Tiny scale opacity fluctuations from VLBA, MERLIN and VLA observations of HI absorption toward 3C 138

The structure function of opacity fluctuations is a useful statistical tool to study tiny scale structures of neutral hydrogen. Here we present high resolution observation of HI absorption towards 3C 138, and estimate the structure function of opacity fluctuations from the combined VLA, MERLIN and VLBA data. The angular scales probed in this work are ~ 10-200 milliarcsec (about 5-100 AU). The structure function in this range is found to be well represented by a power law S_tau(x) ~ x^{beta} with index beta ~ 0.33 +/- 0.07 corresponding to a power spectrum P_tau(U) ~ U^{-2.33}. This is slightly shallower than the earlier reported power law index of ~ 2.5-3.0 at ~ 1000 AU to few pc scales. The amplitude of the derived structure function is a factor of ~ 20-60 times higher than the extrapolated amplitude from observation of Cas A at larger scales. On the other hand, extrapolating the AU scale structure function for 3C 138 predicts the observed structure function for Cas A at the pc scale correctly. These results clearly establish that the atomic gas has significantly more structures in AU scales than expected from earlier pc scale observations. Some plausible reasons are identified and discussed here to explain these results. The observational evidence of a shallower slope and the presence of rich small scale structures may have implications for the current understanding of the interstellar turbulence.Comment: 6 pages, 5 figures. Accepted for publication in ApJ. The definitive version will be available at http://iopscience.iop.org

Prospects for Direct CP Violaton in Exclusive and Inclusive Charmless B decays

Within the Standard Model, CP rate asymmetries for $B\to K^-\pi^{+,0}$ could reach 10%. With strong final state phases, they could go up to 20--30%, even for $\bar K^0\pi^-$ mode which would have opposite sign. We can account for $K^-\pi^{+}$, $\bar K^0\pi^-$ and $\phi K$ rate data with new physics enhanced color dipole coupling and destructive interference. Asymmetries could reach 40--60% for $K\pi$ and $\phi K$ modes and are all of the same sign. We are unable to account for $K^-\pi^0$ rate. Our inclusive study supports our exclusive results.Comment: Minor changes, correct a small bug in Fig. 1(b). Version to appear in Phys. Rev. Let

Texture of fermion mass matrices in partially unified theories

We investigate the texture of fermion mass matrices in theories with partial unification (for example $SU(2)_L\times SU(2)_R\times SU(4)_c$) at a scale $\sim 10^{12}$ GeV. Starting with the low energy values of the masses and the mixing angles, we find only two viable textures with atmost four texture zeros. One of these corresponds to a somewhat modified Fritzsch textures. A theoretical derivataion of these textures leads to new interesting relations among the masses and the mixing angles.Comment: 10 pages(Latex

Solving rate equations for electron tunneling via discrete quantum states

We consider the form of the current-voltage curves generated when tunneling spectroscopy is used to measure the energies of individual electronic energy levels in nanometer-scale systems. We point out that the voltage positions of the tunneling resonances can undergo temperature-dependent shifts, leading to errors in spectroscopic measurements that are proportional to temperature. We do this by solving the set of rate equations that can be used to describe electron tunneling via discrete quantum states, for a number of cases important for comparison to experiments, including (1) when just one spin-degenerate level is accessible for transport, (2) when 2 spin-degenerate levels are accessible, with no variation in electron-electron interactions between eigenstates, and (3) when 2 spin-degenerate levels are accessible, but with variations in electron-electron interactions. We also comment on the general case with an arbitrary number of accessible levels. In each case we analyze the voltage-positions, amplitudes, and widths of the current steps due to the quantum states.Comment: REVTeX 4, 10 pages, 12 figures, submitted to Phys. Rev. B. Associated programs available at http://www.ccmr.cornell.edu/~ralph

Getting Its Kicks: A VLBA Parallax for the Hyperfast Pulsar B1508+55

The highest velocity neutron stars establish stringent constraints on natal kicks, asymmetries in supernova core collapse, and the evolution of close binary systems. Here we present the first results of a long-term pulsar astrometry program using the VLBA. We measure a proper motion and parallax for the pulsar B1508+55, leading to model-independent estimates of its distance (2.37+0.23-0.20 kpc) and transverse velocity (1083+103-90 km/s), the highest velocity directly measured for a neutron star. We trace the pulsar back from its present Galactic latitude of 52.3 degrees to a birth site in the Galactic plane near the Cyg OB associations, and find that it will inevitably escape the Galaxy. Binary disruption alone is insufficient to impart the required birth velocity, and a natal kick is indicated. A composite scenario including a large kick along with binary disruption can plausibly account for the high velocity.Comment: 5 pages, including 2 figures; accepted by ApJL; associated NRAO press release at http://www.nrao.edu/pr/2005/fastpulsar

Pulsar Magnetospheric Emission Mapping: Images and Implications of Polar-Cap Weather

The beautiful sequences of ``drifting'' subpulses observed in some radio pulsars have been regarded as among the most salient and potentially instructive characteristics of their emission, not least because they have appeared to represent a system of subbeams in motion within the emission zone of the star. Numerous studies of these ``drift'' sequences have been published, and a model of their generation and motion articulated long ago by Ruderman & Sutherland (1975); but efforts thus far have failed to establish an illuminating connection between the drift phemomenon and the actual sites of radio emission. Through a detailed analysis of a nearly coherent sequence of ``drifting'' pulses from pulsar B0943+10, we have in fact identified a system of subbeams circulating around the magnetic axis of the star. A mapping technique, involving a ``cartographic'' transform and its inverse, permits us to study the character of the polar-cap emission ``map'' and then to confirm that it, in turn, represents the observed pulse sequence. On this basis, we have been able to trace the physical origin of the ``drifting-subpulse'' emission to a stably rotating and remarkably organized configuration of emission columns, in turn traceable possibly to the magnetic polar-cap ``gap'' region envisioned by some theories.Comment: latex with five eps figure

Upper Limits On Periodic, Pulsed Radio Emission from the X-Ray Point Source in Cassiopeia A

The Chandra X-ray Observatory recently discovered an X-ray point source near the center of Cassiopeia A, the youngest known Galactic supernova remnant. We have conducted a sensitive search for radio pulsations from this source with the Very Large Array, taking advantage of the high angular resolution of the array to resolve out the emission from the remnant itself. No convincing signatures of a dispersed, periodic source or of isolated dispersed pulses were found, whether for an isolated or a binary source. We derive upper limits of 30 and 1.3 mJy at 327 and 1435 MHz for the phase-averaged pulsed flux density from this source. The corresponding luminosity limits are lower than those for any pulsar with age less than 10^4 years. The sensitivities of our search to single pulses were 25 and 1.0 Jy at 327 and 1435 MHz. For comparison, the Crab pulsar emits roughly 80 pulses per minute with flux densities greater than 100 Jy at 327 MHz and 8 pulses per minute with flux densities greater than 50 Jy at 1435 MHz. These limits are consistent with the suggestion that the X-ray point source in Cas A adds to the growing number of neutron stars which are not radio pulsars.Comment: accepted by ApJ Letter

Two body decays of the bb-quark: Applications to direct CP violation, searches for electro-weak penguins and new physics

A systematic experimental search for two-body hadronic decays of the b-quark of the type b to quark + meson is proposed. These reactions have a well defined experimental signature and they should be theoretically cleaner compared to exclusive decays. Many modes have appreciable branching ratios and partial rate asymmetries may also be quite large (about 8-50%) in several of them. In a few cases electroweak penguins appear to be dominant and may be measurable. CP violating triple correlation asymmetries provide a clean test of the Standard Model.Comment: 12 pages 1 figure 1 tabl

Possible Candidates for SUSY SO(10) Model with an Intermediate Scale

We study the possibility of an intermediate scale existing in supersymmetric SO(10) grand unified theories: The intermediate scale is demanded to be around 10^{12} GeV so that neutrinos can obtain masses suitable for explaining the experimental data on the deficit of solar neutrino with Mikheev-Smirnov-Wolfenstein solution and the existence of hot dark matter. We show that any Pati-Salam type intermediate symmetries are excluded by requiring reasonable conditions and only $SU(2)_L\times SU(2)_R \times SU(3)_C\times U(1)_{B-L}$ is likely to be realized as an intermediate symmetry.Comment: LaTeX, 8 pages + 1 uuencoded eps figure (Error corrected

Large contribution of virtual Delbrueck scattering to the emission of photons by relativistic nuclei in nucleus-nucleus and electron-nucleus collisions

Delbrueck scattering is an elastic scattering of a photon in the Coulomb field of a nucleus via a virtual electron loop. The contribution of this virtual subprocess to the emission of a photon in the collision of ultra-relativistic nuclei Z_1 Z_2 -> Z_1 Z_2 gamma is considered. We identify the incoming virtual photon as being generated by one of the relativistic nuclei involved in the binary collision and the scattered photon as being emitted in the process. The energy and angular distributions of the photons are calculated. The discussed process has no infrared divergence. The total cross section obtained is 14 barn for Au-Au collisions at the RHIC collider and 50 barn for Pb-Pb collisions at the LHC collider. These cross sections are considerably larger than those for ordinary tree-level nuclear bremsstrahlung in the considered photon energy range m_e << E_\gamma << m_e gamma, where gamma is the Lorentz factor of the nucleus. Finally, photon emission in electron-nucleus collisions e Z -> e Z gamma is discussed in the context of the eRHIC option.Comment: 10 pages; 7 figure