Bayesian Conditioning, the Reflection Principle, and Quantum Decoherence

The probabilities a Bayesian agent assigns to a set of events typically change with time, for instance when the agent updates them in the light of new data. In this paper we address the question of how an agent's probabilities at different times are constrained by Dutch-book coherence. We review and attempt to clarify the argument that, although an agent is not forced by coherence to use the usual Bayesian conditioning rule to update his probabilities, coherence does require the agent's probabilities to satisfy van Fraassen's [1984] reflection principle (which entails a related constraint pointed out by Goldstein [1983]). We then exhibit the specialized assumption needed to recover Bayesian conditioning from an analogous reflection-style consideration. Bringing the argument to the context of quantum measurement theory, we show that "quantum decoherence" can be understood in purely personalist terms---quantum decoherence (as supposed in a von Neumann chain) is not a physical process at all, but an application of the reflection principle. From this point of view, the decoherence theory of Zeh, Zurek, and others as a story of quantum measurement has the plot turned exactly backward.Comment: 14 pages, written in memory of Itamar Pitowsk

Properties of 125 GeV Higgs boson in non-decoupling MSSM scenarios

Tantalizing hints of the Higgs boson of mass around 125 GeV have been reported at the LHC. We explore the MSSM parameter space in which the 125 GeV state is identified as the heavier of the CP even Higgs bosons, and study two scenarios where the two photon production rate can be significantly larger than the standard model (SM). In one scenario, $\Gamma(H\to \gamma\gamma)$ is enhanced by a light stau contribution, while the $WW^{\ast}$ ($ZZ^{\ast}$) rate stays around the SM rate. In the other scenario, $\Gamma(H\to b\bar{b})$ is suppressed and not only the $\gamma\gamma$ but also the $WW^{\ast}$ ($ZZ^{\ast}$) rates should be enhanced. The $\tau\bar{\tau}$ rate can be significantly larger or smaller than the SM rate in both scenarios. Other common features of the scenarios include top quark decays into charged Higgs boson, single and pair production of all Higgs bosons in $e^+e^-$ collisions at $\sqrt{s}\lesssim 300$ GeV.Comment: 20 pages, 5 figures, accepted version for publication in JHE

General Gauge Mediation at the Weak Scale

We completely characterize General Gauge Mediation (GGM) at the weak scale by solving all IR constraints over the full parameter space. This is made possible through a combination of numerical and analytical methods, based on a set of algebraic relations among the IR soft masses derived from the GGM boundary conditions in the UV. We show how tensions between just a few constraints determine the boundaries of the parameter space: electroweak symmetry breaking (EWSB), the Higgs mass, slepton tachyons, and left-handed stop/sbottom tachyons. While these constraints allow the left-handed squarks to be arbitrarily light, they place strong lower bounds on all of the right-handed squarks. Meanwhile, light EW superpartners are generic throughout much of the parameter space. This is especially the case at lower messenger scales, where a positive threshold correction to $m_h$ coming from light Higgsinos and winos is essential in order to satisfy the Higgs mass constraint.Comment: 43 pages, 20 figures, mathematica package included in the sourc

A Complete Model of Low-Scale Gauge Mediation

Recent signs of a Standard Model-like Higgs at 125 GeV point towards large A-terms in the MSSM. This presents special challenges for gauge mediation, which by itself predicts vanishing A-terms at the messenger scale. In this paper, we review the general problems that arise when extending gauge mediation to achieve large A-terms, and the mechanisms that exist to overcome them. Using these mechanisms, we construct weakly-coupled models of low-scale gauge mediation with extended Higgs-messenger couplings that generate large A-terms at the messenger scale and viable mu/B_mu-terms. Our models are simple, economical, and complete realizations of supersymmetry at the weak scale.Comment: 33 pages; v2: refs added, minor change

LHC Coverage of RPV MSSM with Light Stops

We examine the sensitivity of recent LHC searches to signatures of supersymmetry with R-parity violation (RPV). Motivated by naturalness of the Higgs potential, which would favor light third-generation squarks, and the stringent LHC bounds on spectra in which the gluino or first and second generation squarks are light, we focus on scenarios dominated by the pair production of light stops. We consider the various possible direct and cascade decays of the stop that involve the trilinear RPV operators. We find that in many cases, the existing searches exclude stops in the natural mass range and beyond. However, typically there is little or no sensitivity to cases dominated by UDD operators or LQD operators involving taus. We propose several ideas for searches which could address the existing gaps in experimental coverage of these signals.Comment: 41 pages, 12 figures; v2: included new searches (see footnote 10), minor corrections and improvement

Supersymmetry in the shadow of photini

Additional neutral gauge fermions -- "photini" -- arise in string compactifications as superpartners of U(1) gauge fields. Unlike their vector counterparts, the photini can acquire weak-scale masses from soft SUSY breaking and lead to observable signatures at the LHC through mass mixing with the bino. In this work we investigate the collider consequences of adding photini to the neutralino sector of the MSSM. Relatively large mixing of one or more photini with the bino can lead to prompt decays of the lightest ordinary supersymmetric particle; these extra cascades transfer most of the energy of SUSY decay chains into Standard Model particles, diminishing the power of missing energy as an experimental handle for signal discrimination. We demonstrate that the missing energy in SUSY events with photini is reduced dramatically for supersymmetric spectra with MSSM neutralinos near the weak scale, and study the effects on limits set by the leading hadronic SUSY searches at ATLAS and CMS. We find that in the presence of even one light photino the limits on squark masses from hadronic searches can be reduced by 400 GeV, with comparable (though more modest) reduction of gluino mass limits. We also consider potential discovery channels such as dilepton and multilepton searches, which remain sensitive to SUSY spectra with photini and can provide an unexpected route to the discovery of supersymmetry. Although presented in the context of photini, our results apply in general to theories in which additional light neutral fermions mix with MSSM gauginos.Comment: 23 pages, 8 figures, references adde

Border Terriers under primary veterinary care in England: demography and disorders

The Border Terrier is a working terrier type that is generally considered to be a relatively healthy and hardy breed. This study aimed to characterise the demography and common disorders of Border Terriers receiving veterinary care in England using de-identified electronic patient record data within the VetCompass™ Programme