Multi-scale Renormalisation Group Improvement of the Effective Potential

Using the renormalisation group and a conjecture concerning the perturbation series for the effective potential, the leading logarithms in the effective potential are exactly summed for $O(N)$ scalar and Yukawa theories.Comment: 19 pages, DIAS STP 94-09. Expanded to check large N limit, typo's corrected, to appear in Phys Rev

Studies of structural, magnetic and dielectric properties of X-type Barium Zinc hexaferrite Ba2Zn2Fe28O46 powder prepared by combustion treatment method using ginger root extract as a green reducing agent

Various quantities of ginger (Zingiber officinale) root extract were used to prepare X-type Barium–Zinc hexaferrite with the chemical composition Ba2Zn2Fe28O46. The powders were prepared using a combustion treatment method, being pre-heated at 550 °C for 4 h with the ginger as a fuel, followed by final heating to 900 °C for 5 h and natural cooling to room temperature to obtain Ba2Zn2Fe28O46 hexagonal ferrite powder. The phase composition of heated powder samples was investigated by X-ray diffraction (XRD), indicating the formation of a mixture of X-type and hematite (α-Fe2O3). Up to 82.6%, X-ferrite was formed at 900 °C with 52.5 g of ginger root extract. Dielectric analysis of the prepared samples shows the frequency-dependent phenomena. All samples were hard magnets, with coercivity values (HC) between 262.2 and 318.3 kA m−1, and squareness ratios > 0.5. The sample prepared with 52.5 g ginger root extract possesses the highest value of saturation magnetisation (MS = 33.87 Am2 kg−1) in comparison with the other prepared samples. Therefore, ginger was shown to be a useful natural plant extract as a reducing fuel for the low-temperature synthesis of X-ferrites. The sample prepared with 35 g ginger root extract shows a broad loss tangent resonance peak between 10 kHz and 100 kHz, while other samples show loss tangent resonance peaks between 300 kHz and 2 MHz frequency range.publishe

Vacuum Stability Higgs Mass Bound Revisited with Implications for Extra Dimension Theories

We take the standard model to be an effective theory including higher dimensional operators suppressed by scale $\Lambda$ and re-examine the higgs mass bounds from the requirements of vacuum stability. Our results show that the effects of the higher dimensional operators on the higgs mass limits are significant. As an implication of our results, we study the vacuum stability higgs mass bounds in theories with extra dimensions.Comment: Latex, 14 pages, 1 figure. Added references. To appear in Phys. Rev.

Bounds on charged higgs boson in the 2HDM type III from Tevatron

We consider the Two Higgs Doublet Model (2HDM) of type III which leads to Flavour Changing Neutral Currents (FCNC) at tree level. In the framework of this model we can use an appropriate form of the Yukawa Lagrangian that makes the type II model limit of the general type III couplings apparent. This way is useful in order to compare with the experimental data which is model dependent. The analytical expressions of the partial width $\Gamma (t \to H^+ b)$ are derived and we compare with the data available at this energy range. We examine the limits on the new parameters $\lambda_{ij}$ from the validness of perturbation theory.Comment: 14 pages, 4 figures, Universidad Nacional de Colombia. typos correcte

Probing flavor changing interactions in hadron collisions

The subprocess $gg \to t\bar{c}+\bar{t}c$ in the two-Higgs-doublet model with flavor-changing scalar couplings is examined at the one loop level. With perturbative QCD factorization theorem, the corresponding cross sections for hadron-hadron collisions are computed numerically. The results are applicable to the whole mass range of the weakly coupled Higgs bosons. In case we could efficiently exclude the severe backgrounds of the $t\bar{c}(\bar{t}c)$ production signal, probing the flavor-changing top-charm-scalar vertex at hadron colliders would be very promising and accessible experimentally.Comment: LaTex file, 14 pages, 8 EPS figure

Design and development of Ga-substituted Z-type hexaferrites for microwave absorber applications: mössbauer, static and dynamic properties

Gallium substituted Z-type Sr3GaxCo2-xFe24O41 (x = 0.0–2.0 in steps of 0.4) hexaferrites were synthesised by the sol-gel auto-combustion process, and sintered at 1150 °C. The structural, morphology, magnetic, Mössbauer, dielectric and microwave absorption properties were examined. XRD results of x = 0.0, 0.4, 0.8, and 1.2 samples show the formation of a single Z-type hexagonal phase. The samples x = 1.6 and 2.0 show the formation of Z and M phases. Hysteresis loops analysis suggest that samples x < 1.6 possess a soft magnetic nature, while the samples x = 1.6 and 2.0 show a hard ferrite characteristics. All samples possess multi-domain microstructures. The composition x = 0.4 [maximum MS = 97.94 Am2kg−1] was fitted with seven sextets (Fe3+) and a paramagnetic doublet-A (Fe3+), while beyond x ≥ 0.8 two more doublets (Fe2+) were observed along with seven sextets in Mössbauer spectra. The maximum values of Fe2+ ions (1.26%) and relative area of paramagnetic doublets (1.91%) were observed for x = 1.6 composition, which is also responsible for the lowest value of MS (69.99 Am2kg−1) for this composition. The average hyperfine magnetic field was found to decrease, whereas average quadrupole splitting was found to increase, with Ga-substitution. The substitution of Ga ions enhanced permeability, dielectric constant, magnetic loss and dielectric loss, in a non-linear fashion. The reflection loss was maximum at lower frequencies for samples x = 0.0 and 0.8, and decreases with frequency. Sample x = 0.8 has maximum reflection loss of −12.44 dB at 8 GHz, a measured thickness of 3 mm, and a bandwidth of −10 dB at 1.18 GHz. The observed absorption has been discussed with the help of the input impedance matching mechanism and quarter wavelength mechanism. The observed coercivity in different samples also influenced microwave absorption which demonstrated potenial in microwave absorber applications.publishe

A Multi-scale Subtraction Scheme and Partial Renormalization Group Equations in the O(N)O(N)-symmetric ϕ4\phi^4-theory

To resum large logarithms in multi-scale problems a generalization of \MS is introduced allowing for as many renormalization scales as there are generic scales in the problem. In the new \lq\lq minimal multi-scale subtraction scheme'' standard perturbative boundary conditions become applicable. However, the multi-loop beta functions depend on the various renormalization scale ratios and a large logarithms resummation has to be performed on them. Using these improved beta functions the \lq\lq partial'' renormalization group equations corresponding to the renormalization point independence of physical quantities allows one to resum the logarithms. As an application the leading and next-to-leading order two-scale analysis of the effective potential in the $O(N)$-symmetric $\phi^4$-theory is performed. This calculation indicates that there is no stable vacuum in the broken phase of the theory for $1<N\leq4$.Comment: 27 pages, LaTex, no figures (a version with three figures is available from the authors

Precision measurement of the half-life and the decay branches of 62Ga

In an experiment performed at the Accelerator Laboratory of the University of Jyvaskyla, the beta-decay half-life of 62Ga has been studied with high precision using the IGISOL technique. A half-life of T1/2 = 116.09(17)ms was measured. Using beta-gamma coincidences, the gamma intensity of the 954keV transition and an upper limit of the beta-decay feeding of the 0+_2 state have been extracted. The present experimental results are compared to previous measurements and their impact on our understanding of the weak interaction is discussed.Comment: 7 pages, 7 figures, submitted to EPJ