62 research outputs found
Non-perturbative Effect on Thermal Relic Abundance of Dark Matter
We point out that thermal relic abundance of the dark matter is strongly
altered by a non-perturbative effect called the Sommerfeld enhancement, when
constituent particles of the dark matter are non-singlet under the SU(2)_L
gauge interaction and much heavier than the weak gauge bosons. Typical
candidates for such dark matter particles are the heavy wino- and higgsino-like
neutralinos. We investigate the non-perturbative effect on the relic abundance
of dark matter for the wino-like neutralino as an example. We show that its
thermal abundance is reduced by 50% compared to the perturbative result. The
wino-like neutralino mass consistent with the observed dark matter abundance
turns out to be 2.7 TeV < m < 3.0 TeV.Comment: 10 pages, 2 figure
Direct Detection of the Wino- and Higgsino-like Neutralino Dark Matters at One-Loop Level
The neutralino-nucleon (\tilde{\chi}^0-N) scattering is an important process
for direct dark matter searches. In this paper we discuss one-loop
contributions to the cross section in the wino-like and Higgsino-like LSP
cases. The neutralino-nucleon scattering mediated by the Higgs
\tilde{\chi}^0\tilde{\chi}^0 and Z\tilde{\chi}^0\tilde{\chi}^0 couplings at
tree level is suppressed by the gaugino-Higgsino mixing at tree level when the
neutralino is close to a weak eigenstate. The one-loop contribution to the
cross section, generated by the gauge interaction, is not suppressed by any
SUSY particle mass or mixing in the wino- and Higgsino-like LSP cases. It may
significantly alter the total cross section when \sigma_{\tilde{\chi}^0 N}\sim
10^{-45} cm^2 or less.Comment: 26 pages, 9 figures. Version to be published in Physical Review
Non-Perturbative Effect on Dark Matter Annihilation and Gamma Ray Signature from Galactic Center
Detection of gamma rays from dark matter annihilation in the galactic center
is one of the feasible techniques to search for dark matter. We evaluate the
gamma ray flux in the case that the dark matter has an electroweak SU(2)_L
charge. Such dark matter is realized in the minimal supersymmetric standard
model (MSSM) when the lightest SUSY particle is the Higgsino- or Wino-like
neutralino. When the dark matter is heavy compared to the weak gauge bosons,
the leading-order calculation of the annihilation cross sections in
perturbation breaks down due to a threshold singularity. We take into account
non-perturbative effects by using the non-relativistic effective theory for the
two-body states of the dark matter and its SU(2)_L partner(s), and evaluate
precise cross sections relevant to the gamma ray fluxes. We find that the
annihilation cross sections may be enhanced by several orders of magnitude due
to resonances when the dark matter mass is larger than 1 TeV. Furthermore, the
annihilation cross sections in the MSSM may be changed by factors even when the
mass is about 500 GeV. We also discuss sensitivities to gamma ray signals from
the galactic center in the GLAST satellite detector and the large Air Cerenkov
Telescope arrays.Comment: 44 pages, 25 figures, some typos in Sec.V-2 (related to fitting
functions) correcte
Flexible Multifunctional Sensors for Wearable and Robotic Applications
This review provides an overview of the current state-of-the-art of the emerging field of flexible multifunctional sensors for wearable and robotic applications. In these application sectors, there is a demand for high sensitivity, accuracy, reproducibility, mechanical flexibility, and low cost. The ability to empower robots and future electronic skin (e-skin) with high resolution, high sensitivity, and rapid response sensing capabilities is of interest to a broad range of applications including wearable healthcare devices, biomedical prosthesis, and human–machine interacting robots such as service robots for the elderly and electronic skin to provide a range of diagnostic and monitoring capabilities. A range of sensory mechanisms is examined including piezoelectric, pyroelectric, piezoresistive, and there is particular emphasis on hybrid sensors that provide multifunctional sensing capability. As an alternative to the physical sensors described above, optical sensors have the potential to be used as a robot or e-skin; this includes sensory color changes using photonic crystals, liquid crystals, and mechanochromic effects. Potential future areas of research are discussed and the challenge for these exciting materials is to enhance their integration into wearables and robotic applications.</p
Blue-emitting acridine-tagged silver(i)-bis-N-heterocyclic carbene
Herein, the photophysical properties of an acridine derivative of a bis-N-heterocyclic carbene silver complex were investigated. The HOMO and LUMO energy differences between 9-[(N-methyl imidazol-2-ylidene)]acridine and 4,5-bis[(N-methyl-imidazol-2-ylidene)methyl]acridine were theoretically compared. Based on the calculation, the 4,5-bis N-heterocyclic carbene-tethered acridine type of ligand was found to be a potential source for tuning the fluorescent nature of the resultant metal derivatives. Thus, a 4,5-bis N-heterocyclic carbene (NHC)-tethered acridine silver(I) salt was synthesized, and its photophysical properties were investigated. The 4,5-bis[(N-isopropylimidazol-2-ylidene)methyl]acridine silver(I) hexafluorophosphate complex was obtained from the reaction between [4,5-bis{(N-isopropylimidazolium)methyl}acridine] hexafluorophosphate and Ag2O in very good yield; this molecule was characterized by elemental analysis and FTIR, multinuclear (1H and 13C) NMR, UV-Vis, and fluorescence spectroscopic techniques. The molecular structure has been confirmed by single-crystal X-ray diffraction analysis, which has revealed that the complex is a homoleptic mononuclear silver(I) cationic solid. The charge of the Ag(I)–NHC cation is balanced by the hexafluorophosphate anion. The cationic moieties are closely packed in the chair and inverted chair forms where silver(I) possesses a quasi-linear geometry. Moreover, the silver complex provided blue emission from all the three excitations with good fluorescence quantum yield. The fluorescence lifetime of the silver(I) complex has been determined using the time-correlated single photon counting technique. Interestingly, the fluorescence decay pattern and the fluorescence lifetimes of the silver complex are largely different from those of the parent ligand acridine imidazolium salt. Moreover, the theoretical predictions have been found to be in good agreement with the experimental results
Short single-stranded DNAs with putative non-canonical structures comprise a new class of plasma cell-free DNA
Tunable Reflection through Size Polydispersity of Chiral-Nematic Liquid Crystal Polymer Particles
Micro-sized chiral-nematic liquid crystal (N* LC) polymer particles have attracted considerable interest as versatile reflective colorants with selective circularly polarized light (CPL) properties. However, challenges in achieving the desired size distribution of N* LC particles have led to an incomplete understanding of their reflective characteristics. In this study, we successfully synthesized N* LC particles via dispersion polymerization, enabling precise control over size polydispersity by manipulating the composition of the polymerization solvent. Our investigation revealed that monodisperse N* LC particles displayed distinct reflection bands with high CPL selectivity, while polydisperse particles exhibited broader reflection with lower CPL selectivity. These findings underscore the potential to synthesize N* LC particles with tailored reflective properties using identical monomeric compounds. Furthermore, we demonstrated the production of multifunctional reflective colorants by blending N* LC particles with varying reflection colors. These discoveries hold significant promise for advancing the development of reflective colorants and anti-counterfeiting printing techniques utilizing micro-sized N* LC particles
Aggregation-Enhanced Room-Temperature Phosphorescence from Au(I) Complexes Bearing Mesogenic Biphenylethynyl Ligands
Gold(I) complexes, enabling to form linear coordination geometry, are promising materials for manifesting both aggregation-induced emission (AIE) behavior due to strong intermolecular Au–Au (aurophilic) interactions and liquid crystalline (LC) nature depending on molecular geometry. In this study, we synthesized several gold(I) complexes with rod-like molecular skeletons where we employed a mesogenic biphenylethynyl ligand and an isocyanide ligand with flexible alkoxyl or alkyl chains. The AIE behavior and LC nature were investigated experimentally and computationally. All synthesized gold(I) complexes exhibited AIE properties and, in crystal, room-temperature phosphorescence (RTP) with a relatively high quantum yields of greater than 23% even in air. We have demonstrated that such strong RTP are drastically changed depending on the crystal-size and/or crystal growth process that changes quality of crystals as well as the aggregate structure, of e.g., Au–Au distance. Moreover, the complex with longer flexible chains showed LC nature where RTP can be observed. We expect these rod-like gold(I) complexes to have great potential in AIE-active LC phosphorescent applications such as linearly/circularly polarizing phosphorescence materials
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