642 research outputs found
Composite Operators in QCD
We give a formula for the derivatives of a correlation function of composite
operators with respect to the parameters (i.e., the strong fine structure
constant and the quark mass) of QCD in four-dimensional euclidean space. The
formula is given as spatial integration of the operator conjugate to a
parameter. The operator product of a composite operator and a conjugate
operator has an unintegrable part, and the formula requires divergent
subtractions. By imposing consistency conditions we derive a relation between
the anomalous dimensions of the composite operators and the unintegrable part
of the operator product coefficients.Comment: 26 page
Transport and magnetic properties of Co-doped BaFe_{2}As_{2} epitaxial thin films
We report resistivity, Hall coefficient, current-voltage characteristics, and
magneto-optical imaging measurements of epitaxial Co-doped BaFe_{2}As_{2} thin
films deposited on MgO(001) substrate. The Hall resistivity of the films has a
substantial contribution arising from anomalous Hall effect of ferromagnetic
components. The critical current density (J_{c}) of the films is ~2 MA/cm^{2}
at low temperatures. Differential magneto-optical images of the remanent state
give similar J_{c} values and also exhibit presence of extended defects in the
film.Comment: 9 pages, 4 figure
Conformal Window of Gauge Theories with Four-Fermion Interactions and Ideal Walking
We investigate the effects of four-fermion interactions on the phase diagram
of strongly interacting theories for any representation as function of the
number of colors and flavors. We show that the conformal window, for any
representation, shrinks with respect to the case in which the four-fermion
interactions are neglected. The anomalous dimension of the mass increases
beyond the unity value at the lower boundary of the new conformal window. We
plot the new phase diagram which can be used, together with the information
about the anomalous dimension, to propose ideal models of walking technicolor.
We discover that when the extended technicolor sector, responsible for giving
masses to the standard model fermions, is sufficiently strongly coupled the
technicolor theory, in isolation, must have an infrared fixed point for the
full model to be phenomenologically viable. Using the new phase diagram we show
that the simplest one family and minimal walking technicolor models are the
archetypes of models of dynamical electroweak symmetry breaking. Our
predictions can be verified via first principle lattice simulations.Comment: RevTeX4, 22 pages, 16 figure
Chiral symmetry restoration, eigenvalue density of Dirac operator and axial U(1) anomaly at finite temperature
We reconsider constraints on the eigenvalue density of the Dirac operator in
the chiral symmetric phase of 2 flavor QCD at finite temperature. To avoid
possible ultra-violet(UV) divergences, we work on a lattice, employing the
overlap Dirac operator, which ensures the exact "chiral" symmetry at finite
lattice spacings. Studying multi-point correlation functions in various
channels and taking their thermodynamical limit (and then taking the chiral
limit), we obtain stronger constraints than those found in the previous
studies: both the eigenvalue density at the origin and its first and second
derivatives vanish in the chiral limit of 2 flavor QCD. In addition we show
that the axial U(1) anomaly becomes invisible in susceptibilities of scalar and
pseudo scalar mesons, suggesting that the 2nd order chiral phase transition
with the O(4) scaling is not realized in 2 flavor QCD. Possible lattice
artifacts when non-chiral lattice Dirac operator is employed are briefly
discussed.Comment: 39 pages, 1 figure(2 eps files), a version published in PR
Finite volume QCD at fixed topological charge
In finite volume the partition function of QCD with a given is a sum
of different topological sectors with a weight primarily determined by the
topological susceptibility. If a physical observable is evaluated only in a
fixed topological sector, the result deviates from the true expectation value
by an amount proportional to the inverse space-time volume 1/V. Using the
saddle point expansion, we derive formulas to express the correction due to the
fixed topological charge in terms of a 1/V expansion. Applying this formula, we
propose a class of methods to determine the topological susceptibility in QCD
from various correlation functions calculated in a fixed topological sector.Comment: 22pages, references adde
Effects of a Supermassive Black Hole Binary on a Nuclear Gas Disk
We study influence of a galactic central supermassive black hole (SMBH)
binary on gas dynamics and star formation activity in a nuclear gas disk by
making three-dimensional Tree+SPH simulations. Due to orbital motions of SMBHs,
there are various resonances between gas motion and the SMBH binary motion. We
have shown that these resonances create some characteristic structures of gas
in the nuclear gas disk, for examples, gas elongated or filament structures,
formation of gaseous spiral arms, and small gas disks around SMBHs. In these
gaseous dense regions, active star formations are induced. As the result, many
star burst regions are formed in the nuclear region.Comment: 19 pages, 11 figures, accepted for publication in Ap
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
Classical and quantum radiation from a moving charge in an expanding universe
We investigate photon emission from a moving particle in an expanding
universe. This process is analogous to the radiation from an accelerated charge
in the classical electromagnetic theory. Using the framework of quantum field
theory in curved spacetime, we demonstrate that the Wentzel-Kramers-Brillouin
(WKB) approximation leads to the Larmor formula for the rate of the radiation
energy from a moving charge in an expanding universe. Using exactly solvable
models in a radiation-dominated universe and in a Milne universe, we examine
the validity of the WKB formula. It is shown that the quantum effect suppresses
the radiation energy in comparison with the WKB formula.Comment: 16 pages, JCAP in pres
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