| 11. |
- Cornell, Jonathan M., et al.
(författare)
-
Dark matter in minimal universal extra dimensions with a stable vacuum and the right Higgs boson
- 2014
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 89:5, s. 056005-
-
Tidskriftsartikel (refereegranskat)abstract
- The recent discovery of a Higgs boson with mass of about 125 GeV, along with its striking similarity to the prediction from the standard model, informs and constrains many models of new physics. The Higgs mass exhausts one out of three input parameters of the minimal, five-dimensional version of universal extra dimension models, the other two parameters being the Kaluza-Klein (KK) scale and the cutoff scale of the theory. The presence of KK fermions with large coupling to the Higgs implies a short-lived electroweak vacuum, unless the cutoff scale is at most a few times higher than the KK mass scale, providing an additional tight constraint to the theory parameter space. Here, we focus on the lightest KK particle as a dark matter candidate, and investigate the regions of parameter space where such particle has a thermal relic density in accord with the cosmological dark matter density. We find the paradoxical result that, for low enough cutoff scales consistent with vacuum stability, larger than previously thought KK mass scales become preferred to explain the dark matter abundance in the Universe. We explain this phenomenon by pinpointing the additional particles which, at such low cutoffs, become close enough in mass to the dark matter candidate to coannihilate with it. We make predictions for both collider and direct dark matter searches that might soon close in on all viable theory parameter space.
|
|
| 12. |
- Cornell, Jonathan M., et al.
(författare)
-
Kinetic decoupling and small-scale structure in effective theories of dark matter
- 2013
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 88:1, s. 015027-
-
Tidskriftsartikel (refereegranskat)abstract
- The size of the smallest dark matter collapsed structures, or protohalos, is set by the temperature at which dark matter particles fall out of kinetic equilibrium. The process of kinetic decoupling involves elastic scattering of dark matter off of Standard Model particles in the early universe, and the relevant cross section is thus closely related to the cross section for dark matter scattering off of nuclei (direct detection) but also, via crossing symmetries, for dark matter pair production at colliders and for pair annihilation. In this study, we employ an effective-field-theoretic approach to calculate constraints on the kinetic decoupling temperature, and thus on the size of the smallest protohalos, from a variety of direct, indirect and collider probes of particle dark matter.
|
|
| 13. |
- Downing, Andrea S., et al.
(författare)
-
Matching scope, purpose and uses of planetary boundaries science
- 2019
-
Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 14:7
-
Forskningsöversikt (refereegranskat)abstract
- Background: The Planetary Boundaries concept (PBc) has emerged as a key global sustainability concept in international sustainable development arenas. Initially presented as an agenda for global sustainability research, it now shows potential for sustainability governance. Weuse the fact that it is widely cited in scientific literature (>3500 citations) and an extensively studied concept to analyse how it has been used and developed since its first publication. Design: From the literature that cites the PBc, we select those articles that have the terms 'planetary boundaries' or 'safe operating space' in either title, abstract or keywords. Weassume that this literature substantively engages with and develops the PBc. Results: Wefind that 6% of the citing literature engages with the concept. Within this fraction of the literature we distinguish commentaries-that discuss the context and challenges to implementing the PBc, articles that develop the core biogeophysical concept and articles that apply the concept by translating to sub-global scales and by adding a human component to it. Applied literature adds to the concept by explicitly including society through perspectives of impacts, needs, aspirations and behaviours. Discussion: Literature applying the concept does not yet include the more complex, diverse, cultural and behavioural facet of humanity that is implied in commentary literature. Wesuggest there is need for a positive framing of sustainability goals-as a Safe Operating Space rather than boundaries. Key scientific challenges include distinguishing generalised from context-specific knowledge, clarifying which processes are generalizable and which are scalable, and explicitly applying complex systems' knowledge in the application and development of the PBc. We envisage that opportunities to address these challenges will arise when more human social dimensions are integrated, as we learn to feed the global sustainability vision with a plurality of bottom-up realisations of sustainability.
|
|
| 14. |
- Lade, Steven J., et al.
(författare)
-
Analytically tractable climate-carbon cycle feedbacks under 21st century anthropogenic forcing
- 2018
-
Ingår i: Earth System Dynamics. - : Copernicus GmbH. - 2190-4979 .- 2190-4987. ; 9:2, s. 507-523
-
Tidskriftsartikel (refereegranskat)abstract
- Changes to climate-carbon cycle feedbacks may significantly affect the Earth system's response to greenhouse gas emissions. These feedbacks are usually analysed from numerical output of complex and arguably opaque Earth system models. Here, we construct a stylised global climate-carbon cycle model, test its output against comprehensive Earth system models, and investigate the strengths of its climate-carbon cycle feedbacks analytically. The analytical expressions we obtain aid understanding of carbon cycle feedbacks and the operation of the carbon cycle. Specific results include that different feedback formalisms measure fundamentally the same climate-carbon cycle processes; temperature dependence of the solubility pump, biological pump, and CO2 solubility all contribute approximately equally to the ocean climate-carbon feedback; and concentration-carbon feedbacks may be more sensitive to future climate change than climate-carbon feedbacks. Simple models such as that developed here also provide workbenches for simple but mechanistically based explorations of Earth system processes, such as interactions and feedbacks between the planetary boundaries, that are currently too uncertain to be included in comprehensive Earth system models.
|
|
| 15. |
- Mahecha, Miguel D., et al.
(författare)
-
Earth system data cubes unravel global multivariate dynamics
- 2020
-
Ingår i: Earth System Dynamics. - : Copernicus GmbH. - 2190-4979 .- 2190-4987. ; 11:1, s. 201-234
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding Earth system dynamics in light of ongoing human intervention and dependency remains a major scientific challenge. The unprecedented availability of data streams describing different facets of the Earth now offers fundamentally new avenues to address this quest. However, several practical hurdles, especially the lack of data interoperability, limit the joint potential of these data streams. Today, many initiatives within and beyond the Earth system sciences are exploring new approaches to overcome these hurdles and meet the growing interdisciplinary need for data-intensive research; using data cubes is one promising avenue. Here, we introduce the concept of Earth system data cubes and how to operate on them in a formal way. The idea is that treating multiple data dimensions, such as spatial, temporal, variable, frequency, and other grids alike, allows effective application of user-defined functions to co-interpret Earth observations and/or model- data integration. An implementation of this concept combines analysis-ready data cubes with a suitable analytic interface. In three case studies, we demonstrate how the concept and its implementation facilitate the execution of complex workflows for research across multiple variables, and spatial and temporal scales: (1) summary statistics for ecosystem and climate dynamics; (2) intrinsic dimensionality analysis on multiple timescales; and (3) model-data integration. We discuss the emerging perspectives for investigating global interacting and coupled phenomena in observed or simulated data. In particular, we see many emerging perspectives of this approach for interpreting large-scale model ensembles. The latest developments in machine learning, causal inference, and model-data integration can be seamlessly implemented in the proposed framework, supporting rapid progress in data-intensive research across disciplinary boundaries.
|
|
| 16. |
- Niblaeus, Carl, et al.
(författare)
-
Effect of polarisation and choice of event generator on spectra from dark matter annihilations
- 2019
-
Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :10
-
Tidskriftsartikel (refereegranskat)abstract
- If indirect detection searches are to be used to discriminate between dark matter particle models, it is crucial to understand the expected energy spectra of secondary particles such as neutrinos, charged antiparticles and gamma rays emerging from dark matter annihilations in the local Universe. In this work we study the effect that both the choice of event generator and the polarisation of the final state particles can have on these predictions. For a variety of annihilation channels and dark matter masses, we compare yields obtained with Pythia8 and Herwig7 of all of the aforementioned secondary particle species. We investigate how polarised final states can change these results and do an extensive study of how the polarisation can impact the expected flux of neutrinos from dark matter annihilations in the centre of the Sun. We find that differences between the event generators are larger for yields of hadronic end products such as antiprotons, than for leptonic end products. Concerning polarisation, we conversely find the largest differences in the leptonic spectra. The large differences in the leptonic spectra point to the importance of including polarisation effects in searches for neutrinos from dark matter annihilations in the Sun. However, we find that these differences are ultimately somewhat washed out by propagation effects of the neutrinos in the Sun.
|
|
| 17. |
- Steffen, Will, et al.
(författare)
-
Trajectories of the Earth System in the Anthropocene
- 2018
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 115:33, s. 8252-8259
-
Tidskriftsartikel (refereegranskat)abstract
- We explore the risk that self-reinforcing feedbacks could push the Earth System toward a planetary threshold that, if crossed, could prevent stabilization of the climate at intermediate temperature rises and cause continued warming on a Hothouse Earth pathway even as human emissions are reduced. Crossing the threshold would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene. We examine the evidence that such a threshold might exist and where it might be. If the threshold is crossed, the resulting trajectory would likely cause serious disruptions to ecosystems, society, and economies. Collective human action is required to steer the Earth System away from a potential threshold and stabilize it in a habitable interglacial-like state. Such action entails stewardship of the entire Earth System-biosphere, climate, and societies-and could include decarbonization of the global economy, enhancement of biosphere carbon sinks, behavioral changes, technological innovations, new governance arrangements, and transformed social values.
|
|
