Modification of as-cast Al-Mg/B4C composite by addition of Zr

Zirconium was used in Al-Mg/B4C composite to improve compocasting efficiency by increasing particle incorporation. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) results revealed that by addition of zirconium a reaction layer containing Zr, Al, B and C is formed on the interface of B4C-matrix. X-ray diffraction (XRD) analysis of extracted particles unveiled that the ZrB2 phase is the main constituent of this layer. Formation of ZrB2 is an exothermic reaction which can rise temperature locally around particles and agglomerates. Rising temperature around agglomerates in conjunction with turbulent flow of melt facilitates agglomerates wetting and dissolving into molten aluminum. As the result, final product contains more uniformly distributed B4C particles. Besides enhancing compocasting efficiency, addition of Zr and formation of reaction layer by improving particle matrix bonding quality, led to increase in ultimate tensile strength and elongation of the composite around 8% and 30%, respectively. SEM observations of the fracture surfaces confirmed that a proper bonding presents at the interface of particles and matrix in presence of Zr.Peer ReviewedPostprint (author's final draft

The Littlest Higgs

We present an economical theory of natural electroweak symmetry breaking, generalizing an approach based on deconstruction. This theory is the smallest extension of the Standard Model to date that stabilizes the electroweak scale with a naturally light Higgs and weakly coupled new physics at TeV energies. The Higgs is one of a set of pseudo Goldstone bosons in an $SU(5)/SO(5)$ nonlinear sigma model. The symmetry breaking scale $f$ is around a TeV, with the cutoff \Lambda \lsim 4\pi f \sim 10 TeV. A single electroweak doublet, the ``little Higgs'', is automatically much lighter than the other pseudo Goldstone bosons. The quartic self-coupling for the little Higgs is generated by the gauge and Yukawa interactions with a natural size $O(g^2,\lambda_t^2)$, while the top Yukawa coupling generates a negative mass squared triggering electroweak symmetry breaking. Beneath the TeV scale the effective theory is simply the minimal Standard Model. The new particle content at TeV energies consists of one set of spin one bosons with the same quantum numbers as the electroweak gauge bosons, an electroweak singlet quark with charge 2/3, and an electroweak triplet scalar. One loop quadratically divergent corrections to the Higgs mass are cancelled by interactions with these additional particles.Comment: 15 pages. References added. Corrected typos in the discussion of the top Yukawa couplin

Thermal conductivity of anisotropic spin - 1/2 two leg ladder:Green's function approach

We study the thermal transport of a spin-1/2 two leg antiferromagnetic ladder in the direction of legs. The possible effect of spin-orbit coupling and crystalline electric field are investigated in terms of anisotropies in the Heisenberg interactions on both leg and rung couplings. The original spin ladder is mapped to a bosonic model via a bond-operator transformation where an infinite hard-core repulsion is imposed to constrain one boson occupation per site. The Green's function approach is applied to obtain the energy spectrum of quasi-particle excitations responsible for thermal transport. The thermal conductivity is found to be monotonically decreasing with temperature due to increased scattering among triplet excitations at higher temperatures. A tiny dependence of thermal transport on the anisotropy in the leg direction at low temperatures is observed in contrast to the strong one on the anisotropy along the rung direction, due to the direct effect of the triplet density. Our results reach asymptotically the ballistic regime of the spin - 1/2 Heisenberg chain and compare favorably well with exact diagonalization data

Collective Quartics and Dangerous Singlets in Little Higgs

Any extension of the standard model that aims to describe TeV-scale physics without fine-tuning must have a radiatively-stable Higgs potential. In little Higgs theories, radiative stability is achieved through so-called collective symmetry breaking. In this letter, we focus on the necessary conditions for a little Higgs to have a collective Higgs quartic coupling. In one-Higgs doublet models, a collective quartic requires an electroweak triplet scalar. In two-Higgs doublet models, a collective quartic requires a triplet or singlet scalar. As a corollary of this study, we show that some little Higgs theories have dangerous singlets, a pathology where collective symmetry breaking does not suppress quadratically-divergent corrections to the Higgs mass.Comment: 4 pages; v2: clarified the existing literature; v3: version to appear in JHE

Phenomenology of the Littlest Higgs with T-Parity

Little Higgs models offer an interesting approach to weakly coupled electroweak symmetry breaking without fine tuning. The original little Higgs models were plagued by strong constraints from electroweak precision data which required a fine tuning to be reintroduced. An economical solution to this problem is to introduce a discrete symmetry (analogous to R-parity of SUSY) called T-parity. T-parity not only eliminates most constraints from electroweak precision data, but it also leads to a promising dark matter candidate. In this paper we investigate the dark matter candidate in the littlest Higgs model with T-parity. We find bounds on the symmetry breaking scale f as a function of the Higgs mass by calculating the relic density. We begin the study of the LHC phenomenology of the littlest Higgs model with T-parity. We find that the model offers an interesting collider signature that has a generic missing energy signal which could "fake" SUSY at the LHC. We also investigate the properties of the heavy partner of the top quark which is common to all littlest Higgs models, and how its properties are modified with the introduction of T-parity. We include an appendix with a list of Feynman rules specific to the littlest Higgs with T-parity to facilitate further study.Comment: 32 pages, 8 figures; dark matter bounds revised; comphep model files made publicly available at http://www.lns.cornell.edu/public/theory/tparity

Constraining the Littlest Higgs

Little Higgs models offer a new way to address the hierarchy problem, and give rise to a weakly-coupled Higgs sector. These theories predict the existence of new states which are necessary to cancel the quadratic divergences of the Standard Model. The simplest version of these models, the Littlest Higgs, is based on an $SU(5)/SO(5)$ non-linear sigma model and predicts that four new gauge bosons, a weak isosinglet quark, $t'$, with $Q=2/3$, as well as an isotriplet scalar field exist at the TeV scale. We consider the contributions of these new states to precision electroweak observables, and examine their production at the Tevatron. We thoroughly explore the parameter space of this model and find that small regions are allowed by the precision data where the model parameters take on their natural values. These regions are, however, excluded by the Tevatron data. Combined, the direct and indirect effects of these new states constrain the `decay constant' f\gsim 3.5 TeV and m_{t'}\gsim 7 TeV. These bounds imply that significant fine-tuning be present in order for this model to resolve the hierarchy problem.Comment: 31 pgs, 26 figures; bound on t' mass fixed to mt'>2f, conclusions unchange

Ancilla-assisted sequential approximation of nonlocal unitary operations

We consider the recently proposed "no-go" theorem of Lamata et al [Phys. Rev. Lett. 101, 180506 (2008)] on the impossibility of sequential implementation of global unitary operations with the aid of an itinerant ancillary system and view the claim within the language of Kraus representation. By virtue of an extremely useful tool for analyzing entanglement properties of quantum operations, namely, operator-Schmidt decomposition, we provide alternative proof to the "no-go" theorem and also study the role of initial correlations between the qubits and ancilla in sequential preparation of unitary entanglers. Despite the negative response from the "no-go" theorem, we demonstrate explicitly how the matrix-product operator(MPO) formalism provides a flexible structure to develop protocols for sequential implementation of such entanglers with an optimal fidelity. The proposed numerical technique, that we call variational matrix-product operator (VMPO), offers a computationally efficient tool for characterizing the "globalness" and entangling capabilities of nonlocal unitary operations.Comment: Slightly improved version as published in Phys. Rev.

Matrix Gravity and Massive Colored Gravitons

We formulate a theory of gravity with a matrix-valued complex vierbein based on the SL(2N,C)xSL(2N,C) gauge symmetry. The theory is metric independent, and before symmetry breaking all fields are massless. The symmetry is broken spontaneously and all gravitons corresponding to the broken generators acquire masses. If the symmetry is broken to SL(2,C) then the spectrum would correspond to one massless graviton coupled to $2N^2 -1$ massive gravitons. A novel feature is the way the fields corresponding to non-compact generators acquire kinetic energies with correct signs. Equally surprising is the way Yang-Mills gauge fields acquire their correct kinetic energies through the coupling to the non-dynamical antisymmetric components of the vierbeins.Comment: One reference adde

Synthesis ,Characterization and invitro evaluation of anticancer activity of new hydroxamicacid basedHDACi containing substituted thaizolesas a cap linking moiety.

The present study was undertaken to synthesize, characterize  and evaluate the anticancer activity of  new derivatives of hydroxamate –based HDACi  having S-subistituted-5-amino1,3,4thadiazole as a cap linking moiety ,with suitable aliphatic linker.The structures and purity of the targeted compounds were confirmed by TLC , FTIR ,H-NMR and mass spectroscopy and their anticancer activity were evaluated by comparative cytotoxic study , Using HeLa nuclear extract and normal embryonic fibroblasts cell lines.All the synthesized compounds shows good anticancer activity, represented by their high rate of growth inhibition on Hela cell line and low cytotocic effect on normal cell line .Compound (VAb) show the best safety index(SI) that represented by its  selective cytotoxic activity on HeLa cell linewith  low cytotoxic effect on normal embryonic cell line

The Littlest Higgs in Anti-de Sitter Space

We implement the SU(5)/SO(5) littlest Higgs theory in a slice of 5D Anti-de Sitter space bounded by a UV brane and an IR brane. In this model, there is a bulk SU(5) gauge symmetry that is broken to SO(5) on the IR brane, and the Higgs boson is contained in the Goldstones from this breaking. All of the interactions on the IR brane preserve the global symmetries that protect the Higgs mass, but a radiative potential is generated through loops that stretch to the UV brane where there are explicit SU(5) violating boundary conditions. Like the original littlest Higgs, this model exhibits collective breaking in that two interactions must be turned on in order to generate a Higgs potential. In AdS space, however, collective breaking does not appear in coupling constants directly but rather in the choice of UV brane boundary conditions. We match this AdS construction to the known low energy structure of the littlest Higgs and comment on some of the tensions inherent in the AdS construction. We calculate the 5D Coleman-Weinberg effective potential for the Higgs and find that collective breaking is manifest. In a simplified model with only the SU(2) gauge structure and the top quark, the physical Higgs mass can be of order 200 GeV with no considerable fine tuning (25%). We sketch a more realistic model involving the entire gauge and fermion structure that also implements T-parity, and we comment on the tension between T-parity and flavor structure.Comment: 42 pages, 7 figures, 3 tables; v2: minor rewording, JHEP format; v3: to match JHEP versio