Raman Research Institute Digital Repository

    The Japanese space gravitational wave antenna - DECIGO

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    Restricted Access.Gravitational Waves: Proceedings of the Seventh Edoardo Amaldi Conference,2008The objectives of the DECi-hertz Interferometer Gravitational Wave Observatory (DECIGO) are to open a new window of observation for gravitational wave astronomy and to obtain insight into significant areas of science, such as verifying and characterizing inflation, determining the thermal history of the universe, characterizing dark energy, describing the formation mechanism of supermassive black holes in the center of galaxies, testing alternative theories of gravity, seeking black hole dark matter, understanding the physics of neutron stars and searching for planets around double neutron stars. DECIGO consists of four clusters of spacecraft in heliocentric orbits; each cluster employs three drag-free spacecraft, 1000 km apart from each other, whose relative displacements are measured by three pairs of differential Fabry–Perot Michelson interferometers. Two milestone missions, DECIGO pathfinder and Pre-DECIGO, will be launched to demonstrate required technologies and possibly to detect gravitational waves

    Electromagnetically induced transparency with quantum interferometry

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    Restricted AccessWe have shown that electromagnetically induced transparency can be achieved by control-probe interferometry using two delayed phase-locked ultrashort pulses. Two vibrational wavepackets on the excited state, excited by two delayed phase-locked ultrashort pulses, interfere constructively or destructively leading to enhancement or suppression of absorption to a selective set of vibrational levels. Depending on the phase difference and the delay between the pulses with same carrier frequency, one can design different transparency windows between absorption peaks at consecutive even(odd) vibrational levels by eliminating absorption at odd(even) vibrational levels. We have shown that by switching the phase difference of two delayed femtosecond pulses, one can switch to complete elimination of absorption from enhanced absorption to a particular set of vibrational levels in the excited state. Thus, switching of transparency through window between odd vibrational levels to that between even vibrational levels is possible. By properly choosing the temporal width and the carrier frequency of the pulses, lossless transmission of complete or bands of frequencies of the pulses can be achieved through these transparency windows. Hence, designing of single- or multi-mode transparency windows in NaH molecule is feasible by control-probe quantum interferometry

    Constraints on changes in fundamental constants from a cosmologically distant OH absorber or emitter

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    Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We have detected the four 18 cm OH lines from the z˜0.765 gravitational lens toward PMN J0134-0931. The 1612 and 1720 MHz lines are in conjugate absorption and emission, providing a laboratory to test the evolution of fundamental constants over a large lookback time. We compare the HI and OH main line absorption redshifts of the different components in the z˜0.765 absorber and the z˜0.685 lens toward B0218+357 to place stringent constraints on changes in F≡gp[α2/μ]1.57. We obtain [ΔF/F]=(0.44±0.36stat±1.0syst)×10-5, consistent with no evolution over the redshift range 0<z≲0.7. The measurements have a 2σ sensitivity of [Δα/α]<6.7×10-6 or [Δμ/μ]<1.4×10-5 to fractional changes in α and μ over a period of ˜6.5Gyr, half the age of the Universe. These are among the most sensitive constraints on changes in μ

    Sunyaev-zel'dovich effect with the Australia telescope

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    Restricted Access.We have used a Fourier synthesis telescope, the Australia Telescope, to search for the Sunyaev-Zel'dovich effect in clusters of galaxies. Self-consistent models of clusters have been developed to determine the relationship between physical parameters of clusters and measured interferometric visibility functions

    Possible forest of emission lines from protogalaxies

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    Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We discuss the possibility of detecting protogalaxies in the ultraviolet, assuming that galaxy formation occurred at z ~ 5-6. We show that the diffuse gas in collapsing galaxy-sized objects with temperatures ~10^6+0.5 K, and with modest metallicities, should produce many emission lines from highly ionized iron atoms. We compare the expected luminosity from models of galaxy formation with the sensitivity of the Hubble Space Telescope (HST)

    Effects of photoionization on galaxy formation

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    Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We investigate the effects of the observed UV background radiation on galaxy formation. Photoionization by UV radiation decreases the cooling rate of the gas in halos, so that objects with only large density contrasts can self-shield against the background radiation, thereby allowing the shielded neutral cores to cool and form stars. In the context of the cold dark matter (CDM) model, we use the criterion that self-shielding is essential for star formation to calculate the mass function of galaxies based on both Press-Schechter and the peaks formalisms. The ionizing UV radiation causes inhibition of galaxy formation-we show the decrease in the number density of the galaxies quantitatively. We also find that the merging in general is made inefficient by the UV photons through photoionization of the gas in the bigger system into which small objects are incorporated. The latter means that, in a merging-dominated region, where the number density at the low-mass end Mb less than or approximately = 1010 solar mass) is usually expected to decrease with time, the trend is reversed (the number of low-mass galaxies is greater at lower redshifts z) due to the increasing UV flux with time after z approximately 2. We further discuss the implication of our results for the number counts of galaxies and possible evolution of the luminosity function of the galaxies

    Gamma line radiation from stellar winds in the orion complex : a test for the theory of cosmic-ray origin

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    Restricted Access.We consider y-ray emission from heavy nuclei that are accelerated in the shocks of stellar winds and are excited in interactions with the ambient matter in the Orion complex. We show that the recent detection of y-ray lines in the Orion complex by the COMPTEL telescope can be explained by such a scenario, assuming cosmic abundances. The scenario is consistent with recent models of cosmic ray acceleration in the stellar winds of massive stars. Key words: stars: mass-loss - cosmic rays - gamma-rays: theory

    On the source of ionization of the intergalactic medium at z~2.4

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    Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We use the recent detection of H ii absorption at z=2.2-2.6 in the line of sight of the quasar HS 1700+64 to put bounds on the sources of ionization. We find that, given the uncertainty in tau^HI_GP and the model of absorption in the intergalactic medium (IGM), a wide range of possible sources of ionization is still allowed by the observations. We show that a significant contribution from star-forming galaxies is allowed and is consistent with the proximity effect. In the case of photoionization by the UV background radiation, the contribution of star-forming galaxies to the intensity at 912 A can be within a range of ~1-15 times that of the quasars. We also investigate the case of a collisionally ionized IGM. We show that although collisional ionization can be a dominant source of ionization at z~2.4 (taking into account the upper limit on the Compton y-parameter of the microwave background radiation), the thermal state of the IGM cannot yet be determined. We also consider Sciama's model of radiatively decaying neutrinos, and show that the model of decaying neutrinos is consistent with the observations

    On the enrichment of the intergalactic medium by galactic winds

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    Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Observations of metal lines in Ly-alpha absorption systems of small H I column density and their ubiquitous nature suggest that the intergalactic medium (IGM) was enriched to about Z about 0.01 Z(solar) by a redshift z about 3. We investigate the role of winds from small star-forming galaxies at high z in enriching the IGM. The existence of large numbers of small galaxies at high z follows naturally from hierarchical clustering theories. For analytical simplicity we assume that the galactic winds escape the galaxies at a single characteristic redshift z(in), and we model the galactic winds as spherical shock waves propagating through the IGM. We then calculate the probability distribution of the metallicity of the IGM, as a function of time, adopting plausible galaxy mass functions, cooling physics, star formation efficiencies, gas ejection dynamics, and nucleosynthesis yields. We compare this expected distribution with the observed distribution of metallicities in the Ly-alpha forest at z = 3, with the metal-poor stars in the halo of our Galaxy, and with other observational constraints on such a scenario. We find that galactic winds at high z could have enriched the IGM to a mean metallicity of Z about 0.01 Z(solar) at z about 3, with a standard deviation of the same order, if z(in) is less than about 5, and that this satisfies all the observational constraints

    Emission from proto-galaxies in the pristine state

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