Simple derivation of general Fierz-type identities

General Fierz-type identities are examined and their well known connection with completeness relations in matrix vector spaces is shown. In particular, I derive the chiral Fierz identities in a simple and systematic way by using a chiral basis for the complex $4\times4$ matrices. Other completeness relations for the fundamental representations of SU(N) algebras can be extracted using the same reasoning.Comment: 9pages. Few sentences modified in introduction and in conclusion. Typos corrected. An example added in introduction. Title modifie

Structure of potentials with NN Higgs doublets

Extensions of the Standard Model with $N$ Higgs doublets are simple extensions presenting a rich mathematical structure. An underlying Minkowski structure emerges from the study of both variable space and parameter space. The former can be completely parametrized in terms of two future lightlike Minkowski vectors with spatial parts forming an angle whose cosine is $-(N-1)^{-1}$. For the parameter space, the Minkowski parametrization enables one to impose sufficient conditions for bounded below potentials, characterize certain classes of local minima and distinguish charge breaking vacua from neutral vacua. A particular class of neutral minima presents a degenerate mass spectrum for the physical charged Higgs bosons.Comment: 11 pages. Revtex4. Typos corrected. Few comments adde

Formation and Disruption of Cosmological Low Mass Objects

We investigate the evolution of cosmological low mass (low virial temperature) objects and the formation of the first luminous objects. First, the `cooling diagram' for low mass objects is shown. We assess the cooling rate taking into account the contribution of H_2, which is not in chemical equilibrium generally, with a simple argument of time scales. The reaction rates and the cooling rate of H_2 are taken from the recent results by Galli & Palla (1998). Using this cooling diagram, we also estimate the formation condition of luminous objects taking into account the supernova (SN) disruption of virialized clouds. We find that the mass of the first luminous object is several times 10^7 solar mass, because smaller objects may be disrupted by the SNe before they become luminous. Metal pollution of low mass (Ly-alpha) clouds also discussed. The resultant metallicity of the clouds is about 1/1000 of the solar metallicity.Comment: 11 pages, 2 figures, To appear in ApJ

Soft CP violation in K-meson systems

We consider a model with soft CP violation which accommodate the CP violation in the neutral kaons even if we assume that the Cabibbo-Kobayashi-Maskawa mixing matrix is real and the sources of CP violation are three complex vacuum expectation values and a trilinear coupling in the scalar potential. We show that for some reasonable values of the masses and other parameters the model allows to explain all the observed CP violation processes in the $K^0$-$\bar{K}^0$ system.Comment: 19 pages, RevTeX 4. Minor modification

Photoluminescence from silicon dioxide photonic crystal cavities with embedded silicon nanocrystals

One dimensional nanobeam photonic crystal cavities are fabricated in silicon dioxide with silicon nanocrystals. Quality factors of over 9 x 10^3 are found in experiment, matching theoretical predictions, with mode volumes of 1.5(lambda/n)^3 . Photoluminescence from the cavity modes is observed in the visible wavelength range 600-820 nm. Studies of the lossy characteristics of the cavities are conducted at varying temperatures and pump powers. Free carrier absorption effects are found to be significant at pump powers as low as a few hundred nanowatts.Comment: 13 pages 9 figure

The Minimum Total Mass of MACHOs and Halo Models of the Galaxy

If the density distribution \rho (r) of MACHOs is spherically symmetric with respect to the Galactic center, it is shown that the minimal total mass M_{min}^{{ MACHO}} of the MACHOs is 1.7\times 10^{10}\sol \tau_{-6.7}^{{ LMC}} where \tau_{-6.7}^{{ LMC}} is the optical depth (\tau^{{ LMC}}) toward the Large Magellanic Cloud (LMC) in the unit of 2\times 10^{-7}. If \rho (r) is a decreasing function of r, it is proved that M_{min}^{{ MACHO}} is 5.6\times 10^{10}\sol \tau_{-6.7}^{{ LMC}}. Several spherical and axially symmetric halo models of the Galaxy with a few free parameters are also considered. It is found that M_{min}^{{ MACHO}} ranges from 5.6\times 10^{10}\sol \tau_{-6.7}^{{ LMC}} to \sim 3 \times 10^{11}\sol \tau_{-6.7}^{{ LMC}}. For general case, the minimal column density \Sigma_{min}^{{ MACHO}} of MACHOs is obtained as \Sigma_{min}^{{ MACHO}} =25 \sol { pc}^{-2}\tau_{-6.7}^{{ LMC}}. If the clump of MACHOs exist only halfway between LMC and the sun, M_{min}^{{ MACHO}} is 1.5\times 10^9\sol. This shows that the total mass of MACHOs is smaller than 5 \times 10^{10}\sol , i.e. \sim 10\% of the mass of the halo inside LMC, either if the density distribution of MACHOs is unusual or \tau^{{ LMC}}\ll 2\times 10^{-7}.Comment: 5 pages, 5 Encapsulated PostScript figures, Latex, Accepted for publication in Apj. Letter

Self-Regulation of Star Formation in Low Metallicity Clouds

We investigate the process of self-regulated star formation via photodissociation of hydrogen molecules in low metallicity clouds. We evaluate the influence region's scale of a massive star in low metallicity gas clouds whose temperatures are between 100 and 10000 Kelvin. A single O star can photodissociate hydrogen molecules in the whole of the host cloud. If metallicity is smaller than about 10^{-2.5} of the solar metallicity, the depletion of coolant of the the host cloud is very serious so that the cloud cannot cool in a free-fall time, and subsequent star formation is almost quenched. On the contrary, if metallicity is larger than about 10^{-1.5} of the solar metallicity, star formation regulation via photodissociation is not efficient. The typical metallicity when this transition occurs is about 1/100 of the solar metallicity. This indicates that stars do not form efficiently before the metallicity becomes larger than about 1/100 of the solar metallicity and we considered that this value becomes the lower limit of the metallicity of luminous objects such as galaxies.Comment: 14 pages, including 5 figures, To appear in ApJ, Vol. 53

Dental fear: a narrative review

The dental fear and anxiety (DFA) is a common phenomenon around the world. From children to the adults, most of the people become frightened when they face any dental discomfort and they need to visit a dentist and go through a treatment procedure in a dental set up. This narrative review tends to identify the causes behind DFA, its consequences and management of DFA from different studies which were conducted previously. This study is a narrative review of DFA. This study is mainly based on the secondary data from different articles and journals which were available online. After the proper screening from 154 titles, the final review included 68 articles. Based on different studies, it is found that DFA in quiet common in the people of all ages. The studies had found that dental fear and anxiety most often results from a traumatic past dental experience. Friendly dental office environment is an effective way in reducing dental fear and anxiety. Psychotherapeutic management is also important is managing DFA like behavior-management techniques, relaxation techniques, distraction, guided imagery, hypnotherapy, acupuncture, systematic desensitization or exposure therapy, positive reinforcement, cognitive restructuring and pharmacological management. The techniques for managing DFA can be the effective solution for reducing stress and make the treatment process more comfortable.