Illuminating Dark Photons with High-Energy Colliders

High-energy colliders offer a unique sensitivity to dark photons, the mediators of a broken dark U(1) gauge theory that kinetically mixes with the Standard Model (SM) hypercharge. Dark photons can be detected in the exotic decay of the 125 GeV Higgs boson, h -> Z Z_D -> 4l, and in Drell-Yan events, pp -> Z_D -> ll. If the dark U(1) is broken by a hidden-sector Higgs mechanism, then mixing between the dark and SM Higgs bosons also allows the exotic decay h -> Z_D Z_D -> 4l. We show that the 14 TeV LHC and a 100 TeV proton-proton collider provide powerful probes of both exotic Higgs decay channels. In the case of kinetic mixing alone, direct Drell-Yan production offers the best sensitivity to Z_D, and can probe epsilon >~ 9 x 10^(-4) (4 x 10^(-4)) at the HL-LHC (100 TeV pp collider). The exotic Higgs decay h -> Z Z_D offers slightly weaker sensitivity, but both measurements are necessary to distinguish the kinetically mixed dark photon from other scenarios. If Higgs mixing is also present, then the decay h -> Z_D Z_D can allow sensitivity to the Z_D for epsilon >~ 10^(-9) - 10^(-6) (10^(-10) - 10^(-7)) for the mass range 2 m_mu < m_(Z_D) < m_h/2 by searching for displaced dark photon decays. We also compare the Z_D sensitivity at pp colliders to the indirect, but model-independent, sensitivity of global fits to electroweak precision observables. We perform a global electroweak fit of the dark photon model, substantially updating previous work in the literature. Electroweak precision measurements at LEP, Tevatron, and the LHC exclude epsilon as low as 3 x 10^(-2). Sensitivity can be improved by up to a factor of ~2 with HL-LHC data, and an additional factor of ~4 with ILC/GigaZ data.Comment: 36 pages + references, 14 figures, 3 tables. Fixed typos, added reference

Signatures of sub-GeV dark matter beams at neutrino experiments

We study the high-luminosity fixed-target neutrino experiments at MiniBooNE, MINOS and T2K and analyze their sensitivity to light stable states, focusing on MeV--GeV scale dark matter. Thermal relic dark matter scenarios in the sub-GeV mass range require the presence of light mediators, whose coupling to the Standard Model facilitates annihilation in the early universe and allows for the correct thermal relic abundance. The mediators in turn provide a production channel for dark matter at colliders or fixed targets, and as a consequence the neutrino beams generated at fixed targets may contain an additional beam of light dark matter. The signatures of this beam include elastic scattering off electrons or nucleons in the (near-)detector, which closely mimics the neutral current scattering of neutrinos. We determine the event rate at modern fixed target facilities and the ensuing sensitivity to sub-GeV dark matter.Comment: 18 pages, 13 figures, revtex4-

Uncovering light scalars with exotic Higgs decays to bbmumu

The search for exotic Higgs decays are an essential probe of new physics. In particular, the small width of the Higgs boson makes its decay uniquely sensitive to the existence of light hidden sectors. Here we assess the potential of an exotic Higgs decay search for h -> 2X -> bbmumu to constrain theories with light CP-even (X = s) and CP-odd (X = a) singlet scalars in the mass range of 15 to 60 GeV. This decay channel arises naturally in many scenarios, such as the Standard Model augmented with a singlet, the two-Higgs-doublet model with a singlet (2HDM+S) -- which includes the Next-to-Minimal Supersymmetric Standard Model (NMSSM) -- and in hidden valley models. The 2b2mu channel may represent the best discovery avenue for many models. It has competitive reach, and is less reliant on low-pT b- and tau-reconstruction compared to other channels like 4b, 4tau, and 2tau2mu. We analyze the sensitivity of a 2b2mu search for the 8 and 14 TeV LHC, including the HL-LHC. We consider three types of analyses, employing conventional resolved b-jets with a clustering radius of R ~ 0.4, thin b-jets with R=0.2, and jet substructure techniques, respectively. The latter two analyses improve the reach for m_X ~ 15 GeV, for which the two b-jets are boosted and often merged. We find that Br(h -> 2X -> 2b2mu) can be constrained at the few x 10^-5 level across the entire considered mass range of X at the HL-LHC. This corresponds to a 1 - 10% reach in Br(h->2X) in 2HDM+S models, including the NMSSM, depending on the type of Higgs Yukawa couplings.Comment: 13 pages, 6 figures; v3: fix minor typo

Jet diffuser for simulating ram conditions on a turbojet-engine static test stand

A jet diffuser for simulating flight or ram conditions on a turbojet-engine static test stand was designed and investigated. The diffuser utilizes the kinetic energy of the jet from a turbojet engine to reduce the discharge pressure at the exhaust nozzle and thereby provides simulated ram-pressure ratios across the engine. The engine exhaust nozzle discharges into an exhaust chamber (flexibly sealed to the tail pipe), which is connected to a diffuser by a bell-shaped nozzle. The pressure in the exhaust chamber is controlled independently of engine speed by a variable-area shutter at the diffuser discharge. The jet diffuser simulated ram-pressure ratios from 0.95 to 2.2 at various simulated pressure altitudes for a range of engine speeds from 85 to 100 percent of maximum rpm. Agreement of data obtained with and without the jet diffuser for a ram-pressure ratio of 1.0 indicated that the presence of the diffuser did not interfere with the flow through the engine exhaust-nozzle outlet

Adventures in Paragraph Writing: The Development and Refinement of Scalable and Effective Writing Exercises for Large-enrollment Engineering Courses

Adventures in paragraph writing: the development and refinement of scalable and effective writing exercises for large enrollment engineering courses. The ability to communicate effectively is a highly desirable attribute for today’s graduating engineers. Additionally, the inclusion of communication components in technical courses has been shown to enhance learning of technical content and can be leveraged to satisfy non-technical learning outcomes. However, the incorporation of such components in undergraduate engineering curricula remains challenging due to resource limitations, credit hour crunches, and other issues. This paper presents the design considerations and preliminary results from our ongoing work to create an effective, transferrable, low-overhead approach to paragraph writing exercises suitable for inclusion in any large engineering course. Key considerations in the development of these exercises include: identification of the motivations and learning outcomes for each exercise; development and tailoring of writing prompts (questions) appropriate for these outcomes; and the development and implementation of an assessment and feedback strategy,including resource-efficient grading rubrics and techniques.Results are reported from the application of the paragraph writing exercise in a large civil engineering undergraduate fluid mechanics course (120 students; approximately 15 assignments). A primary focus of this first application centered on two key components that must be refined in order for the exercise to be effective and transferrable: (1) the selection of writing prompts, and (2) assessment and feedback. Analysis of student paragraphs highlights the importance of the writing prompts in the success of the exercise, indicating that specific word choice, question focus, and supplemental instruction greatly affected the level of writing students submitted. Some writing prompts were selected to address and enhance technical content in the course, while other writing prompts were developed to broaden student awareness of engineering in societal, environmental, and global contexts. In addition to developing productive writing prompts, the assessment and feedback strategies were evaluated using student surveys and feedback. While minimal marking and holistic rubric assessment methods proved effective from a grading resource standpoint, students were frustrated by the lack of feedback associated with these techniques and uncomfortable with the holistic grading rubric. Data from student surveys point to the importance of giving meaningful feedback to students, and providing them with opportunities to revise their written submissions. Student surveys also highlighted an unforeseen obstacle to the exercise: student resistance to writing in technical courses. We provide several suggestions for overcoming student resistance, as well as improved assessment and feedback strategies that better meet student needs while still not over-burdening instructors and teaching assistants

Surveying Pseudomoduli: the Good, the Bad and the Incalculable

We classify possible types of pseudomoduli which arise when supersymmetry is dynamically broken in infrared-free low-energy theories. We show that, even if the pseudomoduli potential is generated only at higher loops, there is a regime where the potential can be simply determined from a combination of one-loop running data. In this regime, we compute whether the potential for the various types of pseudomoduli is safe, has a dangerous runaway to the UV cutoff of the low-energy theory, or is incalculable. Our results are applicable to building new models of supersymmetry breaking. We apply the results to survey large classes of models.Comment: 34 page

Dynamical Vacuum Selection in String Theory

We study a system of D-branes localized near an intersection of Neveu-Schwarz fivebranes, that is known to exhibit a landscape of supersymmetric and (metastable) supersymmetry breaking vacua. We show that early universe cosmology drives it to a particular long-lived supersymmetry breaking ground state.Comment: 42 pages, 7 figures; references and acknowledgement adde

Lumbar Degenerative Disc Disease: Current and Future Concepts of Diagnosis and Management

Low back pain as a result of degenerative disc disease imparts a large socioeconomic impact on the health care system. Traditional concepts for treatment of lumbar disc degeneration have aimed at symptomatic relief by limiting motion in the lumbar spine, but novel treatment strategies involving stem cells, growth factors, and gene therapy have the theoretical potential to prevent, slow, or even reverse disc degeneration. Understanding the pathophysiological basis of disc degeneration is essential for the development of treatment strategies that target the underlying mechanisms of disc degeneration rather than the downstream symptom of pain. Such strategies ideally aim to induce disc regeneration or to replace the degenerated disc. However, at present, treatment options for degenerative disc disease remain suboptimal, and development and outcomes of novel treatment options currently have to be considered unpredictable