Model independent bounds on the modulus of the pion form factor on the unitarity cut below the omega pi threshold

We calculate upper and lower bounds on the modulus of the pion electromagnetic form factor on the unitarity cut below the omega pi inelastic threshold, using as input the phase in the elastic region known via the Fermi-Watson theorem from the pi pi P-wave phase shift, and a suitably weighted integral of the modulus squared above the inelastic threshold. The normalization at t = 0, the pion charge radius and experimental values at spacelike momenta are used as additional input information. The bounds are model independent, in the sense that they do not rely on specific parametrizations and do not require assumptions on the phase of the form factor above the inelastic threshold. The results provide nontrivial consistency checks on the recent experimental data on the modulus available below the omega pi threshold from e(+)e(-) annihilation and tau-decay experiments. In particular, at low energies the calculated bounds offer a more precise description of the modulus than the experimental data.

125 GeV Higgs state in the context of four generations with two Higgs doublets

We interpret the recent discovery of a 125 GeV Higgs-like state in the context of a two-Higgs-doublet model with a heavy fourth sequential generation of fermions, in which one Higgs doublet couples only to the fourth-generation fermions, while the second doublet couples to the lighter fermions of the first three families. This model is designed to accommodate the apparent heaviness of the fourth-generation fermions and to effectively address the low-energy phenomenology of a dynamical electroweak-symmetry-breaking scenario. The physical Higgs states of the model are, therefore, viewed as composites primarily of the fourth-generation fermions. We find that the lightest Higgs, h, is a good candidate for the recently discovered 125 GeV spin-zero particle, when tan beta similar to O(1), for typical fourth-generation fermion masses of M-4G = 400-600 GeV, and with a large t-t' mixing in the right-handed quark sector. This, in turn, leads to BR(t' -> th) similar to O(1), which drastically changes the t' decay pattern. We also find that, based on the current Higgs data, this two-Higgs-doublet model generically predicts an enhanced production rate (compared to the Standard Model) in the pp -> h -> tau tau channel, and reduced rates in the VV -> h -> gamma gamma and p (p) over bar /pp -> V -> hV -> Vbb channels. Finally, the heavier CP-even Higgs is excluded by the current data up to m(H) similar to 500 GeV, while the pseudoscalar state, A, can be as light as 130 GeV. These heavier Higgs states and the expected deviations from the Standard Model din some of the Higgs production channels can be further excluded or discovered with more data.

A LOWER INITIAL ABUNDANCE OF SHORT-LIVED Ca-41 IN THE EARLY SOLAR SYSTEM AND ITS IMPLICATIONS FOR SOLAR SYSTEM FORMATION

The short-lived radionuclide Ca-41 plays an important role in constraining the immediate astrophysical environment and the formation timescale of the nascent solar system due to its extremely short half-life (0.1 Myr). Nearly 20 years ago, the initial ratio of Ca-41/Ca-40 in the solar system was determined to be (1.41 +/- 0.14) x 10(-8), primarily based on two Ca-Al-rich Inclusions (CAIs) from the CV chondrite Efremovka. With an advanced analytical technique for isotopic measurements, we reanalyzed the potassium isotopic compositions of the two Efremovka CAIs and inferred the initial ratios of Ca-41/Ca-40 to be (2.6 +/- 0.9) x 10(-9) and (1.4 +/- 0.6) x 10(-9) (2 sigma), a factor of 7-10 lower than the previously inferred value. Considering possible thermal processing that led to lower Al-26/Al-27 ratios in the two CAIs, we propose that the true solar system initial value of Ca-41/Ca-40 should have been similar to 4.2 x 10(-9). Synchronicity could have existed between Al-26 and Ca-41, indicating a uniform distribution of the two radionuclides at the time of CAI formation. The new initial Ca-41 abundance is 4-16 times lower than the calculated value for steady-state galactic nucleosynthesis. Therefore, Ca-41 could have originated as part of molecular cloud materials with a free decay time of 0.2-0.4 Myr. Alternative possibilities, such as a last-minute input from a stellar source and early solar system irradiation, could not be definitively ruled out. This underscores the need for more data from diverse CAIs to determine the true astrophysical origin of Ca-41.

High precision Mg isotope measurements of meteoritic samples by secondary ion mass spectrometry

The possibility of establishing an accurate relative chronology of the early solar system events based on the decay of short-lived Al-26 to Mg-26 (half-life of 0.72 Myr) depends on the level of homogeneity (or heterogeneity) of Al-26 and Mg isotopes. However, this level is difficult. to constrain precisely because of the very high precision needed for the determination of isotopic ratios, typically of +/- 5 ppm. In this study, we report for the first time a detailed analytical protocol developed for high precision in situ Mg isotopic measurements ((25)mg/(24)mg and (26)mg/Mg-24 ratios, as well as Mg-26 excess) by MC-SIMS. As the data reduction process is critical for both accuracy and precision of the final isotopic results, factors such as the Faraday cup (FC) background drift and matrix effects on instrumental fractionation have been investigated. Indeed these instrumental effects impacting the measured Mg-isotope ratios can be as large or larger than the variations we are looking for to constrain the initial distribution of Al-26 and Mg isotopes in the early solar system. Our results show that they definitely are limiting factors regarding the precision of Mg isotopic compositions, and that an under- or over-correction of both FC background instabilities and instrumental isotopic fractionation leads to important bias on delta Mg-25, delta(26)mg and Delta Mg-26 values (for example, olivines not corrected for FC background drifts display Delta Mg-26 values that can differ by as much as 10 ppm from the truly corrected value). The new data reduction process described here can then be applied to meteoritic samples (components of chondritic meteorites for instance) to accurately establish their relative chronology of formation.

Queueing delay - error probability tradeoff for point-to-point channels with fixed length block codes

We study the tradeoff between the average error probability and the average queueing delay of messages which randomly arrive to the transmitter of a point-to-point discrete memoryless channel that uses variable rate fixed codeword length random coding. Bounds to the exponential decay rate of the average error probability with average queueing delay in the regime of large average delay are obtained. Upper and lower bounds to the optimal average delay for a given average error probability constraint are presented. We then formulate a constrained Markov decision problem for characterizing the rate of transmission as a function of queue size given an average error probability constraint. Using a Lagrange multiplier the constrained Markov decision problem is then converted to a problem of minimizing the average cost for a Markov decision problem. A simple heuristic policy is proposed which approximately achieves the optimal average cost.

Some implications of lepton flavor violating processes in a supersymmetric Type II seesaw model at TeV scale

We have conceived a supersymmetric Type II seesaw model at TeV scale, which has some additional particles consisting of scalar and fermionic triplet Higgs states, whose masses are around a few hundred GeV. In this particular model, we have studied constraints on the masses of triplet states arising from the lepton flavor violating (LFV) processes, such as mu -> 3e and mu -> e gamma. We have analyzed the implications of these constraints on other observable quantities such as the muon anomalous magnetic moment and the decay patterns of scalar triplet Higgses. Scalar triplet Higgs states can decay into leptons and into supersymmetric fields. We have found that the constraints from LFV can affect these various decay modes.

Crow instability in unitary Fermi gas

In this paper, we investigate the initiation and subsequent evolution of Crow instability in an inhomogeneous unitary Fermi gas using zero-temperature Galilei-invariant nonlinear Schrodinger equation. Considering a cigar-shaped unitary Fermi gas, we generate the vortex-antivortex pair either by phase-imprinting or by moving a Gaussian obstacle potential. We observe that the Crow instability in a unitary Fermi gas leads to the decay of the vortex-antivortex pair into multiple vortex rings and ultimately into sound waves.

Invisible decays of the lightest Higgs boson in supersymmetric models

We consider supersymmetric models in which the lightest Higgs scalar can decay invisibly consistent with the constraints on the 126 GeV state discovered at the CERN LHC. We consider the invisible decay in the minimal supersymmetric standard model (MSSM), as well its extension containing an additional chiral singlet superfield, the so-called next-to-minimal or nonminimal supersymmetric standard model (NMSSM). We consider the case of MSSM with both universal as well as nonuniversal gaugino masses at the grand unified scale, and find that only an E-6 grand unified model with unnaturally large representation can give rise to sufficiently light neutralinos which can possibly lead to the invisible decay h(0) -> (chi) over tilde (0)(1)(chi) over tilde (0)(1). Following this, we consider the case of NMSSM in detail, where we also find that it is not possible to have the invisible decay of the lightest Higgs scalar with universal gaugino masses at the grand unified scale. We delineate the regions of the NMSSM parameter space where it is possible for the lightest Higgs boson to have a mass of about 126 GeV, and then concentrate on the region where this Higgs can decay into light neutralinos, with the soft gaugino masses M-1 and M-2 as two independent parameters, unconstrained by grand unification. We also consider, simultaneously, the other important invisible Higgs decay channel in the NMSSM, namely the decay into the lightest CP-odd scalars, h(1) -> a(1)a(1), which is studied in detail. With the invisible Higgs branching ratio being constrained by the present LHC results, we find that mu(eff) < 170 GeV and M-1 < 80 GeV are disfavored in NMSSM for fixed values of the other input parameters. The dependence of our results on the parameters of NMSSM is discussed in detail.

Top polarization in stop production at the LHC

We survey the expected polarization of the top produced in the decay of a scalar top quark, t -> t((chi) over tildei)(0), i = 1 - 2. The phenomenology is quite interesting, since the expected polarization depends both on the mixing in the stop and neutralino sectors and on the mass differences between the stop and the neutralino. We find that a mixed stop behaves almost like a right-handed stop due to the larger hypercharge that enters the stop/top/gaugino coupling and that these polarisation effects disappear, when m((t) over tilde1) approximate to m(t) +m((chi) over tildei)(0). After a discussion on the expected top polarization from the decay of a scalar top quark, we focus on the interplay of polarization and kinematics at the LHC. We discuss different probes of the top polarization in terms of lab-frame observables. We find that these observables faithfully reflect the polarization of the parent top-quark, but also have a non-trivial dependence on the kinematics of the stop production and decay process. In addition, we illustrate the effect of top polarization on the energy and transverse momentum of the decay lepton in the laboratory frame. Our results show that both spectra are softened substantially in case of a negatively polarized top, particularly for a large mass difference between the stop and the neutralino. Thus, the search strategies, and the conclusions that can be drawn from them, depends not just on the mass difference m((t) over tilde) - m((chi) over tildei)(0) due to the usual kinematic effects but also on the effects of top polarization on the decay kinematics the extent of which depends in turn on the said mass difference.

Near-infrared photoactive Cu2ZnSnS4 thin films by co-sputtering

The thin films of Cu2ZnSnS4 (CZTS) were grown by co-sputtering further the structural, optical and electrical properties were analyzed and confirmed the CZTS phase formation. The photo response of CZTS in near IR photodectection has been demonstrated. The detector response was measured employing both the IR lamp and IR laser illuminations. The calculated growth and decay constants were 130 m sec and 700 m sec followed by the slower components upon lamp illumination. The external quantum efficiency of 15%, responsivity of 13 AW(-1) makes CZTS a suitable candidate for the IR photodectection.

Looking for an invisible Higgs signal at the LHC

While the recent discovery of a Higgs-like boson at the LHC is an extremely important and encouraging step towards the discovery of the complete Standard Model (SM), the current information on this state does not rule out possibility of beyond standard model (BSM) physics. In fact the current data can still accommodate reasonably large values of the branching fractions of the Higgs into a channel with `invisible' decay products, such a channel being also well motivated theoretically. In this study we revisit the possibility of detecting the Higgs in this invisible channel for both choices of the LHC energies, 8 and 14 TeV, for two production modes; vector boson fusion (VBF) and associated production (ZH). We perform a comprehensive collider analysis for all the above channels and project the reach of LHC to constrain the invisible decay branching fraction for both 8 and 14 TeV energies. For the ZH case we consider decays of the Z boson into a pair of leptons as well as a b (b) over bar pair. For the VBF channel the sensitivity is found to be more than 5 sigma for both the energies up to an invisible branching ratio (Br-inv) similar to 0.80, with luminosities similar to 20/30 fb(-1). The sensitivity is further extended to values of Br-inv similar to 0.25 for 300 fb(-1) at 14 TeV. However the reach is found to be more modest for the ZH mode with leptonic final state; with about 3.5 sigma for the planned luminosity at 8 TeV, reaching 8 sigma only for 14 TeV for 50 fb(-1). In spite of the much larger branching ratio (BR) of the Z into a b (b) over bar channel compared to the dilepton case, the former channel, can provide useful reach up to Br-inv greater than or similar to 0.75, only for the higher luminosity (300 fb(-1)) option using both jet-substructure and jet clustering methods. (C) 2013 Elsevier B.V. All rights reserved.

Constraints on Be-10 and Ca-41 distribution in the early solar system from Al-26 and Be-10 studies of Efremovka CAIs

Three refractory coarse grained CAIs from the Efremovka CV3 chondrite, one (E65) previously shown to have formed with live Ca-41, were studied by ion microprobe for their Al-26-Mg-26 and Be-10-B-10 systematic in order to better understand the origin of Be-10. The high precision Al-Mg data and the inferred Al-26/Al-27 values attest that the precursors of the three CAIs evolved in the solar nebula over a period of few hundred thousand years before last melting-crystallization events. The initial Be-10/Be-9 ratios and delta B-10 values defined by the Be-10 isochrons for the three Efremovka CAIs are similar within errors. The CAI Be-10 abundance in published data underscores the large range for initial Be-10/Be-9 ratios. This is contrary to the relatively small range of Al-26/Al-27 variations in CAIs around the canonical ratio. Two models that could explain the origin of this large Be-10/Be-9 range are assessed from the collateral variations predicted for the initial delta B-10 values: (i) closed system decay of Be-10 from a ``canonical'' Be-10/Be-9 ratio and (ii) formation of CAIs from a mixture of solid precursors and nebula gas irradiated during up to a few hundred thousand years. The second scenario is shown to be the most consistent with the data. This shows that the major fraction of Be-10 in CAIs was produced by irradiation of refractory grains, while contributions of galactic cosmic rays trapping and early solar wind irradiation are less dominant. The case for Be-10 production by solar cosmic rays irradiation of solid refractory precursors poses a conundrum for Ca-41 because the latter is easily produced by irradiation and should be more abundant than what is observed in CAIs. Be-10 production by irradiation from solar energetic particles requires high Ca-41 abundance in early solar system, however, this is not observed in CAIs. (C) 2013 Elsevier B.V. All rights reserved.

Beam polarization effects in the radiative production of lightest neutralinos in e(+)e(-) collisions in supersymmetric grand unified models

We study the production of the lightest neutralinos in the process e(+)e(-) -> chi(0)(1)chi(0)(1)gamma in supersymmetric grand unified models for the International Linear Collider energies with longitudinally polarized beams. We consider cases where the standard model gauge group is unified into the grand unified gauge groups SU(5), or SO(10). We have carried out a comprehensive study of this process in the SU(5) and SO(10) grand unified theories which includes the QED radiative corrections. We compare and contrast the dependence of the signal cross section on the grand unified gauge group, and on the different representations of the grand unified gauge group, when the electron and positron beams are longitudinally polarized. To assess the feasibility of experimentally observing the radiative production process, we have also considered in detail the background to this process coming from the radiative neutrino production process e(+)e(-)-> nu(nu) over bar gamma with longitudinally polarized electron and positron beams. In addition we have also considered the supersymmetric background coming from the radiative production of scalar neutrinos in the process e(+)e(-) -> (nu) over tilde(nu) over tilde*gamma with longitudinally polarized beams. The process can be a major background to the radiative production of neutralinos when the scalar neutrinos decay invisibly.

Temporal Envelope Fit of Transient Audio Signals

We address the problem of temporal envelope modeling for transient audio signals. We propose the Gamma distribution function (GDF) as a suitable candidate for modeling the envelope keeping in view some of its interesting properties such as asymmetry, causality, near-optimal time-bandwidth product, controllability of rise and decay, etc. The problem of finding the parameters of the GDF becomes a nonlinear regression problem. We overcome the hurdle by using a logarithmic envelope fit, which reduces the problem to one of linear regression. The logarithmic transformation also has the feature of dynamic range compression. Since temporal envelopes of audio signals are not uniformly distributed, in order to compute the amplitude, we investigate the importance of various loss functions for regression. Based on synthesized data experiments, wherein we have a ground truth, and real-world signals, we observe that the least-squares technique gives reasonably accurate amplitude estimates compared with other loss functions.

Facile synthesis of Cu2CoSnS4 nanoparticles exhibiting red-edge-effect: Application in hybrid photonic devices

Cu2CoSnS4 (CCTS) quaternary semiconducting nanoparticles with size distribution from 20 nm to 60 nm were synthesized by one-pot low temperature time and surfactant dependent hydrothermal route. Nanoparticles were characterized structurally and optically. Excitation dependent fluorescence exhibited a dynamic stoke shift referring to the Red-Edge-Effect with peak shifting by a greater magnitude (>100 nm) towards red side, in all the samples. Hybrid devices, fabricated from CCTS nanoparticle inorganic counterparts benefitting from the conjugation of organic P3HT polymer matrix, were demonstrated for photodetection under infra-red and A. M 1.5 solar light illuminations. Faster rise and decay constants of 37 ms and 166 ms, with one order photocurrent amplification from 1.6 x 10(-6) A in the dark to 6.55 x 10(-5) A, upon the 18.50 mW cm(-2) IR lamp illumination, make CCTS a potential candidate for photodetector and photovoltaic applications. (C) 2013 AIP Publishing LLC.