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Munch June 12th, 2006 |
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How can we test seesaw experimentally?Authors: M. R. Buckley, H. MurayamaComments: 5 pages, 4 figures The seesaw mechanism for the small neutrino mass has been a popular paradigm, yet it has been believed that there is no way to test it experimentally. We present a conceivable outcome from future experiments that would convince us of the seesaw mechanism. It would involve a variety of data from LHC, ILC, cosmology, underground, and low-energy flavor violation experiments to establish the case. Full-text: PostScript, PDF, or Other formatsA re-analysis of the three-year WMAP temperature power spectrum and likelihoodAuthors: H. K. Eriksen, Greg Huey, R. Saha, F. K. Hansen, J. Dick, A. J. Banday, K. M. Gorski, P. Jain, J. B. Jewell, L. Knox, D. L. Larson, I. J. O'Dwyer, T. Souradeep, B. D. WandeltComments: 14 pages, 8 figures, submitted to ApJ We analyze the three-year WMAP temperature anisotropy data seeking to confirm the power spectrum and likelihoods published by the WMAP team. We apply five independent implementations of four algorithms to the power spectrum estimation and two implementations to the parameter estimation. These results are then exhaustively cross-checked by the five different research groups who performed the work. This provides a high degree of confidence that the results are well understood with respect to both implicit and explicit assumptions. Our single most important result is that we broadly confirm the WMAP power spectrum and analysis. Still, we do find two small but potentially important discrepancies: On large angular scales there is a small power excess in the WMAP spectrum (5-10% at l < 50) primarily due to residual foregrounds and secondarily to numerical and statistical issues. On small angular scales there is a systematic difference between the V- and W-band spectra (few percent at l > 300). The origin of the latter discrepancy has not yet been identified, and this requires further attention. As far as the low-l bias is concerned, most parameters are affected by a few tenths of a sigma. The most important effect is seen in n_s, for which the evidence for n_s /= 1 is weakened by 0.4 sigma: For the combination of WMAP, Acbar and BOOMERanG, the significance of n_s /= 1 drops from ~2.7 sigma to ~2.3 sigma when correcting for this bias. Finally, we propose a few simple improvements to the low-l WMAP likelihood code that alleviate the low-l bias, and also introduce a few important extensions to the Gibbs sampling method that allows for proper sampling of the low signal-to-noise regime. Full-text: PostScript, PDF, or Other formatsFormation of Primordial Stars in a LCDM UniverseAuthors: Naoki Yoshida (Nagoya University), Kazuyuki Omukai (NAOJ), Lars Hernquist (CfA-Harvard), Tom Abel (KIPAC, Stanford)Comments: 27 pages, 13 embedded figures. Submitted to ApJ We study the formation of the first generation of stars in the standard cold dark matter model, using a very high-resolution hydordynamic simulations. Our simulation achieves a dynamic range of 10^{10} in length scale. With accurate treatment of atomic and molecular physics, it allows us to study the chemo-thermal evolution of primordial gas clouds to densities up to n = 10^{16}/cc without assuming any a priori equation of state; a six orders of magnitudes improvement over previous three-dimensional calculations. All the relevant atomic and molecular cooling and heating processes, including cooling by collision-induced continuum emission, are implemented. For calculating optically thick H2 cooling at high densities, we use the Sobolev method. To examine possible gas fragmentation owing to thermal instability, we compute explicitly the growth rate of isobaric perturbations. We show that the cloud core does not fragment in either the low-density or high-density regimes. We also show that the core remains stable against gravitational deformation and fragmentation. We obtain an accurate gas mass accretion rate within a 10 Msun innermost region around the protostar. The protostar is accreting the surrounding hot gas at a rate of 0.001-0.01 Msun/yr. From these findings we conclude that primordial stars formed in early minihalos are massive. We carry out proto-stellar evolution calculations using the obtained accretion rate. The resulting mass of the first star is M_ZAMS = 60-100 Msun, with the exact mass dependent on the actual accretion rate. Full-text: PostScript, PDF, or Other formatsNeutrino Oscillation Effects on Supernova Light Element SynthesisAuthors: T. Yoshida (1,2), T. Kajino (2), H. Yokomakura (3), K. Kimura (3), A. Takamura (4), D. H. Hartmann (5) ((1) Tohoku U., (2) NAOJ, (3) Nagoya U., (4) Toyota Coll. Tech., (5) Clemson U.)Comments: 35 pages, 17 figures, accepted for publication in Astrophysical Journal Report-no: NAOJ-Th-Ap 2006, No. 1 Neutrino oscillations affect light element synthesis through the neutrino-process in supernova explosions. The 7Li and 11B yields produced in a supernova explosion of a 16.2 solar-mass star model increase by factors of 1.9 and 1.3 in the case of large mixing angle solution with normal mass hierarchy and sin^{2}2theta_{13} > 0.002 compared with those without the oscillations. In the case of inverted mass hierarchy or nonadiabatic 13-mixing resonance, the increment of their yields is much smaller. Neutrino oscillations raise the reaction rates of charged-current neutrino-process reactions in the region outside oxygen-rich layers. The number ratio of 7Li/11B could be a tracer of normal mass hierarchy and relatively large theta_{13}, still satisfying sin^{2}2theta_{13} < 0.1, through future precise observations in stars having strong supernova component. Full-text: PostScript, PDF, or Other formatsCosmic reionization constraints on the nature of cosmological perturbationsAuthors: Pedro P. Avelino, Andrew R. LiddleComments: 5 pages, 5 figures We study the reionization history of the Universe in cosmological models with non-Gaussian density fluctuations, taking them to have a renormalized $\chi^2$ probability distribution function parametrized by the number of degrees of freedom, $\nu$. We compute the ionization history using a simple semi-analytical model, considering various possibilities for the astrophysics of reionization. In all our models we require that reionization is completed prior to $z=6$, as required by the measurement of the Gunn--Peterson optical depth from the spectra of high-redshift quasars. We confirm previous results demonstrating that such a non-Gaussian distribution leads to a slower reionization as compared to the Gaussian case. We further show that the recent WMAP three-year measurement of the optical depth due to electron scattering, $\tau=0.09 \pm 0.03$, weakly constrains the allowed deviations from Gaussianity on the small scales relevant to reionization if a constant spectral index is assumed. We also confirm the need for a significant suppression of star formation in mini-halos, which increases dramatically as we decrease $\nu$. Full-text: PostScript, PDF, or Other formatsWeighing neutrinos in the presence of a running primordial spectral indexAuthors: Bo Feng, Jun-Qing Xia, Jun'ichi Yokoyama, Xinmin Zhang, Gong-Bo ZhaoComments: 5 pages, 3 figures Revtex4 The three-year WMAP(WMAP3), combined with other cosmological observations from galaxy clustering and Type Ia Supernova (SNIa), prefers a non-vanishing running of the primordial spectral index independent of the low CMB multipoles. Motivated by this feature we study cosmological constraint on the neutrino mass, which severely depends on what prior we adopt for the spectral shape of primordial fluctuations, taking possible running into account. As a result we find a more stringent constraint on the sum of the three neutrino masses, m_\nu < 0.76 eV (2 \sigma), compared with the case where power-law prior is adopted to the primordial spectral shape. Full-text: PostScript, PDF, or Other formatsCan sterile neutrinos be ruled out as warm dark matter candidates?Authors: Matteo Viel, Julien Lesgourgues, Martin G. Haehnelt, Sabino Matarrese, Antonio RiottoComments: 5 pages, 3 figures We present constraints on the mass of Warm Dark Matter (WDM) particles from a combined analysis of the matter power spectrum inferred from the SDSS (Sloan Digital Sky Survey) Lyman-alpha flux power spectrum at 2.2<z<4.2, cosmic microwave background data and the galaxy power spectrum. We obtain a lower limit of m_s > 10 keV (2 sigma) if the WDM consists of sterile neutrinos and m_wdm > 2 keV (2 sigma) for early decoupled thermal relics. These results significantly improve our previous estimates based on high-resolution Lyman-alpha forest data at lower redshift. Our new limits are consistent with those of Seljak et al. (2006), albeit ~ 30 % smaller. If we combine this bound with the constraint derived from X-ray flux observations in the Coma cluster periphery (Boyarsky et al.), we find that the only allowed sterile neutrino mass is ~ 10 keV (in the standard production scenario with non-resonant neutrino oscillations). Adding constraints based on X-ray fluxes from the Andromeda galaxy or the Milky Way, we find that dark matter particles cannot be sterile neutrinos, unless the latter are produced by resonant oscillations or get diluted by some large entropy release. Full-text: PostScript, PDF, or Other formats
The Cosmological Evolution of the Average Mass Per BaryonAuthors: Gary Steigman (The Ohio State University)Comments: 3 pages; no figures Subsequent to the early Universe quark-hadron transition the universal baryon number is carried by nucleons: neutrons and protons. The total number of nucleons is preserved as the Universe expands, but as it cools lighter protons are favored over heavier neutrons reducing the average mass per baryon. During primordial nucleosynthesis free nucleons are transformed into bound nuclides, primarily hydrogen and helium, and the nuclear binding energies are radiated away, further reducing the average mass per baryon. In particular, the reduction in the average mass per baryon resulting from Big Bang Nucleosynthesis modifies the numerical factor relating the baryon (nucleon) mass density to the nucleon number density. Here the average mass per baryon, m_B, is tracked from the early Universe to the present and the result is used to relate the present ratio of baryons to photons (by number) to the present baryon mass density at a level of accuracy commensurate with that of recent cosmological data. Full-text: PostScript, PDF, or Other formatsNon-thermal Production of Dark Matter from Late-Decaying Scalar Field at Intermediate ScaleAuthors: Motoi Endo, Fuminobu TakahashiComments: 21 pages, 1 figure Report-no: DESY 06-071 We examine non-thermal dark matter production from a late-decaying scalar field, with a particular attention on non-renormalizable operators of D=5 through which the scalar field decays into the standard model particles and their superpartners. We show that almost the same number of superparticles as that of particles are generally produced from the decay. To avoid the gravitino overproduction problem, the decay is favored to proceed via interactions with an intermediate cut-off scale M << M_P. This should be contrasted to the conventional scenario using the modulus decay. The bosonic supersymmetry partner of the axion, i.e., saxion, is proposed as a natural candidate for such late-decaying scalar fields. We find that a right amount of the wino/higgsino dark matter with a mass of O(100) GeV is obtained for the saxion mass around the weak scale and axion decay constant, F_A = O(10^{9-12}) GeV. Full-text: PostScript, PDF, or Other formats |
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