69 research outputs found
Fisher's zeros as boundary of renormalization group flows in complex coupling spaces
We propose new methods to extend the renormalization group transformation to
complex coupling spaces. We argue that the Fisher's zeros are located at the
boundary of the complex basin of attraction of infra-red fixed points. We
support this picture with numerical calculations at finite volume for
two-dimensional O(N) models in the large-N limit and the hierarchical Ising
model. We present numerical evidence that, as the volume increases, the
Fisher's zeros of 4-dimensional pure gauge SU(2) lattice gauge theory with a
Wilson action, stabilize at a distance larger than 0.15 from the real axis in
the complex beta=4/g^2 plane. We discuss the implications for proofs of
confinement and searches for nontrivial infra-red fixed points in models beyond
the standard model.Comment: 4 pages, 3 fig
The depressive-like behaviors of chronic unpredictable mild stress-treated mice ameliorated by Tibetan medicine Zuotai: involvement in the hypothalamic–pituitary–adrenal (HPA) axis pathway
Form factors for semi-leptonic B decays
We report on form factors for the B->K l^+ l^- semi-leptonic decay process.
We use several lattice spacings from a=0.12 fm down to 0.06 fm and a variety of
dynamical quark masses with 2+1 flavors of asqtad quarks provided by the MILC
Collaboration. These ensembles allow good control of the chiral and continuum
extrapolations. The b-quark is treated as a clover quark with the Fermilab
interpretation. We update our results for f_\parallel and f_\perp, or,
equivalently, f_+ and f_0. In addition, we present new results for the tensor
form factor f_T. Model independent results are obtained based upon the
z-expansion.Comment: 7 pages, 4 figures, presented at The XXXth International Symposium on
Lattice Field Theory - Lattice 2012, June 24-29, 2012 Cairns, Australia, to
appear as PoS(Lattice 2012)12
form factors with 2+1 flavors
Using the MILC 2+1 flavor asqtad quark action ensembles, we are calculating
the form factors and for the semileptonic decay. A total of six ensembles with lattice spacing from
to 0.06 fm are being used. At the coarsest and finest lattice
spacings, the light quark mass is one-tenth the strange quark mass
. At the intermediate lattice spacing, the ratio ranges from
0.05 to 0.2. The valence quark is treated using the Sheikholeslami-Wohlert
Wilson-clover action with the Fermilab interpretation. The other valence quarks
use the asqtad action. When combined with (future) measurements from the LHCb
and Belle II experiments, these calculations will provide an alternate
determination of the CKM matrix element .Comment: 8 pages, 6 figures, to appear in the Proceedings of Lattice 2017,
June 18-24, Granada, Spai
form factors for new-physics searches from lattice QCD
The rare decay arises from flavor-changing
neutral currents and could be sensitive to physics beyond the Standard Model.
Here, we present the first - QCD calculation of the
tensor form factor . Together with the vector and scalar form factors
and from our companion work [J. A. Bailey , Phys. Rev. D
92, 014024 (2015)], these parameterize the hadronic contribution to
semileptonic decays in any extension of the Standard Model. We obtain the total
branching ratio in
the Standard Model, which is the most precise theoretical determination to
date, and agrees with the recent measurement from the LHCb experiment [R. Aaij
, JHEP 1212, 125 (2012)]. Note added: after this paper was submitted
for publication, LHCb announced a new measurement of the differential decay
rate for this process [T. Tekampe, talk at DPF 2015], which we now compare to
the shape and normalization of the Standard-Model prediction.Comment: V3: Corrected errors in results for Standard-Model differential and
total decay rates in abstract, Fig. 3, Table IV, and outlook. Added new
preliminary LHCb data to Fig. 3 and brief discussion after outlook. Replaced
outdated correlation matrix in Table III with correct final version. Other
minor wording changes and references added. 7 pages, 4 tables, 3 figure
decay form factors from three-flavor lattice QCD
We compute the form factors for the semileptonic decay
process in lattice QCD using gauge-field ensembles with 2+1 flavors of sea
quark, generated by the MILC Collaboration. The ensembles span lattice spacings
from 0.12 to 0.045 fm and have multiple sea-quark masses to help control the
chiral extrapolation. The asqtad improved staggered action is used for the
light valence and sea quarks, and the clover action with the Fermilab
interpretation is used for the heavy quark. We present results for the form
factors , , and , where is the momentum
transfer, together with a comprehensive examination of systematic errors.
Lattice QCD determines the form factors for a limited range of , and we
use the model-independent expansion to cover the whole kinematically
allowed range. We present our final form-factor results as coefficients of the
expansion and the correlations between them, where the errors on the
coefficients include statistical and all systematic uncertainties. We use this
complete description of the form factors to test QCD predictions of the form
factors at high and low . We also compare a Standard-Model calculation of
the branching ratio for with experimental data.Comment: V2: Fig.7 added. Typos text corrected. Reference added. Version
published in Phys. Rev.
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