The Minimal Scale Invariant Extension of the Standard Model

We perform a systematic analysis of an extension of the Standard Model that includes a complex singlet scalar field and is scale invariant at the tree level. We call such a model the Minimal Scale Invariant extension of the Standard Model (MSISM). The tree-level scale invariance of the model is explicitly broken by quantum corrections, which can trigger electroweak symmetry breaking and potentially provide a mechanism for solving the gauge hierarchy problem. Even though the scale invariant Standard Model is not a realistic scenario, the addition of a complex singlet scalar field may result in a perturbative and phenomenologically viable theory. We present a complete classification of the flat directions which may occur in the classical scalar potential of the MSISM. After calculating the one-loop effective potential of the MSISM, we investigate a number of representative scenarios and determine their scalar boson mass spectra, as well as their perturbatively allowed parameter space compatible with electroweak precision data. We discuss the phenomenological implications of these scenarios, in particular, whether they realize explicit or spontaneous CP violation, neutrino masses or provide dark matter candidates. In particular, we find a new minimal scale-invariant model of maximal spontaneous CP violation which can stay perturbative up to Planck-mass energy scales, without introducing an unnaturally large hierarchy in the scalar-potential couplings.Comment: 71 pages, 34 eps figures, numerical error corrected, clarifying comments adde

Light Higgsino from Axion Dark Radiation

The recent observations imply that there is an extra relativistic degree of freedom coined dark radiation. We argue that the QCD axion is a plausible candidate for the dark radiation, not only because of its extremely small mass, but also because in the supersymmetric extension of the Peccei-Quinn mechanism the saxion tends to dominate the Universe and decays into axions with a sizable branching fraction. We show that the Higgsino mixing parameter mu is bounded from above when the axions produced at the saxion decays constitute the dark radiation: mu \lesssim 300 GeV for a saxion lighter than 2m_W, and mu less than the saxion mass otherwise. Interestingly, the Higgsino can be light enough to be within the reach of LHC and/or ILC even when the other superparticles are heavy with mass about 1 TeV or higher. We also estimate the abundance of axino produced by the decays of Higgsino and saxion.Comment: 18 pages, 1 figure; published in JHE

Neutrino Mass and μ→e+γ\mu \rightarrow e + \gamma from a Mini-Seesaw

The recently proposed "mini-seesaw mechanism" combines naturally suppressed Dirac and Majorana masses to achieve light Standard Model neutrinos via a low-scale seesaw. A key feature of this approach is the presence of multiple light (order GeV) sterile-neutrinos that mix with the Standard Model. In this work we study the bounds on these light sterile-neutrinos from processes like \mu ---> e + \gamma, invisible Z-decays, and neutrinoless double beta-decay. We show that viable parameter space exists and that, interestingly, key observables can lie just below current experimental sensitivities. In particular, a motivated region of parameter space predicts a value of BR(\mu ---> e + \gamma) within the range to be probed by MEG.Comment: 1+26 pages, 7 figures. v2 JHEP version (typo's fixed, minor change to presentation, results unchanged

Neutrinoless double beta decay in seesaw models

We study the general phenomenology of neutrinoless double beta decay in seesaw models. In particular, we focus on the dependence of the neutrinoless double beta decay rate on the mass of the extra states introduced to account for the Majorana masses of light neutrinos. For this purpose, we compute the nuclear matrix elements as functions of the mass of the mediating fermions and estimate the associated uncertainties. We then discuss what can be inferred on the seesaw model parameters in the different mass regimes and clarify how the contribution of the light neutrinos should always be taken into account when deriving bounds on the extra parameters. Conversely, the extra states can also have a significant impact, cancelling the Standard Model neutrino contribution for masses lighter than the nuclear scale and leading to vanishing neutrinoless double beta decay amplitudes even if neutrinos are Majorana particles. We also discuss how seesaw models could reconcile large rates of neutrinoless double beta decay with more stringent cosmological bounds on neutrino masses.Comment: 34 pages, 5 eps figures and 1 axodraw figure. Final version published in JHEP. NME results available in Appendi

Disguised Propaganda from Digital to Social Media

Disguised propaganda and political deception in digital media have been studied since the early days of the World Wide Web. At the intersection of internet research and propaganda studies, this chapter explores disguised propaganda on websites and social media platforms. Based on a discussion of key concepts and terminology, this chapter outlines how new modes of deception and source obfuscation emerge in digital and social media environments, and how this development complicates existing conceptual and epistemological frameworks in propaganda studies. The chapter concludes by arguing that contemporary challenges of detecting and countering disguised propaganda can only be resolved, if social media companies are held accountable and provide the necessary support for user contestation

Comparing online campaigning: The evolution of interactive campaigning from Royal to Obama to Hollande

© 2016 Macmillan Publishers Ltd.Studies of election campaigning from a comparative perspective have a long history; this study approaches the topic through a most-similar regime perspective to explore the ebb and flow of innovations in digital campaigning between presidential campaigns in France and the United States. The hype surrounding the 2008 Obama campaign overshadowed innovations in France the previous year, while the 2011 contest gained little serious academic attention. Using a well-established content analysis methodology the research explains the strategic design of the digital dimension of the campaigns of the leading candidates (Sarkozy and Royal in 2007, Obama and McCain in 2008, Hollande and Sarkozy in 2011, and Obama and Romney in 2012). The research then assesses the strategic contribution of each feature using schematics for understanding the flow of communication, as well as the strategy employed by each candidate. The key findings are that the campaigns are becoming more interactive, with the citizens increasingly more able to enter into conversations with the campaign teams, however interactivity when it happens is carefully controlled. Largely, however, there is a strong similarity masked by the sophistication of US contests. Despite the advances in communication technology and the social trends they have instigated, campaign communication remains top-down and digital technologies are used to gather data and push supporters towards activism than creating an inclusive space for the co-creation that cyberoptimists argued would revitalise the structures of democracy