215 research outputs found
QCD inequalities for hadron interactions
We derive generalisations of the Weingarten--Witten QCD mass inequalities for
particular multi-hadron systems. For systems of any number of identical
pseudo-scalar mesons of maximal isospin, these inequalities prove that
interactions between the constituent mesons must be repulsive and that no bound
states can form in these channels. Similar constraints in less symmetric
systems are also extracted. These results are compatible with experimental
results (where known) and recent lattice QCD calculations, and also lead to a
more stringent bound on the nucleon mass than previously derived, .Comment: 5 pages, 2 figure
Lattice QCD study of mixed systems of pions and kaons
The different ground state energies of N-pion and M-kaon systems for N+M <=12
are studied in lattice QCD. These energies are then used to extract the various
two- and three- body interactions that occur in these systems. Particular
attention is paid to additional thermal states present in the spectrum because
of the finite temporal extent. These calculations are performed using one
ensemble of 2+1 flavor anisotropic lattices with a spatial lattice spacing a_s
~ 0.125 fm, an anisotropy factor {\xi}=a_s/a_t=3.5, and a spatial volume L^3 ~
(2.5 fm)^3. The quark masses used correspond to pion and kaon masses of m_{\pi}
~ 383 MeV and m_K ~ 537 MeV, respectively. The isospin and strangeness chemical
potentials of these systems are found to be in the region where chiral
perturbation theory and hadronic models predict a phase transition between a
pion condensed phase and a kaon condensed phase
form factors, differential branching fraction, and angular observables from lattice QCD with relativistic quarks
Using -flavor lattice QCD, we compute the 10 form factors describing
the matrix elements of the vector, axial
vector, and tensor currents. The calculation is based on gauge field ensembles
generated by the RBC and UKQCD Collaborations with a domain-wall action for the
, , and quarks and the Iwasaki gauge action. The quark is
implemented using an anisotropic clover action, tuned nonperturbatively to the
physical point, and the currents are renormalized with a mostly nonperturbative
method. We perform simultaneous chiral, continuum, and kinematic extrapolations
of the form factors through modified expansions. Using our form factor
results, we obtain precise predictions for the differential branching fraction and angular observables in
the Standard Model.Comment: 33 pages, 9 figures, form factor parameters included as ancillary
file
Composite Vector Particles in External Electromagnetic Fields
Lattice quantum chromodynamics (QCD) studies of electromagnetic properties of
hadrons and light nuclei, such as magnetic moments and polarizabilities, have
proven successful with the use of background field methods. With an
implementation of nonuniform background electromagnetic fields, properties such
as charge radii and higher electromagnetic multipole moments (for states of
higher spin) can be additionally obtained. This can be achieved by matching
lattice QCD calculations to a corresponding low-energy effective theory that
describes the static and quasi-static response of hadrons and nuclei to weak
external fields. With particular interest in the case of vector mesons and
spin-1 nuclei such as the deuteron, we present an effective field theory of
spin-1 particles coupled to external electromagnetic fields. To constrain the
charge radius and the electric quadrupole moment of the composite spin-1 field,
the single-particle Green's functions in a linearly varying electric field in
space are obtained within the effective theory, providing explicit expressions
that can be used to match directly onto lattice QCD correlation functions. The
viability of an extraction of the charge radius and the electric quadrupole
moment of the deuteron from the upcoming lattice QCD calculations of this
nucleus is discussed.Comment: 38 page
Baryon properties in meson mediums from lattice QCD
We present results for the ground-state mass shifts of octet baryons due to
the presence of a medium of pions or kaons from a lattice QCD calculation
performed at a single value of the quark mass, corresponding to a pion mass of
~ 390 MeV, and a spatial volume V ~ (4fm)^3. We use a canonical
approach in which correlators are formed using a single baryon propagator and a
fixed number of meson propagators, up to n=9. From the ground-state energies we
calculate two- and three-body interaction parameters. We also extract
combinations of low-energy constants by comparing our results to tree level
chiral perturbation theory at non-zero isospin/kaon chemical potential.Comment: 7 pages, 3 figures, Proceedings of the 31st International Symposium
on Lattice Field Theory (Lattice 2013), July 29 - August 3, 2013, Mainz,
German
Signal/noise enhancement strategies for stochastically estimated correlation functions
We develop strategies for enhancing the signal/noise ratio for stochastically
sampled correlation functions. The techniques are general and offer a wide
range of applicability. We demonstrate the potential of the approach with a
generic two-state system, and then explore the practical applicability of the
method for single hadron correlators in lattice quantum chromodynamics. In the
latter case, we determine the ground state energies of the pion, proton, and
delta baryon, as well as the ground and first excited state energy of the rho
meson using matrices of correlators computed on an exemplary ensemble of
anisotropic gauge configurations. In the majority of cases, we find a modest
reduction in the statistical uncertainties on extracted energies compared to
conventional variational techniques. However, in the case of the delta baryon,
we achieve a factor of three reduction in statistical uncertainties. The
variety of outcomes achieved for single hadron correlators illustrates an
inherent dependence of the method on the properties of the system under
consideration and the operator basis from which the correlators are
constructed.Comment: 40 pages, 21 figures; revisions made to the abstract and Section VI
C, one additional figure and five tables added; published versio
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