Flavor Constraints from Unitarity and Analyticity
PHYSICAL REVIEW LETTERS
Authors: Remmen, Grant N.; Rodd, Nicholas L.
Abstract
We use unitarity and analyticity of scattering amplitudes to constrain fermionic operators in the standard model effective field theory. For four-fermion operators at mass dimension 8, we scatter flavor superpositions in fixed standard model representations and find the Wilson coefficients to be constrained so that their contraction with any pair of pure density matrices is positive. These constraints imply that flavor-violating couplings are upper bounded by their flavor-conserving cousins. For instance, LEP data already appears to preclude certain operators in upcoming mu -> 3e measurements.
Adsorption removal of Cr(VI) by isomeric FeOOH
WATER SCIENCE AND TECHNOLOGY
Authors: Zhang, Di; Liu, Jiaxin; Zhu, Shibei; Xiong, Huixin; Xu, Yiqun
Abstract
The aim of this work is to study the performances of isomeric alpha-, beta-, and gamma-FeOOH (goethite, akaganeite and lepidocrocite, including five samples named as Gth1 and Gth2, Aka1 and Aka2, and Lep, respectively) for removing hexavalent chromium (Cr(VI)) from aqueous solutions. The adsorption mechanisms were explored by kinetic and isothermal experiments. Adsorption efficiencies under the different pH values, anions, and the levels of adsorbate and adsorbent were also measured. Results showed that the Cr(VI) adsorption by isomeric FeOOH could be best described by pseudo-second-order kinetic model. The processes of Cr(VI) isothermal adsorption could be greatly fitted by the Langmuir and Freundlich equations with the high correlation coefficients of R-2 (>0.92). Also, there were the optimum pH values of 3.0-8.0 for FeOOH to adsorb Cr(VI), and their adsorption capacities were tightly related with the active sites of adsorbents. Cr(VI) adsorptions by these adsorbents were easily influenced by H2PO4-, and then SO42-, while there were little effects by Cl-, CO32- and NO3-. These obtained results could provide a potentially theoretical evidence for isomeric FeOOH materials applied in the engineering treatment of the polluted chromate-rich waters.