122963652
Intrinsic density and energy dependence: Exchange effects in alpha-nucleus scattering
The exchange effect for the alpha-nucleus potential has been computed by folding in the density matrices with a finite range effective interaction. The ''effective'' exchange interaction is both density and energy dependent. The potential agrees closely with phenomenology.
30676639
Ultrahigh-energy pulsed emission from Hercules X-1 with anomalous air-shower muon production.
A search for bursts of air-shower events from Hercules X-1 at energies above 50 TeV during the calendar period 2 April 1986 to 5 July 1987 yielded two significant bursts, both occurring on UT 24 July 1986. The events during these bursts were pulsed with a period of 1.235 68 s, significantly different from estimates of the contemporaneous x-ray period. The probability that this represents random statistical fluctuations of the background is estimated to be 2 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}5}$. The muon content of the burst events is anomalous when compared with expectations from $\ensuremath{\gamma}$-ray showers.
331919
Monte Carlo code G3sim for simulation of plastic scintillator detectors with wavelength shifter fiber readout.
A detailed description of a compact Monte Carlo simulation code "G3sim" for studying the performance of a plastic scintillator detector with wavelength shifter (WLS) fiber readout is presented. G3sim was developed for optimizing the design of new scintillator detectors used in the GRAPES-3 extensive air shower experiment. Propagation of the blue photons produced by the passage of relativistic charged particles in the scintillator is treated by incorporating the absorption, total internal, and diffuse reflections. Capture of blue photons by the WLS fibers and subsequent re-emission of longer wavelength green photons is appropriately treated. The trapping and propagation of green photons inside the WLS fiber is treated using the laws of optics for meridional and skew rays. Propagation time of each photon is taken into account for the generation of the electrical signal at the photomultiplier. A comparison of the results from G3sim with the performance of a prototype scintillator detector showed an excellent agreement between the simulated and measured properties. The simulation results can be parametrized in terms of exponential functions providing a deeper insight into the functioning of these versatile detectors. G3sim can be used to aid the design and optimize the performance of scintillator detectors prior to actual fabrication that may result in a considerable saving of time, labor, and money spent.
21268625
Search for signals from Cygnus X-3 at energies above 50 TeV.
Upper limits for the time-averaged flux of air showers from the direction of Cygnus X-3 during the calendar period 2 April 1986 to 3 May 1987 are found to be 1.5 x 10/sup -13/ cm/sup -2/ sec/sup -1/ for all events, and 7.6 x 10/sup -14/ cm/sup -2/ sec/sup -1/ for events with no observed muons in a 44-m/sup 2/ muon detector. These are integral fluxes above 50 TeV on the assumption of an E/sup -1/ primary spectrum. A possible observation of a short-term signal from Cygnus X-3, with an anomalous muon content, phase correlated with the 4.8-h orbital period, with an integral flux above 50 TeV of (8.2 +- 2.0) x 10/sup -13/ cm/sup -2/ sec/sup -1/ is also reported.
13571448
Apparent and Actual Shifts in Mass and Width of ϕ Mesons Produced in Heavy-Ion Collisions
We present a method of analyzing invariant-mass spectra of kaon pairs resulting from decay of ϕ mesons produced in high-energy heavy-ion collisions. It can be used to extract the shifts in the mass and the width (ΔM and ΔΓ) of the ϕ mesons when they are inside the dense matter formed in these collisions. We illustrate our method with the help of available preliminary data. Extracted values of ΔM and ΔΓ are significantly larger than those obtained with an earlier method. Our results are consistent with the experimentally observed pT dependence of the mass shift. Finally, we present a phenomenological relation between ΔM and ΔΓ. It provides a useful constraint on theories which predict the values of these two quantities.
124703371
FEL ACTIVITIES IN INDIA
We are building a Compact Ultrafast TErahertz FreeElectron Laser (CUTE-FEL), designed to lase from 50 – 100 μm. The FEL will be driven by a 10-15 MeV electron beam from a Plane-Wave Transformer (PWT) linac. The undulator is a 5 cm period, 2.5 m long PPM planar undulator. We present details of the FEL design and the present status of activities. We also present very preliminary plans for a short-wavelength SASE FEL in India.
18294133
Thermal effects on two photon decays of pseudoscalars
We study the effect of finite temperatures and Fermion density on the effective pseudo-scalar-photon vertex induced by the triangle diagram. The manifestly covariant calculations show that when the pseudo-scalar mass is much less than the temperature, then there is a large enhancement of the decay rate. Alternatively, when the temperature is much higher than the Fermion mass, or the Fermion chemical potential is large, the lifetime is enhanced. Other related processes, and applications of these results to cosmology and astrophysics, are discussed.
119418840
Pressure and nonlinear susceptibilities in QCD at finite chemical potentials
When the free energy density of QCD is expanded in a Taylor series in the chemical potential $\ensuremath{\mu},$ the coefficients are the nonlinear quark number susceptibilities. We show that these depend on the prescription for putting the chemical potential on the lattice, making all extrapolations in the chemical potential prescription dependent at finite lattice spacing. To put bounds on the prescription dependence, we investigate the magnitude of the nonlinear susceptibilities over a range of temperature, T, in QCD with two degenerate flavors of light dynamical quarks at lattice spacing $1/4T.$ The prescription dependence is removed in quenched QCD through a continuum extrapolation, and the dependence of the pressure P on $\ensuremath{\mu}$ is obtained.
122162744
Regularization and renormalization of nonlinear pion-pion couplings
The fourth-order $\ensuremath{\pi}\ensuremath{-}\ensuremath{\pi}$ scattering resulting from nonlinear pion-pion couplings is investigated to show how such couplings can be regularized by the method of auxiliary fields. Special care is required in the choice of coupling terms involving the auxiliary fields to ensure that all quartic divergences are canceled by the $\ensuremath{\delta}(0)$ terms in the regularized effective interaction. It is found that four counterterms are necessary for the elimination of divergences in the process under consideration. In the limiting case of massless pions, the $\ensuremath{\pi}\ensuremath{-}\ensuremath{\pi}$ scattering result is free from infrared divergence, satisfies Adler's condition, and requires only two counterterms for renormalization.
119419540
Analyticity and the phase diagram of QCD
Some consequences of the analyticity of the free energy (pressure) of QCD at finite chemical potential are deduced. Lattice simulations at imaginary chemical potential are possible due to the positivity of the measure. We show that such a theory cannot be interpreted as a thermodynamic system with a phase diagram in the usual sense. However, simulations at imaginary chemical potential are useful because the free energy can be analytically continued and information on the thermodynamic system at real chemical potential can be extracted by two means-either by the usual method of Taylor expansions, or by using this data to extract Yang-Lee zeroes of the grand-canonical partition function. We also comment on the structure of zeroes expected for the usual picture of the phases of QCD, following a discussion of the physics of imaginary chemical potential.
119252719
Near maximal atmospheric mixing in neutrino mass matrices with two vanishing minors
Abstract In the flavor basis there are seven cases of two vanishing minors in the neutrino mass matrix which can accommodate the present neutrino oscillation data including the recent T2K data. It is found that two of these cases, namely B 5 and B 6 predict near maximal atmospheric neutrino mixing in the limit of large effective neutrino mass. This feature remains irrespective of the values of solar and reactor mixing angles. A non-zero reactor mixing angle is naturally accommodated in these textures.