Global fits of scalar singlet dark matter with GAMBIT

The wide range of probes of physics beyond the standard model leads to the need for tools that combine experimental results to make the most robust possible statements about the validity of theories and the preferred regions of their parameter space. Here we introduce a new code for such analyses: GAMBIT, the Global and Modular BSM Inference Tool. GAMBIT is a flexible and extensible framework for global fits of essentially any BSM theory. The code currently incorporates direct and indirect searches for dark matter, limits on production of new particles from the LHC and LEP, complete flavor constraints from LHCb, LHC Higgs production and decay measurements, and various electroweak precision observables. Here we present an overview of the code's capabilities, followed by preliminary results from scans of the scalar singlet dark matter model.Comment: 7 pages, 2 figures. Contribution to proceedings of ICHEP 2016. v2: References adde

R(K(∗))R({K^{(*)}}) from dark matter exchange

Hints of lepton flavor violation have been observed by LHCb in the rate of the decay $B\to K\mu^+\mu^-$ relative to that of $B\to K e^+e^-$. This can be explained by new scalars and fermions which couple to standard model particles and contribute to these processes at loop level. We explore a simple model of this kind, in which one of the new fermions is a dark matter candidate, while the other is a heavy vector-like quark and the scalar is an inert Higgs doublet. We explore the constraints on this model from flavor observables, dark matter direct detection, and LHC run II searches, and find that, while currently viable, this scenario will be directly tested by future results from all three probes.Comment: 6 pages, 6 figures; v2: added references, changed to Majorana dark matter, direct detection constraints weakened; v3: added references, lepton flavor constraints weakened by including crossed box diagrams in fig. 1; published versio

Dark decay of the neutron

New decay channels for the neutron into dark matter plus other particles have been suggested for explaining a long-standing discrepancy between the neutron lifetime measured from trapped neutrons versus those decaying in flight. Many such scenarios are already ruled out by their effects on neutron stars, and the decay into dark matter plus photon has been experimentally excluded. Here we explore the decay into a dark Dirac fermion $\chi$ and a dark photon $A'$, which can be consistent with all constraints if $\chi$ is a subdominant component of the dark matter. Neutron star constraints are evaded if the dark photon mass to coupling ratio is $m_{A'}/g' \lesssim (45-60)\,$MeV, depending upon the nuclear equation of state. $g'$ and the kinetic mixing between U(1)$'$ and electromagnetism are tightly constrained by direct and indirect dark matter detection, supernova constraints, and cosmological limits.Comment: 10 pages, 2 figures. v2: Clarifications and references added. Submitted to JHEP. v3: Dark matter self scattering cross section and constraints from direct detection corrected, additional constraints added. v4: Typos corrected. Matches published versio

Earthly probes of the smallest dark matter halos

Dark matter kinetic decoupling involves elastic scattering of dark matter off of leptons and quarks in the early universe, the same process relevant for direct detection and for the capture rate of dark matter in celestial bodies; the resulting size of the smallest dark matter collapsed structures should thus correlate with quantities connected with direct detection rates and with the flux of high-energy neutrinos from dark matter annihilation in the Sun or in the Earth. In this paper we address this general question in the context of two widely studied and paradigmatic weakly-interacting particle dark matter models: the lightest neutralino of the minimal supersymmetric extension of the Standard Model, and the lightest Kaluza-Klein particle of Universal Extra Dimensions (UED). We argue and show that while the scalar neutralino-nucleon cross section correlates poorly with the kinetic decoupling temperature, the spin-dependent cross section exhibits a strong correlation in a wide range of models. In UED models the correlation is present for both cross sections, and is extraordinarily tight for the spin-dependent case. A strong correlation is also found, for both models, for the flux of neutrinos from the Sun, especially for fluxes large enough to be at potentially detectable levels. We provide analytic guidance and formulae that illustrate our findings.Comment: 26 pages, 6 figures, to appear in JCA

Contested modelling

We suggest that the role and function of expert computational modelling in real-world decision-making needs scrutiny and practices need to change. We discuss some empirical and theory-based improvements to the coupling of the modelling process and the real world, including social and behavioural processes, which we have expressed as a set of questions that we believe need to be answered by all projects engaged in such modelling.  These are based on a systems analysis of four research initiatives, covering different scales and timeframes, and addressing the complexity of intervention in a sustainability context. Our proposed improvements require new approaches for analysing the relationship between a project’s models and its publics.  They reflect what we believe is a necessary and beneficial dialogue between the realms of expert scientific modelling and systems thinking.  This paper is an attempt to start that process, itself reflecting a robust dialogue between two practitioners sat within differing traditions, puzzling how to integrate perspectives and achieve wider participation in researching this problem space.&nbsp

Baryogenesis from neutron-dark matter oscillations

It was recently suggested that dark matter consists of ~GeV particles that carry baryon number and mix with the neutron. We demonstrate that this could allow for resonant dark matter-neutron oscillations in the early universe, at finite temperature, leading to low-scale baryogenesis starting from a primordial dark matter asymmetry. In this scenario, the asymmetry transfer happens around 30 MeV, just before big bang nucleosynthesis. We illustrate the idea using a model with a dark U(1)' gauge interaction, which has recently been suggested as a way of addressing the neutron lifetime anomaly. The asymmetric dark matter component of this model is both strongly self-interacting and leads to a suppression of matter density perturbations at small scales, allowing to mitigate the small-scale problems of cold dark matter cosmology. Future CMB experiments will be able to consistently probe, or firmly exclude, this scenario.Comment: 14 pages, 6 figures. v3: Added references and made minor clarifications and corrections. Matches published version. v2: Added references and fixed typo

Assessment of the risk due to release of carbon fiber in civil aircraft accidents, phase 2

The risk associated with the potential use of carbon fiber composite material in commercial jet aircraft is investigated. A simulation model developed to generate risk profiles for several airports is described. The risk profiles show the probability that the cost due to accidents in any year exceeds a given amount. The computer model simulates aircraft accidents with fire, release of fibers, their downwind transport and infiltration of buildings, equipment failures, and resulting ecomomic impact. The individual airport results were combined to yield the national risk profile

The Reaction-Diffusion Front for A+B→∅A+B \to\emptyset in One Dimension

We study theoretically and numerically the steady state diffusion controlled reaction $A+B\rightarrow\emptyset$, where currents $J$ of $A$ and $B$ particles are applied at opposite boundaries. For a reaction rate $\lambda$, and equal diffusion constants $D$, we find that when $\lambda J^{-1/2} D^{-1/2}\ll 1$ the reaction front is well described by mean field theory. However, for $\lambda J^{-1/2} D^{-1/2}\gg 1$, the front acquires a Gaussian profile - a result of noise induced wandering of the reaction front center. We make a theoretical prediction for this profile which is in good agreement with simulation. Finally, we investigate the intrinsic (non-wandering) front width and find results consistent with scaling and field theoretic predictions.Comment: 11 pages, revtex, 4 separate PostScript figure