Nonmagnetic impurity perturbation to the quasi-two-dimensional quantum helimagnet LiCu2O2

A complete phase diagram of Zn substituted quantum quasi-two-dimensional helimagnet LiCu2O2 has been presented. Helical ordering transition temperature (T_h) of the original LiCu2O2 follows finite size scaling for less than ~ 5.5% Zn substitution, which implies the existence of finite helimagnetic domains with domain boundaries formed with nearly isolated spins. Higher Zn substitution > 5.5% quenches the long-range helical ordering and introduces an intriguing Zn level dependent magnetic phase transition with slight thermal hysteresis and a universal quadratic field dependence for T_c (Zn > 0.055,H). The magnetic coupling constants of nearest-neighbor (nn) J1 and next-nearest-neighbor (nnn) J2 (alpha=J2/J1) are extracted from high temperature series expansion (HTSE) fitting and N=16 finite chain exact diagonalization simulation. We have also provided evidence of direct correlation between long-range helical spin ordering and the magnitude of electric polarization in this spin driven multiferroic material

Analysis of the Sediment Filtering Action of Grassed Media

The movement of sediment in non-submerged flow through a rigid grass media was studied experimentally by simulating the media with cylindrical nails. Models of sediment movement were developed from probablistic reasoning and from the use of existing parameters describing total bed material in open channel flow. In the probability analysis, the percent sediment trapped was found to be a power function of the number of potential fall paths, Nf,a particle could make from the surface to the bed while traveling through the filter media. The percent trapped was also found to be an inverse power function of the Reynolds number ReT. The characteristic length used in the Reynolds number was a hydraulic radius calculated assuming rectangular open channel flow with a width equal to the spacing between elements and a depth equal to the depth of flow. This is defined as the spacing hydraulic radius, Rs. The percent trapped was finally related exponentially to a combined power function of Nf and ReT. Total bed material transport functions of Graf and Einstein were modified and evaluated as predictors of suspended and bed load. Bed shear was assumed to be equal to γRsS where γ is the weight density of water and S is channel slope. Both Graf\u27s and Einstein\u27s parameters were found to be good predictors of suspended and bed load. Based on the results of the study, procedures are proposed for analyzing the trapping capability of sediment by grass filters

Lepton Flavor Violation and Cosmological Constraints on R-parity Violation

In supersymmetric standard models R-parity violating couplings are severely constrained, since otherwise they would erase the existing baryon asymmetry before the electroweak transition. It is often claimed that this cosmological constraint can be circumvented if the baryon number and one of the lepton flavor numbers are sufficiently conserved in these R-parity violating couplings, because B/3-L_i for each lepton flavor is separately conserved by the sphaleron process. We discuss the effect of lepton flavor violation on the B-L conservation, and show that even tiny slepton mixing angles \theta_{12} \gsim {\cal O}(10^{-4}) and \theta_{23}, \theta_{13}\gsim {\cal O}(10^{-5}) will spoil the separate B/3-L_i conservation. In particular, if lepton flavor violations are observed in experiments such as MEG and B-factories, it will imply that all the R-parity violating couplings must be suppressed to avoid the B-L erasure. We also discuss the implication for the decay of the lightest MSSM particle at the LHC.Comment: 21 pages, 7 figures. v2: minor change

Kaluza-Klein Induced Gravity Inflation

A D-dimensional induced gravity theory is studied carefully in a $4 + (D-4)$ dimensional Friedmann-Robertson-Walker space-time. We try to extract information of the symmetry breaking potential in search of an inflationary solution with non-expanding internal-space. We find that the induced gravity model imposes strong constraints on the form of symmetry breaking potential in order to generate an acceptable inflationary universe. These constraints are analyzed carefully in this paper.Comment: 10 pages, title changed, corrected some typos, two additional comments adde

Inflationary Universe in Higher Derivative Induced Gravity

In an induced-gravity model, the stability condition of an inflationary slow-rollover solution is shown to be $\phi_0 \partial_{\phi_0}V(\phi_0)=4V(\phi_0)$. The presence of higher derivative terms will, however, act against the stability of this expanding solution unless further constraints on the field parameters are imposed. We find that these models will acquire a non-vanishing cosmological constant at the end of inflation. Some models are analyzed for their implication to the early universe.Comment: 6 pages, two typos correcte