246 research outputs found
A Parametrization for
We discuss various models and Chiral Perturbation Theory results for the
form factors and . We check in how much a simple
parametrization with a few parameters can be used to extract information from
experiment.Comment: 19 pages, 14 figure
Hadron structure in tau -> KKpi nu_tau decays
We analyse the hadronization structure of both vector and axial-vector
currents leading to tau -> KKpi nu_tau decays. At leading order in the 1/Nc
expansion, and considering only the contribution of the lightest resonances, we
work out, within the framework of the resonance chiral Lagrangian, the
structure of the local vertices involved in those processes. The couplings in
the resonance theory are constrained by imposing the asymptotic behaviour of
vector and axial-vector spectral functions ruled by QCD. In this way we predict
the hadron spectra and conclude that, contrarily to previous assertions, the
vector contribution dominates by far over the axial-vector one in all KKpi
charge channels.Comment: 32 pages, 7 figure
Reparameterization Invariance to all Orders in Heavy Quark Effective Theory
Heavy Quark Effective Theory splits a heavy quark momentum into a large fixed
momentum and a variable residual momentum, p = m_Q v + k. It thereby suffers a
redundancy of description corresponding to small changes in the choice of the
fixed velocity, v. The fact that full QCD is manifestly v-independent should
lead to a non-trivial constraint on the form of the effective theory, known as
Reparameterization Invariance. For spin-1/2 quarks, the precise form of the
constraint and its solution at the level of the effective lagrangian have
proven to be rather subtle, and the original proposal by Luke and Manohar has
been questioned. In this paper I employ a version of Heavy Quark Effective
Theory containing the ``anti-particle'' field as a non-propagating auxiliary
field, which greatly simplifies keeping track of v-dependence. This permits a
very simple derivation of Reparameterization Invariance from first principles.
The auxiliary field can also be integrated out to return to the standard
formulation of the effective theory, but with the effective lagrangian now
satisfying the full reparameterization constraint. I compare this result with
earlier proposals.Comment: 12 pages, LaTex. Important and confusing typographical error in eq.
(15) corrected. To appear in Phys. Rev.
Obligate Biotroph Pathogens of the Genus Albugo Are Better Adapted to Active Host Defense Compared to Niche Competitors
Recent research suggested that plants behave differently under combined versus single abiotic and biotic stress conditions in controlled environments. While this work has provided a glimpse into how plants might behave under complex natural conditions, it also highlights the need for field experiments using established model systems. In nature, diverse microbes colonize the phyllosphere of Arabidopsis thaliana, including the obligate biotroph oomycete genus Albugo, causal agent of the common disease white rust. Biotrophic, as well as hemibiotrophic plant pathogens are characterized by efficient suppression of host defense responses. Lab experiments have even shown that Albugo sp. can suppress non-host resistance, thereby enabling otherwise avirulent pathogen growth. We asked how a pathogen that is vitally dependent on a living host can compete in nature for limited niche space while paradoxically enabling colonization of its host plant for competitors? To address this question, we used a proteomics approach to identify differences and similarities between lab and field samples of Albugo sp.-infected and -uninfected A. thaliana plants. We could identify highly similar apoplastic proteomic profiles in both infected and uninfected plants. In wild plants, however, a broad range of defense-related proteins were detected in the apoplast regardless of infection status, while no or low levels of defense-related proteins were detected in lab samples. These results indicate that Albugo sp. do not strongly affect immune responses and leave distinct branches of the immune signaling network intact. To validate our findings and to get mechanistic insights, we tested a panel of A. thaliana mutant plants with induced or compromised immunity for susceptibility to different biotrophic pathogens. Our findings suggest that the biotroph pathogen Albugo selectively interferes with host defense under different environmental and competitive pressures to maintain its ecological niche dominance. Adaptation to host immune responses while maintaining a partially active host immunity seems advantageous against competitors. We suggest a model for future research that considers not only host–microbe but in addition microbe–microbe and microbe–host environment factors
pi/K -> e nu branching ratios to O(e^2 p^4) in Chiral Perturbation Theory
We calculate the ratios R_{e/mu}^{(P)} = Gamma(P -> e nu)/Gamma (P -> mu nu)
(P=pi,K) in Chiral Perturbation Theory to order e^2 p^4. We complement the one-
and two-loop effective theory results with a matching calculation of the local
counterterm, performed within the large- expansion. We find
R_{e/mu}^{(\pi)} = (1.2352 \pm 0.0001)*10^{-4} and R_{e/mu}^{(K)} = (2.477 \pm
0.001)*10^{-5}, with uncertainty induced by the matching procedure and chiral
power counting. Given the sensitivity of upcoming new measurements, our results
provide a clean baseline to detect or constrain effects from weak-scale new
physics in these rare decays. As a by-product, we also update the theoretical
analysis of the individual pi/K -> \ell nu modes.Comment: 40 pages, 4 figures, 3 table
Radiative Tau Decays with One Pseudoscalar Meson
We have calculated the decay . We present
the photon energy spectrum, the meson-photon invariant mass spectrum and the
integrated rate as a function of a photon energy cut or an invariant mass cut.
Both the internal bremsstrahlung and the structure dependent radiation have
been taken into account. To this aim we have parametrized the form factors
and , which determine the structure dependent radiation. Observables
especially suited for the measurement of the structure dependent form factors
are found and implications on the width of the discussed.Comment: p.20, TTP93-1, LaTe
Renormalizing Heavy Quark Effective Theory at O(1/m_Q^3)
We present a calculation of the renormalized HQET Lagrangian at order
O(1/m_Q^3) in the one particle sector. The anomalous dimensions of local
operators and time ordered products of dimension 7 contributing at this order
are calculated in the one loop approximation. We show that a careful treatment
of the time ordered products is necessary to arrive at a gauge independent
renormalized lagrangian. Our result sets the stage for an investigation of
reparametrization invariance at O(1/m_Q^3).Comment: Latex, epsfig. Improved teXnology and modified conclusions. The
complete paper, including figures, is also available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/ , or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints
Bounds on Broken R-Parity from Leptonic Meson Decays
Investigating leptonic decays of pi^-, K^-, B^-, pi^0, K_L^0, B_s^0 we
present new bounds on some products of two R-parity violating coupling
constants. For mesons of a similar structure but so far poor experimental data
we give the corresponding formulae, to be used in the future.Comment: Latex, 15 pages, 1 figure; final version which appeared in Phys.Rev.
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