Possible signatures for tetraquarks from the decays of a0(980)a_0(980), a0(1450)a_0(1450)

Based on the recent proposal for the tetraquarks with the mixing scheme, we investigate fall-apart decays of $a_0(980), a_0(1450)$ into two lowest-lying mesons. This mixing scheme suggests that $a_0(980)$ and $a_0(1450)$ are the tetraquarks with the mixtures of two spin configurations of diquark and antidiquark. Due to the relative sign differences in the mixtures, the couplings of fall-apart decays into two mesons are strongly enhanced for $a_0(980)$ but suppressed for $a_0(1450)$. We report that this expectation is supported by their experimental decays. In particular, the ratios of the associated partial decay widths, which depend on some kinematical factors and the couplings, are found to be around $\Gamma [a_0(980)\rightarrow \pi \eta]/\Gamma [a_0(1450)\rightarrow \pi \eta] = 2.51-2.54$, $\Gamma [a_0(980)\rightarrow K\bar{K}]/\Gamma [a_0(1450)\rightarrow K\bar{K}] = 0.52-0.89$, which seems to agree with the experimental ratios reasonably well. This agreement can be interpreted as the tetraquark signatures for $a_0(980), a_0(1450)$.Comment: 6 pages, no figures, more references are added, the version to be published in EPJ

Z_{12-I} Orbifold Compactification toward SUSY Standard Model

We explain the orbifold compactification in string models and present a Z_{12-I} orbifold compactification toward supersymmetric standard models. We also point out an effective R-parity from this string construction. The VEVs of gauge singlets are chosen such that phenomenological constraints are satisfied.Comment: 13 pages with 5 figure. Talk presented at "CTP Symposium on SUSY at LHC", Cairo, 11-14 March 200

Effective Action for the Scalar Field Theory with Higher Vertices

We derive a new kind of recursion relation to obtain the one-particle-irreducible (1PI) Feynman diagrams for the effective action. By using this method, we have obtained the graphical representation of the four-loop effective action in case of the general bosonic field theory which have vertices higher than the four-point vertex

Semidirect Product Groups, Vacuum Alignment and Tribimaximal Neutrino Mixing

The neutrino oscillation data are in very good agreement with the tribimaximal mixing pattern: \sin^2\theta_{23}=1/2, \sin^2\theta_{12}=1/3, and \sin^2\theta_{13}=0. Attempts to generate this pattern based on finite family symmetry groups typically assume that the family symmetry is broken to different subgroups in the charged lepton and the neutrino mass matrices. This leads to a technical problem, where the cross-couplings between the Higgs fields responsible for the two symmetry breaking chains force their vacuum expectation values to align, upsetting the desired breaking pattern. Here, we present a class of models based on the semidirect product group (S_3)^4 \rtimes A_4, where the lepton families belong to representations which are not faithful. In effect, the Higgs sector knows about the full symmetry while the lepton sector knows only about the A_4 factor group. This can solve the alignment problem without altering the desired properties of the family symmetry. Inclusion of quarks into the framework is straightforward, and leads to small and arbitrary CKM mixing angles. Supersymmetry is not essential for our proposal, but the model presented is easily supersymmetrized, in which case the same family symmetry solves the SUSY flavor problem.Comment: Typos fixed, 26 pages in LaTe

Minimax bounds for estimation of normal mixtures

This paper deals with minimax rates of convergence for estimation of density functions on the real line. The densities are assumed to be location mixtures of normals, a global regularity requirement that creates subtle difficulties for the application of standard minimax lower bound methods. Using novel Fourier and Hermite polynomial techniques, we determine the minimax optimal rate - slightly larger than the parametric rate - under squared error loss. For Hellinger loss, we provide a minimax lower bound using ideas modified from the squared error loss case.Comment: Published in at http://dx.doi.org/10.3150/13-BEJ542 the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm

Boltzmann Equation with a Large Potential in a Periodic Box

The stability of the Maxwellian of the Boltzmann equation with a large amplitude external potential $\Phi$ has been an important open problem. In this paper, we resolve this problem with a large $C3-$potential in a periodic box $\mathbb{T}^d$, $d \geq 3$. We use [1] in $L^p-L^{\infty}$ framework to establish the well-posedness and the $L^{\infty}-$stability of the Maxwellian $\mu_E(x,v)=\exp\{-\frac{|v|^2}{2}-\Phi(x)\}$

Compositional changes on GaN surfaces under low-energy ion bombardment studied by synchrotron-based spectroscopies

We have investigated compositional changes on GaNsurfaces under Ar-ion bombardment using synchrotron-based high-resolution x-rayphotoemission (PES) and near-edge x-ray absorption fine structure(NEXAFS)spectroscopy. The low-energy ion bombardment of GaN produces a Ga-rich surface layer which transforms into a metallic Ga layer at higher bombarding energies. At the same time, the photoemissionspectra around N 1s core levels reveal the presence of both uncoordinated nitrogen and nitrogen interstitials, which we have analyzed in more details by x-rayabsorption measurements at N K edge. We have demonstrated that PES and NEXAFS provide a powerful combination for studying the compositional changes on GaNsurfaces. A mechanism for the relocation and loss of nitrogen during ion bombardment in agreement with some recent experimental and theoretical studies of defect formation in GaN has been proposed.P.N.K.D. is grateful for the financial support of the Australian Research Council