• Volume 52, Issue 2

February 1999,   pages  121-235

• Gravitational energy in Brans-Dicke cosmological models

The behaviour of gravitational energy and scalar field during the evolution of the universe within the framework of Brans-Dicke theory has been discussed. With help of the Landau-Lifshitz pseudo-tensor for the flat Friedmann-Robertson-Walker model, it is found that (i) the total energy of the universe is always zero, (ii) the Brans-Dicke scalar field for all Ω &gt;-0 contributes energy to the negative energy of gravitational field and this gets transferred to the vacuum energy which accelerates the expansion of the universe.

• On quark matter in a strong magnetic field

The effect of strong magnetic field on the bulk properties of quark matter is reinvestigated takingu, d ands-quarks as well as electrons in the presence of magnetic field. Here the bag pressure is chosen such that in the absence of magnetic field and at zero temperature the binding energy of theuds-system is &lt;930 MeV while that ofud-system is greater than 940 MeV. It is observed that the equation of state changes significantly in a strong magnetic field. At finite temperature the electron chemical potential varies between 6 and 50 MeV. Thus the expansion of thermodynamical quantities in powers ofT/(Μi2-Mv(i)2)1/2 is valid only up to few MeV. For high temperatures ∼40 MeV the exact integral expressions are to be taken.

• Shower age in correlation with zenith angle

The variation of lateral shower age parameter with zenith angle for different shower size ranges is studied. The observed variation is in agreement with the electron-photon cascade theory and with the other EAS observations. It is found that up to zenith angle 30°, shower ‘age’ is practically independent of zenith angle. So it is difficult to correlate the reported high ‘age’ value of the excess showers from the direction of plausible point sources with zenith angle. The change in the value of shower age with atmospheric depth is studied and is found to be consistent with the prediction of cascade theory and simulation results. From the study of the variation of shower age with shower size for two different zenith angle intervals it is found that the shower age decreases with size but the rate of change of shower age decreases at higher sizes.

• Evaluation ofS,T, U parameters, triple gauge boson vertices and some oblique corrections in extraU(1) superstring inspired model

Explicit evaluation of the following parameters has been carried out in the extraU (1) superstring inspired model: (i) As Mz2 varies from 555 GeV to 620 GeV and (mt) CDF = 175.6 ± 5.7 GeV (Table 1): (a) SNew varies from -0.100 ± 0.089 to -0.130 ± 0.090, (b) TNew varies from -0.098 ± 0.097 to -0.129 ± 0.098, (c) UNew varies from -0.229 ± 0.177 to -0.253 ± 0.206, (d) Τz varies from 2.487 ± 0.027 to 2.486 ± 0.027, (e) ALR varies from 0.0125 ± 0.0003 to 0.0126 ± 0.0003, (f) AFBb remains constant at 0.0080 ± 0.0007. Almost identical values are obtained for (mt)D0 = 169 GeV (see table 2). (ii) Triple gauge boson vertices (TGV) contributions: AsMz2 varies from 555 GeV to 620 GeV and (mt) CDF = 175.6 ±5.7 GeV. (a)√s = 500 GeV, asymptotic case:$$\overline f _1^{Z_1 }$$ varies from -0.301 to -0.179;$$\overline f _{3|Z_1 }^{Z_1 }$$ varies from -0.622 to -0.379;$$f_5^{Z_1 }$$ varies from +0.0061 to 0.0056;$$\overline f _{3|Z_1 }^{\gamma _1 }$$ varies from -3.691 to -2.186.$$\overline f _z^{Z_2 }$$ varies from +0.270 to +0.118;$$\overline f _3^{Z_2 }$$ varies from +0.552 to 0.238;$$f_5^{Z_2 }$$ varies from +0.0004 to +0.0002;$$\overline f _{3|Z_2 }^{\gamma _1 }$$ remains constant at -0.110. (b)√s = 700 GeV, asymptotic case:$$\overline f _1^{Z_1 }$$ varies from -0.297 to -0.176;$$\overline f _3^{Z_1 }$$ varies from -0.609 to -0.370;$$\overline f _5^{Z_1 }$$ varies from -0.0082 to -0.0078;$$\overline f _{3|Z_1 }^{\gamma _1 }$$ varies from -3.680 to -2.171.√s = 700 GeV, nonasymptotic case:$$\overline f _1^{Z_2 }$$ varies from -0.173 to -0.299;$$\overline f _3^{Z_2 }$$ varies from-0.343 to -0.591;$$f_5^{Z_2 }$$ varies from -0.005 to -0.011;$$\overline f _{3|Z_2 }^{\gamma _1 }$$ remains constant at -0.110.

The pattern of form factors values for√s = 1000, 1200 GeV is almost identical to that of√s= 700 GeV. Further the values of the form factors for (mt)D0 (=169 GeV) follow identical pattern as that of (mt) CDF form factors values (see tables 5, 6, 9, 10).

We conclude that the values of all the form factors with the exception of these of$$f_5^{Z_1 }$$,$$f_5^{Z_2 }$$ are comparable or larger than theS, T values and therefore the TGV contributions are important while deciding the use of extraU (1) model for doing physics beyond standard model.

• A tentative multiphoton ionization of CS2 molecule: Spectroscopy of Ã2πu state of CS2+ ion

The spectroscopic study of excited molecular cationCS2+2πu ) by a different method is presented. In this technique the decay of excited states is monitored by measuring the photons emitted. The peaks in the photon spectrum would correspond to the energy levels of the ion. The vibrational-vibrational, vibrational-electronic interactions have been observed. Symmetry forbidden excitation of one quantum of bending vibration is observed which gives unperturbed value for the bending vibration. The Renner-Teller splitting for the δg and Σg- components of the bending mode (v2 = 1) in the upper excited Ã2πu state has been observed. A tentative vibrational analysis of the Ã X system has been made.

• Ultrasonic velocity of binary systems at elevated pressures

Various empirical theories of ultrasonic velocity have been applied to three binary liquid mixtures, under pressures up to 200 MPa and their validity have been tested. A pressure dependent study of ultrasonic velocities has been made at 303.15 K. The agreement between theory and experiment is found to be quite satisfactory.

• Wavevector and frequency dependent dielectric function dynamic structure factor and the instability of plasma waves in two component hot rare quantum and classical plasmas

The full wavevector and frequency dependent complex dielectric function for two component classical and quantum rare hot plasmas have been derived. The real part of dielectric function is obtained in the form of a series. Difference between quantum and classical real and imaginary parts of dielectric function have been brought out by making explicit calculations. The quantum nature of the plasma brings about significant changes in both parts depending upon the magnitude of quantum parameter,R (= 8.93(λth)/λ).

Expressions for the dynamic structure factors for both two component classical and quantum plasma have been evaluated for different values of the mass of the positive componentm+, temperature T+ and wavevector k. It is found that the plasma exhibits well defined collective modes for certain values of ¦k¦ accompanied by varying disorder which depends upon the values of m+ as well as on ¦k¦ and T+. For the quantum case the collective modes are less well defined as compared to the corresponding classical case, thus proving that quantum nature introduces inherent disorder in the system. But for both the cases, increase in temperature destroys collective modes. Another feature is the appearance of a hump near Ω = 0 which becomes smaller and vanishes as the quantum parameter is decreased.

Instability of plasma modes in the presence of constant electric field has also been worked out for the quantum case.

• Helium implanted CuHf as studied by TDPAC and positron lifetime measurements

181Ta time differential perturbed angular correlation (TDPAC) and positron lifetime measurements were carried out on homogeneously α-implanted CuHf samples. TDPAC measurements indicate the trapping of vacancy clusters and helium associated defect complexes by Hf atoms. The presence of helium-vacancy complexes and helium stabilised voids has been identified by positron lifetime measurements. Further the nucleation and growth stages of helium bubbles have been identified. TDPAC and positron lifetime measurements indicate that Hf atoms act as heterogeneous nucleating centers for helium bubbles. Hf atoms are found to suppress the bubble growth in CuHf as indicated by the results of positron lifetime measurements.

• Erratum

• # Pramana – Journal of Physics

Volume 94, 2019
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Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019