can be of
detectable size.Comment: 28 pages, 5 figures. Journal version. A comment on the size of the
non-Gaussianities inserted. Misprints corrected. A reference adde
Horizontal-Branch Models and the Second-Parameter Effect. IV. The Case of M3 and Palomar 3
We present a detailed analysis of the "second-parameter pair" of globular
clusters M3 (NGC 5272) and Palomar 3. Our main results can be summarized as
follows: i) The horizontal-branch (HB) morphology of M3 is significantly bluer
in its inner regions (observed with the Hubble Space Telescope) than in the
cluster outskirts (observed from the ground), i.e., M3 has an internal second
parameter. Most plausibly the mass loss on the red giant branch (RGB) has been
more efficient in the inner than in the outer regions of the cluster. ii) The
dispersion in mass of the Pal 3 HB is found to be very small -- consistent with
zero -- and we argue that this is unlikely to be due to a statistical
fluctuation. It is this small mass dispersion that leads to the most apparent
difference in the HB morphologies of M3 and Pal 3. iii) The relative HB types
of M3 and Pal 3, as measured by mean colors or parameters involving the number
of blue, variable, and red HB stars, can easily be accounted for by a fairly
small difference in age between these clusters, of order 0.5-1 Gyr -- which is
in good agreement with the relative age measurement, based on the clusters'
turnoffs, by VandenBerg (2000).Comment: 20 pages, 12 figures, emulateapj5 style. The Astrophysical Journal,
in press. Figs. 1, 6, 9, 10 are in png format. The preprint (postscript
format) with full resolution (embedded) figures is available from
http://www.astro.virginia.edu/~mc6v
Parafermionic Liouville field theory and instantons on ALE spaces
In this paper we study the correspondence between the
coset conformal field
theories and SU(n) gauge theories on
. Namely we check the correspondence between the
SU(2) Nekrasov partition function on and the
conformal blocks of the parafermion algebra (in and modules).
We find that they are equal up to the U(1)-factor as it was in all cases of
AGT-like relations. Studying the structure of the instanton partition function
on we also find some evidence that this
correspondence with arbitrary takes place up to the U(1)-factor.Comment: 21 pages, 6 figures, misprints corrected, references added, version
to appear in JHE
Mechanisms of arsenic clustering in silicon
A model of arsenic clustering in silicon is proposed and analyzed. The main
feature of the proposed model is the assumption that negatively charged arsenic
complexes play a dominant role in the clustering process. To confirm this
assumption, electron density and concentration of impurity atoms incorporated
into the clusters are calculated as functions of the total arsenic
concentration. A number of the negatively charged clusters incorporating a
point defect and one or more arsenic atoms are investigated. It is shown that
for the doubly negatively charged clusters or for clusters incorporating more
than one arsenic atom the electron density reaches a maximum value and then
monotonically and slowly decreases as total arsenic concentration increases. In
the case of doubly negatively charged cluster incorporating two arsenic atoms,
the calculated electron density agrees well with the experimental data.
Agreement with the experiment confirms the conclusion that two arsenic atoms
participate in the cluster formation. Among all present models, the proposed
model of clustering by formation of doubly negatively charged cluster
incorporating two arsenic atoms gives the best fit to the experimental data and
can be used in simulation of high concentration arsenic diffusion.Comment: 13 pages, 4 figures. Revised and shortened version of the paper has
been published in Phys. Rev. B, Vol.74 (3), art. no. 035205 (2006
Intersections of quadrics, moment-angle manifolds, and Hamiltonian-minimal Lagrangian embeddings
We study the topology of Hamiltonian-minimal Lagrangian submanifolds N in C^m
constructed from intersections of real quadrics in a work of the first author.
This construction is linked via an embedding criterion to the well-known
Delzant construction of Hamiltonian toric manifolds. We establish the following
topological properties of N: every N embeds as a submanifold in the
corresponding moment-angle manifold Z, and every N is the total space of two
different fibrations, one over the torus T^{m-n} with fibre a real moment-angle
manifold R, and another over a quotient of R by a finite group with fibre a
torus. These properties are used to produce new examples of Hamiltonian-minimal
Lagrangian submanifolds with quite complicated topology.Comment: 14 pages, published version (minor changes
The Gould-Hopper Polynomials in the Novikov-Veselov equation
We use the Gould-Hopper (GH) polynomials to investigate the Novikov-Veselov
(NV) equation. The root dynamics of the -flow in the NV equation is
studied using the GH polynomials and then the Lax pair is found. In particulr,
when , one can get the Gold-fish model. The smooth rational solutions
of the NV equation are also constructed via the extended Moutard transformation
and the GH polynomials. The asymptotic behavior is discussed and then the
smooth rational solution of the Liouville equation is obtained.Comment: 22 pages, no figur
Interaction of metals and alloys with gas media under spark discharges
The paper studies the penetration of nitrogen, oxygen, hydrogen, carbon, argon and krypton into copper, nickel, molybdenum, tita-nium, aluminum, iron and different steels under the action of spark discharges in various media based on radioactive indicatorsusing step-by-step radiometric analysis, macro-, micro-, electron-microscopy and activation autoradiography, M`ssbauer andAuger spectroscopy, secondary ion-ionic emission, X-ray diffraction and X-ray microanalysis.The study describes distribution features of penetrating atoms and their concentration profiles. Phase composition of near-surfacelayers is also determined. It is shown that supersaturated solid solutions of iron in copper and copper in iron are formed duringsimultaneous iron and oxygen penetration in copper and spinel (Fe6Cu3O4)4. Diffusion of iron and carbon results in supersaturatedsolid solutions of iron and carbon in copper, copper and carbon in iron, graphite and cementite. Inert gases and nitrogen form solidsolutions with copper
Penetration of the magnetic field into the twinning plane in the type I and II superconductors
It is demonstrated that in the type I and II superconductors with
low-transparent twinning planes (TP) the penetration of external parallel
magnetic field into the region of the twinning plane can be energetically
favorable. In the type I superconductors the twinning planes become similar to
Josephson junctions and the magnetic field penetrates into the center of the TP
in the form of soft Josephson-like vortices. This leads to increase in the
critical magnetic field values. The corresponding phase diagram in the
parameter plane "temperature - magnetic field" essentially differs from the one
obtained without taking the finite value of the magnetic field near the TP into
account. Comparison between obtained phase diagrams and experimental data for
different type I superconductors can allow to estimate the value of the TP
transparency, which is the only fitting parameter in our theory.Comment: 5 pages, 2 figure
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