| 1. |
- Rixen, C., et al.
(författare)
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Winters are changing: snow effects on Arctic and alpine tundra ecosystems
- 2022
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Ingår i: Arctic Science. - : Canadian Science Publishing. - 2368-7460. ; 8:3, s. 572-608
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Tidskriftsartikel (refereegranskat)abstract
- Snow is an important driver of ecosystem processes in cold biomes. Snow accumulation determines ground temperature, light conditions, and moisture availability during winter. It also affects the growing season's start and end, and plant access to moisture and nutrients. Here, we review the current knowledge of the snow cover's role for vegetation, plant-animal interactions, permafrost conditions, microbial processes, and biogeochemical cycling. We also compare studies of natural snow gradients with snow experimental manipulation studies to assess time scale difference of these approaches. The number of tundra snow studies has increased considerably in recent years, yet we still lack a comprehensive overview of how altered snow conditions will affect these ecosystems. Specifically, we found a mismatch in the timing of snowmelt when comparing studies of natural snow gradients with snow manipulations. We found that snowmelt timing achieved by snow addition and snow removal manipulations (average 7.9 days advance and 5.5 days delay, respectively) were substantially lower than the temporal variation over natural spatial gradients within a given year (mean range 56 days) or among years (mean range 32 days). Differences between snow study approaches need to be accounted for when projecting snow dynamics and their impact on ecosystems in future climates.
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| 2. |
- Asadi, Pouya, et al.
(författare)
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Glueballs in a thermal squeezeout model
- 2022
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Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :7
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Tidskriftsartikel (refereegranskat)abstract
- It has been shown that a first order confinement phase transition can drastically change the relic dark matter abundance in confining dark sectors with only heavy dark quarks. We study the phenomenology of one such model with a Z′ portal to Standard Model. We find that dark glueballs are long-lived in this setup and dilute the dark matter abundance after their decay to Standard Model. With this effect, the correct relic abundance is obtained with dark matter masses up to OO(106) TeV. We find that while a part of the parameter space is already ruled out by direct detection and collider searches, there is still a broad space of viable scenarios that can be probed by future experiments.
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| 3. |
- Asadi, Pouya, et al.
(författare)
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WIMPs without weakness : Generalized mass window with entropy injection
- 2022
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 106:1
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Tidskriftsartikel (refereegranskat)abstract
- We study general freeze-out scenarios where an arbitrary number of initial and final dark matter particles participate in the number-changing freeze-out interaction. We consider a simple sector with two particle species undergoing such a thermal freeze-out; one of the relics is stable and gives rise to the dark matter today, while the other one decays to the Standard Model, injecting significant entropy into the thermal bath that dilutes the dark matter abundance. We show that this setup can lead to a stable relic population that reproduces the observed dark matter abundance without requiring weak-scale masses or couplings. The final dark matter abundance is estimated analytically. We carry out this calculation for arbitrary temperature dependence in the freeze-out process and identify the viable dark matter mass and cross section ranges that explain the observed dark matter abundance. This setup can be used to open parameter space for both heavy (above the unitarity bound) or light (sub-GeV) dark matter candidates. We point out that the best strategy for probing most parts of our parameter space is to look for signatures of an early matterdominant epoch.
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| 4. |
- Galli, Silvia, et al.
(författare)
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Systematic uncertainties in constraining dark matter annihilation from the cosmic microwave background
- 2013
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 88:6, s. 063502-
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Tidskriftsartikel (refereegranskat)abstract
- Anisotropies of the cosmic microwave background (CMB) have proven to be a very powerful tool to constrain dark matter annihilation at the epoch of recombination. However, CMB constraints are currently derived using a number of reasonable but yet untested assumptions that could potentially lead to a misestimation of the true bounds (or any reconstructed signal). In this paper we examine the potential impact of these systematic effects. In particular, we separately study the propagation of the secondary particles produced by annihilation in two energy regimes: first following the shower from the initial particle energy to the keV scale, and then tracking the resulting secondary particles from this scale to the absorption of their energy as heat, ionization, or excitation of the medium. We improve both the high- and low-energy parts of the calculation, in particular finding that our more accurate treatment of losses to sub-10.2 eV photons produced by scattering of high-energy electrons weakens the constraints on particular dark matter annihilation models by up to a factor of 2. On the other hand, we find that the uncertainties we examine for the low-energy propagation do not significantly affect the results for current and upcoming CMB data. We include the evaluation of the precise amount of excitation energy, in the form of Lyman-alpha photons, produced by the propagation of the shower, and examine the effects of varying the helium fraction and helium ionization fraction. In the recent literature, simple approximations for the fraction of energy absorbed in different channels have often been used to derive CMB constraints: we assess the impact of using accurate vs approximate energy fractions. Finally we check that the choice of recombination code (between RECFAST V1.5 and COSMOREC), to calculate the evolution of the free electron fraction in the presence of dark matter annihilation, introduces negligible differences.
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