36,480 research outputs found
Regge Closed String Scattering and its Implication on Fixed angle Closed String Scattering
We calculate the complete closed string high energy scattering amplitudes
(HSA) in the Regge regime for arbitrary mass levels. As an application, we
deduce the complete ratios among closed string HSA in the fixed angle regime by
using Stirling number identities. These results are in contrast with the
incomplete set of closed string HSA in the fixed angle regime calculated
previously. The complete forms of the fixed angle amplitudes, and hence the
ratios, were not calculable previously without the input of zero-norm state
calculation. This is mainly due to the lack of saddle point in the fixed angle
closed string calculation.Comment: 10 pages. v2: typos correcte
Magnetism and Mott Transition: A Slave-rotor Study
Motivated by the debate of spin-density-wave (SDW) versus local-moment (LM)
picture in the iron-based superconducting (FeSC) materials, we consider a
two-band orbital-symmetric Hubbard model in which there is robust Fermi surface
nesting at . We obtain the phase diagram of such system by a
mean-field slave-rotor approach, in which the Fermi surface nesting and the SDW
order are explicitly taken into account via a natural separation of scale
between the Hund's coupling and the Coulomb interaction. We find that for a
sizable range of Hund's coupling the Mott transition acquires a strong
first-order character, but there also exists a small range of stronger Hund's
coupling in which an enhancement of magnetization can be observed on the SDW
side. We interpret the former scenario as one in which a sharp distinction can
be drawn between LM and the SDW picture, and the latter scenario as one in
which signs of LM physics begin to develop in the metallic phase. It is
tempting to suggest that some FeSC materials are in the vicinity of the latter
scenario.Comment: 7 pages, 5 figures; v2: Added discussions on anisotropy in
renormalized hopping, clarifications and discussions with regard to orbital
order, new inset in Fig. 3(d), expanded and revised bibliography, plus other
minor revisions. Accepted to PR
Chiral perturbation theory for pentaquark baryons and its applications
We construct a chiral lagrangian for pentaquark baryons assuming that the
recently found Theta^+ (1540) state belongs to an antidecuplet of SU(3) flavor
symmetry with J^P = (1/2)^(+-). We derive the Gell-Mann-Okubo formulae for the
antidecuplet baryon masses, and a possible mixing between the antidecuplet and
the pentaquark octet. Then we calculate the cross sections for pi^- p -> K^-
Theta^+ and gamma n -> K^- Theta^+ using our chiral lagrangian. The resulting
amplitudes respect the underlying chiral symmetry of QCD correctly. We also
describe how to include the light vector mesons in the chiral lagrangian.Comment: 4 page
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