White dwarfs constraints on dark sector models with light particles

The white dwarf luminosity function is well understood in terms of standard model physics and leaves little room for exotic cooling mechanisms related to the possible existence of new weakly interacting light particles. This puts significant constraints on the parameter space of models that contain a massive dark photon and light dark sector particles.Comment: CETUP*2013 proceeding

Superdiffusion and Transport in 2d-systems with L\'evy Like Quenched Disorder

We present an extensive analysis of transport properties in superdiffusive two dimensional quenched random media, obtained by packing disks with radii distributed according to a L\'evy law. We consider transport and scaling properties in samples packed with two different procedures, at fixed filling fraction and at self-similar packing, and we clarify the role of the two procedures in the superdiffusive effects. Using the behavior of the filling fraction in finite size systems as the main geometrical parameter, we define an effective L\'evy exponents that correctly estimate the finite size effects. The effective L\'evy exponent rules the dynamical scaling of the main transport properties and identify the region where superdiffusive effects can be detected.Comment: 12 pages, 19 figure

Singlet Scalar Dark Matter: monochromatic gamma rays and metastable vacua

We calculate the pair-annihilation cross section of real scalar singlet dark matter into two mono-energetic photons. We derive constraints on the theory parameter space from the Fermi limits on gamma-ray lines, and we compare with current limits from direct dark matter detection. We show that the new limits, albeit typically relevant only when the dark matter mass is close to half the Standard Model Higgs mass, rule out regions of the theory parameter space that are otherwise not constrained by other observations or experiments. In particular, the new excluded regions partly overlap with the parameter space where real scalar singlet dark matter might explain the anomalous signals observed by CDMS. We also calculate the lifetime of unstable vacuum configurations in the scalar potential, and show that the gamma-ray limits are quite relevant in regions where the electro-weak vacuum is meta-stable with a lifetime longer than the age of the universe.Comment: 21 pages, 6 figures; references added, minor additions to text and figures, version accepted for publication in Phys. Rev.

Probing Dark Matter with AGN Jets

We study the possibility of detecting a signature of particle dark matter in the spectrum of gamma-ray photons from active galactic nuclei (AGNs) resulting from the scattering of high-energy particles in the AGN jet off of dark matter particles. We consider particle dark matter models in the context of both supersymmetry and universal extra-dimensions (UED), and we present the complete lowest-order calculation for processes where a photon is emitted in dark matter-electron and/or dark matter-proton scattering, where electrons and protons belong to the AGN jet. We find that the process is dominated by a resonance whose energy is dictated by the particle spectrum in the dark matter sector (neutralino and selectron for the case of supersymmetry, Kaluza-Klein photon and electron for UED). The resulting gamma-ray spectrum exhibits a very characteristic spectral feature, consisting of a sharp break to a hard power-law behavior. Although the normalization of the gamma-ray flux depends strongly on assumptions on both the AGN jet geometry, composition and particle spectrum as well as on the particle dark matter model and density distribution, we show that for realistic parameters choices, and for two prominent nearby AGNs (Centaurus A and M87), the detection of this effect is in principle possible. Finally, we compare our predictions and results with recent gamma-ray observations from the Fermi, H.E.S.S. and VERITAS telescopes.Comment: 23 pages, 13 figures, submitte

Dynamics of Relaxed Inflation

The cosmological relaxation of the electroweak scale has been proposed as a mechanism to address the hierarchy problem of the Standard Model. A field, the relaxion, rolls down its potential and, in doing so, scans the squared mass parameter of the Higgs, relaxing it to a parametrically small value. In this work, we promote the relaxion to an inflaton. We couple it to Abelian gauge bosons, thereby introducing the necessary dissipation mechanism which slows down the field in the last stages. We describe a novel reheating mechanism, which relies on the gauge-boson production leading to strong electromagnetic fields, and proceeds via the vacuum production of electron-positron pairs through the Schwinger effect. We refer to this mechanism as Schwinger reheating. We discuss the cosmological dynamics of the model and the phenomenological constraints from CMB and other experiments. We find that a cutoff close to the Planck scale may be achieved. In its minimal form, the model does not generate sufficient curvature perturbations and additional ingredients, such as a curvaton field, are needed.Comment: 39 pages, 3 figures, appendices D and E added, published in JHE

Toward the Integration of Student Advising at a Canadian Higher Education Institution

This Organizational Improvement Plan (OIP) addresses a problem of practice concerning the fragmented state of student advising at a large, urban higher education institution (HEI). Aligned with the sample university’s overarching organizational goal to advance a more student-centred approach, the OIP aims to foster intersections across a specialized model of student advising service provision to better meet the needs of a diverse, 21st century student population. In addition, the OIP responds to environmental realities in which increasing accountabilities, compounded by the rapid pace and growing pervasiveness of reactive change, require building internal capacity for ongoing, continuous adaptation (Lichtenstein et al., 2006). The OIP’s overarching leadership lens is informed by complexity theory (CT), and the complexity leadership (CL) model (Uhl-Bien & Arena, 2017, 2018) is used as the framework to lead the change and to shift perspectives on leadership to more distributed forms. Acknowledging that there is no single correct way to structure student advising in HEIs, the OIP proposes that a traditional service-provider model of student advising may be enhanced by forging interconnections through a combination of technology and adaptive space within which social capital among agents may be fostered across the system of service provision. Specifically, the OIP describes how a planned change to deploy a software solution to support student referrals across the system may be leveraged as a starting point to enable conditions for continuous adaptation. The planned change is used as an opportunity to create adaptive space (Uhl-Bien & Arena, 2017; Uhl-Bien & Marion, 2009) for agents working across the system to connect and work through the change together, thereby shifting traditional, top-down perspectives on leadership and change toward a more bottom-up approach. In this way, the OIP balances leading change for performance with creating conditions for ongoing system adaptation (Uhl-Bien & Arena, 2017). While this OIP presents a context-specific approach to change, the concepts it employs from CL—including creating and maintaining adaptive space, adaptive leadership, and practices—may inform approaches to change in similar contexts at other HEIs. Keywords: adaptation, adaptive space, complexity theory, model of complexity leadership, higher education institutions, student advisin