35,050 research outputs found
Exact O(g^2 alpha_s) top decay width from general massive two-loop integrals
We calculate the b-dependent self-energy of the top quark at O(g^2 \alpha_s)
by using a general massive two-loop algorithm proposed in a previous article.
From this we derive by unitarity the O(\alpha_s) radiative corrections to the
decay width of the top quark, where all effects associated with the quark
mass are included without resorting to a mass expansion. Our results agree with
the analytical results available for the O(\alpha_s) correction to the top
quark width
Constant-temperature molecular-dynamics algorithms for mixed hard-core/continuous potentials
We present a set of second-order, time-reversible algorithms for the
isothermal (NVT) molecular-dynamics (MD) simulation of systems with mixed
hard-core/continuous potentials. The methods are generated by combining
real-time Nose' thermostats with our previously developed Collision Verlet
algorithm [Mol. Phys. 98, 309 (1999)] for constant energy MD simulation of such
systems. In all we present 5 methods, one based on the Nose'-Hoover [Phys. Rev.
A 31, 1695 (1985)] equations of motion and four based on the Nose'-Poincare'
[J.Comp.Phys., 151 114 (1999)] real-time formulation of Nose' dynamics. The
methods are tested using a system of hard spheres with attractive tails and all
correctly reproduce a canonical distribution of instantaneous temperature. The
Nose'-Hoover based method and two of the Nose'-Poincare' methods are shown to
have good energy conservation in long simulations.Comment: 9 pages, 5 figure
Development of stochastic models of window state changes in educational buildings
How people would like to interact with surrounding environment will subsequently influence indoor thermal conditions and further impact building energy performance. In order to understand occupants' adaptive behaviours in terms of environmental control utilization from the point of view of quantification, an investigation on windows operation was carried out in non-air-conditioned educational buildings in the UK during summer time considering the effects of occupant type (active and passive) and the time of a day. Outdoor air temperature was a better predictor or window operation than indoor air temperature. Window operation was found to be time-evolving event. The purpose or criteria of adjusting window states were different at different occupancy stages. Active occupants were more willing to change windows states in response to outdoor air temperature variations. Sub-models predicting transition probabilities of window state for different occupant type and occupancy stages were developed. The results derived from this field study are helpful with improving building simulation accuracy by integrating sub-models into simulation software and further providing guideline on building energy reduction without sacrificing indoor thermal comfort
On-chip III-V monolithic integration of heralded single photon sources and beamsplitters
We demonstrate a monolithic III-V photonic circuit combining a heralded
single photon source with a beamsplitter, at room temperature and telecom
wavelength. Pulsed parametric down-conversion in an AlGaAs waveguide generates
counterpropagating photons, one of which is used to herald the injection of its
twin into the beamsplitter. We use this configuration to implement an
integrated Hanbury-Brown and Twiss experiment, yielding a heralded second-order
correlation that confirms single-photon
operation. The demonstrated generation and manipulation of quantum states on a
single III-V semiconductor chip opens promising avenues towards real-world
applications in quantum information
Hole Spin Coherence in a Ge/Si Heterostructure Nanowire
Relaxation and dephasing of hole spins are measured in a gate-defined Ge/Si
nanowire double quantum dot using a fast pulsed-gate method and dispersive
readout. An inhomogeneous dephasing time
exceeds corresponding measurements in III-V semiconductors by more than an
order of magnitude, as expected for predominately nuclear-spin-free materials.
Dephasing is observed to be exponential in time, indicating the presence of a
broadband noise source, rather than Gaussian, previously seen in systems with
nuclear-spin-dominated dephasing.Comment: 15 pages, 4 figure
Study of isospin violating excitation in
We study the reaction in the vicinity of mass
region. The isospin-violating excitation is accounted for by two major
mechanisms. One is electromagnetic (EM) transition and the other is strong
isospin violations. For the latter, we consider contributions from the
intermediate hadronic meson loops and - mixing as the major
mechanisms via the and s-channel transitions, respectively. By fitting the
recent KLOE data, we succeed in constraining the model parameters and
extracting the branching ratio. It shows that the
branching ratio is sensitive to the excitation line shape and background
contributions. Some crucial insights into the correlation between isospin
violation and Okubo-Zweig-Iizuka (OZI) rule evading transitions are also
learned.Comment: Revised version to appear in J. Phys.
Bosonic Seesaw in the Unparticle Physics
Recently, conceptually new physics beyond the Standard Model has been
proposed by Georgi, where a new physics sector becomes conformal and provides
"unparticle" which couples to the Standard Model sector through higher
dimensional operators in low energy effective theory. Among several
possibilities, we focus on operators involving the (scalar) unparticle, Higgs
and the gauge bosons. Once the Higgs develops the vacuum expectation value
(VEV), the conformal symmetry is broken and as a result, the mixing between the
unparticle and the Higgs boson emerges. In this paper, we consider a natural
realization of bosonic seesaw in the context of unparticle physics. In this
framework, the negative mass squared or the electroweak symmetry breaking
vacuum is achieved as a result of mass matrix diagonalization. In the
diagonalization process, it is important to have zero value in the
(1,1)-element of the mass matrix. In fact, the conformal invariance in the
hidden sector can actually assure the zero of that element. So, the bosonic
seesaw mechanism for the electroweak symmetry breaking can naturally be
understood in the framework of unparticle physics.Comment: 5 pages, no figure; added one more referenc
Transient magnetoconductivity of photoexcited electrons
Transient magnetotransport of two-dimensional electrons with
partially-inverted distribution excited by an ultrashort optical pulse is
studied theoretically. The time-dependent photoconductivity is calculated for
GaAs-based quantum wells by taking into account the relaxation of electron
distribution caused by non-elastic electron-phonon interaction and the
retardation of the response due to momentum relaxation and due to a finite
capacitance of the sample. We predict large-amplitude transient oscillations of
the current density and Hall field (Hall oscillations) with frequencies
corresponding to magnetoplasmon range, which are initiated by the instability
owing to the absolute negative conductivity effect.Comment: 21 pages, 6 fig
Antilocalization of Coulomb Blockade in a Ge-Si Nanowire
The distribution of Coulomb blockade peak heights as a function of magnetic
field is investigated experimentally in a Ge-Si nanowire quantum dot. Strong
spin-orbit coupling in this hole-gas system leads to antilocalization of
Coulomb blockade peaks, consistent with theory. In particular, the peak height
distribution has its maximum away from zero at zero magnetic field, with an
average that decreases with increasing field. Magnetoconductance in the
open-wire regime places a bound on the spin-orbit length ( < 20 nm),
consistent with values extracted in the Coulomb blockade regime ( < 25
nm).Comment: Supplementary Information available at http://bit.ly/19pMpd
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