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.

DETERMINATION OF THE STRONG COUPLING FROM HADRONIC TAU DECAYS USING RENORMALIZATION GROUP SUMMED PERTURBATION THEORY

Be the strong coupling constant alpha(s) from the tau hadronn width using a renormalization group summed (RGS) expansion of the QCD Adler lunction. The main theoretical uncertainty in the extraction of as is due to the manner in which renormalization group invariance is implemented, and the as yet uncalculated higher order terms in the QCD perturbative series. We show that new expansion exhibits good renormalization group improvement and the behavior of the series is similar to that of the standard RGS expansion. The value of the strong coupling in (MS) over bar scheme obtained with the RCS expansion is alpha(s) (M-tau(2)) = 0.338 +/- 0.010. The convergence properties of the new expansion can be improved by Bond transformation and analytic continuation in t he Bond plane. This is discussed elsewhere in these issues.

Establishing a Relation between the Mass and the Spin of Stellar-Mass Black Holes

Stellar mass black holes (SMBHs), forming by the core collapse of very massive, rapidly rotating stars, are expected to exhibit a high density accretion disk around them developed from the spinning mantle of the collapsing star. A wide class of such disks, due to their high density and temperature, are effective emitters of neutrinos and hence called neutrino cooled disks. Tracking the physics relating the observed (neutrino) luminosity to the mass, spin of black holes (BHs) and the accretion rate ((M) over dot) of such disks, here we establish a correlation between the spin and mass of SMBHs at their formation stage. Our work shows that spinning BHs are more massive than nonspinning BHs for a given (M) over dot. However, slowly spinning BHs can turn out to be more massive than spinning BHs if (M) over dot at their formation stage was higher compared to faster spinning BHs.

Dynamics of prolate spheroidal mass distributions with varying eccentricity

In this paper we calculate the potential for a prolate spheroidal distribution as in a dark matter halo with a radially varying eccentricity. This is obtained by summing up the shell-by-shell contributions of isodensity surfaces, which are taken to be concentric and with a common polar axis and with an axis ratio that varies with radius. Interestingly, the constancy of potential inside a shell is shown to be a good approximation even when the isodensity contours are dissimilar spheroids, as long as the radial variation in eccentricity is small as seen in realistic systems. We consider three cases where the isodensity contours are more prolate at large radii, or are less prolate or have a constant eccentricity. Other relevant physical quantities like the rotation velocity, the net orbital and vertical frequency due to the halo and an exponential disc of finite thickness embedded in it are obtained. We apply this to the kinematical origin of Galactic warp, and show that a prolate-shaped halo is not conducive to making long-lived warps - contrary to what has been proposed in the literature. The results for a prolate mass distribution with a variable axis ratio obtained are general, and can be applied to other astrophysical systems, such as prolate bars, for a more realistic treatment.

Simple theoretical analysis of the effective electron mass in semiconductor nanowires

In this paper we study the effective electron mass (EEM) in Nano wires (NWs) of nonlinear optical materials on the basis of newly formulated electron dispersion relation by considering all types of anisotropies of the energy band constants within the framework of k . p formalism. The results for NWs of III-V, ternary and quaternary semiconductors form special cases of our generalized analysis. We have also investigated the EEM in NWs of Bi, IV-VI, stressed Kane type materials, Ge, GaSb and Bi2Te3 by formulating the appropriate 1D dispersion law in each case by considering the influence of energy band constants in the respective cases. It has been found that the 1D EEM in nonlinear optical materials depend on the size quantum numbers and Fermi energy due to the anisotropic spin orbit splitting constant and the crystal field splitting respectively. The 1D EEM is Bi, IV-VI, stressed Kane type semiconductors and Ge also depends on both the Fermi energy and the size quantum numbers which are the characteristic features of such NWs. The EEM increases with increase in concentration and decreasing film thickness and for ternary and quaternary compounds the EEM increases with increase in alloy composition. Under certain special conditions all the results for all the materials get simplified into the well known parabolic energy bands and thus confirming the compatibility test.

Electric current-induced mass flow in very thin infinite metallic films

This paper reports on the mass transport behavior of infinitely extended, continuous, and very thin metallic films under the influence of electric current. Application of direct current of high densities (> 10(8) A/m(2)) results in visible melting of thin film at only one of the electrodes, and the melt then flows towards the other electrode in a circularly symmetric fashion forming a microscale ring pattern. For the two tested thin film systems, namely Cr and Al, of thicknesses ranging from 4 to 20 nm, the above directional flow consistently occurred from cathode to anode and anode to cathode, respectively. Furthermore, application of alternating electric current results in flow of the liquid material from both the electrodes. The dependence of critical flow behavior parameters, such as flow direction, flow velocity, and evolution of the ring diameter, are experimentally determined. Analytical models based on the principles of electromigration in liquid-phase materials are developed to explain the experimental observations.

Flow-enhanced pairing and other unusual effects in Fermi gases in synthetic gauge fields

Recent experiments on fermions in synthetic gauge fields result in systems with a spin-orbit coupling along one spatial axis, a detuning field, and a Zeeman field. We show theoretically that the presence of all three results in interesting and unusual phenomena in a system of interacting fermions (interactions described by a scattering length). For two fermions, bound states appear only over a certain range of the center-of-mass momenta. The deepest bound state appears at a nonzero center-of-mass momentum. For center-of-mass momenta without a bound state, the gauge field induces a resonance-like feature in the scattering continuum resulting in a large scattering phase shift. In the case of many particles, we demonstrate that the system, in a parameter range, shows flow-enhanced pairing, i.e., a Fulde-Farrell-Larkin-Ovchnnikov superfluid state made of robust pairs with a finite center-of-mass momentum. Yet another regime of parameters offers the opportunity to study strongly interacting normal states of spin-orbit-coupled fermionic systems utilizing the resonance-like feature induced by the synthetic gauge field.

Measurement of temperature and pressure on the surface of a blunt cone using FBG sensor in hypersonic wind tunnel

Measurement of temperature and pressure exerted on the leeward surface of a blunt cone specimen has been demonstrated in the present work in a hypersonic wind tunnel using fiber Bragg grating (FBG) sensors. The experiments were conducted on a 30 degrees apex-angle blunt cone with 51 mm base diameter at wind flow speeds of Mach 6.5 and 8.35 in a 300 mm hypersonic wind tunnel of Indian Institute of Science, Bangalore. A special pressure insensitive temperature sensor probe along with the conventional bare FBG sensors was used for explicit temperature and aerodynamic pressure measurement respectively on the leeward surface of the specimen. computational fluid dynamics (CFD) simulation of the flow field around the blunt cone specimen has also been carried out to obtain the temperature and pressure at conditions analogous to experiments. The results obtained from FBG sensors and the CFD simulations are found to be in good agreement with each other.

Bulk Majorana mass terms and Dirac neutrinos in the Randall-Sundrum model

We present a novel scheme where Dirac neutrinos are realized even if lepton number violating Majorana mass terms are present. The setup is the Randall-Sundrum framework with bulk right-handed neutrinos. Bulk mass terms of both Majorana and Dirac type are considered. It is shown that massless zero mode solutions exist when the bulk Dirac mass term is set to zero. In this limit, it is found that the effective 4D small neutrino mass is primarily of Dirac nature, with the Majorana-type contributions being negligible. Interestingly, this scenario is very similar to the one known with flat extra dimensions. Neutrino phenomenology is discussed by fitting both charged lepton masses and neutrino masses simultaneously. A single Higgs localized on the IR brane is highly constrained, as unnaturally large Yukawa couplings are required to fit charged lepton masses. A simple extension with two Higgs doublets is presented, which facilitates a proper fit for the lepton masses.

Role of the cloud adjustment time scale in simulation of the interannual variability of Indian summer monsoon

The simulation of precipitation in a general circulation model relying on relaxed mass flux cumulus parameterization scheme is sensitive to cloud adjustment time scale (CATS). In this study, the frequency of the dominant intra-seasonal mode and interannual variability of Indian summer monsoon rainfall (ISMR) simulated by an atmospheric general circulation model is shown to be sensitive to the CATS. It has been shown that a longer CATS of about 5 h simulates the spatial distribution of the ISMR better. El Nio Southern Oscillation-ISMR relationship is also sensitive to CATS. The equatorial Indian Ocean rainfall and ISMR coupling is sensitive to CATS. Our study suggests that a careful choice of CATS is necessary for adequate simulation of spatial pattern as well as interannual variation of Indian summer monsoon precipitation.

The effect of environmental coupling on tunneling of quasiparticles in Josephson junctions

We study quasiparticle tunneling in Josephson tunnel junctions embedded in an electromagnetic environment. We identify tunneling processes that transfer electrical charge and couple to the environment in a way similar to that of normal electrons, and processes that mix electrons and holes and are thus creating charge superpositions. The latter are sensitive to the phase difference between the superconductors and are thus limited by phase diffusion even at zero temperature. We show that the environmental coupling is suppressed in many environments, thus leading to lower quasiparticle decay rates and better superconductor qubit coherence than previously expected. Our approach is nonperturbative in the environmental coupling strength.

Strong-coupling expansion for ultracold bosons in an optical lattice at finite temperatures in the presence of superfluidity

We develop a strong-coupling (t << U) expansion technique for calculating the density profile for bosonic atoms trapped in an optical lattice with an overall harmonic trap at finite temperature and finite on-site interaction in the presence of superfluid regions. Our results match well with quantum Monte Carlo simulations at finite temperature. We also show that the superfluid order parameter never vanishes in the trap due to the proximity effect. Our calculations for the scaled density in the vacuum-to-superfluid transition agree well with the experimental data for appropriate temperatures. We present calculations for the entropy per particle as a function of temperature which can be used to calibrate the temperature in experiments. We also discuss issues connected with the demonstration of universal quantum critical scaling in the experiments.

Pd-Catalyzed Cross-Coupling Reactions of Hydrazones: Regioselective Synthesis of Highly Branched Dienes

The regioselective formation of highly branched dienes is a challenging task. Design and exploration of alternative working models to achieve such a regioselectivity to accomplish highly branched dienes is considered to be a historical advancement of Heck reaction to construct branched dienes. On the basis of the utility of carbene transfer reactions, in the reaction of hydrazones with Pd(II) under oxidative conditions, we envisioned obtaining a Pd-bis-carbene complex with alpha-hydrogens, which can lead to branched dienes. Herein, we report a novel Pd-catalyzed selective coupling reaction of hydrazones in the presence of t-BuOLi and benzoquinone to form the corresponding branched dienes. The utility of the Pd catalyst for the cross-coupling reactions for synthesizing branched conjugated dienes is rare. The reaction is very versatile and compatible with a variety of functional groups and is useful in synthesizing heterocyclic molecules. We anticipate that this Pd-catalyzed cross-coupling reaction will open new avenues for synthesizing useful compounds.

Cross-Hetero-Dehydrogenative Coupling Reaction of Phosphites: A Catalytic Metal-Free Phosphorylation of Amines and Alcohols

Phosphorylation of amines, alcohols, and sulfoximines are accomplished using molecular iodine as a catalyst and H2O2 as the sole oxidant under mild reaction conditions. This method provides an easy route for synthesizing a variety of phosphoramidates, phosphorus triesters and sulfoximine-derived phosphoramidates which are of biological importance.

NEW MASS LIMIT OF WHITE DWARFS

Is the Chandrasekhar mass limit for white dwarfs (WDs) set in stone? Not anymore, recent observations of over-luminous, peculiar type Ia supernovae can be explained if significantly super-Chandrasekhar WDs exist as their progenitors, thus barring them to be used as cosmic distance indicators. However, there is no estimate of a mass limit for these super-Chandrasekhar WD candidates yet. Can they be arbitrarily large? In fact, the answer is no! We arrive at this revelation by exploiting the flux freezing theorem in observed, accreting, magnetized WDs, which brings in Landau quantization of the underlying electron degenerate gas. This essay presents the calculations which pave the way for the ultimate (significantly super-Chandrasekhar) mass limit of WDs, heralding a paradigm shift 80 years after Chandrasekhar's discovery.