Review of Particle Physics Tanabashi, M.; Nakamura, K.; Tanaka, J. ...
Physical review. D,
08/2018, Letnik:
98, Številka:
3
Journal Article
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The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 2,873 new measurements from 758 papers, we list, evaluate, and average measured properties of ...gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Among the 118 reviews are many that are new or heavily revised, including a new review on Neutrinos in Cosmology.
The cosmic star formation histories are evaluated for different minimum masses of the initial halo structures, with allowance for realistic gas outflows. With a minimum halo mass of 10 super(7)-10 ...super(8) M sub( )and a moderate outflow efficiency, we reproduce both the current baryon fraction and the early chemical enrichment of the IGM. The intensity of the formation rate of "normal" stars is also well constrained by the observations: it has to be dominated by star formation in elliptical galaxies, except perhaps at very low redshift. The fraction of baryons in stars is predicted as are also the Type Ia and II supernova event rates. Comparison with SN observations in the redshift range z = 0-2 allows us to set strong constraints on the time delay of Type Ia supernovae (a delay of 63 Gyr is required to fit the data), the lower end of the mass range of the progenitors (2-8 M sub( )), and the fraction of white dwarfs that reproduce the Type Ia supernova (about 1%). The intensity of zero metallicity star formation below 270 M sub( )must be limited in order to avoid premature overenrichment of the IGM. About 50% of the metals present in the IGM at z = 0 have been produced by Population III stars at very high z. The remaining 50% are ejected later by galaxies forming normal stars. We conclude that about 10 super(-3) of the mass in baryons must lie in the first massive stars in order to produce enough ionizing photons to allow early reionization of the IGM by z 6 15.
Motivated by the Wilkinson Microwave Anisotropy Probe (WMAP) results indicating an early epoch of reionization, we consider alternative cosmic star formation models that are capable of reionizing the ...early intergalactic medium. We develop models that include an early burst of massive stars (with several possible mass ranges) combined with standard star formation. We compute the stellar ionizing flux of photons, and we track the nucleosynthetic yields for several elements: D, super(4)He, C, N, O, Si, S, Fe, and Zn. We compute the subsequent chemical evolution as a function of redshift, both in the intergalactic medium and in the interstellar medium of forming galaxies, starting with the primordial objects that are responsible for the reionization. We apply constraints from the observed abundances in the Lya forest and in damped Lya clouds in conjunction with the ability of the models to produce the required degree of reionization. We also consider possible constraints associated with the observations of the two extremely metal-poor stars HE 0107-5240 and CS 22949-037. We confirm that an early top-heavy stellar component is required, since a standard star formation model is unable to reionize the early universe and reproduce the abundances of the very metal-poor halo stars. A bimodal (or top-heavy) initial mass function (IMF; 40-100 M sub( )) is our preferred scenario, compared with the extreme mass range ( 100 M sub( )) often assumed to be responsible for the early stages of reionization. A mode of even more extreme stellar masses in the range .270 M sub( )has also been considered. All massive stars in this mode collapse entirely into black holes, and as a consequence, chemical evolution and reionization are decorrelated. The ionizing flux from these very massive stars can easily reionize the universe at z 6 17. However, the chemical evolution in this case is exactly the same as in the standard star formation model, and the observed high-redshift abundances are not reproduced. We show that the initial top-heavy mode, which originally was introduced to reionize the early universe, produces rapid initial metal pollution. The existence of old, C-rich halo stars with high O/Fe and C/Fe ratios is predicted as a consequence of these massive stars. The recently observed abundances in the oldest halo stars could trace this very specific stellar population. The extreme mass range is disfavored, and there is no evidence, nor any need, for a hypothesized primordial population of very massive stars in order to account for the chemical abundances of extremely metal-poor halo stars or of the intergalactic medium. The combined population of early-forming normal (0.1-100 M sub( )) and massive (40-100 M sub( )) stars can simultaneously explain the cosmic chemical evolution and the observations of extremely metal-poor halo stars and also account for early cosmological reionization.
Interaction through online social networks potentially results in the contestation of prevailing ideas about health and health care, and to mass protest where health is put at risk or health care ...provision is wanting. Through a review of the academic literature and case studies of four social networking health sites (PatientsLikeMe, Mumsnet, Treatment Action Campaign, and My Pro Ana), we establish the extent to which this phenomenon is documented, seek evidence of the prevalence and character of health‐related networks, and explore their structure, function, participants, and impact, seeking to understand how they came into being and how they sustain themselves. Results indicate mass protest is not arising from these established health‐related networking platforms. There is evidence of changes in policy following campaigning activity prompted by experiences shared through social networking such as improved National Health Service care for miscarriage (a Mumsnet campaign). Platform owners and managers have considerable power to shape these campaigns. Social networking is also influencing health policy indirectly through increasing awareness and so demand for health care. Transient social networking about health on platforms such as Twitter were not included as case studies but may be where the most radical or destabilizing influence on health care policy might arise.
Proposed Post-LEP benchmarks for supersymmetry Battaglia, M.; De Roeck, A.; Ellis, J. ...
The European physical journal. C, Particles and fields,
12/2001, Letnik:
22, Številka:
3
Journal Article
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We propose a new set of supersymmetric benchmark scenarios, taking into account the constraints from LEP, \(b \rightarrow s \gamma, g_\mu - 2\) and cosmology. We work in the specific context of the ...constrained MSSM (CMSSM) with universal soft supersymetry-breaking masses and vanishing trilinear terms, assuming that R parity is conserved. We propose benchmark points that exemplify the different generic possibilities in this context, including focus-point models, points where coannihilation effects on the relic density are important, and points with rapid relic annihilation via direct-channel Higgs poles. We discuss the principal decays and signatures of the different classes of benchmark scenarios, and make initial estimates of the physics reaches of different accelerators, including the Tevatron collider, the LHC, and \(e^+ e^-\) colliders in the sub- and multi-TeV ranges. We stress the complementarity of hadron and lepton colliders, with the latter favoured for non-strongly-interacting particles and precision measurements. We mention features that could usefully be included in future versions of supersymmetric event generators.
Recently, new observations of super(6)Li in Population II stars of the Galactic halo have shown a surprisingly high abundance of this isotope, about a thousand times higher than its predicted ...primordial value. In previous papers, a cosmological model for the cosmic-ray-induced production of this isotope in the intergalactic medium (IGM) has been developed to explain the observed abundance at low metallicity. In this paper, given this constraint on the super(6)Li, we calculate the nonthermal evolution with redshift of D, Be, and B in the IGM. In addition to cosmological cosmic ray interactions in the IGM, we include additional processes driven by supernova explosions: neutrino spallation and a low-energy component in the structures ejected by outflows to the IGM. We take into account CNO CRs impinging on the intergalactic gas. Although subdominant in the Galactic disk, this process is shown to produce the bulk of Be and B in the IGM, due to the differential metal enrichment between structures (where CRs originate) and the IGM. We also consider the resulting extragalactic gamma-ray background, which we find to be well below existing data. The computation is performed in the framework of hierarchical structure formation, considering several star formation histories, including Population III stars. We find that D production is negligible and that a potentially detectable Be and B plateau is produced by these processes at the time of the formation of the Galaxy (z similar to 3).
The origin of dispersion in DLA metallicities Dvorkin, Irina; Silk, Joseph; Vangioni, Elisabeth ...
Monthly notices of the Royal Astronomical Society,
09/2015, Letnik:
452, Številka:
1
Journal Article
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Recent chemical abundance measurements of damped Ly α absorbers (DLAs) revealed an intrinsic scatter in their metallicity of ∼0.5 dex out to z ∼ 5. In order to explore the origin of this scatter, we ...build a semi-analytic model which traces the chemical evolution of the interstellar matter in small regions of the Universe with different mean density, from over- to underdense regions. We show that the different histories of structure formation in these regions, namely halo abundance, mass and stellar content, are reflected in the chemical properties of the protogalaxies, and in particular of DLAs. We calculate mean metallicity–redshift relations and show that the metallicity dispersion arising from this environmental effect amounts to ∼0.25 dex and is an important contributor to the observed overall intrinsic scatter.
Since the 1915 launch of the first international eradication initiative targeting a human pathogen, much has been learned about the determinants of eradicability of an organism. The authors outline ...the first 4 eradication efforts, summarizing the lessons learned in terms of the 3 types of criteria for disease eradication programs: (1) biological and technical feasibility, (2) costs and benefits, and (3) societal and political considerations.
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