401 research outputs found
Analysis of the semileptonic (B_c -> B_u* l+ l-) decay from QCD sum rules
We analyze the semileptonic (B_c -> B_u* l+ l-) decay in the frame work of
the Standard Model. We calculate the (B_c) to (B_u*) transition form factors in
QCD sum rules. Analytical expressions for the spectral densities and gluon
condensates are presented. The branching ratio of the (B_c -> B_u* l+ l-) decay
is calculated, and it is obtained that this decay can be detectable at
forthcoming LHC machines.Comment: 17 pages, no figures, LaTeX formatte
Polarized Dirac fermions in de Sitter spacetime
The tetrad gauge invariant theory of the free Dirac field in two special
moving charts of the de Sitter spacetime is investigated pointing out the
operators that commute with the Dirac one. These are the generators of the
symmetry transformations corresponding to isometries that give rise to
conserved quantities according to the Noether theorem. With their help the
plane wave spinor solutions of the Dirac equation with given momentum and
helicity are derived and the final form of the quantum Dirac field is
established. It is shown that the canonical quantization leads to a correct
physical interpretation of the massive or massless fermion quantum fields.Comment: 19 pages, LaTeX w AMS sym
Model Independent Analysis of the Forward-Backward Asymmetry for the Decay
The sensitivity of the zero position of the forward backward asymmetry
for the exclusive
decay is examined by using most general non-standard 4-fermion interactions.
Our analysis shows that the zero position of the forward backward asymmetry is
very sensitive to the sign and size of the Wilson coefficients corresponding to
the new vector type interactions, which are the counter partners of the usual
Standard Model operators but have opposite chirality. In addition to these, the
other significant effect comes from the interference of Scalar-Pseudoscalar and
Tensor type operators. These results will not only enhance our theoretical
understanding about the axial vector mesons but will also serve as a good tool
to look for physics beyond the SM.Comment: 14 pages, 8 figures, Published version that appears in EPJ
Heavy-to-light transition form factors and their relations in light-cone QCD sum rules
The improved light-cone QCD sum rules by using chiral current correlator is
systematically reviewed and applied to the calculation of all the
heavy-to-light form factors, including all the semileptonic and penguin ones.
By choosing suitable chiral currents, the light-cone sum rules for all the form
factors are greatly simplified and depend mainly on one leading twist
distribution amplitude of the light meson. As a result, relations between these
form factors arise naturally. At the considered accuracy these relations
reproduce the results obtained in the literature. Moreover, since the explicit
dependence on the leading twist distribution amplitudes is preserved, these
relations may be more useful to simulate the experimental data and extract the
information on the distribution amplitude.Comment: 1+16 pages, no figure
Development of E-learning in higher education and future directions
The present paper is based on the work of the ‘Future of E-Learning Group’, a constituent of the EUNIS E-Learning task Force. The group has set up a number of tasks to fulfill its role, one of which, is seeking and disseminating information on the development of e-learning with a view to ensuring the right guide is provided for progress into the future. In our work to date, in this era of globalization, we question the ability of present university systems to respond adequately and appropriately to complex demands of an Information Economy. There’s increasing involvement of private sector in higher education. The effects on future learning on the use of varying tools as well as the design of competency-based performance in e-learning have been reported (Wolrery et al, 2000; Sluijsmans et al, 2006). Several multimedia learning systems are being developed for use as future interactive educational tools (Low et al, 2003). New thinking is required for the new relationships that are being developed between creative subjects and technology when we consider the nature of universities in their present state of existence as public sector institutions. The university of the future can be perceived as a setup, based on international trade in educational services, with universities fulfilling the functions of licensing, quality assurance and cultural custodianship. The pressent paper discusses some of these issues and reports on the future directions of e-learning as they relate to higher education
Rare Decays of \Lambda_b->\Lambda + \gamma and \Lambda_b ->\Lambda + l^{+} l^{-} in the Light-cone Sum Rules
Within the Standard Model, we investigate the weak decays of and with the light-cone
sum rules approach. The higher twist distribution amplitudes of
baryon to the leading conformal spin are included in the sum rules for
transition form factors. Our results indicate that the higher twist
distribution amplitudes almost have no influences on the transition form
factors retaining the heavy quark spin symmetry, while such corrections can
result in significant impacts on the form factors breaking the heavy quark spin
symmetry. Two phenomenological models (COZ and FZOZ) for the wave function of
baryon are also employed in the sum rules for a comparison, which can
give rise to the form factors approximately 5 times larger than that in terms
of conformal expansion. Utilizing the form factors calculated in LCSR, we then
perform a careful study on the decay rate, polarization asymmetry and
forward-backward asymmetry, with respect to the decays of , .Comment: 38 pages, 15 figures, some typos are corrected and more references
are adde
Technology-enhanced learning on campus: insights from EUNIS e-Learning Task Force
In 2010 the EUNIS e-Learning Task Force (ELTF) members collaborated on a review of tools and technologies in use across our member institutions. One of the key features of that paper was the use of technology to give off-campus learners, such as distance learners, those undertaking field studies and learners in the workplace a richly supported learning experience. Building on the success of that collaboration, the ELTF members have turned their attention this year to the use of technology on campus. Whilst technology and distance learning go hand in hand, universities are often slower to take advantage of the possibilities offered by technology to enrich the learning that takes place in our lecture theatres and classrooms. The reasons for this are often cultural as much as financial or technical. Drawing on experience from across the EUNIS member nations we take a look at the types of tools, learning resources and learning activities that are being used to enhance the traditional curriculum, promote deeper learning and bridge the learning that takes place inside and outside the classroom. We look at a range of innovative projects and the benefits they have delivered, ways of overcoming the barriers to technology-enhanced learning on campus and we speculate about the role and function of the campus of the future
Ward Identities, B-> \rho Form Factors and |V_ub|
The exclusive FCNC beauty semileptonic decay B-> \rho is studied using Ward
identities in a general vector meson dominance framework, predicting vector
meson couplings involved. The long distance contributions are discussed which
results to obtain form factors and |V_ub|. A detailed comparison is given with
other approaches.Comment: 30 pages+four postscript figures, an Appendix adde
Invasive fish disrupt host-pathogen dynamics leading to amphibian declines
Sudden disease outbreaks may not necessarily reflect a recent pathogen introduction but may instead arise from the disruption of a host-pathogen equilibrium. Together with invasive species, emerging pathogens pose significant threats to biodiversity. The dynamics of each stressor have been studied separately, yet rarely when interacting. Using a 40-year dataset, we tested the hypothesis that the introduction of an invasive fish leads to such a disruption, manifested by ranavirosis outbreaks on amphibian hosts. MCP sequencing revealed the historical presence of two major Ranavirus clades, with low prevalence. The introduction of fish was not followed by the emergence of new viruses, but rather by an increase in the prevalence of the strains already present, fitting the ‘endemic pathogen hypothesis’. Two decades after the first die-offs, one amphibian species persists in extremely low numbers, but Ranavirus prevalence is closer to the enzootic phase that preceded the outbreaks. Models show that host population collapse and lack of recovery are best explained by the concerted interaction of Ranavirus and invasive fish. We provide robust evidence that invasive species can impact naïve communities by disrupting the host-pathogen balance, exacerbating health threats. This study emphasizes the importance of exploring the historical interactions between multiple stressors to understand population declines.info:eu-repo/semantics/publishedVersio
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