Global analyses of Higgs portal singlet dark matter models using GAMBIT.

We present global analyses of effective Higgs portal dark matter models in the frequentist and Bayesian statistical frameworks. Complementing earlier studies of the scalar Higgs portal, we use GAMBIT to determine the preferred mass and coupling ranges for models with vector, Majorana and Dirac fermion dark matter. We also assess the relative plausibility of all four models using Bayesian model comparison. Our analysis includes up-to-date likelihood functions for the dark matter relic density, invisible Higgs decays, and direct and indirect searches for weakly-interacting dark matter including the latest XENON1T data. We also account for important uncertainties arising from the local density and velocity distribution of dark matter, nuclear matrix elements relevant to direct detection, and Standard Model masses and couplings. In all Higgs portal models, we find parameter regions that can explain all of dark matter and give a good fit to all data. The case of vector dark matter requires the most tuning and is therefore slightly disfavoured from a Bayesian point of view. In the case of fermionic dark matter, we find a strong preference for including a CP-violating phase that allows suppression of constraints from direct detection experiments, with odds in favour of CP violation of the order of 100:1. Finally, we present DDCalc 2.0.0, a tool for calculating direct detection observables and likelihoods for arbitrary non-relativistic effective operators.

Impact of vacuum stability, perturbativity and XENON1T on global fits of Z 2 and Z 3 scalar singlet dark matter.

Scalar singlet dark matter is one of the simplest and most predictive realisations of the WIMP (weakly-interacting massive particle) idea. Although the model is constrained from all directions by the latest experimental data, it still has viable regions of parameter space. Another compelling aspect of scalar singlets is their ability to stabilise the electroweak vacuum. Indeed, models of scalar dark matter are not low-energy effective theories, but can be valid all the way to the Planck scale. Using the GAMBIT framework, we present the first global fit to include both the low-energy experimental constraints and the theoretical constraints from UV physics, considering models with a scalar singlet charged under either a Z 2 or a Z 3 symmetry. We show that if the model is to satisfy all experimental constraints, completely stabilise the electroweak vacuum up to high scales, and also remain perturbative to those scales, one is driven to a relatively small region of parameter space. This region has a Higgs-portal coupling slightly less than 1, a dark matter mass of 1-2 TeV and a spin-independent nuclear scattering cross-section around 10 - 45 cm 2 .

Status of the scalar singlet dark matter model.

One of the simplest viable models for dark matter is an additional neutral scalar, stabilised by a Z 2 symmetry. Using the GAMBIT package and combining results from four independent samplers, we present Bayesian and frequentist global fits of this model. We vary the singlet mass and coupling along with 13 nuisance parameters, including nuclear uncertainties relevant for direct detection, the local dark matter density, and selected quark masses and couplings. We include the dark matter relic density measured by Planck, direct searches with LUX, PandaX, SuperCDMS and XENON100, limits on invisible Higgs decays from the Large Hadron Collider, searches for high-energy neutrinos from dark matter annihilation in the Sun with IceCube, and searches for gamma rays from annihilation in dwarf galaxies with the Fermi-LAT. Viable solutions remain at couplings of order unity, for singlet masses between the Higgs mass and about 300 GeV, and at masses above ∼ 1 TeV. Only in the latter case can the scalar singlet constitute all of dark matter. Frequentist analysis shows that the low-mass resonance region, where the singlet is about half the mass of the Higgs, can also account for all of dark matter, and remains viable. However, Bayesian considerations show this region to be rather fine-tuned.

Ultracompact Minihalos as Probes of Inflationary Cosmology.

Cosmological inflation generates primordial density perturbations on all scales, including those far too small to contribute to the cosmic microwave background. At these scales, isolated ultracompact minihalos of dark matter can form well before standard structure formation, if the perturbations have sufficient amplitude. Minihalos affect pulsar timing data and are potentially bright sources of gamma rays. The resulting constraints significantly extend the observable window of inflation in the presence of cold dark matter, coupling two of the key problems in modern cosmology.

Possible indication of momentum-dependent asymmetric dark matter in the sun.

Broad disagreement persists between helioseismological observables and predictions of solar models computed with the latest surface abundances. Here we show that most of these problems can be solved by the presence of asymmetric dark matter coupling to nucleons as the square of the momentum q exchanged in the collision. We compute neutrino fluxes, small frequency separations, surface helium abundances, sound speed profiles, and convective zone depths for a number of models, showing more than a 6σ preference for q^{2} models over others, and over the standard solar model. The preferred mass (3 GeV) and reference dark matter-nucleon cross section (10^{-37} cm^{2} at q_{0}=40 MeV) are within the region of parameter space allowed by both direct detection and collider searches.

Quantifying impacts of short-term plasticity on neuronal information transfer.

Short-term changes in efficacy have been postulated to enhance the ability of synapses to transmit information between neurons, and within neuronal networks. Even at the level of connections between single neurons, direct confirmation of this simple conjecture has proven elusive. By combining paired-cell recordings, realistic synaptic modeling, and information theory, we provide evidence that short-term plasticity can not only improve, but also reduce information transfer between neurons. We focus on a concrete example in rat neocortex, but our results may generalize to other systems. When information is contained in the timings of individual spikes, we find that facilitation, depression, and recovery affect information transmission in proportion to their impacts upon the probability of neurotransmitter release. When information is instead conveyed by mean spike rate only, the influences of short-term plasticity critically depend on the range of spike frequencies that the target network can distinguish (its effective dynamic range). Our results suggest that to efficiently transmit information, the brain must match synaptic type, coding strategy, and network connectivity during development and behavior.

Gamma rays from ultracompact primordial dark matter minihalos.

Ultracompact minihalos have been proposed as a new class of dark matter structure. They would be produced by phase transitions in the early Universe or features in the inflaton potential, and constitute nonbaryonic massive compact halo objects today. We examine the prospects of detecting these minihalos in gamma rays if dark matter can self-annihilate. We compute present-day fluxes from minihalos produced in the e{+}e{-} annihilation epoch and the QCD and electroweak phase transitions. Even at a distance of 4 kpc, minihalos from the e{+}e{-} epoch would be eminently detectable today by the Fermi satellite or air Cerenkov telescopes, or even in archival EGRET data. Within 2 kpc, they would appear as extended sources to Fermi. At 4 kpc, minihalos from the QCD transition have similar predicted fluxes to dwarf spheroidal galaxies, so might also be detectable by present or upcoming experiments.

Morphology-Related Isometric Trunk Strength of South African Manual Workers: Implications for Prevention of Occupational Low-Back Stress.

Occupational back stress among manual workers in South Africa is now a cause of governmental concern. Yet no data on the back strength of the South African workforce have been published. This study represents a first step in reporting the trunk strength of Xhosa workers in South Africa, in absolute and size-relative terms. Thirty-five male manual workers were tested isometrically while making maximal extension and flexion efforts at 0°, 23°, 46°, 69°, and 92° of stoop. The results show nonlinearity of the extensor-to-flexor (E/F) ratio of the trunk musculature. The E/F ratio increases in deep stoop because of a drop in flexor torques. The data suggest that predictions of flexor from extensor torques or vice versa can confidently be made so long as testing is done away from the fully flexed position. Significant differences between morphologically gracile and robust workers in this sample are discussed. The study has implications for occupational rehabilitation and for prophylaxis, for whereas muscular strength alone may not protect the spine from occupational injury, muscular weakness certainly predisposes it.