118443406
Strange stars in Krori–Barua space-time
The singularity free space-time metric obtained by Krori and Barua (J. Phys. A, Math. Gen. 8:508, 1975) satisfies the physical requirements of a realistic star. Consequently, we explore the possibility of applying the Krori and Barua model to describe ultra-compact objects like strange stars. For it to become a viable model for strange stars, bounds on the model parameters have been obtained. Consequences of a mathematical description to model strange stars have been analyzed.
119307073
Anisotropic strange star with de Sitter spacetime
Stars can be treated as self-gravitating fluid. Krori and Barua (J. Phys. A., Math. Gen. 8:508, 1975) gave an analytical solution to that kind of fluids. In this connection, we propose a de Sitter model for an anisotropic strange star with the Krori–Barua spacetime. We incorporate the existence of the cosmological constant on a small scale to study the structure of anisotropic strange stars and come to the conclusion that this doping is very well compatible with the well-known physical features of strange stars.
117429531
Periodicity of ~155 days in solar electron fluence
In this paper we have investigated the occurrence rate of high energetic(E>10 MeV) solar electron flares measured by IMP-8 spacecraft of NASA for solar cycle 21 (June, 1976 to August, 1986) first time by three different methods to detect periodicities accurately. Power-spectrum analysis confirms a periodicity ~155 days which is in consistent with the result of Chowdhury and Ray (2006), that "Rieger periodicity" was operated throughout the cycle 21 and it is independent on the energy of the electron fluxes.
14627322
The dark energy equation of state
ABSTRACT We perform a study of cosmic evolution with an equation of state parameter ω(t) = ω 0 +ω 1 (tH/H˙ ) by selecting a phenomenological Λ model of the form, Λ˙ ∼ H 3 . This simpleproposition explains both linearly expanding and inﬂation ary Universes with a single set ofequations. We notice that the inﬂation leads to a scaling in t he equation of state parameter,ω(t), and hence in equation of state. In this approach, one of its two parameters have been pinpointed and the other have been delineated. It has been possible to show a connection betweendark energy and Higgs-Boson.Key words: gravitation - cosmological parameters - cosmology: theory- early Universe. 1 INTRODUCTIONCosmological research is mainly concerned with time (and in somecases space as well) evolution of various physical parameters likescale factor, Hubble parameter, matter-energy density etc. Alongwith these parameters, in recent years a new physical entity Λ hasresurrected in the foreground of cosmology. In fact, Λ has becomean essential part of the ﬁeld equations of Einstein after som e ob-servational results (Riess et al. 1998; Perlmutter et al. 1999) indi-cated towards an accelerating Universe. It is believed by most ofthe physicists that the cosmological parameter Λ is responsible fordriving the present acceleration because it can exert negative pres-sure. Moreover, due to some ﬁne-tuning problem (known as cos-mological constant problem), Λ is regarded as a variable quantityrather than a constant.Now, in order to specify exact time-dependence of the un-known physical quantities including Λ, one has to take recourse ofa relationship between cosmic pressure p and matter-energy den-sity ρ involving the equation of state parameter ω. Mathemati-cally speaking, one variable quantity can depend on the productof two other variable quantities. So, one may construct ω as a func-tion of time, red-shift or scale factor (Chervon & Zhuravlev2000;Zhuravlev 2001; Peebles & Ratra 2003). In fact, values of ω at dif-ferent stages of cosmic evolution suggest that it may evolve withtime. As an instance, for the present pressure-less Universe, thevalue of ω is considered as zero, whereas its value was 1/3 in theearly radiation dominated Universe. However, it is convenient toconsider ω as a constant quantity because observational data canhardly distinguish between a varying and a constant equation of
14301959
Do Solar System Tests Permit Higher Dimensional General Relativity?
We perform a survey whether higher dimensional Schwarzschild space-time is compatible with some of the solar system phenomena. As a test we examine four well known solar system effects, viz., (1) Perihelion shift, (2) Bending of light, (3) Gravitational redshift, and (4) Gravitational time delay. It is shown, under a N-dimensional solutions of Schwarzschild type very narrow class of metrics, that the results related to all these physical phenomena are mostly incompatible with the higher dimensional version of general relativity. We compare all these restricted results with the available data in the literature.
15541573
Tolman–Bayin type static charged fluid spheres in general relativity
In a static spherically symmetric Einstein-Maxwell spacetime the class of astrophysical solution found out by Ray and Das (2002) and Pant and Sah (1979) are revisited here in connection to the phenomenological relationship between the gravitational and electromagnetic fields. It is qualitatively shown that the charged relativistic stars of Tolman (1939) and Bayin (1978) type are of purely electromagnetic origin. The existence of this type of astrophysical solutions is a probable extension of Lorentz’s conjecture that electr on-like extended charged particle possesses only ‘electromagnetic mass’ and no ‘material mas s’.
118685443
Quasi-solvability of Calogero-Sutherland model with Anti-periodic Boundary Condition
The U(1) Calogero-Sutherland Model with anti-periodic boundary condition is studied. This model is obtained by applying a vertical magnetic field perpendicular to the plane of one dimensional ring of particles. The trigonometric form of the Hamiltonian is recast by using a suitable similarity transformation. The transformed Hamiltonian is shown to be integrable by constructing a set of momentum operators which commutes with the Hamiltonian and amongst themselves. The function space of monomials of several variables remains invariant under the action of these operators. The above properties imply the quasi-solvability of the Hamiltonian under consideration.
14071447
HAVE WE OBSERVED THE SKIN VIBRATION OF REALISTIC STRANGE STARS (ReSS)
Skin vibration of ReSS and consequent resonance absorption can account for the absorption lines in the spectrum of X-ray emission from many compact stellar objects and in particular, the stars J1210-5226 and RXJ1856-3754. Observations of the X-ray spectrum of these stars is difficult to explain, if they are neutron stars.
55736791
CMB polarization TE power spectrum estimation with non-circular beam
Precise measurements of the Cosmic Microwave Background (CMB) anisotropy have been one of the foremost concerns in modern cosmology as it provides valuable information on the cosmology of the universe. However, an accurate estimation of the CMB power spectrum faces many challenges as the CMB experiments sensitivity increases. Furthermore, for polarization experiments the precision of measurement is complicated by the fact that the polarisation signal is very faint compared to the measured total intensity, and could be impossible to detect in the presence of high level of systematics. One of the most important source of errors in CMB polarization experiment is the beam asymmetry. For large data set the estimation of the CMB polarization power spectrum with standard optimal Maximum Likelihood (ML) is prohibitive for high resolution CMB experiments due to the enormous required computation time. In this paper, we present a semi-analytical framework using the pseudo-$C_{l}$ estimator to compute the power spectrum TE of the temperature anisotropy and the E-component of the polarization radiation field using non-circular beams. We adopt a model of beams obtained from a perturbative expansion of the beam around a circular (axisymmetric) one in harmonic space, and compute the resulting bias matrix which relates the true power spectrum with the observed one using an efficient algorithm for rapid computation. We show that for a multipole up to $l_{max}=500$, the bias matrix can be computed in less than one second with a single CPU processor at 2.53 GHz. We find that the uncertainties induced by the beam asymmetry in the polarization power spectrum at the peak of the bias matrix for WMAP and Planck experiments can be as large as a few 10 to 20% (upper limit for Planck LFI 30 GHz)
119362075
Strange stars at finite temperature
We calculate strange star properties, using large Nc approximation with built-in chiral symmetry restoration (CSM). We used a relativistic Hartree Fock meanfield approximation method, using a modified Richardson potential with two scale parameters Λ and Λ', to find a new set of equation of state (EOS) for strange quark matter. We take the effect of temperature (T) on gluon mass, in addition to the usual density dependence, and find that the transition T from hadronic matter to strange matter is 80 MeV. Therefore formation of strange stars may be the only signal for formation of QGP with asymptotic freedom (AF) and CSM.
117728803
Gauge momentum operators for the Calogero-Sutherland model with anti-periodic boundary condition
The integrability of a classical Calogero systems with anti-periodic boundary condition is studied. This system is equivalent to the periodic model in the presence of a magnetic field. Gauge momentum operators for the anti-periodic Calogero system are constructed. These operators are hermitian and simultaneously diagonalizable with the Hamiltonian. A general scheme for constructing such momentum operators for trigonometric and hyperbolic Calogero-Sutherland model is proposed. The scheme is applicable for both periodic and anti-periodic boundary conditions. The existence of these momentum operators ensures the integrability of the system. The interaction parameter $\lambda$ is restricted to a certain subset of real numbers. This restriction is in fact essential for the construction of the hermitian gauge momentum operators.