10,569 research outputs found
On the Kinetic Energy and Radiative Efficiency of Gamma-Ray Bursts
Using measured X-ray luminosities to 17 Gamma-Ray Bursts (GRBs) during the
afterglow phase and accounting for radiative losses, we calculate the kinetic
energy of these bursts and investigate its relation to other GRB properties. We
then use the observed radiated energy during the prompt phase to determine the
radiative efficiency of these bursts, and explore how the efficiency relates to
other GRB observables. We find that the kinetic energy in the afterglow phase
is directly correlated with the radiated energy, total energy as well as
possibly the jet opening angle and spectral peak energy. More importantly, we
find the intriguing fact that the efficiency is correlated with the radiated
energy, and mildly with the total energy, jet opening angle and spectral peak
energy. XRF020903 also seems to follow the trends we find for our GRB sample.
We discuss the implications of these results for the GRB radiation and jet
models.Comment: 9 pages, 7 figures; Revised version, accepted to Ap
Kondo correlation and spin-flip scattering in spin-dependent transport through a quantum dot coupled to ferromagnetic leads
We investigate the linear and nonlinear dc transport through an interacting
quantum dot connected to two ferromagnetic electrodes around Kondo regime with
spin-flip scattering in the dot. Using a slave-boson mean field approach for
the Anderson Hamiltonian having finite on-site Coulomb repulsion, we find that
a spin-flip scattering always depresses the Kondo correlation at arbitrary
polarization strength in both parallel and antiparallel alignment of the lead
magnetization and that it effectively reinforces the tunneling related
conductance in the antiparallel configuration. For systems deep in the Kondo
regime, the zero-bias single Kondo peak in the differential conductance is
split into two peaks by the intradot spin-flip scattering; while for systems
somewhat further from the Kondo center, the spin-flip process in the dot may
turn the zero-bias anomaly into a three-peak structure.Comment: 4 pages, 2 figure
Effects of density-dependent quark mass on phase diagram of three-flavor quark matter
Considering the density dependence of quark mass, we investigate the phase
transition between the (unpaired) strange quark matter and the
color-flavor-locked matter, which are supposed to be two candidates for the
ground state of strongly interacting matter. We find that if the current mass
of strange quark is small, the strange quark matter remains stable unless
the baryon density is very high. If is large, the phase transition from
the strange quark matter to the color-flavor-locked matter in particular to its
gapless phase is found to be different from the results predicted by previous
works. A complicated phase diagram of three-flavor quark matter is presented,
in which the color-flavor-locked phase region is suppressed for moderate
densities.Comment: 4 figure
Elimination of negative differential conductance in an asymmetric molecular transistor by an ac-voltage
We analyze resonant tunneling subject to a non-adiabatic time-dependent
bias-voltage through an asymmetric single molecular quantum dot with coupling
between the electronic and vibrational degrees of freedom using a {\em
Tien-Gordon-type} rate equation. Our results clearly exhibit the appearance of
photon-assisted satellites in the current-voltage characteristics and the
elimination of hot-phonon-induced negative differential conductance with
increasing ac driving amplitude for an asymmetric system. This can be ascribed
to an {\em ac-induced suppression} of unequilibrated (hot) phonons in an
asymmetric system.Comment: Accepted by Appl. Phys. Let
Finite-frequency current (shot) noise in coherent resonant tunneling through a coupled-quantum-dot interferometer
We examine the shot noise spectrum properties of coherent resonant tunneling
in coupled quantum dots in both series and parallel arrangements by means of
quantum rate equations and MacDonald's formula. Our results show that, for a
series-CQD with a relatively high dot-dot hopping ,
( denotes the dot-lead tunnel-coupling
strength), the noise spectrum exhibits a dip at the Rabi frequency, ,
in the case of noninteracting electrons, but the dip is supplanted by a peak in
the case of strong Coulomb repulsion; furthermore, it becomes a dip again for a
completely symmetric parallel-CQD by tuning enclosed magnetic-flux.Comment: 8 pages, 5 figure
Tensor-polarized structure function in the standard convolution description of the deuteron
Tensor-polarized structure functions of a spin-1 hadron are additional
observables which do not exist for the spin-1/2 nucleon. They could probe novel
aspects of the internal hadron structure. Twist-2 tensor-polarized structure
functions are and , and they are related by the Callan-Gross-like
relation in the Bjorken scaling limit. In this work, we theoretically calculate
in the standard convolution description for the deuteron. Two different
theoretical models, a basic convolution description and a virtual nucleon
approximation, are used for calculating and their results are compared
with the HERMES measurement. We found large differences between our theoretical
results and the data. Although there is still room to improve by considering
higher-twist effects and in the experimental extraction of from the spin
asymmetry , there is a possibility that the large differences require
physics beyond the standard deuteron model for their interpretation. Future
studies could shed light on a new field of hadron physics. In particular,
detailed experimental studies of will start soon at the Thomas Jefferson
National Accelerator Facility. In addition, there are possibilities to
investigate tensor-polarized parton distribution functions and at Fermi
National Accelerator Laboratory and a future electron-ion collider. Therefore,
further theoretical studies are needed for understanding the tensor structure
of the spin-1 deuteron, including a new mechanism to explain the large
differences between the current data and our theoretical results.Comment: 12 pages, 7 eps figures, 3 style files, typos are corrected as
published in Phys. Rev. D 95, 074036 (2017
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