Neutrino Splitting and Density-Dependent Dispersion Relations

We show that particles can split only when their group velocity exceeds their phase velocity. In this sense the splitting process is the quantum analog of the modulational instability in anomalous dispersive media. In the case of a neutrino whose dispersion relation contains a subdominant Lorentz-violating correction of the form aP^k, the neutrino will decay into two neutrinos and an antineutrino at a rate proportional to a^3G_F^2E^{2+3k}. Unlike the Cohen-Glashow instability, the splitting instability exists even if all particles involved in the interaction have the same dispersion relations at the relevant energy scales. We show that this instability leads to strong constraints even if the energy E is a function of both the momentum P and also of the background density rho, for example we show that it alone would have been sufficient to eliminate any model of the MINOS/OPERA velocity anomaly which modifies the neutrino dispersion relation while leaving those of other particles intact.Comment: 23 pages, 1 figure, focus shifted from superluminality to a general treatment of splitting constraint

Leptonic dark matter annihilation in the evolving universe: constraints and implications

The cosmic electron and positron excesses have been explained as possible dark matter (DM) annihilation products. In this work we investigate the possible effects of such a DM annihilation scenario during the evolution history of the Universe. We first calculate the extragalactic $\gamma$-ray background (EGRB), which is produced through the final state radiation of DM annihilation to charged leptons and the inverse Compton scattering between electrons/positrons and the cosmic microwave background. The DM halo profile and the minimal halo mass, which are not yet well determined from the current N-body simulations, are constrained by the EGRB data from EGRET and Fermi telescopes. Then we discuss the impact of such leptonic DM models on cosmic evolution, such as the reionization and heating of intergalactic medium, neutral Hydrogen 21 cm signal and suppression of structure formation. We show that the impact on the Hydrogen 21 cm signal might show interesting signatures of DM annihilation, but the influence on star formation is not remarkable. Future observations of the 21 cm signals could be used to place new constraints on the properties of DM.Comment: 24 pages, 6 figures and 2 tables. Improved treatment of the energy deposition process, the suppression on structure formation is weaker. Accepted for publication by JCA

ANALYSIS AND DESIGN OF SILICON-BASED MILLIMETER-WAVE AMPLIFIERS

Ph.DDOCTOR OF PHILOSOPH

Neutrino emission from dark matter annihilation/decay in light of cosmic e±e^{\pm} and pˉ\bar{p} data

A self-consistent global fitting method based on the Markov Chain Monte Carlo technique to study the dark matter (DM) property associated with the cosmic ray electron/positron excesses was developed in our previous work. In this work we further improve the previous study to include the hadronic branching ratio of DM annihilation/decay. The PAMELA $\bar{p}/p$ data are employed to constrain the hadronic branching ratio. We find that the 95% ($2\sigma$) upper limits of the quark branching ratio allowed by the PAMELA $\bar{p}/p$ data is $\sim 0.032$ for DM annihilation and $\sim 0.044$ for DM decay respectively. This result shows that the DM coupling to pure leptons is indeed favored by the current data. Based on the global fitting results, we further study the neutrino emission from DM in the Galactic center. Our predicted neutrino flux is some smaller than previous works since the constraint from $\gamma$-rays is involved. However, it is still capable to be detected by the forth-coming neutrino detector such as IceCube. The improved points of the present study compared with previous works include: 1) the DM parameters, both the particle physical ones and astrophysical ones, are derived in a global fitting way, 2) constraints from various species of data sets, including $\gamma$-rays and antiprotons are included, and 3) the expectation of neutrino emission is fully self-consistent.Comment: 13 pages, 2 figures, 1 table; Published in IJMPA 201

A Dual-Band Microwave Filter Design for Modern Wireless Communication Systems

Nowadays, modern communication system relies on the designs of high-performance devices to enhance communication effect for a high quality of life and smart city system. As a crucial signal processing step, microwave filter removes unwanted frequency components away from the received signal and enhances the useful ones. However, large loss, bulky size, and single-band greatly limit the practical applications in urban computing. Therefore, the filters with dual-band characteristic are highly desirable for modern wireless communication, such as device-to-device communication, environment monitoring, and automatic driving. In this paper, a dual-band microwave filter is designed and fabricated based on the theory of Mie-resonance extraordinary transmission. An electromagnetic wave cannot propagate through a subwavelength aperture drilled in a metallic film. By adding two dielectric cuboids of different sizes into the two apertures, two passbands appear in the frequency range of 10.0-12.0 GHz. In this range, the insertion loss is less than 0.4 dB, and 3-dB bandwidth is more than 48 MHz. Particularly, the two passband frequencies can be tuned by adjusting the size of the dielectric cuboids. This approach opens a way for designing tunable dual-band microwave bandpass filter, which is benefit for enhancing spectrum resource utilization