86 research outputs found
Sea quark effects in B Spectroscopy and Decay Constants
We present comprehensive results for the spectrum and decay constants of
hadrons containing a single b quark. The heavy quark is simulated using an
NRQCD action and the light quark using the tadpole-improved
clover action on gauge configurations containing two degenerate flavours of sea
quarks at provided by the HEMCGC collaboration. We present
detailed results for the lower lying and wave meson states and the
baryon. We find broad agreement with experiment. In addition, we
present results for the pseudoscalar and, for the first time, the vector decay
constants fully consistent to and . We present an investigation of sea quark effects
in the spectrum and decay constants. We compare our results with those from
similar quenched simulations at . For the spectrum, the
quenched results reproduce the experimental spectrum well and there is no
significant difference between the quenched and results. For the decay
constants, our results suggest that sea quark effects may be large. We find
that increases by approximately 25% between and .Comment: 49 pages, 16 figures, revtex, the discussion of systematic errors and
the comparison of the pseudoscalar decay constant at nf=0 and nf=2 has been
expande
Heavy-Light Mesons with Quenched Lattice NRQCD: Results on Decay Constants
We present a quenched lattice calculation of heavy-light meson decay
constants, using non-relativistic (NRQCD) heavy quarks in the mass region of
the quark and heavier, and clover-improved light quarks. The NRQCD
Hamiltonian and the heavy-light current include the corrections at first order
in the expansion in the inverse heavy quark mass. We study the dependence of
the decay constants on the heavy meson mass , for light quarks with the tree
level ( = 1), as well as the tadpole improved clover coefficient. We
compare decay constants from NRQCD with results from clover () heavy
quarks.
Having calculated the current renormalisation constant in one-loop
perturbation theory, we demonstrate how the heavy mass dependence of the
pseudoscalar decay constants changes after renormalisation. For the first time,
we quote a result for from NRQCD including the full one-loop matching
factors at .Comment: 45 pages, latex, 24 postscript figure
B meson leptonic decay constant with quenched lattice NRQCD
We present a lattice NRQCD study of the B meson decay constant in the
quenched approximation with emphasis given to the scaling behavior. The NRQCD
action and the heavy-light axial current we use include all terms of order 1/M
and the perturbative and corrections. Using
simulations at three value of couplings =5.7, 5.9 and 6.1 on lattices of
size and , we find no significant
dependence in if the correction is included in the
axial current. We obtain MeV, MeV and , with the
first error being statistical, the second systematic, and the third due to
uncertainty of strange quark mass, while quenching errors being not included.Comment: 31 pages, 24 eps figure
and coupling constants in QCD sum rules
The coupling constants and
are calculated in the framework of
three-point QCD sum rules. The correlation functions responsible for these
coupling constants are evaluated considering contributions of both and
mesons as off-shell states, but in the absence of radiative
corrections. The results, and are
obtained for the considered strong coupling constants.Comment: 13 Pages and 11 Figure
Towards an Asymptotic-Safety Scenario for Chiral Yukawa Systems
We search for asymptotic safety in a Yukawa system with a chiral
symmetry, serving as a toy model for the
standard-model Higgs sector. Using the functional RG as a nonperturbative tool,
the leading-order derivative expansion exhibits admissible non-Ga\ssian
fixed-points for which arise from a conformal threshold
behavior induced by self-balanced boson-fermion fluctuations. If present in the
full theory, the fixed-point would solve the triviality problem. Moreover, as
one fixed point has only one relevant direction even with a reduced hierarchy
problem, the Higgs mass as well as the top mass are a prediction of the theory
in terms of the Higgs vacuum expectation value. In our toy model, the fixed
point is destabilized at higher order due to massless Goldstone and fermion
fluctuations, which are particular to our model and have no analogue in the
standard model.Comment: 16 pages, 8 figure
B --> pi and B --> K transitions in partially quenched chiral perturbation theory
We study the properties of the B-->pi and B-->K transition form factors in
partially quenched QCD by using the approach of partially quenched chiral
perturbation theory combined with the static heavy quark limit. We show that
the form factors change almost linearly when varying the value of the sea quark
mass, whereas the dependence on the valence quark mass contains both the
standard and chirally divergent (quenched) logarithms. A simple strategy for
the chiral extrapolations in the lattice studies with Nsea=2 is suggested. It
consists of the linear extrapolations from the realistically accessible quark
masses, first in the sea and then in the valence quark mass. From the present
approach, we estimate the uncertainty induced by such extrapolations to be
within 5%.Comment: Published versio
Leptonic and Semileptonic Decays of Charm and Bottom Hadrons
We review the experimental measurements and theoretical descriptions of
leptonic and semileptonic decays of particles containing a single heavy quark,
either charm or bottom. Measurements of bottom semileptonic decays are used to
determine the magnitudes of two fundamental parameters of the standard model,
the Cabibbo-Kobayashi-Maskawa matrix elements and . These
parameters are connected with the physics of quark flavor and mass, and they
have important implications for the breakdown of CP symmetry. To extract
precise values of and from measurements, however,
requires a good understanding of the decay dynamics. Measurements of both charm
and bottom decay distributions provide information on the interactions
governing these processes. The underlying weak transition in each case is
relatively simple, but the strong interactions that bind the quarks into
hadrons introduce complications. We also discuss new theoretical approaches,
especially heavy-quark effective theory and lattice QCD, which are providing
insights and predictions now being tested by experiment. An international
effort at many laboratories will rapidly advance knowledge of this physics
during the next decade.Comment: This review article will be published in Reviews of Modern Physics in
the fall, 1995. This file contains only the abstract and the table of
contents. The full 168-page document including 47 figures is available at
http://charm.physics.ucsb.edu/papers/slrevtex.p
Asymptotic safety of simple Yukawa systems
We study the triviality and hierarchy problem of a Z_2-invariant Yukawa
system with massless fermions and a real scalar field, serving as a toy model
for the standard-model Higgs sector. Using the functional RG, we look for UV
stable fixed points which could render the system asymptotically safe. Whether
a balancing of fermionic and bosonic contributions in the RG flow induces such
a fixed point depends on the algebraic structure and the degrees of freedom of
the system. Within the region of parameter space which can be controlled by a
nonperturbative next-to-leading order derivative expansion of the effective
action, we find no non-Gaussian fixed point in the case of one or more fermion
flavors. The fermion-boson balancing can still be demonstrated within a model
system with a small fractional flavor number in the symmetry-broken regime. The
UV behavior of this small-N_f system is controlled by a conformal Higgs
expectation value. The system has only two physical parameters, implying that
the Higgs mass can be predicted. It also naturally explains the heavy mass of
the top quark, since there are no RG trajectories connecting the UV fixed point
with light top masses.Comment: 14 pages, 3 figures, v2: references added, typos corrected, minor
numerical correction
Interactions between β-Catenin and the HSlo Potassium Channel Regulates HSlo Surface Expression
Multicomponent self-assembly as a tool to harness new properties from peptides and proteins in material design
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