121,505 research outputs found
Free-standing all-polymer microring resonator optical filter
Free-standing all-polymer microring resonator optical filters as prototypical elements in flexible integrated lightwave circuits are demonstrated. The fabrication and measurement methods are discussed. The measured spectrum shows good agreement with theoretical expectations. The crucial 'critical' coupling condition is achieved, resulting in a measurement limited -27 dB extinction of the filter output on resonances
Pion Form Factor in the Factorization Formalism
Based on the light-cone (LC) framework and the factorization formalism,
the transverse momentum effects and the different helicity components'
contributions to the pion form factor are recalculated. In
particular, the contribution to the pion form factor from the higher helicity
components (), which come from the spin-space Wigner
rotation, are analyzed in the soft and hard energy regions respectively. Our
results show that the right power behavior of the hard contribution from the
higher helicity components can only be obtained by fully keeping the
dependence in the hard amplitude, and that the dependence in LC wave
function affects the hard and soft contributions substantially. As an example,
we employ a model LC wave function to calculate the pion form factor and then
compare the numerical predictions with the experimental data. It is shown that
the soft contribution is less important at the intermediate energy region.Comment: 21 pages, 4 figure
Cosmological perturbations and noncommutative tachyon inflation
The motivation for studying the rolling tachyon and non-commutative inflation
comes from string theory. In the tachyon inflation scenario, metric
perturbations are created by tachyon field fluctuations during inflation. We
drive the exact mode equation for scalar perturbation of the metric and
investigate the cosmological perturbations in the commutative and
non-commutative inflationary spacetime driven by the tachyon field which have a
Born-Infeld Lagrangian.Comment: 6 two-column pages, no figur
Semileptonic decays in the light-cone QCD sum rules
Semileptonic () decays are investigated systematically in the
light-cone QCD sum rules. Special emphasis is put on the LCSR calculation on
weak form factors with an adequate chiral current correlator, which turns out
to be particularly effective to control the pollution by higher twist
components of spectator mesons. The result for each channel depends on the
distribution amplitude of the the producing meson. The leading twist
distribution amplitudes of the related heavy mesons and charmonium are worked
out by a model approach in the reasonable way. A practical scenario is
suggested to understand the behavior of weak form factors in the whole
kinematically accessible ranges. The decay widths and branching ratios are
estimated for several () decay modes of current interest.Comment: 8 pages, talk given by the first arthur at 4th International
Conference on Flavor Physics (ICFP 2007), Beijing, China, Sept 24-28, 200
A Generic Dynamical Model of Gamma-ray Burst Remnants
The conventional generic model is deemed to explain the dynamics of
-ray burst remnants very well, no matter whether they are adiabatic or
highly radiative. However, we find that for adiabatic expansion, the model
could not reproduce the Sedov solution in the non-relativistic phase, thus the
model needs to be revised. In the present paper, a new differential equation is
derived. The generic model based on this equation has been shown to be correct
for both radiative and adiabatic fireballs, and in both ultra-relativistic and
non-relativistic phase.Comment: 10 pages, LaTeX, 4 postscript figures, accepted for publication in
MNRA
Cancellation of Infrared Divergences in Hadronic Annihilation Decays of Heavy Quarkonia
In the framework of a newly developed factorization formalism which is based
on NRQCD, explicit cancellations are shown for the infrared divergences that
appeared in the previously calculated hadronic annihilation decay rates of
P-wave and D-wave heavy quarkonia. We extend them to a more general case that
to leading order in and next-to-leading order in , the infrared
divergences in the annihilation amplitudes of color-singlet
pair can be removed by including the contributions of
color-octet operators ,
, ... in NRQCD. We also give the decay widths of
at leading order in .Comment: 8 pages, LaTex(3 figures included), to be publishe
Transverse momentum dependence in the perturbative calculation of pion form factor
By reanalysing transverse momentum dependence in the perturbative calculation
of pion form factor an improved expression of pion form factor which takes into
account the transverse momentum dependenc in hard scattering amplitude and
intrinsic transverse momentum dependence associated with pion wave functions is
given to leading order, which is available for momentum transfers of the order
of a few GeV as well as for . Our scheme can be extended to
evaluate the contributions to the pion form factor beyond leading order.Comment: 13 pages in LaTeX, plus 3 Postscript figure
Weak gravity conjecture constraints on inflation
We consider the gravitational correction to the coupling of the scalar
fields. Weak gravity conjecture says that the gravitational correction to the
running of scalar coupling should be less than the contribution from scalar
fields. For instance, a new scale sets a UV cutoff
on the validity of the effective theory. Furthermore, this
conjecture implies a possible constraint on the inflation model, e.g. the
chaotic inflation model might be in the swampland.Comment: 11 pages, 3 figs; monor corrections; some clarifying remarks added
and the final version for publication in JHE
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