Neutrino oscillations in dark matter Choi, Ki-Young; Chun, Eung Jin; Kim, Jongkuk
PHYSICS OF THE DARK UNIVERSE,
December 2020, 2020-12-00, Volume:
30
Journal Article
Peer reviewed
Open access
We study neutrino oscillations in a medium of dark matter which generalizes the standard matter effect. A formula is derived to describe the effect of medium and its mediator to neutrinos. Neutrinos ...and anti-neutrinos receive opposite contributions from asymmetric distribution of (dark) matter and anti-matter, and thus it could appear in precision measurements of neutrino or anti-neutrino oscillations. Furthermore, it leads to an amusing possibility that neutrino oscillations can occur from the dark-matter-induced flavorful potential even for massless neutrinos.
Display omitted
•Surface defects were reduced via positive duct bias on a 1 µm thick ta-C coating.•Surface defect reduction increased the sp3 fraction.•Carbon transfer layer was formed as ...spikes/droplet made the surface of Si3N4 ball rough.•Pore defects increased wear debris size and, thus, the friction coefficient.
Surface defects of tetrahedral amorphous carbon coatings are typically defined as spikes, droplets, and pores. In this study, a hybrid filtering method using a fixed physical and electrical filter (duct bias voltage) in a filtered cathodic vacuum arc system was used to control the surface defects. The introduction of the duct bias can control to trap the negatively charged macro-particles which is transported to the base material due to a floating potential and duct wall sheath that depend on the positive voltage. The applied positive duct bias voltage was 10, 15, 20, and 30 V. The results of this experiment revealed that as the duct bias voltage increased up to 30 V, the spikes and droplets were almost completely removed on the tetrahedral amorphous carbon surface and only the pores remained. The pores could not create a rough surface for the relative motion between interfaces due to which the friction coefficient increased as the duct bias voltage increased up to 30 V. It was concluded that the spike and droplet defects were positive elements and were required to introduce a carbon-based transfer interface and maintain a stable coefficient of friction.
Tetrahedral amorphous carbon (ta-C) has a relatively high hardness, and it can be used to enhance film properties such as wear resistance. However, the high hardness of ta-C can adversely affect a ...counterpart and accelerate its wear, and the resulting wear imbalance between the film and its counterpart can cause vibrations. This issue may be resolved by improving the wear of the counterpart. This study aimed to reduce the hardness and improve the fracture toughness of ta-C films to enhance the durability of a tribosystem, which was achieved by toughening a composite and ductile phase. A multilayered nanocrystalline (nc)-Cu/ta-C nanocomposite film was fabricated that allowed for reductions in the wear of the film and its counterpart of more than 88% and 99%, respectively.
Display omitted
Display omitted
•O2-plasma-irradiated ta-C film improved the surface energy and wettability.•High surface energy causes wear debris to aggregate and promote tribofilm formation.•Tribological ...behaviors of ta-C in running-in are improved by O2 plasma irradiation.
During running-in, there is drastic wear and the coefficient of friction (CoF) is high, because the interacting surfaces are unstable. Therefore, the running-in period should be shortened to reduce the wear of a film. When a tribofilm forms, the tribological behaviors reach a steady-state. A tetrahedral amorphous carbon (ta-C) film was irradiated with O2 plasma, to promote tribofilm formation. This reduced the running-in cycles, CoF, and wear rate by 60%, 35%, and 62%, respectively. It was confirmed that the attractive force induced by the high surface energy agglomerated the wear debris generated during the running-in period.
We study a successful model to explain the muon anomalous magnetic moment originating from Yukawa-type interactions in a supersymmetric theory. Thanks to a modular A4 flavor symmetry, any lepton ...flavor violations that spoil the model are forbidden. We also investigate a predictive radiative seesaw model including a dark matter (DM) candidate. At first, we construct the minimum model to satisfy the neutrino oscillation data and obtain several predictions such as Dirac CP and Majorana phases, the neutrino masses through χ2 analysis. However, the minimum model would not provide our promising DM candidate. Thus, we minimally extend the model and find a good DM candidate. In the extended framework, we show the allowed regions to satisfy the muon anomalous magnetic moment and the observed relic density of dark matter in addition to predictions of the lepton sector.
•Fabrication of the superhydophobic surface to improve the heat transfer resistance was proposed using the microblasting and nanostructured F-DLC coating.•Microtextures fabricated by the ...microblasting induced Cassie-state contact angle on Al6061 surface.•Nanostructured F-DLC coating led the transformation of condensation mode from FWC to DWC.•The heat transfer efficiency in the steam condensation system was improved 205% on average following the transformation to DWC mode.•The stable contact angle hysteresis before and after the steam condensation analysis specified the durability of nanostructured F-DLC coating under steam condensing environment.
Dropwise condensation (DWC) is one of the most important phenomena to improve the heat transfer performance of steam condensation system. To promote DWC on hydrophilic metals, non-metallic hydrophobic promoters are coated on the surface. Non-metallic coatings are relatively easy to be degraded due to lack of mechanical and chemical properties. In this study, fluorine-doped diamond-like carbon (F-DLC) was used to obtain DWC on Al6061. Prior to F-DLC coating, microtextures were fabricated on Al6061 for the structural wettability control. DWC was successfully obtained with a small size of condensates after the microblasting and nanostructured F-DLC coating on Al6061. The synergic effects of microtextures with Cassie-state contact angle and hydrophobicity of nanostructured F-DLC led the superhydrophobic transformation of the surface. The contact angle increased about 115% from 66° to 142° after the microblasting and nanostructured F-DLC coating. The resulting DWC improved heat transfer performance of Al6061 significantly, 205%, as the dropwise condensates were rapidly eliminated from the surface. The variations on contact angle hysteresis before and after the steam condensation analysis revealed that the superhydrophobicity and DWC mode can be stably maintained under the steam condensing conditions.
We report the case of a 31-year-old man with superior mesenteric artery syndrome after reoperation due to postoperative complications from rectal cancer. Although initial total parenteral nutrition ...(TPN) therapy failed, he underwent endoscopy-assisted feeding tube placement without complications instead of surgery. After 2 weeks of dual feeding (enteral feeding and TPN), he improved, gaining 6 kg; and an oral diet was advanced.
We consider the production of right-handed (RH) sneutrino dark matter in a model of Dirac neutrino where neutrino Yukawa coupling constants are very small. Dark matter RH sneutrinos are produced by ...scatterings and decays of thermal particles in the early Universe without reaching thermal equilibrium due to the small Yukawa couplings. We show that not only decays of thermal particles but also the thermal scatterings can be a dominant source as well as non-thermal production in a scenario with light sneutrinos and charged sleptons while other supersymmetric particles are heavy. We also discuss the cosmological implications of this scenario.
Recently CDF II Collaboration reported that they measured W boson mass
precisely. The measurement is deviated from the Standard Model (SM) Prediction
at 7$\sigma$. Also, the recent FNAL measurement ...of the muon magnetic moment
shows a $4.2\sigma$ deviation. To resolve the W boson as well as the muon
$(g-2)$ anomalies, we explore the type-X two Higgs doublet model (2HDM). We
analyze the $(m_A, \tan\beta)$ parameter space of the type-X 2HDM consistent
with the muon $(g-2)$, lepton universality test and recent $W$ boson mass
measurments from the CDF II collaboration. We find that the measurement of the
$h\to AA$ branching ratio gives a strong lower mass bound on $m_H$.
The structure and properties of tetrahedral amorphous carbon (ta-C) coatings depend on the main process parameters and bending angles of the magnetic field filter used in the filtered cathodic vacuum ...arc (FCVA). During the process, it is possible to effectively control the plasma flux of carbon ions incident on the substrate by controlling the arc discharge current, thereby influencing the mechanical properties of the coating film. Furthermore, we can control the size and amount of large particles mixed during carbon film formation while conforming with the bending angle of the mechanical filter mounted on the FCVA; therefore, it also influences the mechanical properties. In this study, we consider tribological characteristics for filtered bending angles of 45° and 90° as a function of arc discharge currents of 60 and 100 A, respectively. Experiment results indicate that the frictional behavior of the ta-C coating film is independent of the bending angle of the filter. However, its sliding wear behavior significantly changes according to the bending angle of the FCVA filter, unlike the effect of the discharge current. Further, upon changing the bending angle from 45° to 90°, abrasive wear gets accelerated, thereby changing the size and mixing amount of macro particles inside the coating film.
PDF
