Renormalizable 1/N_f Expansion for Field Theories in Extra Dimensions

We demonstrate how one can construct renormalizable perturbative expansion in formally nonrenormalizable higher dimensional field theories. It is based on $1/N_f$-expansion and results in a logarithmically divergent perturbation theory in arbitrary high space-time dimension. First, we consider a simple example of $N$-component scalar filed theory and then extend this approach to Abelian and non-Abelian gauge theories with $N_f$ fermions. In the latter case, due to self-interaction of non-Abelian fields the proposed recipe requires some modification which, however, does not change the main results. The resulting effective coupling is dimensionless and is running in accordance with the usual RG equations. The corresponding beta function is calculated in the leading order and is nonpolynomial in effective coupling. It exhibits either UV asymptotically free or IR free behaviour depending on the dimension of space-time. The original dimensionful coupling plays a role of a mass and is also logarithmically renormalized. We analyze also the analytical properties of a resulting theory and demonstrate that in general it acquires several ghost states with negative and/or complex masses. In the former case, the ghost state can be removed by a proper choice of the coupling. As for the states with complex conjugated masses, their contribution to physical amplitudes cancels so that the theory appears to be unitary.Comment: 32 pages, 20 figure

[Pb2F2](SeO4): a heavier analogue of grandreefite, the first layered fluoride selenate

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Co-precipitation of PbF 2 and PbSeO 4 in weakly acidic media results in the formation of [Pb 2 F 2 ](SeO 4 ), the selenate analogue of the naturally occurring mineral grandreefite, [Pb 2 F 2 ](SO 4 ). The new compound is monoclinic, C2/c, a = 14.0784(2) Å, b = 4.6267(1) Å, c = 8.8628(1) Å, β = 108.98(1)°, V = 545.93(1) Å 3 . Its structure has been refined from powder data to R B = 1.55%. From thermal studies, it is established that the compound is stable in air up to about 300 °C, after which it gradually converts into a single phase with composition [Pb 2 O](SeO 4 ), space group C2/m, and lattice parameters a = 14.0332(1) Å, b = 5.7532(1) Å, c = 7.2113(1) Å, β = 115.07(1)°, V = 527.37(1) Å 3 . It is the selenate analogue of lanarkite, [Pb 2 O](SO 4 ), and phoenicochroite, [Pb 2 O](CrO 4 ), and its crystal structure was refined to R B = 1.21%. The formation of a single decomposition product upon heating in air suggests that this happens by a thermal hydrolysis mechanism, i.e., Pb 2 F 2 SeO 4 + H 2 O (vapor) → Pb 2 OSeO 4 + 2HF↑

[Pb2F2](SeO4): a heavier analogue of grandreefite, the first layered fluoride selenate

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Co-precipitation of PbF 2 and PbSeO 4 in weakly acidic media results in the formation of [Pb 2 F 2 ](SeO 4 ), the selenate analogue of the naturally occurring mineral grandreefite, [Pb 2 F 2 ](SO 4 ). The new compound is monoclinic, C2/c, a = 14.0784(2) Å, b = 4.6267(1) Å, c = 8.8628(1) Å, β = 108.98(1)°, V = 545.93(1) Å 3 . Its structure has been refined from powder data to R B = 1.55%. From thermal studies, it is established that the compound is stable in air up to about 300 °C, after which it gradually converts into a single phase with composition [Pb 2 O](SeO 4 ), space group C2/m, and lattice parameters a = 14.0332(1) Å, b = 5.7532(1) Å, c = 7.2113(1) Å, β = 115.07(1)°, V = 527.37(1) Å 3 . It is the selenate analogue of lanarkite, [Pb 2 O](SO 4 ), and phoenicochroite, [Pb 2 O](CrO 4 ), and its crystal structure was refined to R B = 1.21%. The formation of a single decomposition product upon heating in air suggests that this happens by a thermal hydrolysis mechanism, i.e., Pb 2 F 2 SeO 4 + H 2 O (vapor) → Pb 2 OSeO 4 + 2HF↑

Synthesis, crystal structure, spectroscopic properties, and thermal behavior of rare-earth oxide selenates, Ln2O2SeO4 (Ln = La, Pr, Nd): The new perspectives of solid-state double-exchange synthesis

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Three rare-earth oxide selenates Ln2O2SeO4 (Ln = La, Pr, Nd) have been prepared via double-exchange solid-state reactions between respective LnOCl oxyhalides and potassium selenate. This approach succeeded to obtain singlephase specimens of La2O2SeO4 and Nd2O2SeO4, previously known as transients upon thermal decomposition of the corresponding selenates, as well as a new compound Pr2O2SeO4. Refinement of their crystal structures from powder X-ray diffraction data confirmed previous attributions to the grandreefite (Pb2F2SO4) structure type observed also for the Ln2O2SO4 oxide sulfates. According to polythermic X-ray studies, La2O2SeO4 is stable until at least 700 C. All compounds were characterized by infrared and X-ray photoelectron spectroscopy