The Dark Side of QSO Formation at High Redshifts

Observed high-redshift QSOs, at z~6, may reside in massive dark matter (DM) halos of more than 10^{12} Msun and are thus expected to be surrounded by overdense regions. In a series of 10 constrained simulations, we have tested the environment of such QSOs. Comparing the computed overdensities with respect to the unconstrained simulations of regions empty of QSOs, assuming there is no bias between the DM and baryon distributions, and invoking an observationally-constrained duty-cycle for Lyman Break Galaxies, we have obtained the galaxy count number for the QSO environment. We find that a clear discrepancy exists between the computed and observed galaxy counts in the Kim et al. (2009) samples. Our simulations predict that on average eight z~6 galaxies per QSO field should have been observed, while Kim et al. detect on average four galaxies per QSO field compared to an average of three galaxies in a control sample (GOODS fields). While we cannot rule out a small number statistics for the observed fields to high confidence, the discrepancy suggests that galaxy formation in the QSO neighborhood proceeds differently than in the field. We also find that QSO halos are the most massive of the simulated volume at z~6 but this is no longer true at z~3. This implies that QSO halos, even in the case they are the most massive ones at high redshifts, do not evolve into most massive galaxy clusters at z=0.Comment: 12 pages, 7 figures, revised after the referee comments, to be published by the Astrophysical Journa

The 3.5 keV Line from Stringy Axions

An interesting result in particle astrophysics is the recent detection of an unexplained 3.5 keV line from galaxy clusters. A promising model, which can explain the morphology of the signal and its non-observation in dwarf spheroidal galaxies, involves a 7 keV dark matter particle decaying into a pair of ultra-light axions that convert into photons in the magnetic field of the clusters. Given that light axions emerge naturally in 4D string vacua, in this paper we present a microscopic realisation of this model within the framework of type IIB flux compactifications. Dark matter is a local closed string axion which develops a tiny mass due to subdominant poly-instanton corrections to the superpotential and couples via kinetic mixing to an almost massless open string axion living on a D3-brane at a singularity. The interaction of this ultra-light axion with photons is induced by U(1) kinetic mixing. After describing the Calabi-Yau geometry and the brane set-up, we discuss in depth moduli stabilisation, the resulting mass spectrum and the strength of all relevant couplings.Comment: 27 pages + appendices, 1 figure; typos corrected, references added, additional comments on the cosmological history and DM production in the conclusion

Late Bilinguals Are Sensitive to Unique Aspects of Second Language Processing: Evidence from Clitic Pronouns Word-Order.

In two self-paced reading experiments we asked whether late, highly proficient, English-Spanish bilinguals are able to process language-specific morpho-syntactic information in their second language (L2). The processing of Spanish clitic pronouns' word order was tested in two sentential constructions. Experiment 1 showed that English-Spanish bilinguals performed similarly to Spanish-English bilinguals and revealed sensitivity to word order violations for a grammatical structure unique to the L2. Experiment 2 replicated the pattern observed for native speakers in Experiment 1 with a group of monolingual Spanish speakers, demonstrating the stability of processing clitic pronouns in the native language. Taken together, the results show that late bilinguals can process aspects of grammar that are encoded in L2-specific linguistic constructions even when the structure is relatively subtle and not affected for native speakers by the presence of a second language

Primordial Black Holes from String Inflation

We present a single-field string inflationary model which allows for the generation of primordial black holes in the low mass region where they can account for a significant fraction of the dark matter abundance. The potential is typical of type IIB fibre inflation models and features a plateau at CMB scales and a near inflection point at large distance scales where the power spectrum is enhanced due to a period of ultra slow-roll. The tunability of the underlying parameters is guaranteed by scanning through the string landscape and their stability against quantum corrections is ensured by an effective shift symmetry.Comment: Updated references, typos fixed. Version submitted to JCA