70 research outputs found
g-coupling (g_B*Bpi,g_D*Dpi); A quark model with Dirac equation
We discuss the strong coupling of heavy mesons to a pion g, in the heavy
quark limit. This quantity is quite remarkable since its values as estimated by
different methods (various quark models and the QCD sum rules), are
surprisingly different. The present quark models are mostly based on free
spinors and their predictions depend crucially on the choice of the light quark
mass. We propose a quark model based on the Dirac equation in a central
potential, which gives a more refined description of Dirac spinors. We show
that within such a Dirac model, the value of g is stable and large: g = 0.6(1),
where we assume no quark current renormalization ((g_A)q = 1). Such a large
result is strongly constrained by requiring that the model parameters fit the
spectrum; we show that this implies a large ``effective'' light mass. It is
also supported phenomenologically by a similar situation with heavy baryons, as
well as by experience with nucleon (if one invokes additivity). We also
calculate the couplings to heavy meson excitations, and show that the
Adler-Weisberger sum rule is well saturated by a few levels (in contrast to the
case of small g). We discuss uncertainties of our approach, and rise several
questions which remain to be answered. The main mystery is the large, unusual
discrepancy with QCD sum rules for g, whereas a good agreement is found for
orbital excitations.Comment: 20 pages, LaTeX file, uses JHEP.cls, (2 references added
H(650) -> W+W-/ZZ predicts H++ -> W+W+ and H+ -> ZW+, as indicated by LHC data
Several indications for neutral scalars are observed at the LHC. One of them,
a broad resonance peaked at about 650 GeV which we call H(650), was first
observed by an outsider combining published histograms from ATLAS and CMS on ZZ
->4 leptons searches, and this combination shows a local significance close to
4 s.d. Since then, CMS has reported two other indications at the same mass,
with similar local significances: H ->WW -> lepton nu lepton nu and H->bbh(125)
where h(125) ->2 photons. ATLAS has completed its analysis of ZZ->4 leptons
from which we infer an indication for H(650) with 3.5 s.d. significance.
Assuming that the mass is already known from the former set, and combining
these three results, one gets a global statistical significance above 6 s.d.
H(650) has a coupling to WW similar to h(125) and therefore we argue that a sum
rule (SR) required by unitarity for WW scattering implies that there should be
a compensating effect from a doubly charged scalar H++, with a large coupling
to W+W+. We therefore predict that this mode should become visible through the
vector boson fusion process W+W+->H++, naturally provided by LHC. A recent
indication for H++(450)->W+W+ from ATLAS allows a model independent
interpretation of this result through the SR constraint which gives
BR(H++->W+W+)=10%, implying the occurrence of additional decay modes H+W+ and
H+H+ from one or several light H+ with masses below mH++ - mW or MH++/2, that
is mH+ ZW,
indicated by ATLAS and CMS. Both channels suggest a scalar field content
similar to the Georgi Machacek model with triplets, at variance with the models
usually considered.Comment: 17 pages, 6 figures, Work in preparation of the 2023 ECFA Workshop on
Higgs/EW/Top factories in Paestum (Salerno) / Italy from 11 - 13 October 202
Pseudoscalar Vertex and Quark Masses
We analyse available data on the quark pseudoscalar vertex and extract the
contribution og the Goldstone boson pole. The strength of the pole is found to
be quite large at presently accessible scales. We draw the important
consequences of this finding for the various definitions of quark masses.Comment: LATTICE99 (Improvement and Renormalization), 3 p., 3 fi
The strong decays of K1 resonances
We investigate the K1--> K pi pi strong interaction decays. Using the 3P0
quark-pair-creation model to derive the basic parametrization, we discuss in
detail how to obtain the various partial wave amplitudes into the possible
quasi-two-body decay channels as well as their relative phases from the
currently available experimental data. We obtain the K1 mixing angle to be
thetaK1= 60 deg, in agreement with previous works. Our study can be applied to
extract the information needed for the photon polarization determination of the
radiative B--> K1 gamma decay.Comment: 57 pages, 10 figure
The controversy about "1/m_Q duality violation" ; a quark model point of view
A detailed discussion based on exact calculations, possible in the non
relativistic quark model, is given to show that there is no 1/m_Q term in the
heavy quark expansion of totally integrated semileptonic decay rates. More
generally, it is shown that OPE holds with very few terms in the expansion, at
least in the harmonic oscillator model.Comment: 10 pages, full articl
Searches for scalars at LHC and interpretation of the findings
In view of the future Higgs factories, this work presents the status of
scalar searches at the LHC with an emphasis on the H(650) resonance which has
been observed in WW, ZZ and h(95)h(125) channels, with a cumulative evidence of
about 7 s.d. global significance. Its interpretation in models, restricted to
extension of the scalar sector by SU(2) singlets and doublets, is clearly
excluded, while its interpretation in models with additional triplets requires
an extension with respect to the conventional Georgi-Machacek model. A general
picture of these searches is updated, showing that h(95) is also reaching a
similar level of evidence while two other candidates, A(400) and h(151),
although less prominent, are above the 4 s.d. global evidence.Comment: 14 pages, 9 figures, Work presented by F. Richard at the ECFA
workshop on Higgs/EW/top factories in DESY, October 202
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