A number of important observables exhibit logarithms in their perturbative description that are induced by emissions at widely separated rapidities. These include transverse-momentum (qT) logarithms, ...logarithms involving heavy-quark or electroweak gauge boson masses, and small-x logarithms. In this paper, we initiate the study of rapidity logarithms, and the associated rapidity divergences, at subleading order in the power expansion. This is accomplished using the soft collinear effective theory (SCET). We discuss the structure of subleading-power rapidity divergences and how to consistently regulate them. We introduce a new pure rapidity regulator and a corresponding MS¯\ \overline{\mathrm{MS}} \-like scheme, which handles rapidity divergences while maintaining the homogeneity of the power expansion. We find that power-law rapidity divergences appear at subleading power, which give rise to derivatives of parton distribution functions. As a concrete example, we consider the qT spectrum for color-singlet production, for which we compute the complete qT2/Q2 suppressed power corrections at Oαs\ \mathcal{O}\left({\alpha}_s\right) \, including both logarithmic and nonlogarithmic terms. Our results also represent an important first step towards carrying out a resummation of subleading-power rapidity logarithms.
Summary
Simultaneous characterization of taxonomic composition, metabolic gene content and gene expression in marine oxygen minimum zones (OMZs) has potential to broaden perspectives on the microbial ...and biogeochemical dynamics in these environments. Here, we present a metatranscriptomic survey of microbial community metabolism in the Eastern Tropical South Pacific OMZ off northern Chile. Community RNA was sampled in late austral autumn from four depths (50, 85, 110, 200 m) extending across the oxycline and into the upper OMZ. Shotgun pyrosequencing of cDNA yielded 180 000 to 550 000 transcript sequences per depth. Based on functional gene representation, transcriptome samples clustered apart from corresponding metagenome samples from the same depth, highlighting the discrepancies between metabolic potential and actual transcription. BLAST‐based characterizations of non‐ribosomal RNA sequences revealed a dominance of genes involved with both oxidative (nitrification) and reductive (anammox, denitrification) components of the marine nitrogen cycle. Using annotations of protein‐coding genes as proxies for taxonomic affiliation, we observed depth‐specific changes in gene expression by key functional taxonomic groups. Notably, transcripts most closely matching the genome of the ammonia‐oxidizing archaeon Nitrosopumilus maritimus dominated the transcriptome in the upper three depths, representing one in five protein‐coding transcripts at 85 m. In contrast, transcripts matching the anammox bacterium Kuenenia stuttgartiensis dominated at the core of the OMZ (200 m; 1 in 12 protein‐coding transcripts). The distribution of N. maritimus‐like transcripts paralleled that of transcripts matching ammonia monooxygenase genes, which, despite being represented by both bacterial and archaeal sequences in the community DNA, were dominated (> 99%) by archaeal sequences in the RNA, suggesting a substantial role for archaeal nitrification in the upper OMZ. These data, as well as those describing other key OMZ metabolic processes (e.g. sulfur oxidation), highlight gene‐specific expression patterns in the context of the entire community transcriptome, as well as identify key functional groups for taxon‐specific genomic profiling.
Marine oxygen minimum zones (OMZs) support diverse microbial communities with roles in major elemental cycles. It is unclear how the taxonomic composition and metabolism of OMZ microorganisms vary ...between particle-associated and free-living size fractions. We used amplicon (16S rRNA gene) and shotgun metagenome sequencing to compare microbial communities from large (>1.6 μm) and small (0.2-1.6 μm) filter size fractions along a depth gradient in the OMZ off Chile. Despite steep vertical redox gradients, size fraction was a significantly stronger predictor of community composition compared to depth. Phylogenetic diversity showed contrasting patterns, decreasing towards the anoxic OMZ core in the small size fraction, but exhibiting maximal values at these depths within the larger size fraction. Fraction-specific distributions were evident for key OMZ taxa, including anammox planctomycetes, whose coding sequences were enriched up to threefold in the 0.2-1.6 μm community. Functional gene composition also differed between fractions, with the >1.6 μm community significantly enriched in genes mediating social interactions, including motility, adhesion, cell-to-cell transfer, antibiotic resistance and mobile element activity. Prokaryotic transposase genes were three to six fold more abundant in this fraction, comprising up to 2% of protein-coding sequences, suggesting that particle surfaces may act as hotbeds for transposition-based genome changes in marine microbes. Genes for nitric and nitrous oxide reduction were also more abundant (three to seven fold) in the larger size fraction, suggesting microniche partitioning of key denitrification steps. These results highlight an important role for surface attachment in shaping community metabolic potential and genome content in OMZ microorganisms.
The N-jettiness observable TN provides a way of describing the leading singular behavior of the N-jet cross section in the τ=TN/Q→0 limit, where Q is a hard interaction scale. We consider ...subleading-power corrections in the τ≪1 expansion, and employ soft-collinear effective theory to obtain analytic results for the dominant αsτlnτ and αs2τln3τ subleading terms for thrust in e+e− collisions and 0-jettiness for qq¯-initiated Drell-Yan–like processes at hadron colliders. These results can be used to significantly improve the numerical accuracy and stability of the N-jettiness subtraction technique for performing fixed-order calculations at next-to-leading order and next-to-next-to-leading order. They reduce the size of missing power corrections in the subtractions by an order of magnitude. We also point out that the precise definition of N-jettiness has an important impact on the size of the power corrections and thus the numerical accuracy of the subtractions. The sometimes employed definition of N-jettiness in the hadronic center-of-mass frame suffers from power corrections that grow exponentially with rapidity, causing the power expansion to deteriorate away from central rapidity. This degradation does not occur for the original N-jettiness definition, which explicitly accounts for the boost of the Born process relative to the frame of the hadronic collision, and has a well-behaved power expansion throughout the entire phase space. Integrated over rapidity, using this N-jettiness definition in the subtractions yields another order of magnitude improvement compared to employing the hadronic-frame definition.
Microbial oceanography of anoxic oxygen minimum zones Ulloa, Osvaldo; Canfield, Donald E; DeLong, Edward F ...
Proceedings of the National Academy of Sciences - PNAS,
10/2012, Volume:
109, Issue:
40
Journal Article
Peer reviewed
Open access
Vast expanses of oxygen-deficient and nitrite-rich water define the major oxygen minimum zones (OMZs) of the global ocean. They support diverse microbial communities that influence the nitrogen ...economy of the oceans, contributing to major losses of fixed nitrogen as dinitrogen (N ₂) and nitrous oxide (N ₂O) gases. Anaerobic microbial processes, including the two pathways of N ₂ production, denitrification and anaerobic ammonium oxidation, are oxygen-sensitive, with some occurring only under strictly anoxic conditions. The detection limit of the usual method (Winkler titrations) for measuring dissolved oxygen in seawater, however, is much too high to distinguish low oxygen conditions from true anoxia. However, new analytical technologies are revealing vanishingly low oxygen concentrations in nitrite-rich OMZs, indicating that these OMZs are essentially anoxic marine zones (AMZs). Autonomous monitoring platforms also reveal previously unrecognized episodic intrusions of oxygen into the AMZ core, which could periodically support aerobic metabolisms in a typically anoxic environment. Although nitrogen cycling is considered to dominate the microbial ecology and biogeochemistry of AMZs, recent environmental genomics and geochemical studies show the presence of other relevant processes, particularly those associated with the sulfur and carbon cycles. AMZs correspond to an intermediate state between two “end points” represented by fully oxic systems and fully sulfidic systems. Modern and ancient AMZs and sulfidic basins are chemically and functionally related. Global change is affecting the magnitude of biogeochemical fluxes and ocean chemical inventories, leading to shifts in AMZ chemistry and biology that are likely to continue well into the future.
In the ocean's major oxygen minimum zones (OMZs), oxygen is effectively absent from sea water and life is dominated by microorganisms that use chemicals other than oxygen for respiration. Recent ...studies that combine advanced genomic and chemical detection methods are delineating the different metabolic niches that microorganisms can occupy in OMZs. Understanding these niches, the microorganisms that inhabit them, and their influence on marine biogeochemical cycles is crucial as OMZs expand with increasing seawater temperatures.
Teleost fish represent the most diverse of the vertebrate groups and play important roles in food webs, as ecosystem engineers, and as vectors for microorganisms. However, the microbial ecology of ...fishes remains underexplored for most host taxa and for certain niches on the fish body. This is particularly true for the gills, the key sites of respiration and waste exchange in fishes. Here we provide a comprehensive analysis of the gill microbiome. We focus on ecologically diverse taxa from coral reefs around Moorea, sampling the gills and intestines of adults and juveniles representing 15 families. The gill microbiome composition differed significantly from that of the gut for both adults and juveniles, with fish-associated niches having lower alpha diversity values and higher beta diversity values than those for seawater, sediment, and alga-associated microbiomes. Of ∼45,000 operational taxonomic units (OTUs) detected across all samples, 11% and 13% were detected only in the gill and the intestine, respectively. OTUs most enriched in the gill included members of the gammaproteobacterial genus
and the family
In adult fish, both gill and intestinal microbiomes varied significantly among host species grouped by diet category. Gill and intestinal microbiomes from the same individual were more similar to one another than to gill and intestinal microbiomes from different individuals. These results demonstrate that distinct body sites are jointly influenced by host-specific organizing factors operating at the level of the host individual. The results also identify taxonomic signatures unique to the gill and the intestine, confirming fish-associated niches as distinct reservoirs of marine microbial diversity.
Fish breathe and excrete waste through their gills. The gills are also potential sites of pathogen invasion and colonization by other microbes. However, we know little about the microbial communities that live on the gill and the factors shaping their diversity. Focusing on ecologically distinct types of coral reef fish, we provide a comprehensive analysis of the fish gill microbiome. By comparison to microbiomes of the gut and the surrounding environment, we identify microbes unique to the gill niche. These microbes may be targets for further studies to determine the contribution of the microbiome to waste exchange or host immunity. We also show that despite exhibiting a unique taxonomic signature, the gill microbiome is influenced by factors that also influence the gut microbiome. These factors include the specific identity of the host individual. These results suggest basic principles describing how association with fishes structures the composition of microbial communities.
Summary
The honey bee, the world's most important agricultural pollinator, relies exclusively on plant‐derived foods for nutrition. Nectar and pollen collected by honey bees are processed and matured ...within the nest through the activities of honey bee‐derived microbes and enzymes. In order to better understand the contribution of the microbial community to food processing in the honey bee, we generated a metatranscriptome of the honey bee gut microbiome. The function of the microbial community in the honey bee, as revealed by metatranscriptome sequencing, resembles that of other animal guts and food‐processing environments. We identified three major bacterial classes that are active in the gut (γ‐Proteobacteria, Bacilli and Actinobacteria), all of which are predicted to participate in the breakdown of complex macromolecules (e.g. polysaccharides and polypeptides), the fermentation of component parts of these macromolecules, and the generation of various fermentation products, such as short‐chain fatty acids and alcohol. The ability of the microbial community to metabolize these carbon‐rich food sources was confirmed through the use of community‐level physiological profiling. Collectively, these findings suggest that the gut microflora of the honey bee harbours bacterial members with unique roles, which ultimately can contribute to the processing of plant‐derived food for colonies.
N-jettiness subtractions provide a general approach for performing fully-differential next-to-next-to-leading order (NNLO) calculations. Since they are based on the physical resolution variable ...N-jettiness, TN, subleading power corrections in τ=TN/Q, with Q a hard interaction scale, can also be systematically computed. We study the structure of power corrections for 0-jettiness, T0, for the gg→H process. Using the soft-collinear effective theory we analytically compute the leading power corrections αsτlnτ and αs2τln3τ (finding partial agreement with a previous result in the literature), and perform a detailed numerical study of the power corrections in the gg, gq, and qq¯ channels. This includes a numerical extraction of the αsτ and αs2τln2τ corrections, and a study of the dependence on the T0 definition. Including such power suppressed logarithms significantly reduces the size of missing power corrections, and hence improves the numerical efficiency of the subtraction method. Having a more detailed understanding of the power corrections for both qq¯ and gg initiated processes also provides insight into their universality, and hence their behavior in more complicated processes where they have not yet been analytically calculated.
Jet vetoes are essential in many analyses at the LHC and Tevatron. Typical signals have a specific number of hard jets or leptons, while backgrounds have additional jets. Vetoing undesired jets ...efficiently discriminates signal and background. For a sample with ≥N jets, the veto to give N energetic jets defines an "exclusive" N-jet cross section. This strongly restricts the phase space and causes large double logarithms in perturbation theory that must be summed. Jet vetoes are typically implemented using jet algorithms, yielding complicated phase-space restrictions, and reliance on leading-log parton-shower Monte Carlo simulations. We introduce a global event shape "N jettiness" τN, which is defined for events with N signal jets. Requiring τN≪1 constrains radiation between the signal jets and provides a theoretically well-controlled jet veto. N jettiness yields a factorization formula with inclusive jet and beam functions.
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