arXiv subjects

R. Sharma

Publications and source records attributed to R. Sharma.

90 records · Page 5Linked to original sources

arXiv2013

Measurement of Neutrino and Antineutrino Oscillations Using Beam and Atmospheric Data in MINOS

We report measurements of oscillation parameters from $ν_{mu}$ and $\barν_μ$ disappearance using beam and atmospheric data from MINOS. The data comprise exposures of \unit[$10.71 \times 10^{20}$]{protons on target (POT)} in the $ν_μ$-dominated beam, $\unit[3.36\times10^{20}]{POT}}$ in the $\barν_μ$-enhanced beam, and 37.88 kton-years of atmospheric neutrinos. Assuming identical $ν$ and $\barν$ oscillation parameters, we measure \mbox{$|Δm^2}| = \unit[2.41^{+0.09}_{-0.10}) \times 10^{-3}]{eV^{2}}$} and $\sin^{2}/!/left(2θ\right) = 0.950^{+0.035}_{-0.036}$. Allowing independent $ν$ and $\barν$ oscillations, we measure antineutrino parameters of $|Δ\bar{m}^2| = \unit[(2.50 ^{+0.23}_{-0.25}) \times 10^{-3}]{eV^{2}}$ and $\sin^{2}/!/left(2\barθ \right) = 0.97^{+0.03}_{-0.08}$, with minimal change to the neutrino parameters.

hep-ex↗

arXiv2013

Electron neutrino and antineutrino appearance in the full MINOS data sample

We report on $ν_e$ and $\barν_e$ appearance in $ν_μ$ and $\barν_μ$ beams using the full MINOS data sample. The comparison of these $ν_e$ and $\barν_e$ appearance data at a 735 km baseline with $θ_{13}$ measurements by reactor experiments probes $δ$, the $θ_{23}$ octant degeneracy, and the mass hierarchy. This analysis is the first use of this technique and includes the first accelerator long-baseline search for $\barν_μ\rightarrow\barν_e$. Our data disfavor 31% (5%) of the three-parameter space defined by $δ$, the octant of the $θ_{23}$, and the mass hierarchy at the 68% (90%) C.L. We measure a value of 2sin$^2(2θ_{13})$sin$^2(θ_{23})$ that is consistent with reactor experiments.

hep-ex↗

arXiv2013

A search for flavor-changing non-standard neutrino interactions by MINOS

We report new constraints on flavor-changing non-standard neutrino interactions (NSI) using data from the MINOS experiment. We analyzed a combined set of beam neutrino and antineutrino data, and found no evidence for deviations from standard neutrino mixing. The observed energy spectra constrain the NSI parameter to the range $-0.20 < \varepsilon_{μτ} < 0.07\;\text{(90% C.L.)}$

hep-ex↗

arXiv2012

Measurements of atmospheric neutrinos and antineutrinos in the MINOS Far Detector

This paper reports measurements of atmospheric neutrino and antineutrino interactions in the MINOS Far Detector, based on 2553 live-days (37.9 kton-years) of data. A total of 2072 candidate events are observed. These are separated into 905 contained-vertex muons and 466 neutrino-induced rock-muons, both produced by charged-current $ν_μ$ and $\barν_μ$ interactions, and 701 contained-vertex showers, composed mainly of charged-current $ν_{e}$ and $\barν_{e}$ interactions and neutral-current interactions. The curvature of muon tracks in the magnetic field of the MINOS Far Detector is used to select separate samples of $ν_μ$ and $\barν_μ$ events. The observed ratio of $\barν_μ$ to $ν_μ$ events is compared with the Monte Carlo simulation, giving a double ratio of $R^{data}_{\barν/ν}/R^{MC}_{\barν/ν} = 1.03 \pm 0.08 (stat.) \pm 0.08 (syst.)$. The $ν_μ$ and $\barν_μ$ data are separated into bins of $L/E$ resolution, based on the reconstructed energy and direction of each event, and a maximum likelihood fit to the observed $L/E$ distributions is used to determine the atmospheric neutrino oscillation parameters. This fit returns 90% confidence limits of $|Δm^{2}| = (1.9 \pm 0.4) \times 10^{-3} eV^{2}$ and $sin^{2} 2θ> 0.86$. The fit is extended to incorporate separate $ν_μ$ and $\barν_μ$ oscillation parameters, returning 90% confidence limits of $|Δm^{2}|-|Δ\bar{m}^{2}| = 0.6^{+2.4}_{-0.8} \times 10^{-3} eV^{2}$ on the difference between the squared-mass splittings for neutrinos and antineutrinos.

hep-ex↗

arXiv2012

Non-adiabatic radiative collapse of a relativistic star under different initial conditions

We examine the role of space-time geometry in the non-adiabatic collapse of a star dissipating energy in the form of radial heat flow, studying its evolution under different initial conditions. The collapse of a star with interior comprising of a homogeneous perfect fluid is compared with that of a star filled with inhomogeneous imperfect fluid with anisotropic pressure. Both the configurations are spherically symmetric, however, in the latter case, the physical space $t= constant$ of the configurations is assumed to be inhomogeneous endowed with spheroidal or pseudo-spheroidal geometry. It is observed that as long as the collapse is shear-free, its evolution depends only on the mass and size of the star at the onset of collapse.

gr-qc↗

arXiv2012

Space-time inhomogeneity, anisotropy and gravitational collapse

We investigate the evolution of non-adiabatic collapse of a shear-free spherically symmetric stellar configuration with anisotropic stresses accompanied with radial heat flux. The collapse begins from a curvature singularity with infinite mass and size on an inhomogeneous space-time background. The collapse is found to proceed without formation of an even horizon to singularity when the collapsing configuration radiates all its mass energy. The impact of inhomogeneity on various parameters of the collapsing stellar configuration is examined in some specific space-time backgrounds.

gr-qc↗

arXiv2012

An improved measurement of muon antineutrino disappearance in MINOS

We report an improved measurement of muon anti-neutrino disappearance over a distance of 735km using the MINOS detectors and the Fermilab Main Injector neutrino beam in a muon anti-neutrino enhanced configuration. From a total exposure of 2.95e20 protons on target, of which 42% have not been previously analyzed, we make the most precise measurement of the anti-neutrino "atmospheric" delta-m squared = 2.62 +0.31/-0.28 (stat.) +/- 0.09 (syst.) and constrain the anti-neutrino atmospheric mixing angle >0.75 (90%CL). These values are in agreement with those measured for muon neutrinos, removing the tension reported previously.

hep-ex↗

arXiv2012

Search for Lorentz invariance and CPT violation with muon antineutrinos in the MINOS Near Detector

We have searched for sidereal variations in the rate of antineutrino interactions in the MINOS Near Detector. Using antineutrinos produced by the NuMI beam, we find no statistically significant sidereal modulation in the rate. When this result is placed in the context of the Standard Model Extension theory we are able to place upper limits on the coefficients defining the theory. These limits are used in combination with the results from an earlier analysis of MINOS neutrino data to further constrain the coefficients.

hep-ex↗

arXiv2011

Voltage controlled terahertz transmission through GaN quantum wells

We report measurements of radiation transmission in the 0.220--0.325 THz frequency domain through GaN quantum wells grown on sapphire substrates at room and low temperatures. A significant enhancement of the transmitted beam intensity with the applied voltage on the devices under test is found. For a deeper understanding of the physical phenomena involved, these results are compared with a phenomenological theory of light transmission under electric bias relating the transmission enhancement to changes in the differential mobility of the two-dimensional electron gas.

cond-mat.mes-hall↗

arXiv2010

Relativistic Drude Response of Photoexcited Dirac Quasiparticles in Graphene

Graphene, a monolayer of carbon atoms arranged in a hexagonal pattern, provides a unique two-dimensional (2D) system exhibiting exotic phenomena such as quantum Hall effects, massless Dirac quasiparticle excitations and universal absorption & conductivity. The linear energy-momentum dispersion relation in graphene also offers the opportunity to mimic the physics of far-away relativistic particles like neutron stars and white dwarfs. In this letter, we perform a counterintuitive ultrafast pump-probe experiment with high photon energies to isolate the Drude-like intraband dynamics of photoexcited carriers. We directly demonstrate the relativistic nature of the photoexcited Dirac quasiparticles by observing a nonlinear scaling of the response with the density of photoexcited carriers. This is in striking contrast to the linear scaling that is usually observed in conventional materials. Our results also indicate strong electron-phonon coupling in graphene, leading to a sub-100 femtosecond thermalization between high energy photoexcited carriers and optical phonons.

cond-mat.mes-hall↗

arXiv2009

Magnetotransport in polycrystalline La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ thin films of controlled granularity

Polycrystalline La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ (LSMO) thin films were synthesized by pulsed laser ablation on single crystal (100) yttria-stabilized zirconia (YSZ) substrates to investigate the mechanism of magneto-transport in a granular manganite. Different degrees of granularity is achieved by using the deposition temperature (T$_{D}$) of 700 and 800 $^{0}$C. Although no significant change in magnetic order temperature (T$_C$) and saturation magnetization is seen for these two types of films, the temperature and magnetic field dependence of their resistivity ($ρ$(T, H)) is strikingly dissimilar. While the $ρ$(T,H) of the 800 $^{0}$C film is comparable to that of epitaxial samples, the lower growth temperature leads to a material which undergoes insulator-to-metal transition at a temperature (T$_{P}$ $\approx$ 170 K) much lower than T$_C$. At T $\ll$ T$_P$, the resistivity is characterized by a minimum followed by ln $\emph{T}$ divergence at still lower temperatures. The high negative magnetoresistance ($\approx$ 20$%$) and ln $\emph{T}$ dependence below the minimum are explained on the basis of Kondo-type scattering from blocked Mn-spins in the intergranular material. Further, a striking feature of the T$_D$ = 700 $^{0}$C film is its two orders of magnitude larger anisotropic magnetoresistance (AMR) as compared to the AMR of epitaxial films. We attribute it to unquenching of the orbital angular momentum of 3d electrons of Mn ions in the intergranular region where crystal field is poorly defined.

cond-mat.str-el↗

arXiv2008

Boson star and dark matter

Bound states of complex scalar fields (boson stars) have long been proposed as possible candidates for the dark matter in the universe. Considerable work has already been done to study various aspects of boson stars. In the present work, assuming a particular anisotropic matter distribution, we solve the Einstein-Klein-Gordon equations with a cosmological constant to obtain bosonic configurations by treating the problem geometrically. The results are then applied to problems covering a wide range of masses and radii of the boson stars and the relevant self interaction parameters are calculated. We compare our results with earlier treatments to show the applicability of the geometrical approach.

gr-qc↗

arXiv2008

Lattice-mismatch-induced granularity in CoPt-NbN and NbN-CoPt superconductor-ferromagnet heterostructures: Effect of strain

The effect of strain due to lattice mismatch and of ferromagnetic (FM) exchange field on superconductivity (SC) in NbN-CoPt bilayers is investigated. Two different bilayer systems with reversed deposition sequence are grown on MgO (001) single crystals. While robust superconductivity with high critical temperature (T_c ~ 15.3 K) and narrow transition width DelT_c ~ 0.4 K) is seen in two types of CoPt-NbN/MgO heterostructures where the magnetic anisotropy of CoPt is in-plane in one case and out-of-plane in the other, the NbN-CoPt/MgO system shows markedly suppressed SC response. The reduced SC order parameter of this system, which manifests itself in Tc, temperature dependence of critical current density J_c (T), and angular (Phi) variation of flux-flow resistivity Rho_f is shown to be a signature of the structure of NbN film and not a result of the exchange field of CoPt. The Rho_f (H,T,Phi) data further suggest that the domain walls in the CoPt film are of the Neel type and hence do not cause any flux in the superconducting layer. A small, but distinct increase in the low-field critical current of the CoPt-NbN couple is seen when the magnetic layer has perpendicular anisotropy.

cond-mat.supr-con↗

arXiv2008

Correlations between morphology, crystal structure and magnetization of epitaxial cobalt-platinum films grown with pulsed laser ablation

The effects of growth rate (G_r), deposition temperature (T_d), film thickness (t_F), and substrate induced strain (epsilon) on morphological, crystallographic and magnetic characteristics of equiatomic CoPt epitaxial films synthesized with PLD are investigated. The (001) substrates of MgO, STO and LAO provide different degree of epitaxial strain for growth of the disordered face centered cubic (fcc) and ordered face centered tetragonal (L1_0) phases of CoPt. The films deposited at T_d~600 ^0C on all three substrates are fcc with in-plane magnetization and a narrow hysteresis loop of width~200 Oe. The L1_0 phase, stabilized only at T_d~700 ^0C becomes predominantly c-axis oriented as T_d is increased to 800 ^0C. While the crystallographic structure of the films depends solely on the T_d, their microstructure and magnetization characteristics are decided by the growth rate. At the higher G_r (~1A/sec) the L1_0 films have a maze-like structure which converts to a continuous film as the t_F is increased from 20 to 50 nm. The H_c of these films increases as the L1_0 phase fraction grows with T_d and its orientation becomes out of the film plane. The evolution of microstructure with T_d is remarkably different at lower growth rate (~0.4A /sec). Here the structure changes from a self-similar fractal pattern to an assembly of nano-dots as the T_d is raised from 700 to 800 ^0C, and is understood in terms of the imbalance between strain and interfacial energies. MFM of such films reveals no distinct domain walls within the nano-islands while a clear contrast is seen between the islands of reversed magnetization. The simple picture of coherent rotation of moment appears incompatible with the time dependence of the remanent magnetization in these films.

cond-mat.mtrl-sci↗

arXiv2007

On surface tension for compact stars

In an earlier treatment it was demonstrated that general relativity gives higher values of surface tension in strange stars with quark matter than neutron stars.We generate the modified Tolman-Oppenheimer-Volkoff equation to incorporate anisotropic matter and use this to show that pressure anisotropy provides for a wide range of behaviour in the surface tension than is the case with isotropic pressures. In particular it is possible that anisotropy drastically decreases the value of the surface tension.

gr-qc↗

arXiv2007

The role of pressure anisotropy on the maximum mass of cold compact stars

We study the physical features of a class of exact solutions for cold compact anisotropic stars. The effect of pressure anisotropy on the maximum mass and surface redshift is analysed in the Vaidya-Tikekar model. It is shown that maximum compactness, redshift and mass increase in the presence of anisotropic pressures; numerical values are generated which are in agreement with observation.

gr-qc↗

arXiv2007

A class of relativistic stars with a linear equation of state

By assuming a particular mass function we find new exact solutions to the Einstein field equations with an anisotropic matter distribution. The solutions are shown to be relevant for the description of compact stars. A distinguishing feature of this class of solutions is that they admit a linear equation of state which can be applied to strange stars with quark matter.

gr-qc↗

arXiv2001

Toward Natural Gesture/Speech Control of a Large Display

In recent years because of the advances in computer vision research, free hand gestures have been explored as means of human-computer interaction (HCI). Together with improved speech processing technology it is an important step toward natural multimodal HCI. However, inclusion of non-predefined continuous gestures into a multimodal framework is a challenging problem. In this paper, we propose a structured approach for studying patterns of multimodal language in the context of a 2D-display control. We consider systematic analysis of gestures from observable kinematical primitives to their semantics as pertinent to a linguistic structure. Proposed semantic classification of co-verbal gestures distinguishes six categories based on their spatio-temporal deixis. We discuss evolution of a computational framework for gesture and speech integration which was used to develop an interactive testbed (iMAP). The testbed enabled elicitation of adequate, non-sequential, multimodal patterns in a narrative mode of HCI. Conducted user studies illustrate significance of accounting for the temporal alignment of gesture and speech parts in semantic mapping. Furthermore, co-occurrence analysis of gesture/speech production suggests syntactic organization of gestures at the lexical level.

cs.CV↗