1,806 research outputs found
Neutron electric dipole moment with external electric field method in lattice QCD
We discuss a possibility that the Neutron Electric Dipole Moment (NEDM) can
be calculated in lattice QCD simulations in the presence of the CP violating
term. In this paper we measure the energy difference between spin-up
and spin-down states of the neutron in the presence of an uniform and static
external electric field. We first test this method in quenched QCD with the RG
improved gauge action on a lattice at 2 GeV,
employing two different lattice fermion formulations, the domain-wall fermion
and the clover fermion for quarks, at relatively heavy quark mass . We obtain non-zero values of NEDM from calculations with both
fermion formulations. We next consider some systematic uncertainties of our
method for NEDM, using lattice at the same lattice spacing only
with the clover fermion. We finally investigate the quark mass dependence of
NEDM and observe a non-vanishing behavior of NEDM toward the chiral limit. We
interpret this behavior as a manifestation of the pathology in the quenched
approximation.Comment: LaTeX2e, 51 pages, 43 figures, uses revtex4 and graphicx, References
and comments added, typos corrected, accepted by PR
Two-photon decay of the neutral pion in lattice QCD
We perform non-perturbative calculation of the \pi^0 to {\gamma}{\gamma}
transition form factor and the associated decay width using lattice QCD. The
amplitude for two-photon final state, which is not an eigenstate of QCD, is
extracted through an Euclidean time integral of the relevant three-point
function. We utilize the all-to-all quark propagator technique to carry out
this integral as well as to include the disconnected quark diagram
contributions. The overlap fermion formulation is employed on the lattice to
ensure exact chiral symmetry on the lattice. After examining various sources of
systematic effects except for possible discretization effect, we obtain
\Gamma=7.83(31)(49) eV for the pion decay width, where the first error is
statistical and the second is our estimate of the systematic error.Comment: 5 pages, 4 figures. Changes made addressing to referee's comments,
version accepted by PR
Full QCD calculation of neutron electric dipole moment with the external electric field method
We have calculated the neutron electric dipole moment (NEDM) in the presence
of the CP violating term in lattice QCD with 2-flavor dynamical clover
quarks, using the external electric field method. Accumulating a large number
of statistics by the averages over 16 different source points and over forward
and backward nucleon propagators, we have obtained non-zero signals of neutron
and proton EDM beyond one standard deviation at each quark mass in full QCD. We
have investigated the quark mass dependence of nucleon EDM in full QCD, and
have found that nucleon EDM in full QCD does not decrease toward the chiral
limit, as opposed to the theoretical expectation. We briefly discuss possible
reasons for this behavior.Comment: 27 pages, 15 figures, 2 tables, reference added, tyops corrected,
published versio
A lecture on the Liouville vertex operators
We reconsider the construction of exponential fields in the quantized
Liouville theory. It is based on a free-field construction of a continuous
family or chiral vertex operators. We derive the fusion and braid relations of
the chiral vertex operators. This allows us to simplify the verification of
locality and crossing symmetry of the exponential fields considerably. The
calculation of the matrix elements of the exponential fields leads to a
constructive derivation of the formula proposed by Dorn/Otto and the brothers
Zamolodchikov.Comment: Contribution to the proceedings of the 6th International Conference
on CFTs and Integrable Models, Chernogolovka, Russia, 2002 v2: Remarks added,
typos correcte
Metaplectic Ice
Spherical Whittaker functions on the metaplectic n-fold cover of GL(r+1) over
a nonarchimedean local field containing n distinct n-th roots of unity may be
expressed as the partition functions of statistical mechanical systems that are
variants of the six-vertex model. If n=1 then in view of the Casselman-Shalika
formula this fact is related to Tokuyama's deformation of the Weyl character
formula. It is shown that various properties of these Whittaker functions may
be expressed in terms of the commutativity of row transfer matrices for the
system. Potentially these properties (which are already proved by other
methods, but very nontrivial) are amenable to proof by the Yang-Baxter
equation
Neutron electric dipole moment from lattice QCD
We carry out a feasibility study for the lattice QCD calculation of the
neutron electric dipole moment (NEDM) in the presence of the term. We
develop the strategy to obtain the nucleon EDM from the CP-odd electromagnetic
form factor at small , in which NEDM is given by where is the momentum transfer and is the
nucleon mass. We first derive a formula which relates , a matrix element
of the electromagnetic current between nucleon states, with vacuum expectation
values of nucleons and/or the current. In the expansion of , the
parity-odd part of the nucleon-current-nucleon three-point function contains
contributions not only from the parity-odd form factors but also from the
parity-even form factors multiplied by the parity-odd part of the nucleon
two-point function, and therefore the latter contribution must be subtracted to
extract . We then perform an explicit lattice calculation employing the
domain-wall quark action with the RG improved gauge action in quenched QCD at
GeV on a lattice. At the quark mass
, corresponding to , we accumulate 730
configurations, which allow us to extract the parity-odd part in both two- and
three-point functions. Employing two different Dirac matrix
projections, we show that a consistent value for cannot be obtained
without the subtraction described above. We obtain 0.024(5) fm for the neutron and
0.021(6) fm for the
proton.Comment: LaTeX2e, 43 pages, 42 eps figures, uses revtex4 and graphicx,
comments added and typos corrected, final version to appear in Phys. Rev.
Hadron Structure on the Lattice
A few chosen nucleon properties are described from a lattice QCD perspective:
the nucleon sigma term and the scalar strangeness in the nucleon; the vector
form factors in the nucleon, including the vector strangeness contribution, as
well as parity breaking effects like the anapole and electric dipole moment;
and finally the axial and tensor charges of the nucleon. The status of the
lattice calculations is presented and their potential impact on phenomenology
is discussed.Comment: 17 pages, 9 figures; proceedings of the Conclusive Symposium of the
Collaborative Research Center 443 "Many-body structure of strongly
interacting systems", Mainz, February 23-25, 201
QCD corrections to the electric dipole moment of the neutron in the MSSM
We consider the QCD corrections to the electric dipole moment of the neutron
in the Minimal Supersymmetric Standard Model. We provide a master formula for
the Wilson coefficients at the low energy scale including for the first time
the mixing between the electric and chromoelectric operators and correcting
widely used previous LO estimates. We show that, because of the mixing between
the electric and chromoelectric operators, the neutralino contribution is
always strongly suppressed. We find that, in general, the effect of the QCD
corrections is to reduce the amount of CP violation generated at the high
scale. We discuss the perturbative uncertainties of the LO computation, which
are particularly large for the gluino-mediated contribution. This motivates our
Next-to-Leading order analysis. We compute for the first time the order alpha_s
corrections to the Wilson coefficients for the gluino contributions, and
recompute the two-loop anomalous dimension for the dipole operators. We show
that the large LO uncertainty disappears once NLO corrections are taken into
account.Comment: 23 pages, 5 figures, added references, corrected typo
Delirium and mortality risk prediction: a story in evolution
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