2,611 research outputs found
Light-cone behavior of the pion Bethe-Salpeter wave function in the ladder model
The Bethe-Salpeter wave function χ(q^ν+P^ν, q^ν) for two spin-½ quarks bound by the exchange of a scalar meson is examined in the ladder model. We seek the behavior of χ as the squared momentum, (q+P)^2, on one leg becomes infinite while the squared momentum, q^2, on the other leg remains fixed. This behavior is investigated by making a Wick rotation, expanding χ in partial-wave amplitudes χ^i_J(q^2) of the group O(4), and then looking for the rightmost poles of χ^i_J(q^2) in the complex J plane. Our results verify (in the ladder model) the useful hypothesis that the locations of these poles are independent of q^2 and can thus be computed in the q^2→∞ limit by using conformal invariance
Large-Q^2 behavior of the pion electromagnetic form factor
We study the large-Q^2 behavior of the electromagnetic form factor of the pion, which is viewed as a quark-antiquark bound state in a (nongauge) quantum field theory. When the pion's Bethe-Salpeter wave function is expanded in O(4) partial waves, it is found that the information needed about the partial-wave amplitudes is their scaling behavior at large momentum and the locations of their poles in the complex J plane. This information is determined by using the operator-product expansion, conformal invariance at short distances, and a regularity property that holds at least in the ladder model. The resulting behavior of the form factor is roughly F(Q^2)~(Q^2)^(-1), with corrections due to anomalous dimensions
Effective Field Theory and Unification in AdS Backgrounds
This work is an extension of our previous work, hep-th/0204160, which showed
how to systematically calculate the high energy evolution of gauge couplings in
compact AdS_5 backgrounds. We first directly compute the one-loop effects of
massive charged scalar fields on the low energy couplings of a gauge theory
propagating in the AdS background. It is found that scalar bulk mass scales
(which generically are of order the Planck scale) enter only logarithmically in
the corrections to the tree-level gauge couplings. As we pointed out
previously, we show that the large logarithms that appear in the AdS one-loop
calculation can be obtained within the confines of an effective field theory,
by running the Planck brane correlator from a high UV matching scale down to
the TeV scale. This result exactly reproduces our previous calculation, which
was based on AdS/CFT duality. We also calculate the effects of scalar fields
satisfying non-trivial boundary conditions (relevant for orbifold breaking of
bulk symmetries) on the running of gauge couplings.Comment: LaTeX, 27 pages; minor typos fixed, comments adde
Mapping of strongly correlated steady-state nonequilibrium to an effective equilibrium
By mapping steady-state nonequilibrium to an effective equilibrium, we
formulate nonequilibrium problems within an equilibrium picture where we can
apply existing equilibrium many-body techniques to steady-state electron
transport problems. We study the analytic properties of many-body scattering
states, reduce the boundary condition operator in a simple form and prove that
this mapping is equivalent to the correct linear-response theory. In an example
of infinite-U Anderson impurity model, we approximately solve for the
scattering state creation operators, based on which we derive the bias operator
Y to construct the nonequilibrium ensemble in the form of the Boltzmann factor
exp(-beta(H-Y)). The resulting Hamiltonian is solved by the non-crossing
approximation. We obtain the Kondo anomaly conductance at zero bias, inelastic
transport via the charge excitation on the quantum dot and significant
inelastic current background over a wide range of bias. Finally, we propose a
self-consistent algorithm of mapping general steady-state nonequilibrium.Comment: 15 pages, 9 figure
Renormalization of One-Pion Exchange and Power Counting
The renormalization of the chiral nuclear interactions is studied. In leading
order, the cutoff dependence is related to the singular tensor interaction of
the one-pion exchange potential. In S waves and in higher partial waves where
the tensor force is repulsive this cutoff dependence can be absorbed by
counterterms expected at that order. In the other partial waves additional
contact interactions are necessary. The implications of this finding for the
effective-field-theory program in nuclear physics are discussed.Comment: 19 pages, 18 figure
Role of the (1535) in the and reactions
We study the and
reactions with a unitary chiral approach. We find that the unitary chiral
approach, which generates the dynamically, can describe the data
reasonably well, particularly the ratio of the integrated cross sections. This
study provides further support for the unitary chiral description of the
. We also discuss some subtle differences between the coupling
constants determined from the unitary chiral approach and those determined from
phenomenological studies.Comment: version to appear in PRC; certain features of the approach clarifie
Scalar-Tensor Gravity in Two 3-brane System
We derive the low-energy effective action of four-dimensional gravity in the
Randall-Sundrum scenario in which two 3-branes of opposite tension reside in a
five-dimensional spacetime. The dimensional reduction with the Ansatz for the
radion field by Charmousis et al., which solves five-dimensional linearized
field equations, results in a class of scalar-tensor gravity theories. In the
limit of vanishing radion fluctuations, the effective action reduces to the
Brans-Dicke gravity in accord with the results of Garriga and Tanaka:
Brans-Dicke gravity with the corresponding Brans-Dicke parameter (for positive tension brane) and (for negative
tension brane). In general the gravity induced a brane belongs to a class of
scalar-tensor gravity with the Brans-Dicke parameter which is a function of the
interval and the radion. In particular, gravity on a positive tension brane
contains an attractor mechanism toward the Einstein gravity.Comment: 8 pages, discussion expanded, references adde
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