Discovering hidden sectors with mono-photon Z' searches

In many theories of physics beyond the Standard Model, from extra dimensions to Hidden Valleys and models of dark matter, Z' bosons mediate between Standard Model particles and hidden sector states. We study the feasibility of observing such hidden states through an invisibly decaying Z' at the LHC. We focus on the process pp -> \gamma Z' -> \gamma X X*, where X is any neutral, (quasi-) stable particle, whether a Standard Model (SM) neutrino or a new state. This complements a previous study using pp -> Z Z' -> l+ l- X X*. Only the Z' mass and two effective charges are needed to describe this process. If the Z' decays invisibly only to Standard Model neutrinos, then these charges are predicted by observation of the Z' through the Drell-Yan process, allowing discrimination between Z' decays to SM neutrinos and invisible decays to new states. We carefully discuss all backgrounds and systematic errors that affect this search. We find that hidden sector decays of a 1 TeV Z' can be observed at 5 sigma significance with 50 fb^{-1} at the LHC. Observation of a 1.5 TeV state requires super-LHC statistics of 1 ab^{-1}. Control of the systematic errors, in particular the parton distribution function uncertainty of the dominant Z \gamma background, is crucial to maximize the LHC searchComment: 13 pages, 4 figure

Expected Limits on the Ocean Acidification Buffering Potential of a Temperate Seagrass Meadow

Ocean acidification threatens many marine organisms, especially marine calcifiers. The only global‐scale solution to ocean acidification remains rapid reduction in CO2 emissions. Nevertheless, interest in localized mitigation strategies has grown rapidly because of the recognized threat ocean acidification imposes on natural communities, including ones important to humans. Protection of seagrass meadows has been considered as a possible approach for localized mitigation of ocean acidification due to their large standing stocks of organic carbon and high productivity. Yet much work remains to constrain the magnitudes and timescales of potential buffering effects from seagrasses. We developed a biogeochemical box model to better understand the potential for a temperate seagrass meadow to locally mitigate the effects of ocean acidification. Then we parameterized the model using data from Tomales Bay, an inlet on the coast of California, USA which supports a major oyster farming industry. We conducted a series of month‐long model simulations to characterize processes that occur during summer and winter. We found that average pH in the seagrass meadows was typically within 0.04 units of the pH of the primary source waters into the meadow, although we did find occasional periods (hours) when seagrass metabolism may modify the pH by up to ±0.2 units. Tidal phasing relative to the diel cycle modulates localized pH buffering within the seagrass meadow such that maximum buffering occurs during periods of the year with midday low tides. Our model results suggest that seagrass metabolism in Tomales Bay would not provide long‐term ocean acidification mitigation. However, we emphasize that our model results may not hold in meadows where assumptions about depth‐averaged net production and seawater residence time within the seagrass meadow differ from our model assumptions. Our modeling approach provides a framework that is easily adaptable to other seagrass meadows in order to evaluate the extent of their individual buffering capacities. Regardless of their ability to buffer ocean acidification, seagrass meadows maintain many critically important ecosystem goods and services that will be increasingly important as humans increasingly affect coastal ecosystems

A randomised trial into the effect of an isolated hip abductor strengthening programme and a functional motor control programme on knee kinematics and hip muscle strength

Background: Dynamic knee valgus and internal femoral rotation are proposed to be contributory risk factors for patellofemoral pain and anterior cruciate ligament injuries. Multimodal interventions including hip abductor strengthening or functional motor control programmes have a positive impact of pain, however their effect on knee kinematics and muscle strength is less clear. The aim of this study was to examine the effect of isolated hip abductor strengthening and a functional motor control exercise on knee kinematics and hip abductor strength. Methods: This prospective, randomised, repeated measures design included 29 asymptomatic volunteers presenting with increase knee valgus and femoral internal rotation. Participants completed either isolated hip abductor strengthening or a functional motor control exercise for 5 weeks. Knee kinematics were measured using inertial sensors during 2 functional activities and hip abductor strength measured using a load cell during isometric hip abduction. Results: There were no significant differences in dynamic knee valgus and internal rotation following the isolated hip abductor or functional motor control intervention, and no significant differences between the groups for knee angles. Despite this, the actual magnitude of reduction in valgus was 10° and 5° for the functional motor control group and strengthening group respectively. The actual magnitude of reduction in internal rotation was 9° and 18° for the functional motor control group and strengthening group respectively. Therefore there was a tendency towards clinically significant improvements in knee kinematics in both exercise groups. A statistically significant improvement in hip abductor strength was evident for the functional motor control group (27% increase; p = 0.008) and strengthening group (35% increase; p = 0.009) with no significant difference between the groups being identified (p = 0.475). Conclusions: Isolated hip strengthening and functional motor control exercises resulted in non-statistically significant changes in knee kinematics, however there was a clear trend towards clinically meaningful reductions in valgus and internal rotation. Both groups demonstrated similar significant gains in hip abductor strength suggesting\ud either approach could be used to strengthen the hip abductors

Simplified Models for LHC New Physics Searches

This document proposes a collection of simplified models relevant to the design of new-physics searches at the LHC and the characterization of their results. Both ATLAS and CMS have already presented some results in terms of simplified models, and we encourage them to continue and expand this effort, which supplements both signature-based results and benchmark model interpretations. A simplified model is defined by an effective Lagrangian describing the interactions of a small number of new particles. Simplified models can equally well be described by a small number of masses and cross-sections. These parameters are directly related to collider physics observables, making simplified models a particularly effective framework for evaluating searches and a useful starting point for characterizing positive signals of new physics. This document serves as an official summary of the results from the "Topologies for Early LHC Searches" workshop, held at SLAC in September of 2010, the purpose of which was to develop a set of representative models that can be used to cover all relevant phase space in experimental searches. Particular emphasis is placed on searches relevant for the first ~50-500 pb-1 of data and those motivated by supersymmetric models. This note largely summarizes material posted at http://lhcnewphysics.org/, which includes simplified model definitions, Monte Carlo material, and supporting contacts within the theory community. We also comment on future developments that may be useful as more data is gathered and analyzed by the experiments.Comment: 40 pages, 2 figures. This document is the official summary of results from "Topologies for Early LHC Searches" workshop (SLAC, September 2010). Supplementary material can be found at http://lhcnewphysics.or

Dark sectors 2016 Workshop: community report

This report, based on the Dark Sectors workshop at SLAC in April 2016, summarizes the scientific importance of searches for dark sector dark matter and forces at masses beneath the weak-scale, the status of this broad international field, the important milestones motivating future exploration, and promising experimental opportunities to reach these milestones over the next 5-10 years

US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report

This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in Dark Matter" held at University of Maryland on March 23-25, 2017.Comment: 102 pages + reference

Physical dynamics influencing dissolved oxygen over the shelf in the central and northern California Current System

Eastern Boundary Upwelling Systems (EBUS) are highly productive biomes, which provide benefit to society and support local ecosystems. Although EBUS total area is small when compared to other pelagic ecosystems, a growing body of literature demonstrate that climate impacts on EBUS will have disproportionately large consequences for human society. Like other EBUS, the California Current System (CCS) is experiencing a number of inextricably linked stressors: acidification, oxygen stress (hypoxia), altered food webs, and warming temperatures. Each stressor has the potential to change species interactions; alter the abundance and distribution of organisms; and can even result in mortality for certain organisms. Wind forcing and freshwater input drive change in the coastal zone, and result in heterogeneous expression of multiple stressors in time and space. River-flow and winds are both anticipated to change in magnitude and timing due to human- and climate-induced changes, which drive associated impacts to physical and biogeochemical processes in estuaries and continental shelves. A step towards better understanding drivers of multiple stressor interactions includes analysis of subsurface observations to identify relationships and trends in shelf waters. In this work we focus on the physical dynamics which influence dissolved oxygen (DO) over the shelf off northern California and Washington, to better understand the physical dynamics that influence hypoxia. In the CCS, and other EBUS, high productivity is supported by coastal wind-driven upwelling that supplies the shelf with nutrient-rich waters. However, high rates of productivity in the coastal zone may operate at the expense of (1) decreasing aragonite and calcite saturation states and decreasing dissolved oxygen (DO) concentrations because the water that is upwelled to the continental shelf also has reduced DO levels, lower pH, and higher concentrations of dissolved inorganic carbon (DIC); and (2) high productivity maintains a high standing stock of particulate organic carbon (POC), which builds a respiration signal in the water column and at the sediment/water interface and results in a decline in DO. These are two mechanisms that make EBUS, including the CCS, prone to hypoxia and acidification, which threaten ecosystems and the communities they support. The coastal waters of Washington (and southern British Columbia) have the highest primary productivity in the CCS, but this high productivity is not co-located with the strongest upwelling-favorable alongshore winds (which occur off northern California). This mismatch has been explored (e.g, by Hickey and Banas 2008), and results point to additional mechanisms that facilitate the region's high productivity beyond the traditional focus of the coastal wind field. The work presented in this dissertation, to explore the physical dynamics which influence DO over the shelf in two regions of the CCS, was motivated by (1) the link between productivity and hypoxia (and the mismatch of productivity/wind forcing); (2) reports of extreme low DO observed off Washington in the summers of 2017 - 2019; and (3) a lack of subsurface DO time-series observations off northern California (where peak upwelling wind stress occurs). Two chapters of this dissertation focus on the central CCS (off northern California), a region for which which DO time-series are scarce; and one chapter addresses the northern CCS (off Washington) and is comprised of an analysis of a 10-year record of DO, temperature and salinity at multiple sites along with wind and river discharge data to better understand the timing and severity of shelf hypoxia. Although the CCS is one of the most highly observed ocean regions in the world, there has been comparatively limited research on subsurface DO and carbonate system parameters in the central CCS off northern California (from 37°N to 42°N). Since long time-series of subsurface DO are relatively scarce, management decisions are made without a proper understanding of regional risk. Scientifically we are left wondering: (1) what DO levels occur in a section of the CCS that experiences the strongest upwelling favorable winds (~8x stronger than the Pacific Northwest)?; and (2) how DO levels respond to upwelling and relaxation events in this subregion? We collected time-series mooring data (temperature, salinity and DO), which are used to describe patterns and timing of hypoxia, and explore how DO levels respond to upwelling and relaxation events in the northern California coastal upwelling region. A deeper, mid-shelf site (~54m) is located in the Gulf of the Farallones, offshore San Francisco Bay, and within the more stratified upwelling shadow south of Point Reyes. The lowest DO concentrations and most persistent hypoxia were present at the mid-shelf site. At the shallower sites, (~18 and 30m), results show highly variable DO values with brief hypoxic events outside the core upwelling season (i.e., strongest winds and coldest water did not associate with the lowest DO levels). At the deeper, mid-shelf site, two distinct modes of variability were observed. During the first mode, upwelling events related to DO decline and relaxation events to increasing DO. During the second mode, the opposite occurs: upwelling related to an increase in DO and relaxation events to declining DO. At the shallower inner-shelf sites, and for the entire time-series, upwelling generally relates to DO decline and relaxation events to increasing DO. The importance of source water is clear during the first half of the mid-shelf deployment, and the overall trend and second half shows the importance of local drawdown. We also explored the seasonality of DO over a submarine bank (Cordell Bank) located at the shelf-break off northern California. Results show a recurrent seasonal cycle in temperature and DO. The similarity of seasonal patterns of temperature across years (2014 - 2018) is interesting, especially given the diverse set of oceanographic conditions the CCS experienced from 2014 – 2019. Although the coolest water occurs over the bank early in the upwelling season, the DO minimum occurs later, towards the end of the upwelling season and often during the relaxation season. Deviations from the seasonal trend observed are likely attributed to a combination of physical and biogeochemical processes working together. Specifically, we hypothesize that the interplay of wind-driven mixing and surface productivity can explain internanual differences, but additional work is needed to fully understand the role of these drivers. At Cordell Bank, DO concentrations were often below the threshold of mild hypoxia (2.45 ml/L), but only one instance of intermediate hypoxia was observed (1.4 to 2.45 ml/L) during the relaxation season (July 2017). Overall DO off northern California appears higher (fewer hypoxic events) than those observed in the northern CCS, but the upwelling favorable winds are also eight times stronger off northern California. Finally, observed DO is also lower than predicted using two source waters (PEW and PSUW) thus pointing to the likely importance of local drawdown (and potentially presence of more than two source water masses).We focused on the physical dynamics which influence shelf DO in the northern CCS (off Washington), in attempt to better understand the physical dynamics that influenced the extreme low DO observed in the summers of 2017 - 2019. Mooring data (2011 - 2020) are used to describe the timing and severity of hypoxia off Washington. River and winds data (1991 - 2020) are also used to better understand the coastal environment and drivers of low DO. From this work we found significant interannual variability in DO. The 2016-2019 low DO period is statistically associated with spicier water, suggesting a link between source waters impacted by the El Niño, very, very low North Pacific Gyre Oscillation Index, marine heat wave presence and low DO over the shelf. When compared to historical DO records, summertime hypoxic exposure appears to have worsened on the Washington shelf. However, 2011 – 2020 shows significant interannual variability without a clear downward trend. We also observed a north-south trend with lower DO in the south, which can be explained by several hypotheses, ranging from shelf width to canyons to stratification. However, the relationship between stratification, surface salinity and DO is complex. Within periods with similar surface salinity, more stratification is related to lower DO, but overall higher stratification is caused by lower surface salinity and is associated with higher DO. This likely demonstrates a complex relationship between the presence of river water advected northward by downwelling-favorable winds and vertical mixing driven by downwelling. Additional work to further assess the impact of timing of the Columbia and Fraser Rivers relative to wind events is important to understand DO and carbonate chemistry off Washington, and help make predictions for future climate conditions

Physical dynamics influencing dissolved oxygen over the shelf in the central and northern California Current System

Eastern Boundary Upwelling Systems (EBUS) are highly productive biomes, which provide benefit to society and support local ecosystems. Although EBUS total area is small when compared to other pelagic ecosystems, a growing body of literature demonstrate that climate impacts on EBUS will have disproportionately large consequences for human society. Like other EBUS, the California Current System (CCS) is experiencing a number of inextricably linked stressors: acidification, oxygen stress (hypoxia), altered food webs, and warming temperatures. Each stressor has the potential to change species interactions; alter the abundance and distribution of organisms; and can even result in mortality for certain organisms. Wind forcing and freshwater input drive change in the coastal zone, and result in heterogeneous expression of multiple stressors in time and space. River-flow and winds are both anticipated to change in magnitude and timing due to human- and climate-induced changes, which drive associated impacts to physical and biogeochemical processes in estuaries and continental shelves. A step towards better understanding drivers of multiple stressor interactions includes analysis of subsurface observations to identify relationships and trends in shelf waters. In this work we focus on the physical dynamics which influence dissolved oxygen (DO) over the shelf off northern California and Washington, to better understand the physical dynamics that influence hypoxia. In the CCS, and other EBUS, high productivity is supported by coastal wind-driven upwelling that supplies the shelf with nutrient-rich waters. However, high rates of productivity in the coastal zone may operate at the expense of (1) decreasing aragonite and calcite saturation states and decreasing dissolved oxygen (DO) concentrations because the water that is upwelled to the continental shelf also has reduced DO levels, lower pH, and higher concentrations of dissolved inorganic carbon (DIC); and (2) high productivity maintains a high standing stock of particulate organic carbon (POC), which builds a respiration signal in the water column and at the sediment/water interface and results in a decline in DO. These are two mechanisms that make EBUS, including the CCS, prone to hypoxia and acidification, which threaten ecosystems and the communities they support. The coastal waters of Washington (and southern British Columbia) have the highest primary productivity in the CCS, but this high productivity is not co-located with the strongest upwelling-favorable alongshore winds (which occur off northern California). This mismatch has been explored (e.g, by Hickey and Banas 2008), and results point to additional mechanisms that facilitate the region's high productivity beyond the traditional focus of the coastal wind field. The work presented in this dissertation, to explore the physical dynamics which influence DO over the shelf in two regions of the CCS, was motivated by (1) the link between productivity and hypoxia (and the mismatch of productivity/wind forcing); (2) reports of extreme low DO observed off Washington in the summers of 2017 - 2019; and (3) a lack of subsurface DO time-series observations off northern California (where peak upwelling wind stress occurs). Two chapters of this dissertation focus on the central CCS (off northern California), a region for which which DO time-series are scarce; and one chapter addresses the northern CCS (off Washington) and is comprised of an analysis of a 10-year record of DO, temperature and salinity at multiple sites along with wind and river discharge data to better understand the timing and severity of shelf hypoxia. Although the CCS is one of the most highly observed ocean regions in the world, there has been comparatively limited research on subsurface DO and carbonate system parameters in the central CCS off northern California (from 37°N to 42°N). Since long time-series of subsurface DO are relatively scarce, management decisions are made without a proper understanding of regional risk. Scientifically we are left wondering: (1) what DO levels occur in a section of the CCS that experiences the strongest upwelling favorable winds (~8x stronger than the Pacific Northwest)?; and (2) how DO levels respond to upwelling and relaxation events in this subregion? We collected time-series mooring data (temperature, salinity and DO), which are used to describe patterns and timing of hypoxia, and explore how DO levels respond to upwelling and relaxation events in the northern California coastal upwelling region. A deeper, mid-shelf site (~54m) is located in the Gulf of the Farallones, offshore San Francisco Bay, and within the more stratified upwelling shadow south of Point Reyes. The lowest DO concentrations and most persistent hypoxia were present at the mid-shelf site. At the shallower sites, (~18 and 30m), results show highly variable DO values with brief hypoxic events outside the core upwelling season (i.e., strongest winds and coldest water did not associate with the lowest DO levels). At the deeper, mid-shelf site, two distinct modes of variability were observed. During the first mode, upwelling events related to DO decline and relaxation events to increasing DO. During the second mode, the opposite occurs: upwelling related to an increase in DO and relaxation events to declining DO. At the shallower inner-shelf sites, and for the entire time-series, upwelling generally relates to DO decline and relaxation events to increasing DO. The importance of source water is clear during the first half of the mid-shelf deployment, and the overall trend and second half shows the importance of local drawdown. We also explored the seasonality of DO over a submarine bank (Cordell Bank) located at the shelf-break off northern California. Results show a recurrent seasonal cycle in temperature and DO. The similarity of seasonal patterns of temperature across years (2014 - 2018) is interesting, especially given the diverse set of oceanographic conditions the CCS experienced from 2014 – 2019. Although the coolest water occurs over the bank early in the upwelling season, the DO minimum occurs later, towards the end of the upwelling season and often during the relaxation season. Deviations from the seasonal trend observed are likely attributed to a combination of physical and biogeochemical processes working together. Specifically, we hypothesize that the interplay of wind-driven mixing and surface productivity can explain internanual differences, but additional work is needed to fully understand the role of these drivers. At Cordell Bank, DO concentrations were often below the threshold of mild hypoxia (2.45 ml/L), but only one instance of intermediate hypoxia was observed (1.4 to 2.45 ml/L) during the relaxation season (July 2017). Overall DO off northern California appears higher (fewer hypoxic events) than those observed in the northern CCS, but the upwelling favorable winds are also eight times stronger off northern California. Finally, observed DO is also lower than predicted using two source waters (PEW and PSUW) thus pointing to the likely importance of local drawdown (and potentially presence of more than two source water masses).We focused on the physical dynamics which influence shelf DO in the northern CCS (off Washington), in attempt to better understand the physical dynamics that influenced the extreme low DO observed in the summers of 2017 - 2019. Mooring data (2011 - 2020) are used to describe the timing and severity of hypoxia off Washington. River and winds data (1991 - 2020) are also used to better understand the coastal environment and drivers of low DO. From this work we found significant interannual variability in DO. The 2016-2019 low DO period is statistically associated with spicier water, suggesting a link between source waters impacted by the El Niño, very, very low North Pacific Gyre Oscillation Index, marine heat wave presence and low DO over the shelf. When compared to historical DO records, summertime hypoxic exposure appears to have worsened on the Washington shelf. However, 2011 – 2020 shows significant interannual variability without a clear downward trend. We also observed a north-south trend with lower DO in the south, which can be explained by several hypotheses, ranging from shelf width to canyons to stratification. However, the relationship between stratification, surface salinity and DO is complex. Within periods with similar surface salinity, more stratification is related to lower DO, but overall higher stratification is caused by lower surface salinity and is associated with higher DO. This likely demonstrates a complex relationship between the presence of river water advected northward by downwelling-favorable winds and vertical mixing driven by downwelling. Additional work to further assess the impact of timing of the Columbia and Fraser Rivers relative to wind events is important to understand DO and carbonate chemistry off Washington, and help make predictions for future climate conditions

Paleoceanographic Insights on Recent Oxygen Minimum Zone Expansion: Lessons for Modern Oceanography

Climate-driven Oxygen Minimum Zone (OMZ) expansions in the geologic record provide an opportunity to characterize the spatial and temporal scales ofOMZ change. Here we investigate OMZ expansion through the global- scale warming event of the most recent deglaciation (18- 11 ka), an event with clear relevance to understanding modern anthropogenic climate change. Deglacial marine sediment records were compiled to quantify the vertical extent, intensity, surface area and volume impingements of hypoxic waters upon continental margins. By integrating sediment records (183-2,309 meters below sea level; mbsl) containing one or more geochemical, sedimentary or microfossil oxygenation proxies integrated with analyses of eustatic sea level rise, we reconstruct the timing, depth and intensity of seafloor hypoxia. The maximum vertical OMZ extent during the deglaciation was variable by region: Subarctic Pacific (similar to 600-2,900 mbsl), California Current (similar to 330-1,500 mbsl), Mexico Margin (similar to 330-830 mbsl), and the Humboldt Current and Equatorial Pacific (similar to 110-3,100 mbsl). The timing ofOMZ expansion is regionally coherent but not globally synchronous. Subarctic Pacific and California Current continental margins exhibit tight correlation to the oscillations of Northern Hemisphere deglacial events (Termination IA, Bolling-Allerod, Younger Dryas and Termination IB). Southern regions (Mexico Margin and the Equatorial Pacific and Humboldt Current) exhibit hypoxia expansion prior to Termination IA (similar to 14.7 ka), and no regional oxygenation oscillations. Our analyses provide new evidence for the geographically and vertically extensive expansion of OMZs, and the extreme compression of upper-ocean oxygenated ecosystems during the geologically recent deglaciation