6,781 research outputs found
Grand unification using a generalized Yang-Mills theory
Generalized Yang-Mills theories have a covariant derivative that employs both
scalar and vector bosons. Here we show how grand unified theories of the
electroweak and strong interactions can be constructed with them. In particular
the SU(5) GUT can be obtained from SU(6) with SU(5)xU(1) as a maximal subgroup.
The choice of maximal subgroup also determines the chiral structure of the
theory. The resulting Lagrangian has only two terms, and only two irreducible
representations are needed, one for fermions and another for bosons.Comment: 10 pages, no figure
Unification of SU(2)xU(1) Using a Generalized Covariant Derivative and U(3)
A generalization of the Yang-Mills covariant derivative, that uses both
vector and scalar fields and transforms as a 4-vector contracted with Dirac
matrices, is used to simplify and unify the Glashow-Weinberg-Salam model. Since
SU(3) assigns the wrong hypercharge to the Higgs boson, it is necessary to use
a special representation of U(3) to obtain all the correct quantum numbers. A
surplus gauge scalar boson emerges in the process, but it uncouples from all
other particles.Comment: 12 pages, no figures. To be published in Int. J. Mod. Phys.
The role of abscisic acid and water relations in drought responses of subterranean clover
The role of water relations and abscisic acid (ABA) in the responses to drought were studied in a mediterranean forage crop, Trifolium subterraneum L. under field conditions. soil and plant water status, leaf gas exchange parameters, and xylem sap ABA content were determined at different times during a long-term soil drying episode in irrigated and droughted plants. The diurnal time-courses of these parameters were also measured at the end of a drought period. In response to soil drying stomatal conductance (g) was reduced early to 50% that of irrigated plants before any substantial change in water potential was detected. A close logarithmic regression between photosynthesis rate (A) and g was present. For the first weeks of drought the decline in A was less pronounced than in g, thus increasing water use efficiency. Stomatal conductance during diurnal time-courses showed no consistent relationships with respect to either ABA or leaf water potential. throughout the experimental period dependence of g on leaf water status was evident from the tight correlation (r(2) = 0.88, P < 0.01) achieved between stomatal conductance and midday water potential, but the correlation was also high when comparing g with respect to ABA content in xylem sap (r(2) = 0.83, P < 0.001). However, the stomata from drought acclimated plants were apparently more sensitive to xylem ABA content. For similar xylem ABA concentrations stomatal conductance was significantly higher in irrigated than in water-stressed plants.info:eu-repo/semantics/publishedVersio
Quantum computing with incoherent resources and quantum jumps
Spontaneous emission and the inelastic scattering of photons are two natural
processes usually associated with decoherence and the reduction in the capacity
to process quantum information. Here we show that when suitably detected, these
photons are sufficient to build all the fundamental blocks needed to perform
quantum computation in the emitting qubits while protecting them from
deleterious dissipative effects. We exemplify by showing how to teleport an
unknown quantum state and how to efficiently prepare graph states for the
implementation of measurement-based quantum computation.Comment: 5 pages, 5 figure
(Giant) Vortex - (anti) vortex interaction in bulk superconductors: The Ginzburg-Landau theory
The vortex-vortex interaction potential in bulk superconductors is calculated
within the Ginzburg-Landau (GL) theory and is obtained from a numerical
solution of a set of two coupled non-linear GL differential equations for the
vector potential and the superconducting order parameter, where the merger of
vortices into a giant vortex is allowed. Further, the interaction potentials
between a vortex and a giant vortex and between a vortex and an antivortex are
obtained for both type-I and type-II superconductors. Our numerical results
agree asymptotically with the analytical expressions for large inter-vortex
separations which are available in the literature. We propose new empirical
expressions valid over the full interaction range, which are fitted to our
numerical data for different values of the GL parameter
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