Simulating spin-\frac{3}{2} particles at colliders

Support for interactions of spin- $\frac{3}{2}$ particles is implemented in the FeynRules and ALOHA packages and tested with the MadGraph 5 and CalcHEP event generators in the context of three phenomenological applications. In the first, we implement a spin- $\frac{3}{2}$ Majorana gravitino field, as in local supersymmetric models, and study gravitino and gluino pair-production. In the second, a spin- $\frac{3}{2}$ Dirac top-quark excitation, inspired from compositeness models, is implemented. We then investigate both top-quark excitation and top-quark pair-production. In the third, a general effective operator for a spin- $\frac{3}{2}$ Dirac quark excitation is implemented, followed by a calculation of the angular distribution of the s-channel production mechanism.     

Analytical treatment of synchronization of spin-torque oscillators by microwave magnetic fields

An analytical approach is presented for the study of synchronization effects in spin-transfer-driven nanomagnets subjected to radio-frequency magnetic fields. The conditions are derived and discussed under which the current-induced magnetization precession is synchronized by the radio-frequency field. Exact analytical results are obtained for the case when the problem exhibits uniaxial symmetry around the axis perpendicular to the device plane. It is demonstrated that the magnetization dynamics under nonzero current and nonzero rf field is identical in structure to that under zero current. On this basis, analytical predictions are obtained for: the existence of phase-locking between current-induced magnetization precession and rf field oscillations; the frequency pulling effect in proximity of phase locking; the occurrence of hysteresis effects in phase-locking as a function of the spin-polarized current. The proposed approach is valid for arbitrary rf field amplitude and current intensity.     

Rapid screening of natural products by high-resolution high-temperature gas chromatography

The crude ethanol extracts from the leaves of three Croton hemiargyrus hemiargyreus plants are fractionated by thin-layer chromatography, yielding five fractions. The fractions and the crude extract are analyzed by high-temperature high-resolution gas chromatography coupled with mass spectrometry (HT-HRGC-MS). Several natural products, including thermolabile components, can be characterized directly in the samples, such as alkaloids, terpenes, flavonoids, acids, alcohols, etc. The cold on-column technique proves to be appropriate for the injection of these thermolabile compounds. HT-HRGC-MS is shown to be a valuable tool and an alternative technique to classical phytochemical procedures for the simple and fast routine analysis of natural products in crude extracts.     

Ab initio analysis of some fluoride and oxide structures doped with Pr and Yb

Doping effects are analyzed by means of the ab initio perturbed ion (aiPI) method via substitution of the fluorides and oxides of zirconium, hafnium, and thorium. Lattice relaxation is simulated through the calculation of vibrational breathing modes and substitutional effects on the compound are thereby analyzed. In addition, the band gaps (in the pure species) and impurity levels (where substitutional ions Pr⁺⁴ and Yb⁺³ are considered in the doped species) of the fluorides are estimated via the transition energy calculated at the aiPI‐optimized geometry of the pure and doped crystal clusters by means of the configuration interaction with single excitations (CIS) method that accounts for electronic correlation. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Thermal decomposition kinetics of PrMO<Subscript>3</Subscript> (M = Ni or Co) ceramic materials via thermogravimetry

Thermogravimetric data using the non-isothermal kinetic models of Flynn and Wall and “Model-free Kinetics” were used to determine the activation energy to study the decomposition kinetics of the ligand groups with system’s metallic ions that takes part in the synthesis of PrMO₃ (M = Ni or Co). This activation energy was determined for the stage of highest decomposition of the organic matter to establish parameters in synthesis condition optimization and application of the proposed material.     

Shannon and Fisher entropies for a hydrogen atom under soft spherical confinement

We calculate Shannon and Fisher entropies in the position and momentum space, and some complexity measures for a variationally described hydrogen atom confined in soft and hard spherical boxes of varying dimension $r_c$ and selected values of strength $U_0$. We include calculations for a free particle trapped in impenetrable boxes. It is found that the Shannon entropy $S_r$ becomes negative for small cavity radii and large values of $U_0$, due to the highly localized nature of the particle. For soft confinement and small cavity dimensions, the entropies change very rapidly over short radial intervals.     

The confined helium atom: An information–theoretic approach

In this article, we study the helium atom confined in a spherical impenetrable cavity by using informational measures. We use the Ritz variational method to obtain the energies and wave functions of the confined helium atom as a function of the cavity radius $r_0$. As trial wave functions we use one uncorrelated function and five explicitly correlated basis sets in Hylleraas coordinates with different degrees of electronic correlation. We computed the Shannon entropy, Fisher information, Kullback–Leibler entropy, Tsallis entropy, disequilibrium and Fisher–Shannon complexity, as a function of $r_0$. We found that these entropic measures are sensitive to electronic correlation and can be used to measure it. As expected these entropic measures are less sensitive to electron correlation in the strong confinement regime ( a.u.).     

Quantum gravity at the LHC

We study the production of massless gravitons at the LHC and compare our results to those obtained in extra-dimensional models. The signature in both cases is missing energy plus jets. In case of non-observation, the LHC could be used to put the tightest limit to date on the value of the Planck mass.     

Memory effects in the two-level model for glasses

We study an ensemble of two-level systems interacting with a thermal bath. This is a well-known model for glasses. The origin of memory effects in this model is a quasistationary but nonequilibrium state of a single two-level system, which is realized due to a finite-rate cooling and slow thermally activated relaxation. We show that single-particle memory effects, such as negativity of the specific heat under reheating, vanish for a sufficiently disordered ensemble. In contrast, a disordered ensemble displays a collective memory effect [similar to the Kovacs effect], where nonequilibrium features of the ensemble are monitored via a macroscopic observable. An experimental realization of the effect can be used to further assess the consistency of the model.