8,984 research outputs found
Effect of Dynamical Coulomb Correlations on the Fermi Surface of Na_0.3CoO_2
The t2g quasi-particle spectra of Na_0.3CoO_2 are calculated within the
dynamical mean field theory. It is shown that as a result of dynamical Coulomb
correlations charge is transfered from the nearly filled e_g' subbands to the
a_1g band, thereby reducing orbital polarization among Co t2g states. Dynamical
correlations therefore stabilize the small e_g' Fermi surface pockets, in
contrast to angle-resolved photoemission data, which do not reveal these
pockets.Comment: 4 pages, to appear in PR
Total Width of 125 GeV Higgs Boson
By using the LHC and Tevatron measurements of the cross sections to various
decay channels relative to the standard model Higgs boson, the total width of
the putative 125 GeV Higgs boson is determined as 6.1 +7.7-2.9 MeV. We describe
a way to estimate the branching fraction for Higgs decay to dark matter. We
also discuss a No-Go theorem for the gammagamma signal of the Higgs boson at
the LHC.Comment: 11 pages, 2 figure
Searching for Stoponium along with the Higgs boson
Stoponium, a bound state of top squark and its antiparticle in a
supersymmetric model, may be found in the ongoing Higgs searches at the LHC.
Its WW and ZZ detection ratios relative to the Standard Model Higgs boson can
be more than unity from WW* threshold to the two Higgs threshold. The gamma
gamma channel is equally promising. Some regions of the stoponium mass below
150 GeV are already being probed by the ATLAS and CMS experiments.Comment: 10 pages 5 figure
Correlation between Superconducting Transition Temperature and Increase of Nuclear Spin-Lattice Relaxation Rate Devided by Temperature at in the Hydrate Cobaltate NaCoOHO
We have performed Co-nuclear quadrupole resonance (NQR) studies on
NaCoOHO compounds with different Na () and hydrate
() contents. Two samples with different Na contents but nearly the same
values ( = 0.348, = 4.7 K ; = 0.339, = 4.6 K) were
investigated. The spin-lattice relaxation rate in the superconducting
(SC) and normal states is almost the same for the two samples except just above
. NQR measurements were also performed on different-hydrate-content
samples with different values, which were prepared from the same
Na-content ( = 0.348) sample. From measurements of using the
different-hydrate-content samples, it was found that a low- sample with
K has a larger residual density of states (DOS) in the SC state and
a smaller increase of just above than a high- sample with
= 4.7 K. The former behavior is consistent with that observed in
unconventional superconductors, and the latter suggests the relationship
between and the increase in DOS just above . This increase, which is
seemingly associated with the two-dimensionality of the CoO plane, is
considered to be one of the most important factors for the occurrence of
superconductivity.Comment: 5 pages, 5 figures, To be published in J. Phys. Soc. Jp
Effects to Scalar Meson Decays of Strong Mixing between Low and High Mass Scalar Mesons
We analyze the mass spectroscopy of low and high mass scalar mesons and get
the result that the coupling strengths of the mixing between low and high mass
scalar mesons are very strong and the strengths of mixing for scalar
mesons and those of I=0 scalar mesons are almost same. Next, we analyze the
decay widths and decay ratios of these mesons and get the results that the
coupling constants for which represents the coupling of high
mass scalar meson -> two pseudoscalar mesons are almost same as the
coupling for the I=0. On the other hand, the coupling constant for
which represents the low mass scalar meson -> are far
from the coupling constant for I=0. We consider a resolution for this
discrepancy. Coupling constant for glueball -> is smaller than
the coupling . is .Comment: 15 pages, 6 figure
Rise of Kp Total Cross Section and Universality
The increase of the measured hadronic total cross sections at the highest
energies is empirically described by squared log of center-of-mass energy sqrt
s as sigma(tot)= B (log s)2, consistent with the energy dependence of the
Froissart unitarity bound. The coefficient B is argued to have a universal
value, but this is not proved directly from QCD. In the previous tests of this
universality, the p(pbar)p, pi p, and K p forward scatterings were analyzed
independently and found to be consistent with B(pp) = B(pip) = B(Kp), although
the determined value of B(Kp) had large uncertainty. In the present work, we
have further analyzed forward Kp scattering to obtain a more exact value of
B(Kp). Making use of continuous moment sum rules(CMSR) we have fully exploited
the information of low-energy scattering data to predict the high-energy
behavior of the amplitude hrough duality. The estimation of B(Kp) is improved
remarkably, and our result strongly supports the universality of B.Comment: 12 pages, 3 figure
Estimates of isospin breaking contributions to baryon masses
We estimate the isospin breaking contributions to the baryon masses which we
analyzed recently using a loop expansion in the heavy baryon approximation to
chiral effective field theory. To one loop, the isospin breaking corrections
come from the effects of the quark mass difference, the Coulomb and
magnetic moment interactions, and effective point interactions attributable to
color-magnetic effects. The addition of the first meson loop corrections
introduces new structure. We estimate the resulting low-energy, long-range
contributions to the mass splittings by regularizing the loop integrals using
connections to dynamical models for finite-size baryons. We find that the
resulting contributions to the isospin breaking corrections are of the right
general size, have the correct sign pattern, and agree with the experimental
values within the margin of error.Comment: 15 pages, 5 figures; changed title and conten
Evidence for Strong-coupling S-wave Superconductivity in MgB2 :11B NMR Study
We have investigated a gap structure in a newly-discovered superconductor,
MgB2 through the measurement of 11B nuclear spin-lattice relaxation rate,
^{11}(1/T_1). ^{11}(1/T_1) is proportional to the temperature (T) in the normal
state, and decreases exponentially in the superconducting (SC) state, revealing
a tiny coherence peak just below T_c. The T dependence of 1/T_1 in the SC state
can be accounted for by an s-wave SC model with a large gap size of 2\Delta
/k_BT_c \sim 5 which suggests to be in a strong-coupling regime.Comment: 2 pages with 1 figur
Detectability of the First Cosmic Explosions
We present a fully self-consistent simulation of a synthetic survey of the
furthermost cosmic explosions. The appearance of the first generation of stars
(Population III) in the Universe represents a critical point during cosmic
evolution, signaling the end of the dark ages, a period of absence of light
sources. Despite their importance, there is no confirmed detection of
Population III stars so far. A fraction of these primordial stars are expected
to die as pair-instability supernovae (PISNe), and should be bright enough to
be observed up to a few hundred million years after the big bang. While the
quest for Population III stars continues, detailed theoretical models and
computer simulations serve as a testbed for their observability. With the
upcoming near-infrared missions, estimates of the feasibility of detecting
PISNe are not only timely but imperative. To address this problem, we combine
state-of-the-art cosmological and radiative simulations into a complete and
self-consistent framework, which includes detailed features of the
observational process. We show that a dedicated observational strategy using
per cent of total allocation time of the James Webb Space
Telescope mission can provide us up to detectable PISNe per year.Comment: 9 pages, 8 figures. Minor corrections added to match published
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