Right-Handed Neutrinos as the Origin of the Electroweak Scale

The insular nature of the Standard Model may be explained if the Higgs mass parameter is only sensitive to quantum corrections from physical states. Starting from a scale-free electroweak sector at tree-level, we postulate that quantum effects of heavy right-handed neutrinos induce a mass term for a scalar weak doublet that contains the dark matter particle. In turn, below the scale of heavy neutrinos, the dark matter sector sets the scale of the Higgs potential. We show that this framework can lead to a Higgs mass that respects physical naturalness, while also providing a viable scalar dark matter candidate, realistic light neutrino masses, and the baryon asymmetry of the Universe via leptogenesis. The proposed scenario can remain perturbative and stable up to the Planck scale, thereby accommodating simple extensions to include a high scale (2\times 10^{16} GeV) inflationary sector, implied by recent measurements. In that case, our model typically predicts that the dark matter scalar is close to 1 TeV in mass and could be accessible in near future direct detection experiments.Comment: Revtex4, 10 pages, 6 figures. An appendix on a classically scale invariant scenario for right-handed neutrino masses, as well as new references added. Version accepted for publication in PR

Dark Matter from Hidden Forces

We examine the possibility that dark matter may be the manifestation of dark forces of a hidden sector, i.e. "Dark Force = Dark Matter." As an illustrative and minimal example we consider the hidden SU(2)_h x U(1)_h gauge group. The hidden dynamics is indirectly coupled to the Standard Model (SM) through kinetic mixing of U(1)_h with the U(1)_Y of hypercharge. We assume a hidden symmetry breaking pattern analogous to that of the SM electroweak symmetry, augmented with an extra scalar that allows both the "hidden Z boson" Z_h and the "hidden photon" \gamma_h to be massive. The "hidden W" bosons W_h are dark matter in this scenario. This setup can readily accommodate a potential direct detection signal for dark matter at ~10 GeV from CDMSII-Si data. For some choices of parameters, the model can lead to signals both in "dark matter beam" experiments, from Z_h\to W_h W_h, as well as in experiments that look for visible signals of dark photons, mediated by \gamma_h. Other possible phenomenological consequences are also briefly discussed.Comment: 11 pages, 4 figures; References and additional comments added. Results unchange

Threshold Resummed and Approximate NNLO results for W+W- Pair Production at the LHC

The next-to-leading order (NLO) QCD radiative corrections to W+W- production at hadron colliders are well understood. We combine NLO perturbative QCD calculations with soft-gluon resummation of threshold logarithms to find a next-to-next-to leading logarithmic (NNLL) prediction for the total cross section and the invariant mass distribution at the LHC. We also obtain approximate next-to-next-to-leading order (NNLO) results for the total W+W- cross section at the LHC which includes all contributions from the scale dependent leading singular terms. Our result for the approximate NNLO total cross section is the most precise theoretical prediction available. Uncertainties due to scale variation are shown to be small when the threshold logarithms are included. NNLL threshold resummation increases the W+W- invariant mass distribution by ~ 3-4% in the peak region for both \sqrt{S}=8 and 14 TeV. The NNLL threshold resummed and approximate NNLO cross sections increase the NLO cross section by 0.5-3% for \sqrt{S}=7, 8, 13, and 14 TeV.Comment: 29 pages, 7 figures, 3 tables. Discussion added to introduction, references updated, and typos correcte

Non-resonant Collider Signatures of a Singlet-Driven Electroweak Phase Transition

We analyze the collider signatures of the real singlet extension of the Standard Model in regions consistent with a strong first-order electroweak phase transition and a singlet-like scalar heavier than the Standard Model-like Higgs. A definitive correlation exists between the strength of the phase transition and the trilinear coupling of the Higgs to two singlet-like scalars, and hence between the phase transition and non-resonant scalar pair production involving the singlet at colliders. We study the prospects for observing these processes at the LHC and a future 100 TeV $pp$ collider, focusing particularly on double singlet production. We also discuss correlations between the strength of the electroweak phase transition and other observables at hadron and future lepton colliders. Searches for non-resonant singlet-like scalar pair production at 100 TeV would provide a sensitive probe of the electroweak phase transition in this model, complementing resonant di-Higgs searches and precision measurements. Our study illustrates a strategy for systematically exploring the phenomenologically viable parameter space of this model, which we hope will be useful for future work.Comment: 34 pages + 4 appendices, 13 figures. Comments welcome

Shedding Light on Top Partner at the LHC

We investigate the sensitivity of the 14 TeV LHC to pair-produced top partners ($T$) decaying into the Standard Model top quark ($t$) plus either a gluon ($g$) or a photon ($\gamma$). The decays $T\rightarrow tg$ and $T\rightarrow t\gamma$ can be dominant when the mixing between the top partner and top quark are negligible. In this case, the conventional decays $T\rightarrow bW$, $T\rightarrow tZ$, and $T\rightarrow th$ are highly suppressed and can be neglected. We take a model-independent approach using effective operators for the $T$-$t$-$g$ and $T$-$t$-$\gamma$ interactions, considering both spin-$\frac{1}{2}$ and spin-$\frac{3}{2}$ top partners. We perform a semi-realistic simulation with boosted top quark tagging and an appropriate implementation of a jet-faking-photon rate. Despite a simple dimensional analysis indicating that the branching ratios ${\rm BR}(T\rightarrow t\gamma)\ll {\rm BR}(T\rightarrow tg)$ due to the electric-magnetic coupling being much smaller than the strong force coupling, our study shows that the LHC sensitivity to $T\bar{T}\rightarrow t\overline{t}\gamma g$ is more significant than the sensitivity to $T\overline{T}\rightarrow t\overline{t}gg$. This is due to much smaller backgrounds attributed to the isolated high-$p_T$ photon. We find that with these decay channels and 3 ab$^{-1}$ of data, the LHC is sensitive to top partner masses $m_T\lesssim 1.4-1.8$~TeV for spin-$\frac{1}{2}$ and spin-$\frac{3}{2}$ top partners, respectively.Comment: 33 pages, 10 figures, 7 table

NLO corrections to double Higgs boson production in the Higgs singlet model

Higgs pair production at the LHC from gluon fusion is small in the Standard Model but can be enhanced in models where a resonant enhancement is allowed. We examine the effect of a resonant contribution from a second scalar arising in a model with a gauge singlet scalar field in addition to the usual SU(2) scalar doublet, with mass up to MH∼600  GeV, and discuss the interference effects in double Higgs production. The interference effects distort the double Higgs invariant mass distributions and, depending on MH, can enhance the total cross section by up to ∼20% or decrease by ∼30% for viable mixing parameters. We compute the next-to-leading-order QCD corrections in the large mt limit. The corrections are large and can also significantly distort kinematic distributions near the resonance peak