3,787 research outputs found
The K\"ahler-Ricci flow with positive bisectional curvature
We show that the K\"ahler-Ricci flow on a manifold with positive first Chern
class converges to a K\"ahler-Einstein metric assuming positive bisectional
curvature and certain stability conditions.Comment: 15 page
Leptogenesis from Pseudo-Scalar Driven Inflation
We examine recent claims for a considerable amount of leptogenesis, in some
inflationary scenarios, through the gravitational anomaly in the lepton number
current. We find that when the short distances contributions are properly
included the amount of lepton number generated is actually much smaller.Comment: JHEP style, 11 pages. Corrected typ
Local Features with Large Spiky non-Gaussianities during Inflation
We provide a dynamical mechanism to generate localized features during
inflation. The local feature is due to a sharp waterfall phase transition which
is coupled to the inflaton field. The key effect is the contributions of
waterfall quantum fluctuations which induce a sharp peak on the curvature
perturbation which can be as large as the background curvature perturbation
from inflaton field. Due to non-Gaussian nature of waterfall quantum
fluctuations a large spike non-Gaussianity is produced which is narrowly peaked
at modes which leave the Hubble radius at the time of phase transition. The
large localized peaks in power spectrum and bispectrum can have interesting
consequences on CMB anisotropies.Comment: 22 pages, 2 figure
Semiclassical Quantization for the Spherically Symmetric Systems under an Aharonov-Bohm magnetic flux
The semiclassical quantization rule is derived for a system with a
spherically symmetric potential and an
Aharonov-Bohm magnetic flux. Numerical results are presented and compared with
known results for models with . It is shown that the
results provided by our method are in good agreement with previous results. One
expects that the semiclassical quantization rule shown in this paper will
provide a good approximation for all principle quantum number even the rule is
derived in the large principal quantum number limit . We also discuss
the power parameter dependence of the energy spectra pattern in this
paper.Comment: 13 pages, 4 figures, some typos correcte
The Monge-Amp\`ere operator and geodesics in the space of K\"ahler potentials
It is shown that geodesics in the space of K\"ahler potentials can be
uniformly approximated by geodesics in the spaces of Bergman metrics. Two
important tools in the proof are the Tian-Yau-Zelditch approximation theorem
for K\"ahler potentials and the pluripotential theory of Bedford-Taylor,
suitably adapted to K\"ahler manifolds.Comment: 25 pages, no figure, minor misprints correcte
Non-Gaussianity from violation of slow-roll in multiple inflation
Multiple inflation is a model based on N=1 supergravity wherein there are
sudden changes in the mass of the inflaton because it couples to 'flat
direction' scalar fields which undergo symmetry breaking phase transitions as
the universe cools. The resulting brief violations of slow-roll evolution
generate a non-gaussian signal which we find to be oscillatory and yielding
f_NL ~ 5-20. This is potentially detectable by e.g. Planck but would require
new bispectrum estimators to do so. We also derive a model-independent result
relating the period of oscillations of a phase transition during inflation to
the period of oscillations in the primordial curvature perturbation generated
by the inflaton.Comment: 21 pages, 6 figures; Clarifying comments and references added;
Accepted for publication in JCA
Consistency relation for the Lorentz invariant single-field inflation
In this paper we compute the sizes of equilateral and orthogonal shape
bispectrum for the general Lorentz invariant single-field inflation. The
stability of field theory implies a non-negative square of sound speed which
leads to a consistency relation between the sizes of orthogonal and equilateral
shape bispectrum, namely . In
particular, for the single-field Dirac-Born-Infeld (DBI) inflation, the
consistency relation becomes . These consistency relations are also valid in the
mixed scenario where the quantum fluctuations of some other light scalar fields
contribute to a part of total curvature perturbation on the super-horizon scale
and may generate a local form bispectrum. A distinguishing prediction of the
mixed scenario is . Comparing
these consistency relations to WMAP 7yr data, there is still a big room for the
Lorentz invariant inflation, but DBI inflation has been disfavored at more than
68% CL.Comment: 4 pages, 2 figures; v2: title changed, some mistakes corrected; v3:
refs added, version accepted for publication in JCA
Vertical transport and electroluminescence in InAs/GaSb/InAs structures: GaSb thickness and hydrostatic pressure studies
We have measured the current-voltage (I-V) of type II InAs/GaSb/InAs double
heterojunctions (DHETs) with 'GaAs like' interface bonding and GaSb thickness
between 0-1200 \AA. A negative differential resistance (NDR) is observed for
all DHETs with GaSb thickness 60 \AA below which a dramatic change in the
shape of the I-V and a marked hysteresis is observed. The temperature
dependence of the I-V is found to be very strong below this critical GaSb
thickness. The I-V characteristics of selected DHETs are also presented under
hydrostatic pressures up to 11 kbar. Finally, a mid infra-red
electroluminescence is observed at 1 bar with a threshold at the NDR valley
bias. The band profile calculations presented in the analysis are markedly
different to those given in the literature, and arise due to the positive
charge that it is argued will build up in the GaSb layer under bias. We
conclude that the dominant conduction mechanism in DHETs is most likely to
arise out of an inelastic electron-heavy-hole interaction similar to that
observed in single heterojunctions (SHETs) with 'GaAs like' interface bonding,
and not out of resonant electron-light-hole tunnelling as proposed by Yu et al.
A Zener tunnelling mechanism is shown to contribute to the background current
beyond NDR.Comment: 8 pages 12 fig
Large non-Gaussianity from two-component hybrid inflation
We study the generation of non-Gaussianity in models of hybrid inflation with
two inflaton fields, (2-brid inflation). We analyse the region in the parameter
and the initial condition space where a large non-Gaussianity may be generated
during slow-roll inflation which is generally characterised by a large f_NL,
tau_NL and a small g_NL. For certain parameter values we can satisfy
tau_NL>>f_NL^2. The bispectrum is of the local type but may have a significant
scale dependence. We show that the loop corrections to the power spectrum and
bispectrum are suppressed during inflation, if one assume that the fields
follow a classical background trajectory. We also include the effect of the
waterfall field, which can lead to a significant change in the observables
after the waterfall field is destabilised, depending on the couplings between
the waterfall and inflaton fields.Comment: 16 pages, 6 figures; v2: comments and references added, typos
corrected, matches published versio
Magnetic Phase Diagram of the Ferromagnetically Stacked Triangular XY Antiferromagnet: A Finite-Size Scaling Study
Histogram Monte-Carlo simulation results are presented for the magnetic-field
-- temperature phase diagram of the XY model on a stacked triangular lattice
with antiferromagnetic intraplane and ferromagnetic interplane interactions.
Finite-size scaling results at the various transition boundaries are consistent
with expectations based on symmetry arguments. Although a molecular-field
treatment of the Hamiltonian fails to reproduce the correct structure for the
phase diagram, it is demonstrated that a phenomenological Landau-type
free-energy model contains all the esstential features. These results serve to
complement and extend our earlier work [Phys. Rev. B {\bf 48}, 3840 (1993)].Comment: 5 pages (RevTex 3.0), 6 figures available upon request, CRPS 93-
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