We investigate the effect of non-evaporating primordial black holes (PBHs) on the ionization and thermal history of the universe. X-rays emitted by gas accretion onto PBHs modify the cosmic recombination history, producing measurable effects on the spectrum and anisotropies of the Cosmic Microwave Background (CMB). Using the third-year WMAP data and FIRAS data we improve existing upper limits on the abundance of PBHs with masses > 0.1 M ⊙ by several orders of magnitude.Fitting WMAP3 data with cosmological models that do not allow for non-standard recombination histories, as produced by PBHs or other early energy sources, may lead to an underestimate of the best-fit values of the amplitude of linear density fluctuations (σ 8 ) and the scalar spectral index (n s ). Cosmological parameter estimates are affected because models with PBHs allow for larger values of the Thomson scattering optical depth, whose correlation with other parameters may not be correctly taken into account when PBHs are ignored. Values of τ e ∼ 0.2, n s ∼ 1 and σ 8 ∼ 0.9 are allowed at 95% CF. This result that may relieve recent tension between WMAP3 data and clusters data on the value of σ 8 .PBHs may increase the primordial molecular hydrogen abundance by up to two orders of magnitude, this promoting cooling and star formation. The suppression of galaxy formation due to X-ray heating is negligible for models consistent with the CMB data. Thus, the formation rate of the first galaxies and stars would be enhanced by a population of PBHs. Subject headings: cosmology: theory -cosmology: observations -early universe -cosmic microwave background -cosmological parameters -black hole physics
We discuss the possibilities for the growth of primordial black holes (PBHs) via the accretion of dark matter. In agreement with previous works, we find that accretion during the radiation-dominated era does not lead to a significant mass increase. However, during matter domination, PBHs may grow by up to 2 orders of magnitude in mass through the acquisition of large dark matter halos. We discuss the possibility of PBHs being an important component in dark matter halos of galaxies, as well as their potential to explain the ultraluminous X-ray sources (ULXs) observed in nearby galactic disks. We point out that although PBHs are ruled out as the dominant component of dark matter, there is still a great deal of parameter space that is open to their playing a role in the modern-day universe. For example, a primordial halo population of PBHs each at 10 2.5 M , making up 0.1% of the dark matter, grows to 10 4.5 M via the accumulation of dark matter halos and accounts for $10% of the dark matter mass by a redshift of z % 30. These intermediate-mass black holes may then ''light up'' when passing through molecular clouds, becoming visible as ULXs at the present day, or they may form the seeds for supermassive black holes at the centers of galaxies.
We investigate the Lyth relationship between the tensor-scalar ratio, r, and the variation of the inflaton field, ∆φ, over the course of inflation. For inflationary models that produce at least 55 e-folds of inflation, there is a correlation between r and ∆φ as anticipated by Lyth, but the scatter around the relationship is huge. However, for inflationary models that satisfy current observational constraints on the scalar spectral index and its first derivative, the Lyth relationship is much tighter. In particular, any inflationary model with r > ∼ 10 −3 must have ∆φ > ∼ m pl . Large field variations are therefore required if a tensor mode signal is to be detected in any foreseeable cosmic microwave background (CMB) polarization experiment.
Concerted effort is currently ongoing to open up the Epoch of Reionization (z ∼15-6) for studies with IR and radio telescopes. Whereas IR detections have been made of sources (Lyman-α emitters, quasars and drop-outs) in this redshift regime in relatively small fields of view, no direct detection of neutral hydrogen, via the redshifted 21-cm line, has yet been established. Such a direct detection is expected in the coming years, with ongoing surveys, and could open up the entire universe from z ∼6-200 for astrophysical and cosmological studies, opening not only the Epoch of Reionization, but also its preceding Cosmic Dawn (z ∼30-15) and possibly even the later phases of the Dark Ages (z ∼200-30). All currently ongoing experiments attempt statistical detections of the 21-cm signal during the Epoch of Reionization, with limited signal-to-noise. Direct imaging, except maybe on the largest (degree) scales at lower redshifts, as well as higher redshifts will remain out of reach. The Square Kilometre Array (SKA) will revolutionize the field, allowing direct imaging of neutral hydrogen from scales of arc-minutes to degrees over most of the redshift range z ∼6-28 with SKA1-LOW, and possibly even higher redshifts with the SKA2-LOW. In this SKA will be unique, and in parallel provide enormous potential of synergy with other upcoming facilities (e.g. JWST). In this chapter we summarize the physics of 21-cm emission, the different phases the universe is thought to go through, and the observables that the SKA can probe, referring where needed to detailed chapters in this volume. This is done within the framework of the current SKA1 baseline design and a nominal CD/EoR straw-man survey, consisting of a shallow, medium-deep and deep survey, the latter probing down to ∼1 mK brightness temperature on arc-minute scales at the end of reionization. Possible minor modifications to the design of SKA1 and the upgrade to SKA2 are discussed, in addition to science that could be done already during roll-out when SKA1 still has limited capabilities and/or core collecting area.Advancing Astrophysics with the Square Kilometre Array
Now that conventional weakly interacting massive particle (WIMP) dark matter searches are approaching the neutrino floor, there has been a resurgence of interest in detectors with sensitivity to nuclear recoil directions. A large-scale directional detector is attractive in that it would have sensitivity below the neutrino floor, be capable of unambiguously establishing the galactic origin of a purported dark matter signal, and could serve a dual purpose as a neutrino observatory. We present the first detailed analysis of a 1000 m 3 -scale detector capable of measuring a directional nuclear recoil signal at low energies. We propose a modular and multi-site observatory consisting of time projection chambers (TPCs) filled with helium and SF6 at atmospheric pressure. By comparing several available readout technologies, we identify high-resolution strip readout TPCs as the optimal tradeoff between performance and cost. We estimate that suitable angular resolution and head-tail recognition is achievable down to helium recoil energies of ∼6 keVr. Depending on the readout technology, an average of only 4-5 detected 100-GeV c −2 WIMP-fluorine recoils above 50 keVr are sufficient to rule out an isotropic recoil distribution at 90% CL. An average of 10-20 helium recoils above 6 keVr or only 3-4 helium recoils above 20 keVr would suffice to distinguish a 10 GeV c −2 WIMP signal from the solar neutrino background. High-resolution TPC charge readout also enables powerful electron background rejection capabilities well below 10 keV. We detail background and site requirements at the 1000 m 3 -scale, and identify materials that require improved radiopurity. The final experiment, which we name Cygnus-1000, will be able to observe ∼ 10-40 neutrinos from the Sun, depending on the final energy threshold. With the same exposure, the sensitivity to spin independent cross sections will extend into presently unexplored sub-10 GeV c −2 parameter space. For spin dependent interactions, already a 10 m 3 -scale experiment could compete with upcoming generation-two detectors, but Cygnus-1000 would improve upon this considerably. Larger volumes would bring sensitivity to neutrinos from an even wider range of sources, including galactic supernovae, nuclear reactors, and geological processes.
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