12,039 research outputs found
LOFF Pairing vs. Breached Pairing in Asymmetric Fermion Superfluids
A general analysis for the competition between breached pairing (BP) and LOFF
pairing mechanisms in asymmetric fermion superfluids is presented in the frame
of a four fermion interaction model. Two physical conditions which can induce
mismatched Fermi surfaces are considered: (1) fixed chemical potential
asymmetry and (2) fixed fermion number asymmetry . In case
(1), the BP state is ruled out because of Sarma instability and LOFF state is
thermodynamically stable in a narrow window of . In case (2), while
the Sarma instability can be avoided and both the BP and LOFF states can
survive provided is less than the corresponding critical value, the BP
state suffers magnetic instability and the LOFF state is always
thermodynamically stable. While the LOFF window in case (2) is much larger than
the one in the conventional case (1), for small the longitudinal
superfluid density of the LOFF state is negative and it suffers also magnetic
instability.Comment: 12 pages, 13 figures, published in Physical Review B. Notice: an
algebra error in Equation (39) correcte
Exclusive Decays and CP Violation in the General two-Higgs-doublet Model
We calculate all the branching ratios and direct CP violations of
decays in a most general two-Higgs-doublet model with spontaneous CP violation.
As the model has rich CP-violating sources, it is shown that the new physics
effects to direct CP violations and branching ratios in some channels can be
significant when adopting the generalized factorization approach to evaluate
the hadronic matrix elements, which provides good signals for probing new
physics beyond the SM in the future B experiments.Comment: 21 page
Broadband phased array antenna steering by means of coherent signal combining in an integrated ring resonator-based optical beamformer
A squint-free, continuously tunable optical beamformer for broadband phased array receive antennas is proposed. The complete system is demonstrated, including E/O and O/E conversions, and optical signal processing. The latter involves delay synchronization and coherent optical combining, which is performed in an integrated ring resonator-based optical beam forming network, realized in low-loss, CMOScompatible TriPleX technology. Successful combination of four beamformer input channels has been demonstrated by means of RF-to-RF measurements
Spectral and dynamic characteristics of buried-heterostructure single quantum well (Al,Ga)As lasers
We demonstrate that, as predicted, (Al,Ga)As single quantum well (SQW) lasers have substantially narrower spectral linewidths than bulk double-heterostructure lasers. We have observed a further major reduction (>3×) in the linewidth of these SQW lasers when the facet reflectivities are enhanced. This observation is explained theoretically on the basis of the very low losses in coated SQW lasers and the value of the spontaneous emission factor at low threshold currents. We also report on the modulation frequency response parameter of these SQW lasers
Paramagnetic Meissner Effect and Finite Spin Susceptibility in an Asymmetric Superconductor
A general analysis of Meissner effect and spin susceptibility of a uniform
superconductor in an asymmetric two-component fermion system is presented in
nonrelativistic field theory approach. We found that, the pairing mechanism
dominates the magnetization property of superconductivity, and the asymmetry
enhances the paramagnetism of the system. At the turning point from BCS to
breached pairing superconductivity, the Meissner mass squared and spin
susceptibility are divergent at zero temperature. In the breached pairing state
induced by chemical potential difference and mass difference between the two
kinds of fermions, the system goes from paramagnetism to diamagnetism, when the
mass ratio of the two species increases.Comment: 17pages, 2 figures, published in Physical Review
Multiwavelength optical beam forming network with ring resonator-based binary-tree architecture for broadband phased array antenna systems
Integrated optical beam forming networks (OBFNs) offer many advantages for phased array applications. ORR-based true-time-delay units can be cascaded in a binary tree topology and tuned for continuously-adjustable broadband time delay. Nonetheless, with large number of antenna elements, the OBFN may become very complex. A novel idea is proposed to exploit the frequency periodicity of the ORRs and the WDM technique to achieve multiple-signal-paths on a single beamformer, thus reducing complexity and costs. The use of high index contrast waveguides in Si-compatible technology further reduces chip footprint and allows the use of integrated OBFNs for large arrays and multi-beam applications
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