Effective field theory of the deuteron with dibaryon field

Pionless effective field theory with dibaryon fields is reexamined for observables involving the deuteron. The electromagnetic form factors of the deuteron and the total cross sections of radiative neutron capture on the proton, $np \to d\gamma$, are calculated. The low energy constants of vector(photon)-dibaryon-dibaryon vertices in the effective lagrangian are fixed primarily by the one-body vector(photon)-nucleon-nucleon interactions. This scheme for fixing the values of the low energy constants satisfactorily reproduces the results of the effective range theory. We also show that, by including higher order corrections, one can obtain results that are close to those of Argonne v18 potential model.Comment: 25 pages and 11 figures; 16 references added, Figure 6 and 7 replotted, text revised a lot. To be published in Phys. Rev.

Low energy proton-proton scattering in effective field theory

Low energy proton-proton scattering is studied in pionless effective field theory. Employing the dimensional regularization and MS-bar and power divergence subtraction schemes for loop calculation, we calculate the scattering amplitude in 1S0 channel up to next-to-next-to leading order and fix low-energy constants that appear in the amplitude by effective range parameters. We study regularization scheme and scale dependence in separation of Coulomb interaction from the scattering length and effective range for the S-wave proton-proton scattering.Comment: 23 pages, 6 eps figures, revised considerably, accepted for publication in Phys. Rev.

Critical behavior of two-dimensional random hopping fermions with \pi-flux

A two dimensional random hopping model with N-species and \pi-flux is studied. The field theory at the band center is shown to be in the universality class of GL(4m,R)/O(4m) nonlinear sigma model. Vanishing beta function suggests delocalised states at the band center. Contrary to the similar universality class with broken time reversal symmetry, the present class is expected to have at least two fixed point. Large N-systems are shown to be in the weak-coupling fixed point, which is characterized by divergent density of state, while small N systems may be in the strong-coupling fixed point.Comment: 12 pages, revtex, 1 figur

Effective field theory approach for the M1 properties of A=2 and 3 nuclei

The magnetic moments of ${}^2{H}$, ${}^3{He}$ and ${}^3{H}$ as well as the thermal neutron capture rate on the proton are calculated using heavy baryon chiral perturbation theory {\it \`{a} la} Weinberg. The M1 operators have been derived up to {N$^3$LO}. The nuclear matrix elements are evaluated with the use of wave functions obtained by carrying out variational Monte Carlo calculations for a realistic nuclear Hamiltonian involving high-precision phenomenological potentials like Argonne Av18 and Urbana IX tri-nucleon interactions. We discuss the potential- and cutoff-dependence of the results.Comment: 14 pages, 2figure

Five-body resonances of 8He using the complex scaling method

The 0+ states of 8He are studied in a five-body 4He+n+n+n+n cluster model. Many-body resonances are treated on the correct boundary condition as Gamow states using the complex scaling method. The 0+_2 state of 8He is predicted as a five-body resonance in the excitation energy of 6.3 MeV with a width of 3.2 MeV, which mainly has a (p_{3/2})^2(p_{1/2})^2 configuration. In this state, number of the 0+ neuron pair shows almost two, which is different from the ground state having a large amount of the 2+ pair component. The monopole transition of 8He from the ground state into the five-body unbound states is also evaluated. It is found that the 7He+n component mostly exhausts the strength, while the 0+_2 contribution is negligible. The final states are dominated by 6He+n+n, not 4He+n+n+n+n. The results indicate the sequential breakup process of 8He to 7He+n to 6He+n+n by the monopole excitation.Comment: 6 pages, 6 figures, table I is updated for the experimental value

Localization in the quantum Hall regime

The localization properties of electron states in the quantum Hall regime are reviewed. The random Landau model, the random matrix model, the tight-binding Peierls model, and the network model of Chalker and Coddington are introduced. Descriptions in terms of equivalent tight-binding Hamiltonians, and the 2D Dirac model, are outlined. Evidences for the universal critical behavior of the localization length are summarized. A short review of the supersymmetric critical field theory is provided. The interplay between edge states and bulk localization properties is investigated. For a system with finite width and with short-range randomness, a sudden breakdown of the two-point conductance from $ne^{2}/h$ to 0 ($n$ integer) is predicted if the localization length exceeds the distance between the edges.Comment: 16 pages, to be published in Physica E, Proceedings of the Symposium "Quantum Hall Effect: Past, Present and Future