288 research outputs found
Pumping in quantum dots and non-Abelian matrix Berry phases
We have investigated pumping in quantum dots from the perspective of
non-Abelian (matrix) Berry phases by solving the time dependent Schr{\"o}dinger
equation exactly for adiabatic changes. Our results demonstrate that a pumped
charge is related to the presence of a finite matrix Berry phase. When
consecutive adiabatic cycles are performed the pumped charge of each cycle is
different from the previous ones
Search for solar axions in XMASS, a large liquid-xenon detector
XMASS, a low-background, large liquid-xenon detector, was used to search for
solar axions that would be produced by bremsstrahlung and Compton effects in
the Sun. With an exposure of 5.6ton days of liquid xenon, the model-independent
limit on the coupling for mass 1keV is
(90% C.L.), which is a factor of two stronger than the existing experimental
limit. The bounds on the axion masses for the DFSZ and KSVZ axion models are
1.9 and 250eV, respectively. In the mass range of 10-40keV, this study produced
the most stringent limit, which is better than that previously derived from
astrophysical arguments regarding the Sun to date
Search for exotic neutrino-electron interactions using solar neutrinos in XMASS-I
We have searched for exotic neutrino-electron interactions that could be produced by a neutrino millicharge, by a neutrino magnetic moment, or by dark photons using solar neutrinos in the XMASS-I liquid xenon detector. We observed no significant signals in 711 days of data. We obtain an upper limit for neutrino millicharge of 5.4 × 10−12e at 90% confidence level assuming all three species of neutrino have common millicharge. We also set flavor-dependent limits assuming the respective neutrino flavor is the only one carrying a millicharge, 7.3 × 10−12e for νe , 1.1 × 10−11e for νμ, and 1.1 × 10−11e for ντ . These limits are the most stringent yet obtained from direct measurements. We also obtain an upper limit for the neutrino magnetic moment of 1.8 × 10−10 Bohr magnetons. In addition, we obtain upper limits for the coupling constant of dark photons in the U(1)B−L model of 1.3 × 10−6 if the dark photon mass is 1 × 10−3 MeV/c2, and 8.8 × 10−5 if it is 10 MeV/c2
Search for dark matter in the form of hidden photons and axion-like particles in the XMASS detector
Hidden photons and axion-like particles are candidates for cold dark matter if they were produced non-thermally in the early universe. We conducted a search for both of these bosons using 800 live-days of data from the XMASS detector with 327 kg of liquid xenon in the fiducial volume. No significant signal was observed, and thus we set constraints on the α´/α parameter related to kinetic mixing of hidden photons and the coupling constant gAe of axion-like particles in the mass range from 40 to 120 keV/c2, resulting in α´/α < 6 × 10−26 and gAe < 4 × 10−13. These limits are the most stringent over this mass range derived from both direct and indirect searches to date
Direct dark matter search in XMASS-I
A search for dark matter using an underground single-phase liquid xenon detector was conducted at the Kamioka Observatory in Japan, particularly for Weakly Interacting Massive Particles (WIMPs). We have used 705.9 live days of data in a fiducial volume containing 97 kg of liquid xenon at the center of the detector. The event rate in the fiducial volume after the data reduction was (4.2 ± 0.2) × 10−3 day−1 kg−1 keVee−1 at 5 keVee, with a signal efficiency of 20%. All the remaining events are consistent with our background evaluation, mostly of the “mis-reconstructed events” originated from 210Pb in the copper plates lining the detector’s inner surface. The obtained upper limit on a spin-independent WIMP-nucleon cross section was 2.2 × 10−44 cm2 for a WIMP mass of 60 GeV/c2 at the 90% confidence level, which was the most stringent limit among results from single-phase liquid xenon detectors
The First Magnetic Fields
We review current ideas on the origin of galactic and extragalactic magnetic
fields. We begin by summarizing observations of magnetic fields at cosmological
redshifts and on cosmological scales. These observations translate into
constraints on the strength and scale magnetic fields must have during the
early stages of galaxy formation in order to seed the galactic dynamo. We
examine mechanisms for the generation of magnetic fields that operate prior
during inflation and during subsequent phase transitions such as electroweak
symmetry breaking and the quark-hadron phase transition. The implications of
strong primordial magnetic fields for the reionization epoch as well as the
first generation of stars is discussed in detail. The exotic, early-Universe
mechanisms are contrasted with astrophysical processes that generate fields
after recombination. For example, a Biermann-type battery can operate in a
proto-galaxy during the early stages of structure formation. Moreover, magnetic
fields in either an early generation of stars or active galactic nuclei can be
dispersed into the intergalactic medium.Comment: Accepted for publication in Space Science Reviews. Pdf can be also
downloaded from http://canopus.cnu.ac.kr/ryu/cosmic-mag1.pd
The first direct search for inelastic boosted dark matter with COSINE-100
A search for inelastic boosted dark matter (IBDM) using the COSINE-100 detector with 59.5 days of data is presented. This relativistic dark matter is theorized to interact with the target material through inelastic scattering with electrons, creating a heavier state that subsequently produces standard model particles, such as an electron-positron pair. In this study, we search for this electron-positron pair in coincidence with the initially scattered electron as a signature for an IBDM interaction. No excess over the predicted background event rate is observed. Therefore, we present limits on IBDM interactions under various hypotheses, one of which allows us to explore an area of the dark photon parameter space that has not yet been covered by other experiments. This is the first experimental search for IBDM using a terrestrial detector
A search for solar axion induced signals with COSINE-100
We present results from a search for solar axions with the COSINE-100 detector. We find no evidence of solar axion events from a data set of 6,303.9 kg⋅days exposure and set a 90\,\% confidence level upper limit on the axion-electron coupling, gae, at 1.70~×~10−11 for an axion mass less than 1\,keV/c2. This limit excludes QCD axions heavier than 0.59\,eV/c2 in the DFSZ model and 168.1\,eV/c2 in the KSVZ model
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