Weyl geometry, anti-De Sitter space, and Φ4\Phi^4-theory

We study the Gaussian approximation to the quantum fluctuations of the metric of the four dimensional anti-De Sitter spacetime. The associated massless scalar field has a quartic self interaction, for which we construct the generating functional of the $n$-point correlation functions. The concomitant infrared divergence is cured by a mass renormalization provided by the cosmological constant, which is also responsible for the renormalization of the coupling constant of the field theory.Comment: 9 pages, 1 figur

Bundle Theory of Improper Spin Transformations

{\it We first give a geometrical description of the action of the parity operator ($\hat{P}$) on non relativistic spin ${{1}\over{2}}$ Pauli spinors in terms of bundle theory. The relevant bundle, $SU(2)\odot \Z_2\to O(3)$, is a non trivial extension of the universal covering group $SU(2)\to SO(3)$. $\hat{P}$ is the non relativistic limit of the corresponding Dirac matrix operator ${\cal P}=i\gamma_0$ and obeys $\hat{P}^2=-1$. Then, from the direct product of O(3) by $\Z_2$, naturally induced by the structure of the galilean group, we identify, in its double cover, the time reversal operator ($\hat{T}$) acting on spinors, and its product with $\hat{P}$. Both, $\hat{P}$ and $\hat{T}$, generate the group $\Z_4 \times \Z_2$. As in the case of parity, $\hat{T}$ is the non relativistic limit of the corresponding Dirac matrix operator ${\cal T}=\gamma^3 \gamma^1$, and obeys $\hat{T}^2=-1$.}Comment: 8 pages, Plaintex; titled changed, minor text modifications, one reference complete

On the non-relativistic limit of charge conjugation in QED

Even if at the level of the non-relativistic limit of full QED, C is not a symmetry, the limit of this operation does exist for the particular case when the electromagnetic field is considered a classical external object coupled to the Dirac field. This result extends the one obtained when fermions are described by the Schroedinger-Pauli equation. We give the expressions for both the C matrix and the $\hat{C}$ operator for galilean electrons and positrons interacting with the external electromagnetic field. The result is relevant in relation to recent experiments with antihydrogen.Comment: 7 page

Remark on charge conjugation in the non relativistic limit

We study the non relativistic limit of the charge conjugation operation $\cal C$ in the context of the Dirac equation coupled to an electromagnetic field. The limit is well defined and, as in the relativistic case, $\cal C$, $\cal P$ (parity) and $\cal T$ (time reversal) are the generators of a matrix group isomorphic to a semidirect sum of the dihedral group of eight elements and $\Z_2$. The existence of the limit is supported by an argument based in quantum field theory. Also, and most important, the limit exists in the context of galilean relativity. Finally, if one complexifies the Lorentz group and therefore the galilean spacetime $x_\mu$, then the explicit form of the matrix for $\cal C$ allows to interpret it, in this context, as the complex conjugation of the spatial coordinates: $\vec{x} \to \vec{x}^*$. This result is natural in a fiber bundle description.Comment: 8 page

Structural and magnetic behavior of ferrogels obtained by freezing thawing of polyvinyl alcohol/poly (acrylic acid) (PAA)-coated iron oxide nanoparticles

Superparamagnetic ferrogels with high swelling ability and potential applications as solvent absorbers and stimuli-responsive drug delivery devices were obtained by a non-toxic and environmentally friendly route based on dispersion of poly(acrylic acid)-coated iron oxide nanoparticles (PAA-coated NPs) in poly(vinyl alcohol) (PVA) solutions followed by freezing–thawing. Presence of carboxylate groups arising from the PAA coating allowed hydrogen bonding formation between NPs and PVA and enabled the synthesis of optically homogenous, superparamagnetic materials formed by a homogenous distribution of NPs diffuse clusters in the PVA matrix. The addition of PAA-coated NPs produced a remarkable increase in crystallinity degree, thermal degradation and swelling percentage respect to the neat matrix, which demonstrates that ferrogels with improved properties can be obtained by this procedure. Thereafter, combination of a cryogenic technique with the use of non-toxic components and magnetic NPs coated by a pH sensitive polymer makes these ferrogels very promising for applications in the biomedical field.Fil: Moscoso Londoño, Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; ArgentinaFil: Gonzalez, Jimena Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata; ArgentinaFil: Muraca, D.. Universidade Estadual de Campinas. Instituto de Física ’Gleb Wataghin’. Laboratorio de Materiais e Baixas Temperaturas; Brasil;Fil: Hoppe, Cristina Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata; ArgentinaFil: Alvarez, Vera Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata; ArgentinaFil: López Quintela, A.. Universidad de Santiago de Compostela; España;Fil: Socolovsky, Leandro Martin. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto D/tec.y Cs.de la Ing.;Fil: Pirota, K. R.. Universidade Estadual de Campinas. Instituto de Física ’Gleb Wataghin’. Laboratorio de Materiais e Baixas Temperaturas; Brasil