Non-Fermi liquid behavior in nearly charge ordered layered metals

Non-Fermi liquid behavior is shown to occur in two-dimensional metals which are close to a charge ordering transition driven by the Coulomb repulsion. A linear temperature dependence of the scattering rate together with an increase of the electron effective mass occur above T*, a temperature scale much smaller than the Fermi temperature. It is shown that the anomalous temperature dependence of the optical conductivity of the quasi-two-dimensional organic metal alpha-(BEDT-TTF)2MHg(SCN)4, with M=NH4 and Rb, above T*=50-100 K, agrees qualitatively with our predictions for the electronic properties of nearly charge ordered two-dimensional metals.Comment: accepted in Phys. Rev. Let

New two-colour light curves of Q0957+561: time delays and the origin of intrinsic variations

We extend the gr-band time coverage of the gravitationally lensed double quasar Q0957+561. New gr light curves permit us to detect significant intrinsic fluctuations, to determine new time delays, and thus to gain perspective on the mechanism of intrinsic variability in Q0957+561. We use new optical frames of Q0957+561 in the g and r passbands from January 2005 to July 2007. These frames are part of an ongoing long-term monitoring with the Liverpool robotic telescope. We also introduce two photometric pipelines that are applied to the new gr frames of Q0957+561. The transformation pipeline incorporates zero-point, colour, and inhomogeneity corrections to the instrumental magnitudes, so final photometry to the 1-2% level is achieved for both quasar components. The two-colour final records are then used to measure time delays. The gr light curves of Q0957+561 show several prominent events and gradients, and some of them (in the g band) lead to a time delay between components of 417 +/- 2 d (1 sigma). We do not find evidence of extrinsic variability in the light curves of Q0957+561. We also explore the possibility of a delay between a large event in the g band and the corresponding event in the r band. The gr cross-correlation reveals a time lag of 4.0 +/- 2.0 d (1 sigma; the g-band event is leading) that confirms a previous claim of the existence of a delay between the g and r band in this lensed quasar. The time delays (between quasar components and between optical bands) from the new records and previous ones in similar bands indicate that most observed variations in Q0957+561 (amplitudes of about 100 mmag and timescales of about 100 d) are very probably due to reverberation within the gas disc around the supermassive black hole.Comment: 13 pages, 9 figures. Accepted for publication in A&

Generating Higher-Order Lie Algebras by Expanding Maurer Cartan Forms

By means of a generalization of the Maurer-Cartan expansion method we construct a procedure to obtain expanded higher-order Lie algebras. The expanded higher order Maurer-Cartan equations for the case $\mathcal{G}=V_{0}\oplus V_{1}$ are found. A dual formulation for the S-expansion multialgebra procedure is also considered. The expanded higher order Maurer Cartan equations are recovered from S-expansion formalism by choosing a special semigroup. This dual method could be useful in finding a generalization to the case of a generalized free differential algebra, which may be relevant for physical applications in, e.g., higher-spin gauge theories

PROGRAMAS DE INFORMÁTICA PARA COMPARAÇÕES ENTRE CORRELAÇÕES: AMOSTRAS DEPENDENTES

Existe una variedad de técnicas para probar las diferencias entre correlaciones dependientes que no están disponibles en los programas estadísticos estándar para el investigador. Se presentan ejemplos de estas técnicas para evaluar diferentes hipótesis dentro del contexto de correlaciones en muestras dependientes, junto con programas informáticos interactivos, de fácil uso y libre distribución.There are a variety of techniques for testing the differences between dependent correlations that are not available using the standard statistical software packages.  Examples of these techniques for examining different hypotheses within the dependent correlational realm are presented along with the output and interpretation from easily attainable, user-friendly, interactive software.Existe uma variedade de técnicas para provar as diferencias entre correlações dependentes que não estão disponíveis nos programas estatísticos familiares para o investigador. Apresentam-se exemplos destas técnicas para avaliar diferentes hipóteses dentro do contexto de correlações em amostras dependentes, junto com programas de informáticas interativos, amigáveis e livre distribuição

A topological charge selection rule for phase singularities

We present an study of the dynamics and decay pattern of phase singularities due to the action of a system with a discrete rotational symmetry of finite order. A topological charge conservation rule is identified. The role played by the underlying symmetry is emphasized. An effective model describing the short range dynamics of the vortex clusters has been designed. A method to engineer any desired configuration of clusters of phase singularities is proposed. Its flexibility to create and control clusters of vortices is discussed.Comment: 4 pages, 3 figure

Charged Current Neutrino Cross Section and Tau Energy Loss at Ultra-High Energies

We evaluate both the tau lepton energy loss produced by photonuclear interactions and the neutrino charged current cross section at ultra-high energies, relevant to neutrino bounds with Earth-skimming tau neutrinos, using different theoretical and phenomenological models for nucleon and nucleus structure functions. The theoretical uncertainty is estimated by taking different extrapolations of the structure function F2 to very low values of x, in the low and moderate Q2 range for the tau lepton interaction and at high Q2 for the neutrino-nucleus inelastic cross section. It is at these extremely low values of x where nuclear shadowing and parton saturation effects are unknown and could be stronger than usually considered. For tau and neutrino energies E=10^9 GeV we find uncertainties of a factor 4 for the tau energy loss and of a factor 2 for the charged current neutrino-nucleus cross section.Comment: 20 pages and 11 figure

Even-dimensional topological gravity from Chern-Simons gravity

It is shown that the topological action for gravity in 2n-dimensions can be obtained from the 2n+1-dimensional Chern-Simons gravity genuinely invariant under the Poincare group. The 2n-dimensional topological gravity is described by the dynamics of the boundary of a 2n+1-dimensional Chern-Simons gravity theory with suitable boundary conditions. The field $\phi^{a}$, which is necessary to construct this type of topological gravity in even dimensions, is identified with the coset field associated with the non-linear realizations of the Poincare group ISO(d-1,1)