Wormhole Core, Extra Dimensions, and Physical Universe

We created a model of several dimensional physical universe. The extra dimensions associated with the four dimensional physical universe is assumed to have modified Gidding-Strominger wormhole core. This core is separated by a flexible wall, but it allows the adiabatic pressure generated in the wormhole to penetrate in the extra dimensions. We assume that the extra dimensions are a contracting Robinson-Walker space. We show that the associated physical universe accelerates under certain restriction of the parameters introduced. The extra dimensional space is very large at the begining, however at present time this space will be very reduced. As a result the physical universe will appear to us four dimensional the way we observe it now.Comment: 8 pages, Festschrift Contributio

Searching for the reionization sources

Using a reionization model simultaneously accounting for a number of experimental data sets, we investigate the nature and properties of reionization sources. Such model predicts that hydrogen reionization starts at z \approx 15, is initially driven by metal-free (PopIII) stars, and is 90% complete by z \approx 8. We find that a fraction f_\gamma >80% of the ionizing power at z > 7 comes from haloes of mass M<10^9 M_sun predominantly harbouring PopIII stars; a turnover to a PopII-dominated phase occurs shortly after, with this population, residing in M>10^9 M_sun haloes, yielding f_\gamma \approx 60% at z=6. Using Lyman-break broadband dropout techniques, J-band detection of sources contributing to 50% (90%) of the ionizing power at z \sim 7.5 requires to reach a magnitude J_{110,AB} = 31.2 (31.7), where about 15 (30) (PopIII) sources/arcmin^2 are predicted. We conclude that z>7 sources tentatively identified in broadband surveys are relatively massive (M \approx 10^9 M_sun) and rare objects which are only marginally (\approx 1%) adding to the reionization photon budget.Comment: Extended discussions. Accepted to MNRAS Letter

Evolution of X-ray spectra of Cygnus X-3 with radio flares

Cygnus X-3, among the X-ray binaries, is one of the brightest in the radio band, repeatedly exhibiting huge radio flares. The X-ray spectra shows two definite states, low (correspondingly hard) and high (correspondingly soft). During the hard state the X-ray spectra shows a pivoting behaviour correlated to the radio emission. In the high state the X-ray spectra shows a gamut of behaviour which controls the radio flaring activity of the source. The complete evolution of the X-ray spectra along with the radio flaring activity is reported here, for the first time for this source.Comment: Bibliography has been correctly adde

Regular and Singular Pulse and Front Solutions and Possible Isochronous Behavior in the Short-Pulse Equation: Phase-Plane, Multi-Infinite Series and Variational Approaches

In this paper we employ three recent analytical approaches to investigate the possible classes of traveling wave solutions of some members of a family of so-called short-pulse equations (SPE). A recent, novel application of phase-plane analysis is first employed to show the existence of breaking kink wave solutions in certain parameter regimes. Secondly, smooth traveling waves are derived using a recent technique to derive convergent multi-infinite series solutions for the homoclinic (heteroclinic) orbits of the traveling-wave equations for the SPE equation, as well as for its generalized version with arbitrary coefficients. These correspond to pulse (kink or shock) solutions respectively of the original PDEs. Unlike the majority of unaccelerated convergent series, high accuracy is attained with relatively few terms. And finally, variational methods are employed to generate families of both regular and embedded solitary wave solutions for the SPE PDE. The technique for obtaining the embedded solitons incorporates several recent generalizations of the usual variational technique and it is thus topical in itself. One unusual feature of the solitary waves derived here is that we are able to obtain them in analytical form (within the assumed ansatz for the trial functions). Thus, a direct error analysis is performed, showing the accuracy of the resulting solitary waves. Given the importance of solitary wave solutions in wave dynamics and information propagation in nonlinear PDEs, as well as the fact that not much is known about solutions of the family of generalized SPE equations considered here, the results obtained are both new and timely.Comment: accepted for publication in Communications in Nonlinear Science and Numerical Simulatio

Detection of anti-correlated hard X-ray time lag in Cygnus X-3

The wide-band X-ray spectra of the high mass X-ray binary Cygnus X-3 exhibits a pivoting behavior in the `low' (as well as `hard') state, correlated to the radio emission. The time scale of the soft and hard X-rays' anti-correlation, which gave rise to the pivoting feature, was found to be less than a day from the monitoring observations by RXTE--ASM and CGRO--BATSE. In this Letter we report the detection of a lag of $\lesssim$ 1000s in the anti-correlation of the hard X-ray emission (20--50 keV) to that of the soft X-ray emission (2--7 keV), which may be attributed to the viscous time scale of flow of matter in the accretion disk. This suggests the geometrical picture of a truncated accretion disc with a Compton cloud inside the disc, the relative sizes of which determine the spectral shape. Any change in the disc structure will take place in a viscous time scale, with corresponding anti-correlated change in the Compton cloud. We also report the pivoting in the spectra in one span of a pointed observation when an episode of the rearranging of the accretion system is serendipitously observed. This is the first such observation of hard X-ray delay seen in the persistent Galactic microquasars, within the precincts of the hard state.Comment: Accepted in The Astrophysical Journal (Letters): in pres