8,715 research outputs found
Phase Diagram of the Holstein-Hubbard Two-Leg Ladder
Using a functional renormalization group method, we obtain the phase diagram
of the two-leg ladder system within the Holstein-Hubbard model, which includes
both electron-electron and electron-phonon interactions. Our renormalization
group technique allows us to analyze the problem for both weak and strong
electron-phonon coupling. We show that, in contrast results from conventional
weak coupling studies, electron-phonon interactions can dominate
electron-electron interactions because of retardation effects.Comment: 4 page
Multi-wavelength emissions from the millisecond pulsar binary PSR J1023+0038 during an accretion active state
Recent observations strongly suggest that the millisecond pulsar binary PSR
J1023+0038 has developed an accretion disk since 2013 June. We present a
multi-wavelength analysis of PSR J1023+0038, which reveals that 1) its
gamma-rays suddenly brightened within a few days in June/July 2013 and has
remained at a high gamma-ray state for several months; 2) both UV and X-ray
fluxes have increased by roughly an order of magnitude, and 3) the spectral
energy distribution has changed significantly after the gamma-ray sudden flux
change. Time variabilities associated with UV and X-rays are on the order of
100-500 seconds and 50-100 seconds, respectively. Our model suggests that a
newly formed accretion disk due to the sudden increase of the stellar wind
could explain the changes of all these observed features. The increase of UV is
emitted from the disk, and a new component in gamma-rays is produced by inverse
Compton scattering between the new UV component and pulsar wind. The increase
of X-rays results from the enhancement of injection pulsar wind energy into the
intra-binary shock due to the increase of the stellar wind. We also predict
that the radio pulses may be blocked by the evaporated winds from the disk and
the pulsar is still powered by rotation.Comment: 8 pages, 3 figures; accepted for publication in Ap
Cosmic axion thermalization
Axions differ from the other cold dark matter candidates in that they form a
degenerate Bose gas. It is shown that their huge quantum degeneracy and large
correlation length cause cold dark matter axions to thermalize through
gravitational self-interactions when the photon temperature reaches
approximately 500 eV. When they thermalize, the axions form a Bose-Einstein
condensate. Their thermalization occurs in a regime, herein called the
`condensed regime', where the Boltzmann equation is not valid because the
energy dispersion of the particles is smaller than their interaction rate. We
derive analytical expressions for the thermalization rate of particles in the
condensed regime, and check the validity of these expressions by numerical
simulation of a toy model. We revisit axion cosmology in light of axion
Bose-Einstein condensation. It is shown that axions are indistinguishable from
ordinary cold dark matter on all scales of observational interest, except when
they thermalize or rethermalize. The rethermalization of axions that are about
to fall in a galactic potential well causes them to acquire net overall
rotation as they go to the lowest energy state consistent with the total
angular momentum they acquired by tidal torquing. This phenomenon explains the
occurrence of caustic rings of dark matter in galactic halos. We find that
photons may reach thermal contact with axions and investigate the implications
of this possibility for the measurements of cosmological parameters.Comment: 38 pages, 1 figur
Dynamical mean-field theory of the Anderson-Hubbard model with local and nonlocal disorder in tensor formulation
To explore correlated electrons in the presence of local and non-local
disorder, the Blackman-Esterling-Berk method for averaging over off-diagonal
disorder is implemented into dynamical mean-field theory using tensor notation.
The impurity model combining disorder and correlations is solved using the
recently developed fork tensor-product state solver, which allows one to
calculate the single particle spectral functions on the real-frequency axis. In
the absence of off-diagonal hopping, we establish exact bounds of the spectral
function of the non-interacting Bethe lattice with coordination number . In
the presence of interaction, the Mott insulating paramagnetic phase of the
one-band Hubbard model is computed at zero temperature in alloys with site- and
off-diagonal disorder. When the Hubbard parameter is increased, transitions
from an alloy band-insulator through a correlated metal into a Mott insulating
phase are found to take place.Comment: 15 pages, 5 figures. See ancillary folder for numerical data and
computational detail
Measurement of Cosmic-ray Muons and Muon-induced Neutrons in the Aberdeen Tunnel Underground Laboratory
We have measured the muon flux and production rate of muon-induced neutrons
at a depth of 611 m water equivalent. Our apparatus comprises three layers of
crossed plastic scintillator hodoscopes for tracking the incident cosmic-ray
muons and 760 L of gadolinium-doped liquid scintillator for producing and
detecting neutrons. The vertical muon intensity was measured to be cmssr. The yield of
muon-induced neutrons in the liquid scintillator was determined to be
neutrons/(gcm). A fit to the recently measured neutron
yields at different depths gave a mean muon energy dependence of for liquid-scintillator targets.Comment: 14 pages, 17 figures, 3 table
RNF17 blocks promiscuous activity of PIWI proteins in mouse testes
PIWI proteins and their associated piRNAs protect germ cells from the activity of mobile genetic elements. Two classes of piRNAs-primary and secondary-are defined by their mechanisms of biogenesis. Primary piRNAs are processed directly from transcripts of piRNA cluster loci, whereas secondary piRNAs are generated in an adaptive amplification loop, termed the ping-pong cycle. In mammals, piRNA populations are dynamic, shifting as male germ cells develop. Embryonic piRNAs consist of both primary and secondary species and are mainly directed toward transposons. In meiotic cells, the piRNA population is transposon-poor and largely restricted to primary piRNAs derived from pachytene piRNA clusters. The transition from the embryonic to the adult piRNA pathway is not well understood. Here we show that RNF17 shapes adult meiotic piRNA content by suppressing the production of secondary piRNAs. In the absence of RNF17, ping-pong occurs inappropriately in meiotic cells. Ping-pong initiates piRNA responses against not only transposons but also protein-coding genes and long noncoding RNAs, including genes essential for germ cell development. Thus, the sterility of Rnf17 mutants may be a manifestation of a small RNA-based autoimmune reaction
Topological correlations in soap froths
Correlation in two-dimensional soap froth is analysed with an effective
potential for the first time. Cells with equal number of sides repel (with
linear correlation) while cells with different number of sides attract (with
NON-bilinear) for nearest neighbours, which cannot be explained by the maximum
entropy argument. Also, the analysis indicates that froth is correlated up to
the third shell neighbours at least, contradicting the conventional ideas that
froth is not strongly correlated.Comment: 10 Pages LaTeX, 6 Postscript figure
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