Search for Periodic Time Variations of the Solar

We report a search for time variations of the solar ^{8}B neutrino flux using 5804 live days of Super-Kamiokande data collected between May 31, 1996, and May 30, 2018. Super-Kamiokande measured the precise time of each solar neutrino interaction over 22 calendar years to search for solar neutrino flux modulations with unprecedented precision. Periodic modulations are searched for in a dataset comprising five-day interval solar neutrino flux measurements with a maximum likelihood method. We also applied the Lomb-Scargle method to this dataset to compare it with previous reports. The only significant modulation found is due to the elliptic orbit of the Earth around the Sun. The observed modulation is consistent with astronomical data: we measured an eccentricity of (1.53±0.35)%, and a perihelion shift of (-1.5±13.5) days.

Search for Cosmic-Ray Boosted Sub-GeV Dark Matter Using Recoil Protons at Super-Kamiokande.

We report a search for cosmic-ray boosted dark matter with protons using the 0.37 megaton×years data collected at Super-Kamiokande experiment during the 1996-2018 period (SKI-IV phase). We searched for an excess of proton recoils above the atmospheric neutrino background from the vicinity of the Galactic Center. No such excess is observed, and limits are calculated for two reference models of dark matter with either a constant interaction cross section or through a scalar mediator. This is the first experimental search for boosted dark matter with hadrons using directional information. The results present the most stringent limits on cosmic-ray boosted dark matter and exclude the dark matter-nucleon elastic scattering cross section between 10^{-33}cm^{2} and 10^{-27}cm^{2} for dark matter mass from 1 MeV/c^{2} to 300 MeV/c^{2}.

Erratum: Search for Cosmic-Ray Boosted Sub-GeV Dark Matter Using Recoil Protons at Super-Kamiokande [Phys. Rev. Lett. 130, 031802 (2023)].

This corrects the article DOI: 10.1103/PhysRevLett.130.031802.

Pathogenic and free-living amoebae isolated from swimming pools and physiotherapy tubs in Mexico.

A protozoological survey was done to isolate free-living amoebae from swimming pools and physiotherapy tubs in Mexico City. Amoebae were isolated by culture in nonnutritive agar medium combined with Escherichia coli. Identification of the isolates was done by morphology using specialized taxonomic keys and by isoelectric focusing of total proteins and isoenzymes in agarose. Pathogenicity of the isolates was determined in 3-week-old mice by intracerebral and intranasal inoculations. Statistical tools were used to determine the existence of significant differences on the incidence and diversity of the isolates in relation to the two types of water bodies analyzed. Water and environmental temperatures, pH, and chloride concentrations were determined at each sampling site. Twenty-nine amoebic strains from eight genera were isolated. Most frequently found were specimens of the genera (Acanthamoeba (with four pathogenic strains), Vahlkampfia, Hartmannella, and Naegleria. Amoebae were isolated more frequently in spring and summer, and could not be recovered from pools with chloride levels of 5.31 mg/ml or more. This survey demonstrates that chloride concentrations commonly used in recreative pools and therapy tubs are not sufficient to eliminate viable cysts of most free-living amoebae. Significantly higher numbers of isolates were retrieved from the pools than from the tubs.