37,684 research outputs found
Pointwise estimates for the Bergman kernel of the weighted Fock space
We prove upper pointwise estimates for the Bergman kernel of the weighted
Fock space of entire functions in where is a
subharmonic function with a doubling measure. We derive estimates
for the canonical solution operator to the inhomogeneous Cauchy-Riemann
equation and we characterize the compactness of this operator in terms of
Phenomenology from a U(1) gauged hidden sector
We consider the phenomenological consequences of a hidden Higgs sector
extending the Standard Model (SM), in which the matter content are uncharged
under the SM gauge groups. We consider a simple case where the hidden sector is
gauged under a U(1) with one Higgs singlet. The only couplings between SM and
the hidden sector are through mixings between the neutral gauge bosons of the
two respective sectors, and between the Higgs bosons. We find signals testable
at the LHC that can reveal the existence and shed light on the nature of such a
hidden sector.Comment: 5 pages, 2 figures. Talk given at the Lake Louise Winter Institute
2007, Feb. 19-24, Alberta, Canad
Testing Realistic Quark Mass Matrices in the Custodial Randall-Sundrum Model with Flavor Changing Top Decays
We study quark mass matrices in the Randall-Sundrum (RS) model with bulk
symmetry . The Yukawa couplings are
assumed to be within an order of magnitude of each other, and perturbative. We
find that quark mass matrices of the symmetrical form proposed by Koide
\textit{et. al.} [Y. Koide, H. Nishiura, K. Matsuda, T. Kikuchi and T.
Fukuyama, Phys. Rev. D {\bf 66}, 093006 (2002)] can be accommodated in the RS
framework with the assumption of hierarchyless Yukawa couplings, but not the
hermitian Fritzsch-type mass matrices. General asymmetrical mass matrices are
also found which fit well simultaneously with the quark masses and the
Cabibbo-Kobayashi-Maskawa matrix. Both left-handed (LH) and right-handed (RH)
quark rotation matrices are obtained that allow analysis of flavour changing
decay of both LH and RH top quarks. At a warped down scale of 1.65 TeV, the
total branching ratio of t \ra Z + jets can be as high as for symmetrical mass matrices and for
asymmetrical ones. This level of signal is within reach of the LHC.Comment: 30 pages, 6 figures. Reference added, typos corrected, discussions in
Sec. IV B expanded. Version conforms to the published versio
A Very Narrow Shadow Extra Z-boson at Colliders
We consider the phenomenological consequences of a hidden Higgs sector
extending the Standard Model (SM), in which the ``shadow Higgs'' are uncharged
under the SM gauge groups. We consider a simple U(1) model with one Higgs
singlet. One mechanism which sheds light on the shadow sector is the mixing
between the neutral gauge boson of the SM and the additional U(1) gauge group.
The mixing happens through the usual mass-mixing and also kinetic-mixing, and
is the only way the ``shadow '' couples to the SM. We study in detail
modifications to the electroweak precision tests (EWPTs) that the presence of
such a shadow sector would bring, which in turn provide constraints on the
kinetic-mixing parameter, , left free in our model. The shadow
production rate at the LHC and ILC depends on . We find that
observable event rate at both facilities is possible for a reasonable range of
allowed by EWPTs.Comment: 10 pages, 7 figures. Note and refs. adde
Illumination and annealing characteristics of two-dimensional electron gas systems in metal-organic vapor-phase epitaxy grown AlGaN/AlN/GaN heterostructures
We studied the persistent photoconductivity (PPC) effect in AlGaN/AlN/GaN
heterostructures with two different Al-compositions (x=0.15 and x=0.25). The
two-dimensional electron gas formed at the AlN/GaN heterointerface was
characterized by Shubnikov-de Haas and Hall measurements. Using optical
illumination, we were able to increase the carrier density of the
Al0.15Ga0.85N/AlN/GaN sample from 1.6x10^{12} cm^{-2} to 5.9x1012 cm^{-2},
while the electron mobility was enhanced from 9540 cm2/Vs to 21400 cm2/Vs at T
= 1.6 K. The persistent photocurrent in both samples exhibited a strong
dependence on illumination wavelength, being highest close to the bandgap and
decreasing at longer wavelengths. The PPC effect became fairly weak for
illumination wavelengths longer than 530 nm and showed a more complex response
with an initial negative photoconductivity in the infrared region of the
spectrum (>700 nm). The maximum PPC-efficiency for 390 nm illumination was
0.011% and 0.005% for Al0.25Ga0.75N/AlN/GaN and Al0.15Ga0.85N/AlN/GaN samples,
respectively. After illumination, the carrier density could be reduced by
annealing the sample. Annealing characteristics of the PPC effect were studied
in the 20-280 K temperature range. We found that annealing at 280 K was not
sufficient for full recovery of the carrier density. In fact, the PPC effect
occurs in these samples even at room temperature. Comparing the measurement
results of two samples, the Al0.25Ga0.75N/AlN/GaN sample had a larger response
to illumination and displayed a smaller recovery with thermal annealing. This
result suggests that the energy scales of the defect configuration-coordinate
diagrams for these samples are different, depending on their Al-composition.Comment: 27 pages, 8 figure
Complete controllability of finite-level quantum systems
Complete controllability is a fundamental issue in the field of control of
quantum systems, not least because of its implications for dynamical
realizability of the kinematical bounds on the optimization of observables. In
this paper we investigate the question of complete controllability for
finite-level quantum systems subject to a single control field, for which the
interaction is of dipole form. Sufficient criteria for complete controllability
of a wide range of finite-level quantum systems are established and the
question of limits of complete controllability is addressed. Finally, the
results are applied to give a classification of complete controllability for
four-level systems.Comment: 14 pages, IoP-LaTe
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