The critical radiation intensity for direct collapse black hole formation: dependence on the radiation spectral shape

It has been proposed that supermassive black holes (SMBHs) are originated from direct-collapse black holes (DCBHs) that are formed at z gtrsim 10 in the primordial gas in the case that H2 cooling is suppressed by strong external radiation. In this work, we study the critical specific intensity J^crit required for DCBH formation for various radiation spectral shapes by a series of one-zone calculations of a collapsing primordial- gas cloud. We calculate the critical specific intensity at the Lyman-Werner (LW) bands J^crit_LW,21 (in units of 10^-21 erg s^-1 Hz^-1 sr^-1 cm^-2) for realistic spectra of metal-poor galaxies. We find J^crit is not sensitive to the age or metallicity for the constant star formation galaxies with J^crit_LW,21 = 1300-1400, while J^crit decreases as galaxies become older or more metal-enriched for the instantaneous starburst galaxies. However, such dependence for the instantaneous starburst galaxies is weak for the young or extremely metal-poor galaxies: J^crit_LW,21 = 1000-1400 for the young galaxies and J^crit_LW,21 approx 1400 for the extremely metal-poor galaxies. The typical value of J^crit for the realistic spectra is higher than those expected in the literature, which affects the estimated DCBH number density n_DCBH. By extrapolating the result of Dijkstra, Ferrara and Mesinger, we obtain n_DCBH sim 10^-10 cMpc^-3 at z = 10, although there is still large uncertainty in this estimation.Comment: 11 pages, 6 figures, submitted to MNRA

Developments in Finite Temperature QCD on the Lattice with Dynamical Quarks

I report on some recent developments in nonperturbative studies of finite temperature QCD with dynamical quarks on the lattice. I discuss new studies of improved lattice actions and their application to finite temperature QCD. I also summarize the status of lattice investigations about the order of the finite temperature QCD transition for the case of two flavors of degenerate light quarks, using both staggered and Wilson lattice fermions.Comment: Review presented at the International Workshop on ``Physics of Relativistic Heavy Ion Collisions'', Kyoto, Japan, 9--11 June 1997. To be published in the Proceedings [Prog. Theor. Phys., Suppl.

From Geometry to Quantum Computation

The aim of this paper is to introduce our idea of Holonomic Quantum Computation (Computer). Our model is based on both harmonic oscillators and non-linear quantum optics, not on spins of usual quantum computation and our method is moreover completely geometrical. We hope that therefore our model may be strong for decoherence.Comment: Latex File, 12 pages, A talk at the 2nd International Symposium `` Quantum Theory and Symmetries'', Krakow, 18-21, July, 200

Introduction to Grassmann Manifolds and Quantum Computation

Geometrical aspects of quantum computing are reviewed elementarily for non-experts and/or graduate students who are interested in both Geometry and Quantum Computation. In the first half we show how to treat Grassmann manifolds which are very important examples of manifolds in Mathematics and Physics. Some of their applications to Quantum Computation and its efficiency problems are shown in the second half. An interesting current topic of Holonomic Quantum Computation is also covered. In the Appendix some related advanced topics are discussed.Comment: Latex File, 28 pages, corrected considerably in the process of refereeing. to appear in Journal of Applied Mathematic

Exponentiation of certain Matrices related to the Four Level System by use of the Magic Matrix

In this paper we show how to calculate explicitly the exponential of certain matrices, which are evolution operators governing the interaction of the four level system of atoms and the radiation, etc. We present a consistent method in terms of the magic matrix by Makhlin. As a closely related subject, we derive a closed form expression of the Baker-Campbell-Hausdorff formula for a class of matrices in SU(4), by use of the method developed by the present authors in quant-ph/0610009.Comment: Latex ; 13 pages ; 2 figures ; substantial changes (including the title) made. To appear in Yokohama Mathematical Journal (2007