Neutrinos from Off-Shell Final States and the Indirect Detection of Dark Matter

We revisit the annihilation of dark matter to neutrinos in the Sun near the WW and tt kinematic thresholds. We investigate the potential importance of annihilation to WW* in a minimal dark matter model in which a Majorana singlet is mixed with a vector-like electroweak doublet, but many results generalize to other models of weakly-interacting dark matter. We re-evaluate the indirect detection constraints on this model and find that, once all annihilation channels are properly taken into account, the most stringent constraints on spin-dependent scattering for dark matter mass 60 GeV < mX < mt are derived from the results of the Super-Kamiokande experiment. Moreover, we establish the model-independent statement that Majorana dark matter whose thermal relic abundance and neutrino signals are both controlled by annihilation via an s-channel Z boson is excluded for 70 GeV < mX < mW. In some models, annihilation to tt* can affect indirect detection, notably by competing with annihilation to gauge boson final states and thereby weakening neutrino signals. However, in the minimal model, this final state is largely negligible, only allowing dark matter with mass a few GeV below the top quark mass to evade exclusion.Comment: 22 pages, 5 figure

Exotic Top Partners and Little Higgs

Little Higgs models often give rise to top partners beyond the minimal ones necessary for the cancellation of quadratic divergences. We review how this occurs and discuss the phenomenology of these exotic states. We emphasize the possible importance of new pseudo-Nambu-Goldstone bosons in top partner decays. Indeed, cascade decays of exotic top partners may be the best way to discover these new bosons. We illustrate these points with a new Little Higgs construction based on an SO(10)/SO(5)^2 coset structure, which fills a gap in the model building literature. These observations motivate new search strategies for top partners at the LHC, including for final states with b-jets and a large multiplicity of electroweak bosons.Comment: 27 pages, 2 figures, 4 tables; v3: JHEP revision -- updated to include discussion of naturalness and section 2.1 expande

A study of policies governing the employment of part-time professional nurses in hospitals

Thesis (M.S.)--Boston Universit

Is a Higgs Vacuum Instability Fatal for High-Scale Inflation?

We study the inflationary evolution of a scalar field $h$ with an unstable potential for the case where the Hubble parameter $H$ during inflation is larger than the instability scale $\Lambda_I$ of the potential. Quantum fluctuations in the field of size $\delta h \sim \frac{H}{2 \pi}$ imply that the unstable part of the potential is sampled during inflation. We investigate the evolution of these fluctuations to the unstable regime, and in particular whether they generate cosmological defects or even terminate inflation. We apply the results of a toy scalar model to the case of the Standard Model (SM) Higgs boson, whose quartic evolves to negative values at high scales, and extend previous analyses of Higgs dynamics during inflation utilizing statistical methods to a perturbative and fully gauge-invariant formulation. We show that the dynamics are controlled by the renormalization group-improved quartic coupling $\lambda(\mu)$ evaluated at a scale $\mu = H$, such that Higgs fluctuations are enhanced by the instability if $H > \Lambda_I$. Even if $H > \Lambda_I$, the instability in the SM Higgs potential does not end inflation; instead the universe slowly sloughs off crunching patches of space that never come to dominate the evolution. As inflation proceeds past 50 $e$-folds, a significant proportion of patches exit inflation in the unstable vacuum, and as much as 1% of the spacetime can rapidly evolve to a defect. Depending on the nature of these defects, however, the resulting universe could still be compatible with ours.Comment: 31 pages, 3 figures; v2: references added, journal versio

Rising House Prices in an Open Labour Market

In this paper we explore the consequences of the recent steep rise in house prices for the openness of the Irish labour market. Specifically we look at the possible effect rising house prices may have on the migration decision. Since many immigrants are in the household formation age group, and tend to be highly skilled, we argue that the boom in house prices, by reducing the attractiveness of Ireland for potential immigrants, could reduce labour supply. Thus housing emerges as an important infrastructural constraint affecting the labour market. To formulate the role of house prices in the migration decision we use a structural model of the determination of output, labour supply and labour demand in Ireland. We modify the basic model in a number of ways: firstly we endogenise the determination of house prices using structural equations for the demand and supply of housing; secondly we separate out the user cost of housing in the migrant's cost of living index; and thirdly we endogenise the determination of consumer prices. Simulation results suggest that rising house prices, by discouraging potential migrants, could significantly reduce the growth potential of the economy, shifting the balance of labour market growth from employment to wages, with a consequent deterioration in competitiveness. The welfare effects of this differ for different groups; there are unambiguous gains for current home owners while immigrants, first time buyers and those with lower labour market skills are net losers.housing, labour market, migration

Higgs-photon resonances

We study models that produce a Higgs boson plus photon ($h^0 \gamma$) resonance at the LHC. When the resonance is a $Z'$ boson, decays to $h^0 \gamma$ occur at one loop. If the $Z'$ boson couples at tree-level to quarks, then the $h^0 \gamma$ branching fraction is typically of order $10^{-5}$ or smaller. Nevertheless, there are models that would allow the observation of $Z' \to h^0 \gamma$ at $\sqrt{s} = 13$ TeV with a cross section times branching fraction larger than 1 fb for a $Z'$ mass in the 200--450 GeV range, and larger than 0.1 fb for a mass up to 800 GeV. The 1-loop decay of the $Z'$ into lepton pairs competes with $h^0 \gamma$, even if the $Z'$ couplings to leptons vanish at tree level. We also present a model in which a $Z'$ boson decays into a Higgs boson and a pair of collimated photons, mimicking an $h^0 \gamma$ resonance. In this model, the $h^0 \gamma$ resonance search would be the discovery mode for a $Z'$ as heavy as 2 TeV. When the resonance is a scalar, although decay to $h^0 \gamma$ is forbidden by angular momentum conservation, the $h^0$ plus collimated photons channel is allowed. We comment on prospects of observing an $h^0 \gamma$ resonance through different Higgs decays, on constraints from related searches, and on models where $h^0$ is replaced by a nonstandard Higgs boson.Comment: 22 page