Gluino mass limits with sbottom NLSP in coannihilation scenarios

In view of the recent interest in the pMSSM with light third generation squarks, we consider a hitherto neglected scenario where the lighter bottom squark ($\widetilde{b}_1$) is the next lightest supersymmetric particle (NLSP) which co-annihilates with the lightest supersymmetric particle (LSP), the dark matter (DM) candidate. Since the co-annihilation cross section receives contributions from both electroweak and strong vertices, it is relatively large. As a result relatively large NLSP-LSP mass difference (25 - 35 GeV) is consistent with the PLANCK data. This facilitates the LHC signatures of this scenario. We consider several variants of the sbottom NLSP scenario with and without light stops and delineate the parameter space allowed by the PLANCK data. We point out several novel signal (e.g., $\widetilde{t}_1 \rightarrow \widetilde{b}_1 W$) which are not viable in the stop NLSP scenario of DM production. Finally, we consider gluino ($\widetilde g$) decays in this scenario and using the current ATLAS data in the jets (with or without b-tagging) + $\not \!\! E_T$ channel, obtain new limits in the $m_{\widetilde{b}_1} - m_{\widetilde g}$ mass plane. We find that for $m_{\widetilde{b}_1}$ upto 500 GeV, $m_{\widetilde g} \geq$ 1.1 - 1.2 TeV in this scenario.Comment: 21 pages, 4 figures, few references added; published in JHE

Additivity property and emergence of power laws in nonequilibrium steady states

We show that an equilibriumlike additivity property can remarkably lead to power-law distributions observed frequently in a wide class of out-of-equilibrium systems. The additivity property can determine the full scaling form of the distribution functions and the associated exponents. The asymptotic behavior of these distributions is solely governed by branch-cut singularity in the variance of subsystem mass. To substantiate these claims, we explicitly calculate, using the additivity property, subsystem mass distributions in a wide class of previously studied mass aggregation models as well as in their variants. These results could help in the thermodynamic characterization of nonequilibrium critical phenomena.Comment: Revised longer version, 4 figure

Effect of iron oxide and gold nanoparticles on bacterial growth leading towards biological application

<p>Abstract</p> <p>Background</p> <p>Nanoparticle-metal oxide and gold represents a new class of important materials that are increasingly being developed for use in research and health related activities. The biological system being extremely critical requires the fundamental understanding on the influence of inorganic nanoparticles on cellular growth and functions. Our study was aimed to find out the effect of iron oxide (Fe₃O₄), gold (Au) nanoparticles on cellular growth of <it>Escherichia coli </it>(<it>E. coli</it>) and also try to channelize the obtained result by functionalizing the Au nanoparticle for further biological applications.</p> <p>Result</p> <p>Fe₃O₄and Au nanoparticles were prepared and characterized using Transmission electron microscopy (TEM) and Dynamic Light Scattering (DLS). Preliminary growth analysis data suggest that the nanoparticles of iron oxide have an inhibitory effect on E. coli in a concentration dependant manner, whereas the gold nanoparticle directly showed no such activity. However the phase contrast microscopic study clearly demonstrated that the effect of both Fe₃O₄and Au nanoparticle extended up to the level of cell division which was evident as the abrupt increase in bacterial cell length. The incorporation of gold nanoparticle by bacterial cell was also observed during microscopic analysis based on which glutathione functionalized gold nanoparticle was prepared and used as a vector for plasmid DNA transport within bacterial cell.</p> <p>Conclusion</p> <p>Altogether the study suggests that there is metal nanoparticle-bacteria interaction at the cellular level that can be utilized for beneficial biological application but significantly it also posses potential to produce ecotoxicity, challenging the ecofriendly nature of nanoparticles.</p

Seismic response analysis of steel plate shear wall systems using detailed and simplified models

Ductile Steel Plate Shear Walls (SPSWs) have been accepted widely as a very effective lateral load resisting system. However, their use in retrofit works is very limited because of the design inefficiency arising from the use of thicker than required commercially available infill plates. Consequently the ductility demand for the surrounding framing members is higher than required. SPSWs utilizing light-gauge cold-formed infill plates could be a viable alternative for rehabilitation of seismically deficient buildings. This thesis presents a numerical study using finite element models on the behavior of unstiffened light-gauge steel plate shear walls with welded infill plate connection. The detailed finite element models include both material and geometric non-linearity. This research describes in detail the validation of the key finite element models by comparing the results with that from the available experimental studies. Excellent correlation between the test results and the finite element analysis results has been achieved. For seismic performance evaluation of a multi-storey building with SPSWs, detailed finite element models or a strip model can be used to represent the SPSW components. However, development and analysis of such models often require undesirable effort and excess time for high-to-medium rise buildings. A simplified model is developed in this research to study the behavior of SPSW system. In the simplified model, discrete elements are used for the framing members and the behavior of the infill plate is represented by equivalent diagonal bracing members. The simplified model, Equivalent Braced Model, is developed through repeated static and dynamic validations with experiment and detailed finite element models. The proposed Equivalent Braced Model would facilitate a simplification to the structural modeling of large buildings with SPSWs in order to evaluate the seismic performance using regular structural analysis tools and can prove to be a potential aid in performance-based seismic design of SPSW buildings. Finally, the developed equivalent braced model and the detailed finite element model are used to analyze three multi-storey light-gauge SPSWs (four-storey, six-storey and ten-storey) designed according to the capacity design approach

Scope of strongly self-interacting thermal WIMPs in a minimal U(1)DU(1)_D extension and its future prospects

In this work we have considered a minimal extension of Standard Model by a local $U(1)$ gauge group in order to accommodate a stable (fermionic) Dark Matter (DM) candidate. We have focussed on parameter regions where DM possesses adequate self interaction, owing to the presence of a light scalar mediator (the dark Higgs), alleviating some of the tensions in the small-scale structures. We have studied the scenario in the light of a variety of data, mostly from dark matter direct searches, collider searches and flavour physics experiments, with an attempt to constrain the interactions of the standard model (SM) particles with the ones in the Dark Sector (DS). Assuming a small gauge kinetic mixing parameter, we find that for rather heavy DM %$\gtrsim \mathcal{O}(1-10)\,\, {\rm GeV}$%, the most stringent bound on the mixing angle of the Dark Higgs with the SM Higgs boson comes from dark matter direct detection experiments, while for lighter DM, LHC constraints become more relevant. Note that, due to the presence of very light mediators the usual realisation of direct detection constraints in terms of momentum independent cross sections had to be reevaluated for our scenario. In addition, we find that the smallness of the relevant portal couplings, as dictated by data, critically suppress the viability of DM production by the standard "freeze-out" mechanism in such simplified scenarios. In particular, the viable DM masses are $\lesssim \mathcal{O}(2)$ GeV $i.e.$ in the regions where direct detection limits tend to become weak. For heavier DM with large self-interactions, we hence conclude that non-thermal production mechanisms are favoured. Lastly, future collider reach of such a simplified scenario has also been studied in detail.Comment: 63 pages, 21 figures, 7 table