567 research outputs found
Lattice calculation of the strangeness and electromagnetic nucleon form factors
We report on recent lattice QCD calculations of the strangeness magnetic
moment of the nucleon and the nucleon electromagnetic form factors, when we
allow the electromagnetic current to connect to quark loops as well as to the
valence quarks. Our result for the strangeness magnetic moment is
G_M^s(0)=-0.36+/-0.20. The sea contributions from the u and d quarks are about
80% larger. However, they cancel to a large extent due to their electric
charges, resulting in a smaller net sea contribution of -0.097+/-0.037 mu_N to
the nucleon magnetic moment. As far as the neutron to proton magnetic moment
ratio is concerned, this sea contribution tends to cancel out the cloud-quark
effect from the Z-graphs and results in a ratio of -0.68+/-0.04 which is close
to the SU(6) relation and the experiment. The strangeness Sachs electric
mean-square radius _E is found to be small and negative and the total
sea contributes substantially to the neutron electric form factor.Comment: LATTICE98(matrixelement); 3 pages, no figures, to appear in Lattice
'98 proceeding
One Belt — One Road Initiative: A Window of Opportunity for Russia’s Western Border Regions
In recent years, global geo-economic transformations have been considerably affected by the development of
the People’s Republic of China, its reviving leadership and ambitions, and
its increasing efforts to reformat and
integrate the Eurasian space. The One
Belt — One Road Initiative is a manifesto and a tool to advance China’s
long-term geostrategic interests that
spread to the bordering states and regions and to the prospects of their socioeconomic development. The initiative encompasses transportation and logistics, production and investment, finances, research and technology, humanitarian affairs, and foreign policy.
In this article, we will highlight the
key geoeconomic and geopolitical
aspects of the One Belt — One Road
initiative implementation, based on the
Chinese and Russian studies. Another
goal is to weigh up the risks and benefits associated with the extension of the
project to Russian territories. Special
attention is paid to Russia’s western
borderlands — 17 regions that account
for 8.6 % of the country’s territory,
17.4 % of the total GRP, and 20.8% of
the national population.
We analyse the factors in effect —
including geopolitical ones, as well as
current trends in the development of
Russia’s western borderlands. It is
shown that the inclusion into the Chinese Eurasian integration initiatives
creates additional incentives for a positive re-evaluation of the Russian space as a whole and holds special relevance for Russia’s western borderlands. We analyse the possibility of including Russia’s Baltic regions — the infrastructural and economic island of the Kaliningrad exclave among them —
into the One Belt — One Road Initiative
Nonperturbative renormalisation of composite operators with overlap quarks
We compute non-perturbatively the renormalisation constants of composite
operators on a lattice with lattice spacing = 0.093 fm
for the overlap fermion action by using the regularisation independent (RI)
scheme. The quenched gauge configurations are generated by tadpole improved
plaquette plus rectangle action. We test the perturbative continuum relation
and and find that they agree well above = 1.6 GeV.
We also perform a Renormalisation Group analysis at the next-to-next-to-leading
order and convert the renormalisation constants to the scheme.Comment: Talk given at LHP2003, Cairns, Australi
Holographic dark energy in a universe with spatial curvature and massive neutrinos: a full Markov Chain Monte Carlo exploration
In this paper, we report the results of constraining the holographic dark
energy model with spatial curvature and massive neutrinos, based on a Markov
Chain Monte Carlo global fit technique. The cosmic observational data include
the full WMAP 7-yr temperature and polarization data, the type Ia supernova
data from Union2.1 sample, the baryon acoustic oscillation data from SDSS DR7
and WiggleZ Dark Energy Survey, and the latest measurements of from HST.
To deal with the perturbations of dark energy, we adopt the parameterized
post-Friedmann method. We find that, for the simplest holographic dark energy
model without spatial curvature and massive neutrinos, the phenomenological
parameter at more than confidence level. The inclusion of
spatial curvature enlarges the error bars and leads to only in about
range; in contrast, the inclusion of massive neutrinos does not
have significant influence on . We also find that, for the holographic dark
energy model with spatial curvature but without massive neutrinos, the
error bars of the current fractional curvature density
are still in order of ; for the model with massive neutrinos but
without spatial curvature, the upper bound of the total mass of
neutrinos is eV. Moreover, there exists clear degeneracy
between spatial curvature and massive neutrinos in the holographic dark energy
model, which enlarges the upper bound of by more than 2 times.
In addition, we demonstrate that, making use of the full WMAP data can give
better constraints on the holographic dark energy model, compared with the case
using the WMAP ``distance priors''.Comment: 21 pages, 10 figures; major revision; new figures and discussions
added; accepted by JCA
The seesaw mechanism at TeV scale in the 3-3-1 model with right-handed neutrinos
We implement the seesaw mechanism in the 3-3-1 model with right-handed
neutrinos. This is accomplished by the introduction of a scalar sextet into the
model and the spontaneous violation of the lepton number. We identify the
Majoron as a singlet under symmetry, which makes it
safe under the current bounds imposed by electroweak data. The main result of
this work is that the seesaw mechanism works already at TeV scale with the
outcome that the right-handed neutrino masses lie in the electroweak scale, in
the range from MeV to tens of GeV. This window provides a great opportunity to
test their appearance at current detectors, though when we contrast our results
with some previous analysis concerning detection sensitivity at LHC, we
conclude that further work is needed in order to validate this search.Comment: about 13 pages, no figure
and in the Standard Model and new bounds on R parity violation
We study the pure penguin decays and .
Using QCD factorization, we find . For the pure penguin annihilation process
, analyzed here for the first time, . The smallness of these decays in
the Standard Model makes them sensitive probes for new physics. From the upper
limit of ,we find constraints on R parity violating couplings, , and for . Our new bounds on
are one order of magnitude stronger than
before. Within the available upper bounds for , and
, we find that could
be enhanced to . Experimental searches for these decays
are strongly urged.Comment: 5 pages, 3 figures embede
Scalar Potential Without Cubic Term in 3-3-1 Models Without Exotic Electric Charges
A detailed study of the criteria for stability of the scalar potential, and
the proper electroweak symmetry breaking pattern in some 3-3-1 models without
exotic electric charges is presented. In this paper we concentrate in a scalar
sector with three Higgs scalar triplets, with a potential that does not include
the cubic term, due to the presence of a discrete symmetry. For the analysis we
use, and improve, a method previously developed to study the scalar potential
in the two-Higgs-doublet extension of the standard model. Our main result is to
show the consistency of those 3-3-1 models without exotic electric charges.Comment: 19 page
Pairing symmetry and long range pair potential in a weak coupling theory of superconductivity
We study the superconducting phase with two component order parameter
scenario, such as, , where . We show, that in absence of orthorhombocity, the usual
does not mix with usual symmetry gap in an anisotropic band
structure. But the symmetry does mix with the usual d-wave for . The d-wave symmetry with higher harmonics present in it also mixes with
higher order extended wave symmetry. The required pair potential to obtain
higher anisotropic and extended s-wave symmetries, is derived by
considering longer ranged two-body attractive potential in the spirit of tight
binding lattice. We demonstrate that the dominant pairing symmetry changes
drastically from to like as the attractive pair potential is obtained
from longer ranged interaction. More specifically, a typical length scale of
interaction , which could be even/odd multiples of lattice spacing leads
to predominant wave symmetry. The role of long range interaction on
pairing symmetry has further been emphasized by studying the typical interplay
in the temperature dependencies of these higher order and wave pairing
symmetries.Comment: Revtex 8 pages, 7 figures embeded in the text, To appear in PR
Spin Injection and Detection in Magnetic Nanostructures
We study theoretically the spin transport in a nonmagnetic metal connected to
ferromagnetic injector and detector electrodes. We derive a general expression
for the spin accumulation signal which covers from the metallic to the
tunneling regime. This enables us to discuss recent controversy on spin
injection and detection experiments. Extending the result to a superconducting
device, we find that the spin accumulation signal is strongly enhanced by
opening of the superconducting gap since a gapped superconductor is a low
carrier system for spin transport but not for charge. The enhancement is also
expected in semiconductor devices.Comment: 4 pages, 3 figure
A Lattice Study of the Magnetic Moment and the Spin Structure of the Nucleon
Using an approach free from momentum extrapolation, we calculate the nucleon
magnetic moment and the fraction of the nucleon spin carried by the quark
angular momentum in the quenched lattice QCD approximation. Quarks with three
values of lattice masses, 210, 124 and 80 MeV, are formulated on the lattice
using the standard Wilson approach. At every mass, 100 gluon configurations on
16^3 x 32 lattice with \beta=6.0 are used for statistical averaging. The
results are compared with the previous calculations with momentum
extrapolation. The contribution of the disconnected diagrams is studied at the
largest quark mass using noise theory technique.Comment: 14 pages, 3 figures, Talk given at Lattice2001, Berlin, German
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